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Figur: Shell Eco-maraton, PureChoice vehicle, weighing only 69 kg managed to drive 729 km with the energy in one litre of petrol.

Faculty of Information Technology, Mathematics and Electrical Engineering Department of Electric Power Engineering

Address Org.no. 974 767 880 Location Phone Sem Sælandsvei 5 E-mail: O.S.Bragstadsplass 2 + 47 73 59 42 10 NO-7491 Trondheim postmottak@elkraft.ntnu.no Elektroblokk E, 3.etg Fax http://www.elkraft.ntnu.no NO-7034 Trondheim + 47 73 59 42 79

A summary of Master Theses 2008 This internet published pamphlet gives a summary of all Master Theses submitted to the Department of Electric Power Engineering in 2008. NTNU, 27 September, 2008 Eilif Hugo Hansen Head of the Department

Innholdsfortegnelse:

KANDIDAT VEILEDER TITTEL SideBajracharya, Chandra Molinas, Marta Control of VSC-HVDC for wind power 1Bergene, Jarle Nilssen, Robert Loss Calculations on Roebel-bars using Finite Element Analysis 3Birkelund, Bendik Jørgensen

Høidalen, Hans Kristian

Investigation of Dielectric Response Measurement as a Tool to Detect Copper Sulphide on Insulation Paper

5

Bjørland, Birger Doorman, Gerard Sluttbrukets betydning i energiplanlegging 7Bystøl, Tina Davies Fosso, Olav Bjarte Stabilitetsproblem i distribusjonsnettet med lokal produksjon 8Coll, David Hansen, Eilif Hugo Energisparepotensialer i næringsbygg 10Dietrichson, Harald Hole

Holen, Arne Torstein Optimal forvaltning av reaktiv effekt i regionalnettet i Buskerud 12

Dutta, Saikat Swapan Ildstad, Erling Water absorption and dielectric properties of Epoxy insulation 14Eggerud, Jostein Gjengedal, Terje Evaluation of simulation tools for expansion planning 15

Elvestad, Eirik Nestli, Tom F. Implementation of Permanent Magnet Motors in Electric Vehicles

17

Gammelsæter, Marte Finden, Per Fornybare energiløsninger i Antarktis 18Gorji Ghalamestani, Setareh Nilssen, Robert Electric Generator for Ocean Wave Energy Converter 20

Grudic, Elvedin Norum, Lars Einar Electric Propulsion System for the Shell Eco-marathon PureChoice Vehicle

22

Haileselassie, Temesgen Mulugeta

Undeland, Tore Marvin Control of Multi-terminal VSC-HVDC Systems 25

Hovd, Asbjørn Benjamin Fosso, Olav Bjarte Modal Analysis of Weak Networks with the Integration of Wind

Power 27

Husum, Eirik Mathias Nilssen, Robert Design of a Lab Setup for testing Stator Windings in Ironless Axial Flux Machines

29

Jostedt, Pål Undeland, Tore Marvin Subsea Power Electronics 30

Lamichhane, Chudamani

Undeland, Tore Marvin Advanced Battery Diagnosis for Electric Vehicles 31

Lie, Halvor Fosso, Olav B Teknisk/økonomisk analyse av roterende kompensatorer 34

Lind, Marte Gjengedal, Terje Evaluation of Price Forecasts for Hydropower Expansion Planning Applications

36

Mbuzi, John Høidalen, Hans Kristian

Localisation of ground faults in power systems with distributed production

38

Mogstad, Anne Berit Molinas, Marta New switching pattern for AC/AC converters with RB-IGBTs for offshore wind parks

40

Myhr, Anders Ramberg Doorman, Gerard Integrasjon av vindkraft i Troms 42Noddeland, Børge og Røkke, Astrid Nilssen, Robert Investigating the Potential of Two Large Diameter Magnetic

Bearings 44

Novik, Frode Karstein Nysveen, Arne Power system for electric heating of pipelines 47

Olsen, Jørgen Gjengedal, Terje Offshore vindkraft - Tekniske og økonomiske vurderinger for utbygging og tilkobling.

49

Olsen, Pål Keim Nilssen, Robert Isolasjonssystem for roterende maskiner - analyse av offshore vind generator

51

Simonsen, Bjørn Finden, Per Heat Exchange in a Fluidized Bed Calcination Reactor 53Sommerfelt, Knut Magnus Gjengedal, Terje Offshore Wind Power in the North Sea 55

Stefanussen, Knut Holen, Arne Torstein Beredskap i regionalnett 56

Strand, Bjørn Erik Molinas, Marta Voltage Support in Distributed Generation by Power Electronics 58

Sætre, Frode Runde, Magne Eystein Splicing and Coil Winding of MgB2 Superconductors 60

Timberlid, Erlend Norum, Lars Einar Expert system for hydropower stations developed in Volve Knowledge Tools

62

Torp, Camilla Bakken Finden, Per Energiforsyning til sykehus i Sudan basert på solenergi 64

Wiik, Bjørn Ola Norum, Lars Einar Elektrisk Fremdriftsystem for Shell Eco-marathon PureChoice Kjøretøy

69

Ytterstad, Marit Holbø Ildstad, Erling Kvalitetssikring av polymerisolerte HVDC kabler ved hjelp av spenningsprøving

71

Ørjasæter, Hans Solvang, Eivind Korleis nytte fleirmåls beslutningsanalyse og influensdiagram til vedlikehaldsplanlegging av sjøkabelanlegg.

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Control of VSC based HVDC

Student: Chandra Bajracharya

Supervisor: Marta Molinas

Contact: Faculty of Information Technology, Mathematics and Electrical

Engineering, NTNU Collaboration: none

Problem description

High voltage dc transmission traditionally has been used to transfer large amounts of power

over long distances. The voltage source converter based HVDC technology has recently been

an area of growing interest because of a number of advantages like modularity, independent

control of active and reactive power, low power operation, easy power reversal, possibility to

form an HVDC grid etc.

In voltage source converters, changes in voltage phase angle and magnitude can be obtained

almost instantaneously by using the pulse width modulation technique. Thus from system

point of view, VSC based HVDC acts as a synchronous machine without mass that can

independently control active and reactive power. In PWM converters for ac applications,

vector control strategy is utilized to obtain independent control of active and reactive power.

Vector control uses transformation of three phase voltages and currents into rotating d-q

coordinate system oriented with respect to the ac grid voltage vector. Such transformation

leads to a split of mains current into two parts, one part determines the required power flow

into the dc bus while other part defines the reactive power condition. As vector control

technique offers decoupled control of active and reactive power, it makes the realization of

system control in form of cascade control structure possible. Using the transformation, vectors

of ac currents and voltages occur as constant vectors in steady state and hence, static errors in

control system can be avoided by using simple PI controllers.

Adequate performance of VSC-HVDC system under diverse operating conditions depends on

the selection of robust parameters for the control system. Usually, due to the simple structure

and robustness, PI controllers have been used to adjust the system for desired responses. The

tuning of the converter controller parameters (gain and time constant) is a compromise

between speed of response and stability for small disturbances as well as the robustness to

tolerate large signal disturbances. Furthermore, the control loops are nonlinear in nature, and

hence needs careful selection of control parameters to accommodate a range of operating

conditions.

The task

This thesis focuses on the control structure of VSC based HVDC and tuning of the controllers

for voltage source converter.

A mathematical model of a voltage source converter is presented in the synchronous reference

frame for investigating VSC-HVDC operation. The vector control strategy for decoupled

control of active and reactive power is explained. The model is then used to analyze the

cascade control structure with voltage and current control loops and to study their dynamics.

The transfer functions are derived for the inner and outer control loops.

In investigating the operating conditions for HVDC systems, the tuning of controllers is one

of the critical stages of the design of control loops. In an attempt to establish the criteria for

tuning of the converter controllers, three tuning techniques are discussed and analytical

expressions are derived for calculating the parameters of the current and voltage controllers.

Based on the transfer function structure, the inner current controller is tuned according to

modulus optimum criteria, while the outer voltage controller is tuned according to

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symmetrical optimum criteria. A modification of symmetric optimum criteria to explicitly

specify the closed loop pole-zero configuration is also discussed for the tuning of outer

controller.

Model/ Measurements

Control Block diagram of the System

Figure above shows the control block diagram of the voltage source converter. Based on the

control structure and the governing system equations, transfer functions and tuning criteria of

the controllers are formed. The system is then tested in Matlab using frequency domain

analysis (Bode plot) and time domain analysis (step response) to analyse the system

performance.

The system is also modelled in EMTDC/ PSCAD to test for the robustness of the controller

under different operating conditions.

Results/Conclusion

From the results, it was found that all the tuning criteria optimize the dynamic performance of

the system, and hence provide an adequate performance. The robustness of the controller was

verified through simulations. Tuning of current controller by modulus optimum gives fast

response, as required by the cascaded control structure. The system was stable with sufficient

phase margin, ensuring its robustness. The tuning of voltage controller by symmetrical

optimum, gives fast response along with strong rejection of disturbances. Explicit

specification of complex pole-zero configuration is also possible to set the response of the

system by pole placement interpretation of the symmetrical optimum criteria.

As the system transfer function is derived by using system linearization, the stability analysis

in case of the outer voltage controller, can only predict the local stability but does not provide

any information on the extent of the stability region. Moreover, the overall control design is

based on the assumption of decoupled control by inner and outer loops. Hence, the system

performance under non-ideal operating conditions and the effect of system nonlinearities need

to be further investigated to devise tuning rules that reduce the negative influence on system

performance under these conditions.

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Loss calculations on Roebel-bars using finite element analysis Student: Jarle Bergene Supervisor: Robert Nilssen Conclusion – The simulation results show that a transposed conductor with short circuited strands in both ends maintains its benefit of reducing circulating currents even though the transposition is incomplete. This is true for fractions of 0.5 and above. At 0.5 the performance is on par with the fully transposed model. When the conductor is cut in fractions less than 0.5 the ability to eliminate circulating currents drops significantly. The benefit obtained by replacing a straight stranded wire with a transposed wire varies with the distribution of the strands and also with the number of strands and with the cross sectional area of the strands. It seems to vary also with different combinations of these factors. Simulations done with an imitated field from a PM-machine show that the justification of using transposition is mainly due to the losses caused by the external field. ANSYS provides results that correspond well with anticipated results. Generally the trickiest and most time consuming part of a finite element analysis is to prepare the mesh. The models in this thesis could successfully be meshed by the help of automatic and default mesh controls. Abstract: This master thesis concern modeling and analysis of transposed conductors (roebel-bar). The analysis was conducted in ANSYS which is a finite element analysis (FEA) program. A transposed conductor has a structure that is dependent upon 3D analysis. In that way the 3D capabilities of the program could be put to the test, and by making various fractions of the roebel-bar, interesting research could be carried out at the same time. The research consists in revealing how a transposed conductor performs in terms of joule losses when the transposition is incomplete. Both longitudinal and transverse time varying magnetic fields will be imposed. From theory it is known that the phenomenon of proximity effect will cause circulating currents between strands in a conductor unless each strand experiences the same flux linkage. Incomplete transpositions in a roebel-bar will generally not produce identical flux linkages. Therefore the joule losses per unit of length are expected to be higher than the losses related to a conductor of full transposition. The roebel-bar will be cut in various fractions and the performance-factor of the various fractions is represented as the percentage improvement (reduction in losses) from an equivalent non-transposed wire. Figure 1 shows that there is a local maximum at 75% length, and that the 50% length actually perform a little better than the full length model. Beyond 50% length, the performance drops significantly. Other models with different geometries have different performance factors, but the same trend applies. The results from the simulations with transverse magnetic field gave improvement factors in the order of 80%. This certifies that transposition is indeed useful.

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Figure 1: The performance factor of Model 1 due to applied current. The various fractions are given on the X-axis.

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Investigation of dielectric frequency measurement as a tool to detect copper sulphide on insulation paper Student : Bendik J. Birkelund Supervisor : Prof. Hans Kr. Høidalen Assistant supervisor : Senior Researcher Lars Lundgaard

Researcher Dag Linhjell In co-operation with : SINTEF Problem In recent years several power transformers have failed due to copper sulphide. Corrosive sulphur reacts with the copper in the windings, creating semi-conducting copper sulphide. Eventually the copper sulphide contamination grows through the paper insulation, reducing the electric withstand strength of the transformer. To this day there are no reliable non-destructive methods to detect copper sulphide contamination in a transformer. Assignment Dielectric frequency measurement is an non-destructive test method which gives capacitive parameters as a function to frequency. This approach is used, for instance, to detect water and acid in transformer insulation. This master’s thesis’ main task has been to investigate if copper sulphide contamination on paper is detectable by dielectric frequency measurement. The problem has been divided into two subtasks:

- Find ways to create and document copper sulphide contaminated paper samples. - Investigate the dielectric frequency response of the samples created, at low and high

frequency. Measurements Two different equipments were used for the dielectric frequency measurements:

- Insulation Diagnostic Analyser o Frequency range: 10mHz – 1kHz o Sample size: 75mm

- Alpha-Analyser o Frequency range: 100Hz – 1MHz o Sample size: 25mm

Samples were created in two ways:

- Sample created with paper strips from a transformer with known copper sulphide contamination. Figure 1

- Sample created by growing copper sulphide on a clean piece of paper for 3, 5, 7, 11 and 14 days. Figure 2

-

Contaminated strips Diameter: 25mm and 75mm Created for: Alpha-Analyser Insulation Diagnostic Analyser

Laboratory Diameter: 25mm Created for: Alpha-Analyser

Figure 1 Figure 2

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Copper sulphide contamination documentation was performed in two ways: - Resistance measurements. Figure 3 - Area percentage documentation. Figure 4

Resistance measurements Reading on the surface and through the paper Resistances ranged from 100Ω to 200G Ω

Area percentage Computer program counting pixels above a given brightness level.

Figure 3 Figure 4 Results Important results from sample creation and documentation:

- Growth of samples worked well, but significant variations could occur. - Resistance measurements seemed as the best classification method as it could cope

with large variations in contamination. - Area percentage calculations worked in very limited cases, with homogeneous

contamination and large brightness variations between copper sulphide and paper. Important results from the frequency measurements: Frequency range: 1mHz – 1kHz Frequency range: 100Hz – 1MHz

Figure 5 Figure 6

- At lower frequencies the gaps between the strips gave the most significant effect - At higher frequencies the gaps may give a contribution. - At higher frequencies the grown copper sulphide samples gave significant variations.

However, these variations may still indicate a copper sulphide effect to the permittivity response. More research is needed.

Conclusion and suggestions to future work

- There might be a correlation between copper sulphide and dielectric frequency response. The growth of samples works well as test object provider, and resistance measurements seems to be the best choice for contamination degree classification.

- More research is needed, and it is suggested run samples with no gaps in the entire frequency range. Drying the samples is also recommended.

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Sluttbrukets betydning I energiplanleggingen Student: Birger Bjørland Faglærer: Gerard Doorman Veileder: Bjørn Harald Bakken, Sintef Energiforskning Scarcity of energy and effect is often compensated with higher production or transmission capacity, and there has been little attention on the end-user in traditional energy planning. The reduction potential is huge, and the desire for better knowledge about different end-user actions has a high priority in energy planning at the moment. Actions taken on the production and energy infrastructure can hardly compete on the level of cost with pr KWh decreased by the end-user. That’s why we find reduction in the energy consumption, at the top of the list, of actions to be taken to create sustainable energy systems. In this thesis it’s been looked upon how an advanced end-user model can be implemented into eTransport to be able to analyze how end-user actions that increases short and longterm flexibility affect energy systems. eTransport is a network model developed by SINTEF energy research. The model gives the user the opportunity to analyze the energyand mass flow from supplier to end-user through different energy carriers and technologies simultaneously. The main goal of the model is to assist the energy planner in order to optimize the investments in energy infrastructure and cover the energy demand in the best possible way, both environmentally and economically. The implementation of the end-user model makes it possible is distinguished between delivered and useful energy. This makes it to easier to analyze the influence of different technologies, improving the energy efficiency and price dependent saving at the end user. This has resulted in the modeling of 5 new sub models in eTransport. One for heat- end el specific load that are based upon the same principal, two for investment in increased energy efficiency and one node to separate the end-user from the rest of the energy system. Now the load profiles for the elastic loads represent the useful energy, as a consequence of the changes done in the load models. The demand is elastic and can now be looked upon as the marginal willingness to pay. eTransport is now able to carry out a socio economic analyze where there is a trade-off between benefit of the consumption and the production cost. This is done by cost minimization, where the demand can be reduced at a specific cost. This implies that the model has gone from finding the cost effective solution to a socio economic adaptation. The program is now constructed in a way where every action besides price dependent saving is compensated for in the supply curve. This implies that the demand curve in eTransport is unaltered for investments in new technologies, energy efficiency is increased or there is a switch between different energy carriers. The testing of the components in the model shows that the economical results comport with socio economic theory. Thereby the total socio economic surplus for the different actions has been taken into account in a correct way, and the model is now more socio economic correct.

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Stabilitetsproblem i distribusjonsnett med lokal produksjon Student: Tina Davies Bystøl Faglærer: Professor Olav Bjarte Fosso Veiledere: Trond Toftevaag, SINTEF Energiforskning Astrid Petterteig, SINTEF Energiforskning

Sammendrag I Norge har antall småkraftverk knyttet til distribusjonsnettet økt kraftig de siste årene. Denne avhandlingen undersøker ulike stabilitetsproblemer som kan oppstå i distribusjonsnett med betydelig innslag av lokal kraftproduksjon tilknyttet kraftnettet. Det har blitt undersøkt om det er mulig å identifisere stabilitetsproblemer knyttet til nettkonfigurasjon, størrelsen på produksjonsenhetene, last eller andre karakteristiske egenskaper ved systemet. Videre er det undersøkt om regulatorinnstillinger vil være kritisk for systemets oppførsel eller om problemene er mer knyttet til treghetskonstantene til roterende masser. Kraftsystemsimuleringsprogrammet SIMPOW har blitt benyttet til lastflytanalyser og dynamiske analyser av to case. Case 1 omhandler Snåsa distribusjonsnett (NTE), der 5 småkraftverk er under utbygging, og case 2 tar forseg Breiava kraftverk (Lyse produksjon) der det oppstod effektpendlinger under idriftsettelsesprøvene av kraftverket. SIMPOW hadde ikke en modell for en spenningsregulator med mulighet for Var eller effektfaktor kontroll og det ble derfor valgt å etablere en datamodell for spenningsregulatoren DECS- 100 fra Basler Electrics til analysene i SIMPOW. Det var i første omgang polhjulsvinkelstabiliteten som ble studert i case 1 og case 2. Lineæranalyse ble benyttet for å undersøke om systemene var småsignalstabilt og til å undersøke hvordan ulike forsterkningsparametere i spenningsregulatoren og treghetskonstanten til generatoren påvirket stabiliteten til systemet. Det ble funnet at en økning i treghetskonstanten, H, til generatorene økte systemets kritiske klareringstid. En økning i H fører også til at maskinens elektromekaniske egenfrekvens reduseres. Hvordan forsterkinger i spenningsregulatoren påvirker stabiliteten til systemet vil variere fra system til system. I case 1 førte økning i forsterkningen til spenningsregulatoren til økt demping av systemet. I case 2 er en produksjonsenhet med relativt stor aktiv effektproduksjon koblet til hovedtransformator gjennom en lang linje. En økning i forsterking i spenningsregulatoren eller treghetskonstanten til synkrongeneratoren førte i dette tilfellet til at det oppstod stående

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effektpendlinger når systemet ble utsatt for en forstyrrelse. Det er grunn til å tro, ut ifra de analysene som er gjennomført, at høye maskinreaktanser i denne situasjonen hadde en negativ effekt på generatorens transiente stabilitet.

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Energisparepotensialer i næringsbygg Student: David Coll Faglærer: Veileder: Eilif H. Hansen Utføres i samarbeid med: Siemens/ Adresseavisen ASA Næringsbygg står for en betydelig andel av energibruken i Norge. Både ut fra økonomiske, samfunnsmessige og miljømessige forhold er det i dag et betydelig fokus på å redusere denne energibruken. I denne oppgaven skal ulike energisparepotensialer ved det elektriske energibruket i næringsbygg kartlegges. I tillegg ble det foretatt sammenligninger mellom cellekontorer og kontorlandskap for å se om energibruken i disse områdene er forskjellige fra hverandre og hvilke energisparetiltak som er mest hensiktsmessige for disse inndelingene. To ulike etasjer ble sammenlignet der majoriteten av den ene etasjen bestod av åpent kontorlandskap mens den andre etasjen inneholdt for det meste av cellekontorer. Ved en kartlegging av et byggs energisparepotensialer er det i denne oppgaven blitt benyttet følgende fremgangsmåte:

- Logging av effektuttak på gruppesikringer i ulike underfordelinger på døgn og ukebasis.

- Foretatt tilstedeværelses- og lysbruksregistreringer på cellekontorer og kontorlandskap.

- Foretatt en kartlegging av brukernes vaner og holdninger til eget energibruk på arbeidsplassen.

Ser man bort fra energibruk til ventilasjon, oppvarming og kjøling vil en stor del av det elektriske energibehovet i kontorområder gå til belysning. Målingene som er foretatt viser at det er en forskjell i hvordan energien blir benyttet for belysning i de ulike områdene. Cellekontorene har en variabel energibruk der energibruken synes å følge antallet brukere som er til stede, mens for åpne kontorlandskap er det vanskeligere å se et slikt mønster. Målingene viste et forholdsvis stabilt nivå hele dagen og kvelden, mens det av og til på nattestid ble redusert til et mye lavere nivå. Hvorvidt energibehovet ble redusert på nattestid eller ei var det ikke noe mønster i, som igjen kan tyde på dårlige rutiner på slukking av lys. Det ble også foretatt tilstedeværelses- og lysbruksregistreringer på cellekontorer og i mindre områder av kontorlandskaper med to til fire brukere i hvert område. Målingene viste at brukstiden for kontorlandskapene lå opp mot 15 timer i døgnet, mens den for cellekontorene aldri oversteg 7,5 timer i døgnet. Lystiden var også ulik i de to områdene. På cellekontorene lå lystiden stort sett mellom 7 og 8 timer, mens den for kontorlandskap varierte mer, med flere tilfeller der lyset sto på hele døgnet. Lysstyringen i kontorlandskapene var foretatt ved hjelp sentraliserte bryterpanel der en bryter dekket et stort område med brukere som har forksjellige behov og arbeidstider. Lysstyringen på cellekontorene var betjent med manuelle brytere plassert ved døren.

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Ut fra resultater på spørreskjemaet som ble utlevert kan det tyde på at brukere av cellekontorer har et mer bevisst forhold til eget energibruk på jobb enn brukerne av kontorlandskap. Andelen brukere av cellekontor som oppgav at de slukket lys på eget kontor og sjekket utstyr og lys i andre områder om de forlot området sist, var vesentlig høyere enn for brukere av kontorlandskap. Andelen brukere som oppgir at de slår av datamaskinene etter endt arbeidsdag ligger på 72,7 og 75 % for brukere av henholdsvis cellekontorer og kontorlandskap. Resultatene fra undersøkelsene tyder på at det er et sparepotensial ved det elektriske energibruket i næringsbygg. Det området der det er størst mulighet for energisparing er ved lysbruket i kontorlandskap. Tiltak som bør iverksettes må vurderes for hvert bygg, men resultatene som framkommer av denne oppgaven tyder på at en bedre oppdeling av lysstyringen vil kunne ha positiv effekt, i tillegg til en økt fokusering på brukernes holdninger slik at de slår av utstyr som ikke er i bruk ved arbeidsdagens slutt.

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Optimal forvaltning av reaktiv effekt i regionalnettet i Buskerud Student: Harald Dietrichson Veileder: Arne T. Holen Utføres i samarbeid med: Energiselskapet Buskerud Problemstilling Oppgavens formål har vært å utarbeide en generell metode for å minimere kostnader knyttet til reaktiv effektflyt i regionalnettet og deretter benytte denne metoden for å optimalisere reaktiv effektflyt i regionalnettet eid av Energiselskapet Buskerud. Regulering av reaktiv produksjon i kraftstasjoner og installasjon av kondensatorbatterier er vurdert som mulige tiltak for å endre den reaktive effektflyten. Disse tiltakene medfører kostnader i form av aktive tap i generatorer eller på grunn av kostnader til installasjon av kondensatorbatterier. Reaktiv effektflyt bidrar til kostnader i form av nettap og reaktivt uttak fra sentralnettet tarifferes av Statnett. I optimaliseringen tas det sikte på å minimere summen av disse fire kostnadselementene. Oppgaven Faste kostnader ved installasjon av kondensatorbatterier fører til at optimalisering av reaktiv effektflyt er et diskret optimaliseringsproblem. Optimaliseringen er derfor utført ved bruk av genetisk algoritme, en optimaliseringsmetode som ble antatt å fungere godt for diskrete problemer. Ved optimalisering med genetiske algoritmer er det ikke mulig å fastslå med sikkerhet at optimal løsning blir funnet, og det er derfor knyttet noe usikkerhet til resultatene. Et optimaliseringsprogram ble programmert i Matlab, og programmet Matpower 3.2 ble implementert i optimaliseringsprogrammet for å utføre lastflytberegninger. Metoden for optimalisering av reaktiv effektflyt ble testet på to deler av regionalnettet i Nedre Buskerud. Resultater Resultatene fra optimaliseringen var konsistente og ga en klar kostnadsreduksjon i forhold til dagens drift. Dette tyder på at optimalisering med genetisk algoritme fungerer godt for denne problemstillingen. Beregningstiden for de største optimaliseringene var rundt 5 minutter. Optimalisering av reaktiv effektflyt ble gjennomført for to deler av regionalnettet i Nedre Buskerud. I begge nettene er det i dagens drift noe reaktiv produksjon i kraftstasjoner, men det er også et betydelig reaktivt uttak fra sentralnettet. Begge analysene viste at reaktiv produksjon i nettet bør økes i forhold til dagens nivå, først og fremst på grunn av store besparelser ved redusert reaktivt uttak fra sentralnettet. Også reduserte nettap bidro til kostnadsreduksjonene. Kostnadene kan reduseres betraktelig ved å øke reaktiv produksjon i kraftstasjonene i nettet, men størst kostnadsreduksjon oppnås ved installasjon av nye kondensatorbatterier. Optimaliseringen ble utført for ulike priser på sentralnettsuttak, og resultatene viste at prisen på reaktivt uttak fra sentralnettet må reduseres til under 10 kr/kVAr for at slikt uttak skal være lønnsomt. I dag er prisen på 25 kr/kVAr. I nettet mot Kongsberg ga et kondensatorbatteri på 8 MVAr i Glabak en maksimering av kostnadsreduksjonen. Denne investeringen har en internrente på 10 %. I nettet mot Modum ga

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kondensatorbatterier på 6,5 MVAr i Hokksund T2 og 9 MVAr i Hovde maksimal kostnadsreduksjon. Den samlede investeringen har en internrente på 12 %. Konklusjon Genetiske algoritmer fungerer godt for optimalisering av reaktiv effekt i nett av den størrelsen som ble analysert i oppgaven. I de nettene som ble analysert vil økt reaktiv produksjon i kraftstasjoner eller kondensatorbatterier kunne føre til store kostnadsbesparelser, først og fremst på grunn av reduserte kostnader til uttak av reaktiv effekt fra sentralnettet, men også på grunn av reduserte nettap. Denne konklusjonen er robust for endringer i sentralnettsprisen, energiprisen og kostnader til installasjon av kondensatorbatterier. Installasjon av kondensatorbatterier gir de største kostnadsreduksjonene. Resultatene var så entydige og robuste at gyldigheten av konklusjonene også kan vurderes for andre, lignende deler av regionalnettet.

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Water absorption and dielectric properties of Epoxy insulation Student: Saikat Swapan Dutta Faglærer: Erling Ildstad Veileder: Sverre Hvidsten, Sintef Energiforskning AS This assignment is a part of an ongoing research project at NTNU/SINTEF Energy Research, which is sponsored by industry and the National Research Foundation (NFR). The main aim of this research project is to develop materials and design criteria facilitating development of power equipment for electrification of sub sea oil and gas production. More specific the topics of this project assignment are to:

1. Review findings in the literature and: i) Present the theoretical basis for diffusion and absorption of water in filled epoxy. ii) Review of relevant literature with respect to the effect of water in epoxy related to its electrical and mechanical performance. 2. Perform experimental investigations to examine the effect of water in epoxy related to the following properties: Dielectric Breakdown Strength, Mechanical Strength, Dielectric Response, Glass transition Temperature. Also the effect of electrode materials on dielectric response is to be studied.

Characterization of Epoxy (diglycidyl ether of Bis-phenol A cured with Tri ethylene Tetra amine) without fillers was done. The Water absorption test at 95°C shows that at saturation the epoxy contains a water concentration of 2.089%. The diffusion coefficient of absorption is calculated as 0.021 cm2/s. The diffusion coefficient of desorption is calculated as 0.0987 cm2/s. The diffusion is almost 5 times faster than absorption. Also the material looses weight as the hydrothermal aging progresses. The water in the sample leads to chain scission which leads to the weight loss. The weight loss is more incase of absorption followed by desorption than only absorption. The chain scission leads to decrease in the mechanical strength by around 45%. The diffusion of water from the samples doesn’t affect the mechanical strength of the materials. The glass transition temperature reduces by 20°C with water inside the sample. The diffusion of water out of the sample only increases by around 10°C. The Dielectric response of the material shows that after the water absorption the sample shows high losses at lower frequencies. Also the increase in the real part of the permittivity increases with low frequency. The rapid increase in the real art of the permittivity of the material at lower frequencies can be attributed to a polarization at the electrode due both to accumulation of the charge carriers and to chain migrations. The breakdown test of the samples shows that with water in the sample the breakdown strength of the material decreases by 10 KV, but the material regains its dielectric strength when the water is diffused out. This shows that the chain scission and weight loss of the samples has no or minimum effect on the dielectric strength of the sample.

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Evaluation of simulation tools for expansion planning

Student: Jostein Eggerud Subject teacher: Terje Gjengedal Supervisor: Terje Gjengedal Performed in collaboration with: Statkraft

Problem description

The specialization project from the autumn 2007 with title “Verdi av Effekt” is used as basis for this master thesis. The goal for this master thesis is to evaluate different simulation tools used as decision making support for expansion planning in hydrothermal power markets. The simulation tools are the EOPS model used for longer term planning and the SHOP model used for optimizing in the short term. The SHOP model should be tested with different time horizons, just to determine the optimal horizon.

The aim is to consider if these tools made for use in hydro dominated power systems can interact in order to determine the market value of MW capacity. Specified watercourses with different complexity are chosen in order to determine the possibilities of cooperation between the simulation tools, and to verify their disposal of the hydro resources and the impact of the income for the particular cases.

The thesis will contain one part which deals with the problem statement of determining the value of MW capacity, and how this could be utilized in the shape of an interaction between the models. Thereafter perform an explanation of the functionality and principals of the models, modify price files for use in the simulations, built models of the watercourses, do simulations and perform analysis by use of the simulation tools.

Summary

The report is introduced by some theory presenting the objective of the thesis; How to determine the market value of MW capacity and to quantify it, why it`s important to have reliable and sufficient simulation tools for decision making related to production optimization and expansion planning. Some theory from the Nordic electricity market before and after the restructuring are also commented.

Three watercourses were chosen in this thesis. These watercourses consist of several restrictions and constraints such as minimum release of water and many small reservoirs in a run-off-river plant, which again leads to less storage possibilities. The chosen cases are Rana, Ulla-Førre and a planned watercourse and power station in Devoll in Albania.

The results from the simulations of the three cases show that the reservoir disposals are fairly similar when there are large and well regulated reservoirs in the watercourses. There are some differences in their disposal of the reservoirs and the production of the power plants when we are dealing with small reservoirs.

There have been some difficulties for the SHOP model to hit the disposal from the EOPS model in the end of the week since there are many reservoirs involved, each with restrictions to fulfill.

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Simulation tools and models

Firstly there is presented some theory about the simulation models which is used in this thesis. The simulation tools which is used for analysis in this thesis is the EOPS model and the SHOP model, both frequently used in hydrothermal production planning worldwide and specially within the Nordic electricity market.

The actual tools which are needed to perform the study are the global multi area model, the EMPS-model, for modeling of longer horizons, the one area model, the EOPS-model, for longer- and medium horizon and the SHOP model for short term hydro generation optimization. The physical structure of the models and their mode of operation will be stated before the results are presented. The models can be seen in the illustration in Figure 1.

A statistical description of:

• aggregate hydro production

• thermal production

• hydro power details

• load shedding

• area interchange

A statistical description of:

• aggregate hydro production

• thermal production

• hydro power details

• load shedding

large interconnected areas

• national

• international

strategy phase

strategy phase

simulation

simulation

simulation

simulation

Figure 1 Simulation models used in the master thesis

The EOPS model uses the price forecast from the EMPS model as input, while it uses the stochastic inflow series from more than 70 years to schedule the long term disposal and production. Further is the output parameters from this model used as input for the optimizing model, the SHOP model. The SHOP model uses the price development and the local inflow as deterministic parameters for the actual period of the analysis. There SHOP model is used with seasonal, monthly and weekly time horizons, but the first two horizons has been skipped in the last two cases since these horizon are seen as unrealistic.

There is also presented similar simulation tools which is used and developed in other countries and parts of the world. There are also explained why these simulation tools are chosen in this master thesis.

Conclusion There is in some cases beneficial to use SHOP in interaction with the EOPS model for the optimization process in order to utilize the resources in the best way. But there are some challenges when it comes to the model consistence, especially the PQ (power and discharge) curves versus the detailed turbine curves. There are difficulties to hit the disposal from the EOPS model when there are many small reservoirs because of this inconsistency.

It is observed small increase in the income when the watercourse are well regulated and when the marked price are non-volatile. There are discovered up to 15% increased income in systems which are coupled to markets with larger price variations, such as the Devoll case. This means that it seems beneficial to use SHOP in such markets.

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Implementation of Permanent Magnet Motors in Electric Vehicles

Student: Eirik Elvestad Faglærer: Tom F. Nestli The use of Permanent Magnet machines in electric vehicles is interesting due to the machine type's compactness and low weight. However, contrary to the case with induction and reluctance machines, the permanent excitation is a concern in fault situations and has to be handled with care. The thesis will address implementation of PM motors in electric vehicles, with focus on design requirements, controls and how to handle faults in a feasible way. This thesis has studied permanent magnet motors in electric vehicles (EVs) under the assumption that they are tractable due to a low weight and high compactness. The implementation has been investigated through a case study, which resulted in an EV simulation model. The model contains a maximal torque per ampere and a closed-loop field weakening controller. Faults are a special concern in permanent magnet motors. Fault sources and faulted behaviour are addressed separately. The EV model was used to simulate faulted behaviour. Two passive fault measures are suggested as the most attractive for propulsion purpose motors; these are shutting down the inverter and imposing a balanced short to the machine terminals. The balanced three phase short circuit showed a considerable transient behaviour not seen during inverter shutdown. These results in an increased requirement to the inverter rating using the balanced short. Also, demagnetization risk of rotor magnets is higher under the balanced short. The maximal braking torque during inverter shutdown was high for the simulation model, and exceeded the braking torque of any fault. This concern led to a mathematical examination of the inverter shutdown, resulting in two equations that may be of use during design. The resulting equations are based on simplifications done in the literature, and show the relationship of the balanced short to the inverter shutdown.

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Fornybare energiløsninger i Antarktis Student: Marte Gammelsæter Faglærer: Per Finden Veileder: Øystein Ulleberg, IFE Den norske forskningsstasjonen Troll, ligger i Dronning Maud Land i Antarktis. Etter å ha blitt utvidet til helårsstasjon i 2004 har energibehovet ved stasjonen økt betydelig. Per i dag er stasjonen forsynt med energi fra dieselaggregat. Dette er svært dyrt og lite miljøvennlig. Hensikten med denne oppgaven er å undersøke muligheten for å redusere forbruket av fossilt brensel til fordel for fornybar energi i det frittstående energisystemet ved Troll. Det skal utføres en studie av aktuelle teknologier, samt gjennomføres simuleringer av energisystemet på Troll i tillegg til å gjennomføre en analyse av kostnadene ved en slik omstilling. Oppgaven er en videreføring av høstens prosjektoppgave. Denne rapporten undersøker muligheten for å introdusere fornybar energiproduksjon i det autonome energisystemet på forskningsstasjonen Troll i Antarktis. Per i dag er stasjonen forsynt med energi fra en dieselgenerator. Denne er overdimensjonert for lasten på Troll, og sliter allerede med driftsproblemer av den årsak. Ønsket om å introdusere fornybar energi kommer fra Miljøverndepartementet og Norsk Polarinstitutt, og springer ut av både energiøkonomiske og miljømessige hensyn. I rapporten simuleres energisystemet på Troll for flere konfigurasjoner med fornybart energitilskudd fra sol og vindenergi, både enkeltvis og i kombinasjon. Modellene er bygget opp, og simuleringen utført med energisimuleringsprogrammet TRNSYS. Modellene er størst mulig grad bygget opp av komponenter med spesifikke data for konkrete, anbefalte teknologier som er vurdert som relevante for Troll. Modellene er også basert på målte data for vindhastighet og solinnstråling fra Troll. Målte data for energiforbruket for stasjonen foreligger i svært liten grad, og det har derfor blitt gjennomført en lastestimering på bakgrunn av Norsk Standard, samt kunnskap om bygningsmassen på Troll. Slik systemet på Troll er i dag, er det nødvendig å skifte ut dieselgeneratoren for å kunne dra nytte av et tilskudd fra fornybar energi. I simuleringene brukes en Low Load Diesel (LLD) generator, som kan kjøre på belastninger ned mot 5 % over lengre tid, uten driftsproblemer. På den måten er det mulig å utnytte en svært høy andel fornybar energi når denne er tilgjengelig. Resultatene viser at de gjennomsnittelige vindhastigheten på Troll er noe lav i forhold til det man anbefaler for å investere i vindturbiner. Likevel gir en konfigurasjon med flere små vindturbiner et jevnt bidrag over året. For solenergi er den innstrålte effekten svært god over store deler av året. Unntaket er tre måneder med mørketid, hvor det ikke er noe solenergi tilgjengelig. Likevel gir solenergi et betraktelig større energibidrag totalt enn det man får fra tilsvarende mengde installert effekt for vindturbiner. En kombinasjon av de to kildene gir nødvendigvis det største bidraget. Denne løsningen anbefales likevel ikke, ettersom det vil komplisere energisystemet ytterligere. Det er svært viktig å velge enkle, solide løsninger for å begrense

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driftsproblemer i et svært isolert område. De økonomiske beregningene viser at alle konfigurasjonene som har blitt studert er økonomisk lønnsomme. Også der viser det seg at solenergi er den beste løsningen, som vil generere den største besparelsen i dieselutgifter. Sannsynligvis vil dessuten lønnsomheten av en investering i fornybar energi bare øke ettersom verden for tiden opplever en sterk økning i oljeprisen. I tillegg til å være en god investering fra et økonomisk standpunkt, gir en investering i fornybar energi betydelige miljøbesparelser i form av reduserte CO2-utslipp, samt en positiv miljøprofil utad for NPI.

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Ocean Wave Energy Converter Student: Setareh Gorji Ghalamestani Supervisor: Robert Nilssen Contact: Alexy Matveev Collaboration with: SmartMotor AS Problem description Machine design for a new Wave Energy converter (WEC) proposed by Professor Robert Nilssen is investigated. The machine nominal speed and the rated nominal power is found from see wave parameters. Cost and efficiency of the design were the factors more focused. The winding layout should have been studied. A contribution is made to the SmartCAD software by adding the optimization loop for design of radial flux permanent magnet (RFPM) machines. The program is used to find the optimal design based on the application. The selected design is analysed in FEM.

The task

Based on studying basics in wave energy concept the machine nominal values are found. A literature study about wave energy converters, different types of power take off systems are considered. It is assumed that the system is linear and buoy movement follows the waves. In addition it is assumed that the buoy is a shallow device put in deep water. The radial flux permanent magnet synchronous machine was preferred over the axial flux machine. In low speed application it is a good choice to have high number of poles. It has the advantage that the iron weight per rated torque is low due to rather low flux per pole. If we go high on number of poles it is more advantageous to have concentrated winding with q(number of slots per pole per phase)less than one. The machine copper losses, the copper weight, the material cost and machine total length are lower than case of having distributed winding. For one layer winding, besides of easier fabrication than double layer, fault tolerance is higher. The length of the end windings compared to conventional winding is less than one third. When designing concentrated winding, high fundamental winding factor should be considered. Low winding factor may cause harmonic, sub harmonic, vibration, extra heating and more losses. The winding factor is proportional to the electromagnetic torque. To compensate for low winding factor there should be higher current or more turn, which both are inversely proportional to the winding factor. To have high fundamental winding factor, we can vary the slot pitch or select a good combination of slots and poles. The latter is investigated. Three types of combinations are covered.

1. Combinations having 2s pN N= ± or 4s pN N= ± . 2. Productions of 24 slots and 22 poles (for instance 48 slots and 44 poles), according

to Smart Motor experience.

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3. Productions of 24 slots and 28 poles (for instance 48 slots and 56 poles) according to study and test at university of Bristol, UK.

Theses combination plus some other inputs are used as input variable to the SmartCAD optimization programme. It was proved that the first group having four types of combinations would result in very close designs, which was not preferred. Therefore the four combinations of slots and poles are narrowed down to only one combination having number of pole two more than number of slots. The selection is made based on the fundamental winding factor and cogging forces. Based on our ring design and some mechanical aspects several initial trials were done to set the limits for variables. The optimization with the objective of low cost and high efficiency is done. Cost of production as a new thing is added in a separate window to SmartCAD programme. Plot of the output figure for 1000 design is shown below.

The point with efficiency of 86.7% and total cost of material and production 31110 NOK is chosen. It shows both high efficiency and low cost. Winding layout for such machine is investigated. The FEM analysis of the selected machine is done.

Calculation The generator design for a new WEC is investigated. The buoy has 2m diameter. The generator would have 200w nominal power and 37.5rpm nominal speed. The optimal design would have cost of3110NOK efficiency of 86.7%. The machine would have 74 poles and 72 slots. The winding factor is 0.955 and weight of the machine is around 25kg. The machine outer diameter is 560mm and Stack length of 61.4mm. The usage of concentrated winding is proved to be efficient when having a good selection of number of slots and poles. A generator cost optimization is done. The target of optimization was to bring down the cost total cost of each installed kilowatt hour per year. The average is 4 NOK/KWh in Norway. This cost includes both electrical and mechanical cost. Based on SmartMotor experience, a rough estimation shows that we can reach 10NOK/KWh which is higher than the average. But the cost calculation is according to energy companies for one year. If we assume the average life time of ten years for the WEC, we see that this cost is paid all at the beginning for the whole life time .So extra cost than the average is paid back during the life time.

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Electric Propulsion System for the Shell Eco-marathon PureChoice Vehicle Student: Elvedin Grudic Supervisor: Lars Norum Collaboration with: Shell, Choice Hotels Scandinavia and

Kongsberg Defence & Aerospace Problem description The final propulsion strategy in the PureChoice vehicle has several demands when it comes to components that have to be implemented and what type of components they should be. My main responsibility in this project has been the propulsion of the vehicle, a part I shared with two other students. The areas of responsibility were therefore divided in three parts, these being fuel cells and hydrogen, motor and controller and controlling the lights and alternative storage devices such as batteries and supercapacitors. The task Main task for me was to demonstrate different possibilities when it comes to controlling the lights in the PureChoice vehicle, and to make sure the vehicle had enough energy stored in alternative storage devices in order to have a fully functioning system when it comes to driving the vehicle and managing the safety system onboard. This implied:

• Performing a background research on the necessary components • Choosing and acquiring the right components • Performing laboratory tests and programming different devices to make sure they are

working properly • Implementing the components in the final vehicle

Model/ measurements The work performed during the last semester is divided in six parts.

Designing and programming a self-manufactured controller card for lights

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Programming and implementing a Siemens LOGO! Micro Automation module to control the lights in the PureChoice vehicle.

Constructing and implementing the necessary input switches, LED lights, LED holders and the wiring involved.

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Ordering, constructing and testing a Lithium-ion battery pack for the safety system onboard the vehicle.

Ordering, constructing and testing a supercapacitor module.

Ordering and testing different DC/DC converters.

Conclusion After a successful participation in the Shell Eco-marathon, the PureChoice vehicle, weighing only 69 kg, managed to drive 729 km with the energy in one litre of petrol. The team won second price in the hydrogen driven Urban Concept vehicles and two special awards; the communication award and the safety award. In addition to the occupational work done on the vehicle, a lot of experience was gathered on how it is to work in larger groups. This project has also brought us closer to the industry because we needed to stay in contact with commercial suppliers to obtain the necessary equipment.

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Control of Multiterminal VSC-HVDC (MTDC) System Student: Temesgen M. Haileselassie Supervisor: Prof. Tore Undeland Co-supervisor: Prof. Marta Molinas Problem Description The North Sea has a vast amount of wind energy with largest energy per area densities located about 100-300Km of distance from shore. Should this energy be tapped by offshore wind farms, HVDC transmission would be the more feasible solution at such long subsea distances. On the other hand Norwegian oil/gas platforms in the North Sea use electricity from gas fired turbines at offshore sites. These gas turbines have much less efficiency than onshore generation of electricity and also release large amounts of green house gases. Therefore supplying the platforms with power from onshore transmitted by HVDC will result in both economic and environmental benefits. Given these two interests for HVDC in the Norwegian offshore, use of Multiterminal HVDC (MTDC) is a potential solution for the integration of the wind farms and oil/gas platforms into the onshore grid system. The MTDC system is desired to be capable of interfacing with all kinds of AC grids namely: stiff, weak and passive grid systems. It is also preferable to make the controllers in such a way that there is least need of communications between terminals for system recovery during terminal disconnections. Design of the local and coordinated controls of the different terminals of the MTDC system is the challenge that should be dealt with during development of MTDC system. The Task This thesis focuses on the control aspects of the operation of MTDC system. First literatures are reviewed to understand the use of voltage source converters (VSCs) in HVDC systems. Afterwards controllers will be developed for different AC connections (stiff, weak and passive) and for different DC parameter (power, DC voltage) control modes. Finally control techniques for reliable operation of MTDC will be developed. In order to validate theoretical arguments, all the control schemes that are developed and discussed are simulated in PSCAD/EMTDC simulation software. Thesis Summary VSC has several features that make it the most suitable converter for making of MTDC, the most decisive being its ability of bidirectional power transfer for fixed voltage polarity. VSC-HVDC is also suitable for implementing control in synchronously rotating d-q reference frame which in turn results in decoupled control of active and reactive currents. A VSC-HVDC terminal and its basic control structures are shown in the Figure 1. The phase lock loop (PLL) is used for synchronization of the rotating reference frame and the pulse width modulator (PWM) uses sinusoidal modulating signal. Point X is the reference point for AC measurements (P, Q, Vac, Iac) and also for the PLL.The PI controllers are tuned by applying the modulus optimum and symmetrical optimum techniques. The inner current loop controller consists of the active and reactive current controllers. DC voltage control is achieved by active current control and AC voltage control is achieved by reactive power compensation. For coordinated multiterminal operation, voltage margin control method and DC voltage droop characteristic were used. These are control methods based upon desired P-UDC characteristic curves of converter terminals.

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Figure 1: VSC-HVDC terminal with basic control structure The characteristic P-UDC curves of four-terminal HVDC are shown in Figure 2. Points s,x&o represent sample operating points at various DC voltage levels. When a DC voltage regulating terminal is disconnected, the operating DC voltage will lock to the DC voltage regulator of another terminal with higher or lower setting depending on whether the voltage has risen or dropped during the disconnection. DC voltage regulating terminal A compensates for power unbalances in the MTDC system. UDC

UAref

PPAmax=0PAmin

UDC

UCref

PPCrefPCmin

UDC

PBLoad

x xxo o

P

DC voltage regulator Constant P terminalPassive AC network

P

UDC

UDref

PDmaxPDref

xo

Constant P terminal

ss

Figure 2: MTDC system with voltage margin control: P-UDC characteristic curves for different VSC-HVDC terminals, DC voltage profile and power flow through DC voltage regulating terminal (A). Conclusion In this thesis the control of four-terminal MTDC system with different AC grid connections was shown. Simulation results has shown that voltage margin control method results in reliable operation of MTDC system without the need for communication between terminals. The use of DC voltage droop control along with voltage margin control enables parallel operation of two DC voltage regulating VSC-HVDC terminals.

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Modal analysis with the integration of wind power

Student: Asbjørn Benjamin Hovd Supervisor: Olav B. Fosso Problem Description The main objective is the focus on how different types of wind power facilities affect a network’s dynamic stability when exposed to small disturbances. This implies dynamic simulations for typical wind series and systematically use of linear analysis (eigenvalues, sensitivities, etc) in order to identify critical variables. Analyses shall be carried out for wind power facilities based on both constant speed wind turbines and variable speed wind turbines. Dynamic models of SVC and traditional condenser batteries can be used if found necessary. The following activities shall be included:

• Describe the current models for wind power turbines and demonstrate an understanding of the different models and how these interact.

• Identify crucial parameter values and evaluate the optimal placement of critical eigenvalues.

• Demonstrate how the linear analysing technique can be used to find the interaction between components in a dynamic system and by that contribute to optimal system behaviour.

• Analysis of a small-scale network with a combination of different production sources. Obtain results which are illustrative.

The analyses shall in general be based on the simulation software SIMPOW. MATLAB can also be used to evaluate the results. The Master Thesis is a continuance of a project during the fall of 2007. Summary In this master thesis the theory and practical use of modal analysis is explained, giving an introduction to the possibilities of modal analysis. The master thesis starts with a look at wind power and the design of a modern wind turbine. Two models, one for constant wind speed wind turbines and one for variable speed wind turbines, are presented. An example shows how modal analysis can be utilized to evaluate a network’s dynamic stability. Simulations are performed on a two-area network where different wind power models are tested and compared. Models/Simulations A two-mass model is used to model a constant wind turbine. The models consist of an asynchronous generator, a turbine, and a low speed shaft with a tensional stiffness. The model representing the variable speed wind turbine is based on a DFIG model included in the simulation software.

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Figure 1. Two area network

The two-area network consists of two areas connected together through a long line between Bus 5 and Bus 6. Area 1 has two production sources, one placed in Bus 1 and one placed in Bus 2. The second area represents a large network modelled as a very large synchronous generator with a high inertia. Simulations are performed by testing different productions sources in Bus 1 in order to see how the system reacts to the different models. Figure 2 shows the difference in speed response after a three phase fault when using a two-mass model (SCIG) in Bus 1 and when using an asynchronous generator (Async) in Bus 2.

Figure 2. Speed response Conclusions The calculations have showed how modal analysis can be used to evaluate a system by using linearized differential equations and how the systems robustness towards small disturbances can be altered by changing the systems parameters. Simulations have verified that a two-mass model must be used when modelling a constant speed wind turbine. The inertia of the turbine will greatly influence the model’s behaviour and must therefore be included in the model. Eigenvalues analysis performed during different wind speeds have documented that wind power will not become less stable towards small disturbances when operated at low wind speed conditions.

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Design of a Lab Setup for testing Stator Windings in Ironless Axial Flux Machines

Student: Eirik Mathias Husum Faglærer: Robert Nilssen Veileder: An ironless axial flux dual rotor permanent magnet electrical machine is to be designed and built. The purpose of the machine shall be to test different types of windings, and the machine should therefore be made in such a way that the stator is easily changed. Abstract—Axial flux machines may give higher power-toweight ratios than conventional radial flux machines. As the axial flux machine can easily be constructed with a multi-rotor configuration, it is well suited for ironless stator design, which has gained interest in the latest years due to the development of high permanent flux density permanent magnets. In addition to the reduced eddy current losses and weight of the stator itself, an ironless design eliminates the magnetic forces acting on the stator, so that the necessity of a heavy stator frame is reduced. Several winding topologies exists for ironless stators, and it can be interesting to compare these with each other. For this purpose, an ironless axial flux 110 pole dual rotor permanent magnet machine with easily exchangeable stator has been made. This machine allows preliminary tests on different stator designs before more expensive prototypes are built. As all active parts of the machine are visible, it may also serve as a demonstration model for electro-mechanical energy conversion. Simulations done on a single-layer 3-level-endturn winding with q=6/5 shows an induced voltage of 40.22 V at 50 Hz. This corresponds well with measurements done on a stator segment covering 2/11 of the machine. The measured DC resistance of this segment is equivalent of 2.51 for a complete stator, which even though somewhat less than calculated, is rather large due to long endturns compared to the radial length of the conductors. The measured inductance of the segment equals self and mutual inductances of about 0.55 μH and 0.275 μH for a complete stator, which is significantly less than calculated.

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Subsea Power Electronics Switching of an IGBT module in a subsea converter Student: Pål Jostedt Faglærer: Tore M. Undeland Veileder: Oil and gas is often extracted from large sea depths. And trend is new fields are developed at deeper and deeper depths. Subsea compression for maintaining reservoir pressure in a gas field is important to have a steady production rate of gas as it is extracted from the field. Electrical drives in the several megawatt ranges are suitable to control the compressor motor since it is not desirable to use gears that need maintenance. Megawatt inverters for gas compressors are typical applications for power electronics. The task of the master thesis candidate is to find the important phenomena when controlling and switching a typical IGBT in such an application. Global increases in energy demand will inevitable lead to increased oil and gas exploration in areas not considered economically viable today. In these areas with large depths and hostile conditions subsea system solutions will be beneficiary. Modifications of power electronic components not intended for subsea use might yield good solutions with decreased overall cost. One suggested solution for subsea converters is to encapsulate the power electronics in a vessel with flexible walls and filled with dielectric oil, allowing the pressure on the inside to equal the ambient pressure at sea bed. This solution will reduce overall cost and increase gas field recovery. Theoretical studies on various topics associated with subsea power electronics have been carried out. Among these are topics about subsea processing systems, considerations of condition assessment, working principle of semiconductors with emphasis on the insulated gate bipolar transistor, IGBT. The switching characteristics, including turn-on and turn-off transients and power loss calculations, of an IGBT module operated with two different gate drivers are obtained from double pulse tests with high voltage and current in an H-bridge leg converter set up. Thorough testing of the IGBT module and documentation of results have been performed to achieve well documentation of how the module behaves in air to use as a reference for later testing purposes with module submerged in dielectric oil and high pressure.

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Advanced Battery Diagnosis for Electric Vehicles Student: Chudamani Lamichhane Supervisor: Tore M Undeland In co-operation with: Think Global, Norway Problem Description The primary goal of this thesis is to study on battery technologies for automotive applications and their diagnosis. The challenge of this project is to identify the established test procedures to diagnosis the advanced battery that has been used in electric vehicles. The test procedures that have been developed and followed by the automotive industries and research institutes shall be discussed. The main goal is to prepare an academic report on battery technologies from basic to modern battery testing technology for NTNU. To verify the theoretical studies made, some experimental tests of the battery following the test algorithms and flowchart is to be carried out and result shall be discussed in the thesis. Summary Literatures on battery technologies and diagnosis of its parameters are studied. Battery technologies, mainly for hybrid and electric propulsion has been developed after 1990s with the introduction of Lithium ion (Li-ion) and Sodium Nickel Chloride (ZEBRA) battery in the automotive market. Li-ion has already covered large market in portable electronic goods and now attempts are in progress for commercial production of large Li-ion battery which has high specific energy and high power to meet the energy and power demand of battery powered full electric vehicles. In order to understand and verify the battery performance, the well established test procedures developed by USABC (United States Advanced Battery Consortium) and FreedomCAR has been reviewed. Based on the standard battery test flow diagram, battery test procedures are mainly categorised as below;

1. Test plan and pre-test – readiness review 2. Core performance test – charging, discharging, power, capacity and other special tests 3. Life cycle/ageing test – accelerated ageing, calendar life, abuse and safety

Commercial battery testers are used to carryout the core performance test but electrochemical impedance spectroscopy (EIS) has been used for aging tests and also to investigate the state of health (SOH) and state of charge (SOC) of the battery. The standard test bench as shown below is used for the experiment under the scope of this thesis.

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Figure 1: Standard battery test station Study on impedance based modelling of battery and laboratory experiment to measure the impedance has been carried out. Electrochemical impedance is measured by applying an AC potential to an electrochemical cell and measuring the current through the cell using the shunt in series where battery voltage is measured directly from the terminals as shown in figure 1. Impedance is calculated internally and observed on computer through the battery test program and also observed on Nyquest plot where real part is plotted on the X-axis and imaginary part on Y-axis at one frequency. A typical impedance spectrum of a Li-ion battery tested in the laboratory at 25 0C is presented below which shows the measured impedance for different state of charge (SOC) without dc excitation current.

-60

-50

-40

-30

-20

-10

0

10

2040 50 60 70 80 90 100 110 120 130 140 150 160 170

Re Z [mOhm]

Im Z

[mO

hm]

100% SOC 80% SOC 50% SOC 30% SOC

21.7 mHz

2.1 mHz

289.8 mHz

21.7 Hz

285.7 Hz

ϑ = 25°C

217.3 mHz163.0 mHz

2.1 mHz

Figure 2: Impedance Spectra of a Li-ion battery

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At real impedance Re(Z) ≈ 42 mΩ, the real axis intersection of the impedance spectra is observed in the figure 2. For lower frequencies, all spectra show two semicircles. The first semicircle is comparably small and slightly depressed, whereas the second one is larger, nearly non-depressed and grows remarkably with decreasing state of charge. Finally, at the low-frequency end of the depicted spectra, the diffusion impedance becomes visible. At high states of charge, the diffusion impedance shows a -45°-slope, which is typical of Warburg impedance (state of diffusion at certain frequency). Conclusion Besides the limitations of previous knowledge and test infrastructures on battery technology and its diagnosis inside the NTNU, sufficient knowledge is acquired and presented on thesis. This thesis will be instrumental to establish the test facilities on batteries at the institute and industries. The commercially available battery tester and specialized impedance based spectroscopy are essential tools to perform the battery diagnosis for the advanced battery suitable to full electric vehicles. Development of battery test algorithms and models will be the possible further work to continue this project. Acknowledgement Thanks to professor Tore M Undeland for the guidance and support from the very beginning of this project. Thanks to all team members from ISEA-RWTH Aachen University, Germany who has given the opportunity to participate on different battery tests at their laboratory. Special thanks to Think Global for fruitful discussion and help in many ways to carryout this project work.

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Teknisk/økonomisk analyse av roterende kompensatorer

Et bidrag til effektiv utnyttelse av det norske sentralnettet Student: Halvor Lie Veileder – NTNU: Olav Bjarte Fosso Veileder – Statnett: Øystein Kirkeluten Utføres i samarbeid med: Statnett SF Problemstilling Et mer markedsbasert kraftsystem gjør at driftsmønsteret hos både produsenter og forbrukere i større grad følger prisvariasjoner. Denne endringen gjør at nettet blir utsatt for større lastvariasjoner enn tilfellet var før dereguleringen av markedet samtidig som flyten i nettet vil gå fra områder med lave priser til områder med større betalingsvilje. Det er derfor et stadig økende behov for overføringskapasitet i kraftsystemet. Nettforsterkninger i form av nye linjer er ofte kontroversielt samtidig som dette er kostbart. Alternative løsninger søkes derfor i økende grad for en bedre utnyttelse av foreliggende infrastruktur. Tradisjonelt har reaktiv effekt kompensering vært et tiltak som var effektivt men som har en del begrensninger når det brukes statiske omformere. Spesielt har bruk av HVDC-forbindelser mot UCTE-systemet der forbindelsen på norsk side termineres i områder som periodevis har lav kortslutningsytelse, gjort det nødvendig å vurdere alternative tiltak for styrke nettet. Det er i prosjektoppgave høsten 2007 redegjort for en del problemstillinger og alternative løsninger knyttet til å kombinere reaktiv effektproduksjon med fremskaffelse av kortslutningsytelse. I første rekke skjer dette ved å bruke roterende fasekompensatorer i stedet for statiske kompensatorer som har vært nesten enerådende ved nye anlegg de siste årene. Det ønskes en videre utredning av nytteverdier knyttet til ombygging av eksisterende anlegg som et alternativ til tradisjonelle nettforsterkninger. I tillegg til problemstillinger etablert i prosjektoppgaven fra 2007 skal det redegjøres for en teknisk/økonomisk sammenstilling av egenskaper/kostnader for alternative tiltak. I tillegg til teknisk/økonomiske beregninger skal det inngå dynamiske analyser for å vurdere tekniske egenskaper. Oppgaven Det er perioder behov for økt robusthet i sentralnettet. Kombinasjonen lav last med høy import gir kritisk lave kortslutningsverdier. Det kan føre til svært uheldige konsekvenser for driften av de to HVDC-omformerne i Sør-Norge på Feda og i Kristiansand. Konsekvenser er kommuteringsfeil i omformerne som kutter effektoverføringen og skaper store spenningsfluktuasjoner og i verste fall spenningskollaps. Problemstillingen er økende ettersom det er lønnsomhet i klassiske HVDC-prosjekter for markedsaktørene. Rapporten ser på alternativer for å imøtekomme de eksisterende og økende utfordringene. Teori av drift og regulering av HVDC-omformeren og dens utfordringer mot svake nett er beskrevet. Teorien innebefatter også en innføring av synkronmaskinen samt roterende fasekompensator som en applikasjon til å øke robustheten til nettet. Sammenfatning av tekniske og økonomiske analyser gir anbefalinger mot å investere i 160 MVA fasekompensator, 12 MVA SuperVAR og fasekompensatordrift i Tjørhom. Modell/målinger Kortslutningsberegninger og dynamiske analyser er utført i simuleringsprogrammet PSS/E i et bredt spekter av utfall og driftsforstyrrelser. Det er presentert fem mulige investeringstiltak mot å øke robustheten i Sør-Norge. Av tiltakene er det to konvensjonelle alternativer med 160 MVA fasekompensator (tiltak 2), én applikasjon

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gjennom tomgangskjøring av vannkraftgenerator der turbinen løper i luft (tiltak 1). De to siste tiltakene (4 og 5) (SuperVAR-maskiner) baserer seg på superlederteknologi i synkronmaskinens rotorviklinger som øker det transiente bidraget betraktelig. Samtlige resultater gir marginale forbedringer av systempåliteligheten. 160 MVA fasekompensator gir generelt svært gode bidrag, blant annet ved at HVDC-omformerne tåler feil i sentralnettet i nærmere avstand uten å få kommuteringsfeil etter implementering. SuperVAR-maskinene gir noe varierende resultater. De bidrar effektivt og hurtig med reaktiv kompensering etter forstyrrelser, men det var forventet et større bidrag mot å unngå kommuteringsfeil grunnet deres høye ytelse i transient forløp. Det er utført en Samfunnsøkonomisk lønnsomhetsberegning av alle tiltakene.

Figur 1 Spenning (kV) på Feda ved utfall av Feda – Tonstad (1 og 2) for samtlige tiltak. Beregninger Samfunnsøkonomisk lønnsomhet for tiltak 2 – Flytting av fasekompensator fra Sylling til Feda

Figur 2 Samfunnsøkonomisk lønnsomhet av Tiltak 2 Konklusjon Det å flytte fasekompensatoren på 160 MVA fra Sylling til Feda gir både svært pålitelige driftsforhold for HVDC-omformerne og god lønnsomhet i prosjektet. Ettersom værsituasjonene stadig blir mer ekstreme er det ikke utenkelig at vi en sommer møter lasten med lave magasiner og må importere i stor skala som gjør driften svært sårbar uten denne formen for sikkerhet.

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Beredskap i regionalnett

Student: Marte Lind Faglærer: Terje Gjengedal Utføres i samarabeid med: Statkraft

This Master Thesis deals with the importance of forecasting as exact power prices as possible for use in expansion planning. The work is a continuation of the Project Thesis finalized in December 2007 (Lind & Eggerud, 2007), which indicated certain deviations between the forecasted price fluctuation and the observed market price fluctuation. Consequently, the hypothesis of this report is that the forecasting tool has difficulties simulating under certain conditions. The analysis of prices for year 2000 to 2006 confirms the hypothesis, and states that there are significant deviations between simulated and observed price fluctuation. The deviations seem to be seasonally correlated, and the simulated prices tend to deviate more strongly for the depletion season than for the filling season. Another result is however more important, revealing major deviations for both seasons when considering the difference between the two segments of highest prices. The report shows that the EMPS model used for forecasting undervalues the prices for the heavies loaded hours, while it tends to overvalue the prices for the hours of low load. In addition, a study of monthly average prices throughout the years 2000 to 2003 shows that the model has difficulties forecasting prices during periods of frequent and important changes in price.

How this affects generation and income for the power plants used as case studies in this report is investigated through simulations with the EOPS model. Two price records are used as input in order to point out the importance of forecasting the market prices. The first price record is the simulated output from the EMPS model. The second price record is adjusted according to the study of price deviations, in order to represent the market prices to a larger extent. By improving the price forecasts (represented by adjusted price records) simulations result in considerable increase of income, although production is weakly changed. For the three power plants used in this study, annual income is increased by 0.28 % to 3.25 %. Other parameters have shown to be relevant with respect to the possibility of increasing income, and the power plant’s utilization time seems to be the most important parameter, since this provides larger flexibility. Despite the little change of accumulated production, income is considerably increased. Details on the simulated production pattern shows that this is due to a reallocation of production, from hours of low price to hours of more elevated price.

The report also states that having additional capacity may increase the income per unit of energy produced. This is valid for both price records, although the income is somewhat higher when based on the adjusted price record. Simulations show that a capacity development would give a significantly increased income, and when combined with the improved forecasting, simulated income would be considerably higher.

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In a wider perspective, the report indicates that the extended interconnection with Continental Europe will influence the Nordic power prices. Based on the study of the German and the Dutch power exchanges, it is anticipated that the Nordic countries will experience more fluctuating prices with a larger range within each day. The interconnections will introduce a larger share of thermal and wind generation, causing new challenges for the forecasting tool. Consequently, in order to evaluate a possible hydropower expansion in the future, an improvement of the forecasting will probably be required.

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Localisation of ground faults in power systems with distributed production

Student: John Mbuzi Supervisor: Hans Kristian Høidalen Summary Distribution power systems experience a lot of faults due to high network utilisation and reduced investment in the infrastructure. Single phase faults are the most common. The standard distribution systems are radial operated. Failure of any one component in the series path would result into service disruption to all customers located downstream. Current methods used to localise faults are manual and lengthy. For permanent faults, it is a common practice to sectionalise a feeder to reduce the fault investigation area. The exact location of the fault is obtained by visual inspection. However, with the introduction of the new marketing policy resulting from deregulation and liberalisation of the power industry, utility companies are required to compensate consumers for non delivery of service. Distribution networks also records high growth rates due to new customer connections arising from increased demand for electric energy. An increase in consumption introduces transmission constraints on the distribution network, demanding for reinforcement on the main circuits. The penetration of distributed production facilities intends to curtail such investment costs and provide continuity of supply to the affected customers while the fault is being resolved. The objective of the thesis was to investigate the impacts caused by different power system configurations and parameters on automatic single phase fault localisation in power systems with distributed production using power frequency quantities. It was also required to reveal the present ground fault protection schemes and recommend requirements on a system with distributed generation. The approach used in the thesis included informal conversation, field research, literature review on similar topics, modelling and simulations using PSCAD/EMTDC software. A field research was conducted in Zambia on the pretext of understanding the problem from a practical perspective. The main focus was placed on power system configuration and layout, current methods used to localise faults and fault statistics. Secondary research on automated fault localisation methods for distribution systems based on fundamental power frequency quantities was done. Much of the literature available focuses on typical radial distribution feeders. In the thesis, two different methods were used in the simulation of distances to the fault location so that the findings could be consolidated. One of the methods is a standard approach used in numerical distance protection relays and the other, was derived, taking into account the presence of a distributed generator.

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The distribution system can be solidly grounded, ungrounded, grounded through an arc suppression coil or through a resistor. Each type of grounding configuration has its own impact on fault localisation. Different system grounding possibilities were used in the model when investigating the effect of parameter change, on fault localisation. Simulation results revealed that the distances to the fault locations are adversely affected by all parameters selected for investigation. An increase in load with the same the power factor, had an impact of reducing the distance to the fault. An increase in the fault resistance had an effect of increasing the distance to the fault location. Moving the distributed generator away from the substation was seen to have had an effect of reducing the distance to the fault location. However, investigations were carried out without compensation for any of the parameters. This could have contributed to inaccuracies in the results obtained. While automatic localisation of ground faults is at the premium, it is required to minimise damages at the fault position or neighbouring equipment so that restoration of supply is prompt. This could be achieved with effective operation of the protection system. Integration of distributed production facilities can affect the dynamic behaviour of the distribution network and change the power flow. This affects operation of the conversional protection schemes deployed on the radial distribution systems. Therefore, protection schemes with a directional feature are recommended in order to improve selectivity. It can be deduced that precise ground fault localisation based on the use of power frequency quantities is a challenge due to many influencing parameters. However, automated fault localisation in power systems with distributed production is the future solution, especially from the operational perspective.

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New switching pattern for AC/AC converters with RB-IGBTs for offshore wind parks

Student: Anne Berit Mogstad Supervisor: Marta Molinas Problem description Today the offshore wind parks are located near shore and are placed on the seabed. The future offshore wind parks will be sited far from shore because of good wind conditions and not to disturb people living on the coast. Therefore the turbines most likely have to float and the weight and size of the components must be optimized. The goal of this thesis is to come up with a wind park layout which is better suited for the rough conditions offshore. The task In this thesis a new converter topology for offshore wind parks is proposed and compared with a conventional one. This topology is meant to be for large offshore wind parks sited far from shore. Since the topology is based on DC transmission in stead of AC transmission it is better suited for this type of parks. All the converters are located in the wind turbines and the turbines are connected in series directly connected to shore without any transformation stages. A design of a high frequency high power transformer is carried out and loss calculations for the one-phase AC to three-phase AC converter are performed. The reverse-blocking IGBT is investigated and compared to a normal IGBT. Model In this topology the turbines are connected in series and directly connected to shore without any transformer stages. Since the voltage across the series connected wind turbines are high enough to be transmitted directly, offshore transformer substations are unnecessary. The electrical system, from the generator to the grid connection of the turbine, is modelled in PSCAD. The model consists of an induction machine, a 3-phase AC to 1-phase AC converter,

a high frequency high powertransformer and a full-bridge converteras in the figure to the left. The AC-ACconverter has a new type of reverseblocking IGBTs and the switches arecontrolled with a new switching pattern. A design of the high powhigh frequency transformer for the

converter topology is carried out using a known method. An Excel sheet is made to calcthe necessary values that are needed to dimension the transforme

-

er

ulate r.

3 phase AC / 1 phase

AC

GAC / DC

HF transformer

Nacelle

The one-phase AC to three-phase AC converter is explained and a method to calculate the losses in the converter is given. The loss calculation method is based on the characteristics of the switch found in the data sheet. The conduction losses, turn on, turn off and recovery losses for one switch are calculated and multiplied with the number of switches in the converter. An equation of the total losses per switch is given and there are performed loss simulations for the converter in PSCAD.

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Calculation The simulations show that theswitching pattern gives the expected square wave voltage fromthe AC-AC converter. The conduction losses are simulated the results are shown in the figure to the left. The blue curve shows the conduction losses of one switch. The green peak to the leftof the blue curve is the turn-on losses and the green peak to the

right of the conduction losses is the turn-off losses. T

and

hese losses are for one switch. The design method for the 10 kHz 50 kVA transformer results in a double E-core with a centre leg of 4.5 cm made of the ferrite material N27. Both primary and secondary windings, which will be copper foils, should be wound on the centre leg of the core using a bobbin. The primary windings will be separated in two sections each section having 12 layers with two turns per layer. The secondary windings will be sandwiched between the primary sections and will consist of 24 layers with two turns per layers. Each foil conductor has a height of 4.5 cm and a thickness of 0.3165 mm. By introducing a new switching pattern the number of switching actions is halved. The sinusoidal reference signal for the PWM switching is inverted for half of the carrier period. With a square wave input to the converter, a visual switching pattern is obtained by inverting the switching sequences for half of the carrier period. With the new pattern number of times switched is halved compared to the visual switching. By comparing the RB-IGBTs to the other types of bidirectional switches it can be seen that the on-state voltage drop is halved since a RB-IGBT has the same on-state voltage drop as a normal IGBT but does not have any anti parallel diode. The architecture of the RB-IGBT is almost the same as the IGBT but with an extension of the p+-layer on the edges up to the gate insulation. This separates the sides from the active region of the chip so the leakage currents from the side surfaces of the device are blocked. Conclusion The new topology with a 3-phase AC to 1-phase AC converter, a HF transformer and a full-bridge converter, consists of fewer converter stages than the conventional topology. With one converter less the converter system has fewer switches and less switching losses come in to being. This is important because the converter losses are a great contributor to the total losses of the entire wind park. The proposed converter topology does not include a heavy capacitor and the transformer is smaller due to higher frequency. This is a weight reduction which is important to achieve for offshore wind turbines. A prototype of the converter topology with protection should be made to verify the results of this thesis. Simulation studies for the whole park including the typical characteristics of a wind turbine during operation and faults should also be carried out to see if the topology fits the harsh conditions offshore.

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Integrasjon av vindkraft i Troms

Student: Anders Ramberg Myhr Faglærer: Gerard Doorman Veileder: Harry Løvberg og Knut Vikestad, Tromskraft

Problem Description Troms Kraft (TK) har i en tidligere analyse av vindkraft funnet at lønnsomheten er for dårlig. Det ønskes likevel foretatt en ny analyse basert på simuleringer og på basis av de rammebetingelser og antagelser som foreligger i dag. Analysen skal primært fokusere på Fakken vindkraftanlegg (60 MW). A. Etabler en modell for Fakken vindkraftanlegg og implementer den i TK’s Vansimtap modell. Vurder alternative modelleringer og tidsoppløsning innenfor uka. Etabler en historisk vindserie for den tilsigsperioden som datasettet dekker. Kalibrer og dokumenter modellen. B. Foreta en vurdering av fremtidige nett-, produksjons- og etterspørselsforhold i Nord- Norge og hvilken innvirkning disse vil ha på de prisene som TK kan forvente. C. Gjør en vurdering av miljøvirkningene av vindkraftanlegget og i hvilken grad de eventuelt vil påvirke lønnsomheten. D. Utarbeid en metodikk for lønnsomhetsvurderingen av Fakken vindkraftanlegg. Metodikken baseres på at inntektene fra kraftsalg beregnes ved hjelp av Vansimtap simuleringer for å ivareta samspillet mellom vannkraft og vind. Det skal tas hensyn til usikkerheten i de ulike antagelser som må gjøres. E. Gjennomfør lønnsomhetsanalysen og de relevante følsomhetsanal Troms Kraft (TK) har i en tidligere analyse av vindkraft funnet at lønnsomheten er for dårlig. Det

Abstract Rapporten beskriver hvilken mulig effekt en investering i Fakken vindmøllepark pa Vannøya vil utgjøre for energikonsernet Troms Kraft. Det er under arbeidet utviklet gode verktøy til bruk for investeringsbeslutning. Rapporten gjennomgår og diskuterer viktige risikofaktorer som et vindkraftprosjekt vil møte. I tillegg utredes det hvilken påvirkning prosjektet vil ha for miljø og eksisterende vannkraftportefølje. Vindkraftprosjektet må sees i lys av hvilke begrensninger og muligheter som foreligger i nett, fremtidig forbruk og produksjon. Troms Kraft har tidligere utredet lønnsomheten for en vindmøllepark pa Fakken. Utredningen konkluderte med lite tilfredsstillende lønnsomhet [7]. Man ønsker likevel en ny analyse basert pa simuleringer og pa basis av de rammebetingelser som foreligger i dag. I tillegg til prosjektets lønnsomhet ønskes det ogsa at det gjøres vurderinger av risikoen.

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Denne masteroppgaven konkluderer med at forventet produksjon for en 60 MW vindkraftpark pa Fakken er 172,5 GWh. Risikoen er begrenset til et nedre estimat for produksjonen pa 156 GWh (90 % konfidensintervall). Forventet nåverdi for prosjektet er 86 millioner kroner, forutsatt kraftbransjens eget avkastningskrav og markedets forventninger til fremtidig kraftpris. Sannsynligheten for negativ nåverdi er 17 %, der mest negative scenario vil tilføre Troms Kraft konsernet -70 millioner kroner i verdi. Prosjektet avhenger i stor grad av kapitalkostnaden som prosjektet krever. Forventet internrente for vindkraftprosjektet er 11,7 %. Det er også foretatt en lønnsomhets- og sensitivitetsanalyse med stasjonær forventet prisutvikling lik 37 øre / kWh. Denne kraftprisen tilfører ingen ny verdi (ca 0 kr i nåverdi) og har enorme utslag ved en sensitivitetsanalyse. Pa bakgrunn av at en sensitivitetsanalyse kun tar hensyn til stasjonære priser, mister man betydningen som stor inntjening ved starten av prosjektet vil ha (pga avkastningskrav over lang levetid). Et kritisk punkt i prosjektet er usikkerheten i kraftmarkedet etter 2011. Analysen vurderer flere aktuelle prismodeller, men det er tydelig at man mangler gode modeller og verktøy for fremtidig utvikling over lang tid. Den virkelige prisutviklingen er et svært dynamisk forløp som avhenger av politiske prioriteringer, fremtidig forbruk og kostnadsutviklingen for ny kraftproduksjon. Investeringsbeslutning kan i dag tas pa grunnlag av lønnsomhet i prosjektet. Det anbefales likevel at det utredes et bedre verktøy for a forutse mulige scenarioer for kraftpris og støttereformer. Dette innebærer en vurdering av fremtidig kostnadsutvikling for ny produksjon i kraftsektoren.

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Investigating the Potential of Two Large Diameter Magnetic Bearings Student: Astrid Røkke

Børge Noddeland Teacher: Robert Nilssen Supervisor: Robert Nilssen

Stev Skaar Carried out in cooperation with: SmartMotor AS Problem In 1842 Samuel Earnshaw presented a theorem that is important for magnetic bearings today. The theorem implies that it is impossible to make a purely magnetic bearing (permanent magnet bearing) stable in all dimensions. This signifies that if you want forces that stabilise the system in one direction there will act forces in another direction that are unstabilising. There are ways of bypassing Earshaws theorem for example by using superconductors, controllable electromagnets or induced currents. In this assignment, we have focused on how to achieve a stable, self regulating and simple bearing by combining a permanent magnet bearing with an electrodynamic bearing. An electrodynamic bearing produces stabilising forces from the interaction of induced currents in short-circuited coils and magnetic fields. Summary

A literature study has been conducted to identify promising bearing technologies. One permanent magnet bearing, the PASF bearing, and one heteropolar self regulating electrodynamic bearing, the null flux bearing, were selected for further investigation.

PASF bearings are passive permanent magnet (PM) bearings employing change of magnetic reluctance to create force. SLC is defined as the ratio between the maximum achievable force and the total self-weight of a magnetic bearing. They claim PASF bearings can achieve a SLC up to 450:1, ten times higher than conventional repulsive bearings (RPMBs). With this in mind, we have tried to make a simple PASF bearing.

The bearings have been modelled in COMSOL and further evaluated in MATLAB. Results from the PASF computations showed an axial force shape of the PASF bearing very different from that of the RPMB. The axial force curve is steep in axial direction close to the center position. Axial force increases with radial displacement, as opposed to the RPMB. Stabilizing the PASF bearing might be difficult due to high radial stiffness. Axial PASF bearings work in both axial directions without tradeoffs between force and stiffness or concern of touching. It can be constructed to utilize the magnets in a range of the magnetization curve where they work at the maximum energy product and where the risk of permanent demagnetization is minimal.

Null flux coils are used in Maglev trains, and have also been utilized in flywheel bearings. When they are situated in a desired centre position the sum of magnetic flux through the closed coil loop will be zero, and the coil will neither exert force nor consume power. When displaced from this position there will be a net flux passing through the coil. Moving the coil gives an alternating flux which will induce currents, giving a restoring force. Hence, null flux bearings require speed to function.

Forces were calculated based on equations for induced currents and forces on currents in magnetic fields, as is also done in. Two different drag force equations were found using two different methods. Identifying the right equation will later be done by measurements. Axial forces are proportional to axial displacement, while drag forces are proportional to the square of axial displacement. As a result of a trade off between induced current amplitude and

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coinciding current and magnetic flux density, maximum force occurs when the impedance angle is 45 degrees. The bearing initially suggested, which is to be built, will only produce 5% of its own weight when displaced 2 mm. Connecting a given inductance in series with the existing ones increases the force to 77% of the rotor weight. Speed also influences the performance of the bearing.

The term unloader has been introduced by Lembke. In theory this bearing gives a constant force and no stiffness, hence it does not contribute to bearing stability. It would be very practical in applications exposed to constant forces such as gravity. Calculations performed indicate that theory does not correspond to reality in our. Further investigation is of interest, but has not been carried out in this project.

Earnshaws theorem constitutes the basis for magnetic bearing stability theory. The consequence of the physics described in the theorem is that there is no method of stabilizing a fully levitated bearing with only permanent magnets. However, there are ways of stabilizing permanent magnet bearings. Combinations of a mechanical bearing, electromagnetic bearing, diamagnetic bearing or electrodynamic bearing and a permanent magnet bearing is not covered by the theorem.

Stiffness is the change in force with respect to position. The sum of the bearing stiffnesses in all dimensions must be positive for a bearing to be stable. Earnshaw claims this is not possible for magnetic dipoles, and that the sum will always be zero. Our calculations neither confirmed, nor invalidated this allegation. A null flux bearing can contribute with a positive stiffness, making the sum positive.

For measurement and verification purposes, two test jigs were planned and nearly completed. The test jigs were constructed to allow axial force measurements with radial and axial displacement for both bearing types. Rotor and stator for both the PASF and null flux bearing were to be made of reinforced epoxy cast from the same moulds. This way the construction would be very strong, and changes in bearing design would be easy to implement in new casts. Several aspects of the building process were expected to involve difficulties. Magnet mounting turned out to be easier than suspected. Two of the main challenges when moulding epoxy is air bubbles and releasing the cast from the mould. Air bubbles were practically avoided, but releasing the cast resulted in a broken mould, terminating the building process and postponing the measurements for the time being.

A lot of work is still to be done. Finishing the moulding and assembling and performing the planned measurements are first in line. Further calculations on PASF bearings may include increasing the number of fingers and including back iron in the middle PASF finger. For the null flux bearing, varying the impedance of the coils by serial connecting inductances could improve the performance significantly. Investigating the dynamics of the null flux bearing is essential for further work on the bearing. Finally, combining a weak repulsive bearing with a null flux bearing to realise complete levitation might be feasible. Conclusion The possibility of making a passive magnetic bearing stable with the use of an electrodynamic bearing is neither confirmed nor excluded. The elecrodynamic bearing suggested in this thesis

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was unfortunately too weak. The passive magnetic bearing showed great potential, but was not finished due to manufacture complications. Simulations of the unloader showed characteristics far from what was described in theory.

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Subsea power supply for direct electrical heating of pipelines Student: Frode Karstein Novik Supervisors: Prof. Arne Nysveen, NTNU Ole-Johan Bjerknes, Aker Solutions This summary is written before submitting the master thesis and is therefore not fully completed. Problem description Direct electrical heating (DEH) of pipelines is a flow assurance method that has proven to be a good and reliable solution for preventing the formation of hydrates and wax in multiphase flow lines. The technology is installed on several pipelines in the North Sea and has become StatoilHydros preferred method for flow assurance. Tyrihans is the newest installation with 10 MW DEH for a 43 km pipline. However, the pipeline represents a considerable single-phase load which makes the power system dependent on a balancing unit for providing symmetrical conditions. This limits the step out distance and is not suitable for subsea installation. Aker Solutions has proposed several specially connected transformers for subsea power supply of DEH systems, Scott-T being one of them. This transformer provides balanced electrical power between a 2-phase and 3-phase system. This transformer has been analysed in the Specialisation Project of fall 2007. The main objective of this master thesis and study is to investigate and analyse the operational characteristics of a DEH system with the specially connected transformer implemented to it. In addition the results found in the Specialisation Project are verified. More specific, the master thesis includes:

- Design of possible configurations for DEH which can be used for long step out and for subsea installations

- Establishment of a user defined model for the Scott-T transformer in the simulation software SIMPOW for DEH system simulations. Use Dynamic Simulation Language

- Simulations on the DEH system with the Scott-T implemented during different operational modes (maintain temperature/heating) and especially investigations on the flow of reactive power

- Introduction of different fault scenarios for investigating the degree of unsymmetry in the rest of the power system

Summary of Master Thesis The Scott-T transformer is a 3-to-2-phase transformer which provides balanced electrical power between the two systems when the two secondary 1-phase loads are equal. By implementing this transformer, it can be possible to install the power supply subsea as there is no need for a balancing unit. In addition, the system may be applicable for long step outs. This is because the pipeline is inductive and can consume the reactive power produced by the long cable connected to it. Figure 1 shows a configuration of the DEH system as a 2-phase load.

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Figure 1

The DEH system in Figure 1 is divided by an onshore- and a subsea power system. The cable for supplying the load at bus 3 (pump, compressor) is 100 km long. The feeder cable for the DEH system on bus 4 is 50 km long and the pipeline itself is 100 km. The transformer T4 is the Scott-T transformer connecting the pipeline to the 3-phase system. Note that the pipeline is divided in two equal sections making it a 2-phase load. There are however some limitations on this system using the Scott-T. There is a large random variation of the magnetic permeability between individual joints in the pipeline. This can result in different load impedance of the two pipe sections connected to the Scott-T transformer. The result is unbalance in the power system. The method of symmetrical components is applied to investigate the behaviour during unbalanced loading of the Scott-T transformer, T4. The relationship between the negative sequence- and positive sequence component of the current is used to express the degree of unsymmetry. For the simulations in SIMPOW, a model for the Scott-T is established. Figure 2 shows the result from SIMPOW when varying load impedance 2 on the Scott-T.

Figure 2

The black graph shows the degree of unsymmetry when varying the impedance and the red line is the maximum continuous current that is allowed (15%). The maximum limit is exceeded when Load 2 is lower than 74% and larger than 135% of Load 1. Further work is needed on the DEH system with the Scott-T implemented in order to bring forward a conclusion, but the initial simulations show promising results.

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Offshore vindkraft - Tekniske og økonomiske vurderinger for utbygging og tilkobling

Kandidatens navn: Jørgen Olsen Faglærer: Terje Gjengedal Veiledere: Magnus Korpås, John Olav Tande Bakgrunn Fokuset på globale klimaendringer og lokal forurensing har ført til økt etterspørsel på fornybar energi i hele Europa. EU har satt seg mål om at minst 20 prosent av energiforbruket i EU-landene skal komme fra fornybar energi innen 2020. Satsning på offshore vindkraft kan bidra til å nå dette målet. Det er også behov for kraftutbygging i Norge på grunn av økende forbruk og ujevn vannkraftproduksjon. Kraftutbygging basert på andre fornybare ressurser og økt overføringskapasitet til utlandet kan bedre forsyningssikkerheten og stabilisere kraftprisene. Norge har gode vindforhold offshore, og flere selskaper arbeider med å utvikle teknologi for både bunnfaste og flytende vindturbiner. En storskala utbygging av offshore vindkraft krever også et godt overføringssystem. Kraften kan enten ilandføres med dedikert kabel eller ved tilknytting til forbindelser mellom områder. Oppgave Det skal gjøres rede for teknologi vedrørende offshore vindkraft og kraftoverføring. Oppgaven skal videre belyse dagens situasjon, utbyggingsplaner og vurdere de tekniske og økonomiske mulighetene for bygge offshore vindparker som kan tilkobles dedikert kabel eller fremtidige utenlandsforbindelser. Forbindelser til Danmark og Tyskland skal vektlegges, da disse alternativene (Skagerrak 4 og NorGer) er under planlegging. Det skal etableres simuleringsmodeller som beregner bedriftsøkonomisk lønnsomhet i ulike valgte prosjekter og utføres sensitivitetsanalyser av resultat. Sammendrag Det er behov for kraftutbygging i Norge på grunn av økende forbruk og tørrårsproblematikk. Ny kraftproduksjon basert på andre ressurser og økt overføringskapasitet til utlandet kan bedre forsyningssikkerheten og stabilisere kraftprisene. Det utredes i denne sammenheng muligheter for internasjonale kabelprosjekter og flere norske selskaper arbeider med å utvikle teknologi for bunnfaste og flytende vindturbiner. Potensialet for offshore vindkraft i norsk økonomisk sone er meget stort, men teknologien er umoden og dårlige rammevilkår i europeisk sammenheng hemmer utvikling og utbygging. De første prøveprosjektene for flytende vindkraft vil realiseres i løpet av 2009. I oppgaven utføres det en rekke simuleringer med en MATLAB-modell utviklet for å undersøke bedriftsøkonomisk lønnsomhet og sensitivitet til ulike offshore vindkraftprosjekter. Simulering av et prosjekt med 400 MW installert vindkraft tilkoblet dedikert kabel til Norge

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viser at nødvendig støtte må være en innmatingstariff på rundt 600 kr/MWh. Hvis vindkraftutbygger mottar produksjonsstøtte, må tillegget være i underkant av 400 kr/MWh med dagens kraftprisnivå. Det vil også bli mulig å koble offshore vindkraft til internasjonale forbindelser. Det er mange usikkerhetsmomenter knyttet til et slikt prosjekt. Derfor utføres det simuleringer med ulike forutsetninger for å illustrere konsekvenser av noen mulige utfall. En park med 400 MW installert vindkraft tilkoblet en forbindelse mellom Norge og Tyskland på 1000 MW blir undersøkt. Vindkraften i et slikt prosjekt viser seg å være ulønnsom med valgte forutsetninger og dagens norske støtteordning. Store inntekter på grunn av krafthandel fører allikevel til at prosjektet får en positiv nåverdi. Handelsinntektene er kun avhengig av prisforskjellen mellom områdene. Internasjonale kabelprosjekter er altså veldig lønnsomt under gitte forutsetninger. Beregningene viser at en 1000 MW kabel til Tyskland gir en netto nåverdi på om lag 5,7 milliarder kroner med 8 prosent diskonteringsrente og levetid på 25 år. I følge beregningene har kabelprosjektet positiv nåverdi selv om prisene i de to områdene jevner seg ut med om lag 50 prosent. Modellen viser at det kan være gunstig for en privat utbygger å inngå et samarbeid med Statnett som er systemansvarlig i Norge. Statnetts motivasjon for å inngå et samarbeid vil være deres berettigede del av handelsinntektene og en rekke positive samfunnsøkonomiske virkninger. En av simuleringene som er foretatt forutsetter at Statnett kompenserer for tapt støtte ved eksport av vindkraft til utland. Dersom det intalleres 400 MW vindkraft og den private aktøren eier 40 prosent av kabelen blir nåverdien rundt 1,7 milliarder kroner. På grunn av kostnadsdelingen med Statnett er risikoen mindre. Vindkraftutbyggeren får i dette tilfellet en mindre andel av inntektene fra krafthandel. En eventuell prisutjevning mellom Tyskland og Norge vil dermed få mindre konsekvenser.

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Insulation System for Rotating Machines - Optimal Solution for Offshore Wind Turbine Generator

Student: Pål Keim Olsen Faglærer: Robert Nilssen Veileder: Stev Skaar Utføres i samarbeid med: Smartmotor Problemstilling

I offshore vindgeneratorsystem er det sannsynlig at effektnivået for vindmøllene vil økes i forhold til dagens løsninger på land. Man ser i dag at de største kommersielle offshore vindmøllene ligger i effektområdet 4-6 MW. I fremtidens løsninger antar man at effektnivået vil komme opp i 8-12 MW. Økningen i effekt medfører en utfordring mht parallellkobling av store strømmer i anleggene. I dagens løsninger benyttes oftest 690 V systemspenning. For ett 12 MW anlegg antar man at spenningsnivået må økes for å få en optimal systemløsning. I denne oppgaven tar man utgangspunkt i ett 12 MW PMSM generatorsystem med fullomformer system. Oppgaven utføres som en del av ett større FoU prosjekt ved SmartMotor AS.

Optimalisering av systemspenningen avhenger av mange faktorer; generatordesign, kabling, terminering, omformeranlegg, transformatorer og landtilknytning. I FoU prosjektet har man identifisert 3,3 kV som den mest optimale systemløsningen de neste 5 – 10 år. Bakgrunnen for valget av systemspenningen ligger blant annet i tilgjengelighet og pris for omformere og transformatorer.

Utbygging av offshore vindkraft går senere enn forventet på grunn av at de installerte anleggene opplever feil i anleggsdelene. Investeringen i de store parkene ligger i milliard klassen. Usikkerhet rundt teknologi begrenser i dag offshore satsningen. Ett av hovedelementene i denne oppgaven blir å designe ett sikkert isolasjonssystem der man kan dokumentere levetid igjennom akselerert testing. Oppgaven

One of the most influential factors on the reliability of an electrical machine is the quality of the insulation system. This work proposes a way of designing insulation systems for rotating

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machinery and the method is used to analyze the requirements for an offshore wind generator. A theoretical background for insulation systems in electrical machines is presented, the aim is to give insight into fundamental material properties, how material ages and different failure mechanisms. This theoretical basis constitutes the core knowledge in the design procedure. The design procedure emphasizes the holistic system approach; the insulation system has to be viewed in correlation to the machine it is a part of and the surroundings of the machine. To design a successful insulation system thermal, magnetic, electric and mechanical aspects have to be integrated into the analysis. This approach is implemented with tools from the field of system dynamics, thermodynamics, electromagnetics and mechanics. The main steps in the procedure are 1) Specifications of the machine, limiting factors; 2) Analysis, determination of the insulation system requirements; 3) Synthesis, selection of materials, securing manufacturing quality and alternative measures to secure desired life time; 4) Testing. The procedure is of an iterative nature, i.e. in the process the engineer will move up and down the steps several times to be able to propose an ideal insulation system. Finally, a short discussion of the consequences and risks involved when increasing the operating voltage of a machine is included. Konklusjon Three main strategies for enhancing reliability of the machine are outlined: The system approach, the material approach and the manufacturing quality approach. The system approach involves the use of suitable converter topologies and electric filtering on the machine terminals, appropriate cable impedance and length, enclosure of the electric machine with air filtering and a winding design which results in low electric stresses. The material approach involves the proper selection of insulation materials and the optimum insulation thickness, the importance of good turn insulation is stressed. The manufacturing quality approach involves thorough analysis of the coil forming process and the coil installation process. The insulation system design process itself is of an iterative nature and relies on experience with electric drive trains and knowledge about insulation materials. To verify the abilities of the design, extensive testing is necessary.

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Heat Exchange in a Fluidized Bed

Calcination Reactor

Student: Bjørn Simonsen Faglærer: Per Finden Veileder:

Problem Description At the planned HyNor node at Romerike, hydrogen gas is to be produced from solar energy and bio energy. The bio energy which will be used will most likely be land fill gas from the land fill at Bøler in Skedsmo municipality. The hydrogen production unit is planned to be located at the site of Akershus Fjernvarme AS’s new central heating plant in Lillestrøm. The hydrogen production from the land fill gas will be carried out via SE-SMR(Sorption Enhanced Steam Methane Reforming). The main focus of the thesis will be on the SE-SMR reactor. The physical and thermochemical processes are studied closer, with a special emphasis on the regeneration/calcination of the CO2 sorbent which is a central part of SE-SMR, and different ways of providing the necessary heat for the calcination. In using an appropriate modelling program, the necessary heat exchange in the calcination reactor will be modelled. The model will be based upon parameters from the planned hydrogen production at HyNor Romerike.

Abstract Sorption Enhanced Steam Methane Reforming (SE-SMR) is a novel way of reforming natural gas to high purity hydrogen gas with in-situ CO2 capture by the introduction of a CO2 sorbent. The process is carried out in two steps. In the first step, hydrogen is produced and CO2 is absorbed by the sorbent. In the second step, the sorbent is exposed to high temperature heat and the CO2 is released. For the reforming to run continuously, two bubbling fluidized beds (BFB) can be coupled, one working as a reformer and the other one as a regenerator of the CO2 sorbent. The reformer works at a temperature around 500°C and the regenerator at around 900°C. Once the reactions in the reformer are being carried out the reformer works at a near autothermal state due to the exothermic reaction between CO2 and the sorbent. The regenerator however needs to be continuously supplied with heat to maintain at least 900°C and for the endothermic calcination reaction of the sorbent to be carried out. One of the ways of providing heat to the process is by internal heat exchanger tubes. The advantage of using heat exchanger tubes is that no extra gas is added to the gas already in the bed (used interchangeably with reactor), thus not disturbing the volumetric flow and gas composition of the bed. For sequestration purposes, if the gases within the bed are not disturbed by for example nitrogen, N2, they will be easier to separate and sequester. An analytical calculation of the energy balance of a calcination reactor with horizontal heat transfer tubes was carried out, and the necessary effect was found to be 14.02kW, which equates to a heat exchanger with 96

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tubes in 8 rows, taking up 26cm height in the reactor. Transferring heat via exhaust gas through metal tubes does however not yield a high thermal efficiency. One way of improving the efficiency of the calcinator is burning fuel gas directly in the reactor. This will lead to a direct heat exchange between the exhaust gas and the sorbent. On the other hand will the direct burning with air as an oxidizer lead to high fractions of N2 in the reactor. Considering that the gas in question in this work is biogas, the release of CO2 from the combustion is technically carbon neutral. Calculations for the necessary heat exchanger surface area and combustion rate of methane for the in-reactor combustion alternative have been carried out analytically, and a model of the in-reactor combustion has been established. At first, a fully fluidized bed model with integrated methane combustion was planned. Due to limitations of the modeling program and conversations with experts on the scope of the work in relation to the time-frame of the thesis, which is more closely discussed in Appendix H, the problem was reduced to a fixed bed approximation with “black box” combustion of methane outside the reactor. A heat balance, dependent on the rate of calcination was applied in the finite element modeling program COMSOL Multiphysics, and the resulting temperatures in the reactor were examined on the basis of what kind of fuel gas was used. In the first case, upgraded biogas, or SNG(Sustainable Natural Gas) was used as fuel gas. SNG is ~100% CH4, and the biogas has a CH4 content of ~48%. From the model it was seen that the mean temperature of the bed with SNG was 1218K, or 945°C, and with the biogas the temperature of the bed was 1248K, or 975°C. The calcination rate was found to be from 72.5 to 86.3% of the optimum. The lower results might be due to the adiabatic flame temperature of the gas and/or the relatively low heat capacity of the gas.

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Offshore wind power in the North Sea Student: Knut Magnus Sommerfelt Teacher: Terje Gjengedal Supervisor: Terje Gjengedal In cooperation with: Statkraft Development AS Abstact Norway has great potential for offshore wind power, but the depths just outside the coast probably make floating wind turbines necessary. In order to use today’s technology for offshore wind turbines with foundations on the seabed, water depths cannot be much larger than 60 meters. It is possible to install the wind turbines at such depths, but the distance to these areas make AC cable transmission difficult because of the reactive power production in the cables. VSC HVDC is a technology well suited for offshore wind power, and HVDC Light is now commercially available for rating up to 1174 MW. Theory for VSC HVDC in systems in general is given first in the thesis. The case for this thesis is grid integration of a 1000 MW offshore wind farm into the Norwegian power system. PSS/E was used in simulations of grid integration of the offshore wind power. Two possible connection points in the south of Norway were found based on load flow simulations; Feda and Kårstø. Only a load flow situation with peak load and production in the isolated Norwegian power system was provided. Different load flow situations for the two connection points were established in order to investigate the dynamic response at the connection points for situations with lower load and production. A case with two sets of 100 km AC cables was used for the dynamic simulations as well as a HVDC Light link with a 600 km cable. SVCs were added at the connection point for the case with AC cable connection in order to fulfil the requirement for capacitive and inductive power factor at the connection point to the grid for wind power. No such compensation of reactive power is necessary for HVDC Light, as the converter can adjust the power factor. The voltage at the connection points is 300 kV. Dynamic simulations were done based on the fault ride through requirement from the Norwegian TSO Statnett for power plants connected to voltage level higher than 200 kV. Different disturbances were done in the power system onshore close to the two connection points. The simulations done with AC cables and SVCs for reactive power compensation showed that the power system was not able to return to a stable operating point in all the simulations. With HVDC Light on the other side, simulations showed that the voltage at the connection points recovered to the pre fault value in all the simulations. The voltage recovery was within the voltage profile defined in the fault ride through requirement, and the wind turbines had to stay connected. The wind farm was modelled as one equivalent generator offshore, and a standard PSS/E induction generator model was used. For the case with HVDC Light, the voltage offshore was practically unaffected by the disturbances onshore. The energy produced during the fault was stored as rotational kinetic energy in the wind turbine in order to avoid the DC voltage to increase drastically. This is an approximation done in this thesis. Wind projects planned with HVDC Light will have a DC chopper. A fault onshore will not affect the wind farm, as the power produced during the fault is dissipated in the DC resistance.

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Beredskap i Regionalnett Student: Knut Stefanussen Faglærer: Arne T. Holen Veileder: Arne T Holen Utføres i samarbeid med: Safetec Nordic AS

Problemstilling Trondheim Energi Nett AS har satt i gang et arbeid med å etablere et grunnlag for å kunne dimensjonere beredskapslager for komponenter til regionalnettet i og omkring Trondheim. I samarbeid med Safetec Nordic AS ønsker man å utvikle en metode som balanserer hensynet til forsyningssikkerhet mot kostnadene ved å holde et beredskapslager: type og antall av komponenter. Denne masteroppgaven inngår som del av dette arbeidet.

Oppgaven omfatter følgende hoveddeler:

1. Metodikk for kartlegging av behov for beredskapslager 2. Gjennomføre en analyse basert på metodikken i regionalnettet i Trondheim 3. Vurdere resultater av analysen 4. Evaluere metodikk basert på gjennomført analyse

Sammendrag

Det er i denne rapporten utviklet en metodikk for å kartlegge beredskapsbehov for

reservekomponenter og utstyr spesielt tilpasset regionale kraftnett. Metoden er anvendt i

praksis ved en analyse utført på regionalnettet til Trondheim Energi Nett AS.

Denne metodikkens særtrekk er at det først gjøres en risikoanalyse av stasjonene i

regionalnettet som grupperer stasjonene i forhold til risiko på en oversiktlig måte i en

risikomatrise. Ut fra den kartleggingen av risiko som gjøres erverves kunnskaper om nettet og

man velger ut enkelte stasjoner som det gjøres en teknisk og økonomisk optimalisering av

beredskapen for. De vurderingene av behovet for beredskap for de utvalgte stasjonene vil i

stor grad også gjelde for de andre stasjonene i samme risikogruppe.

På denne måten kan det gjøres tekniske og økonomiske modelleringer og vurderinger av

beredskapen for et lite utvalg stasjoner som kan anvendes for flere andre stasjoner. Metoden

er tidsbesparende og dokumenter at nettselskapet har et bevisst forhold til sin beredskap av

reservekomponenter og anleggsdeler.

I analysen ved Trondheim Energi Nett er det gjort en teknisk og økonomisk modellering av to

utvalgte stasjoner for å kartlegge beredskapsbehovet for endeavslutninger og skjøteutstyr i

kabelnettet.

Det er laget forskjellige scenarioer som skisserer de økonomiske aspekter ved alternative

beredskapsløsninger for Lade og Gaustad. Scenarioene indikerer blant annet at et samarbeid

om beredskap i regionalnettet mellom flere netteiere kan være gunstig.

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Konklusjon

Som et resultat av det som er gjort i denne rapporten er det dokumentert konkrete forslag til

løsninger til beredskap av endeavslutninger og skjøteutstyr for forbindelsene til fem stasjoner

i regionalnettet til Trondheim Energi Nett AS. Metodikken kan med de foreslåtte endringer,

benyttes som et godt generelt grunnlag for å kartlegge beredskapsbehov i regionalnett.

I tillegg indikerer scenarioene som er beskrevet i rapporten at et samarbeid mellom flere

netteiere om beredskapen i regionalnettet kan være gunstig både for forsyningssikkerhet og

økonomi.

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Voltage Support in Distributed Generation by Power Electronics Student: Bjørn Erik Strand Supervisor: Professor Marta Molinas Problem description There is an increasing amount of power processed through power electronics in the areas of generation interface, energy storage and loads. This increment enables possibilities for improved solutions for efficient generation and use of electric power. Traditionally loads in AC distribution systems have been seen as passive and individual elements rather than active components of the system. An AC distribution system with high percentage of power electronic loads can be susceptible for instability under abnormal operation conditions if the converter controls are not designed for such conditions. The task This thesis introduces a solution of reactive current control for a constant power load (CPL) in an AC distribution system. A CPL is a load that draws a constant amount of active power without regard to any drops in system voltage. The resistance seen from the AC distribution system to the CPL is known as a negative input resistance which is characteristic for this kind of load. A drop in AC system voltage will result in increased current and vice versa. Hence the resulting resistance will be negative. Negative resistance behaviour is not favourable for system stability and the work has focused on a control of the converter that reduces the instability effect of the load. By controlling the reactive current component to inject current for support of the AC distribution system voltage during faults and other interferences, the load becomes an active participant in the AC distribution system. Model/ measurements The figure shows a system built in EMTDC/ PSCAD. An asynchronous generator and a fixed capacitor are used as distributed generation. The CPL consists of an AC/DC converter and a voltage dependent current source in order to keep constant DC power at the load. Focus has been on the converter control implementing a voltage oriented vector control based on a two phase rotational reference frame. Measurements of current and voltage with different voltage drop levels have been done for comparison of a CPL with and without reactive current control.

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Calculation The simulation example has verified the negative resistance phenomenon of the CPL and this is shown in the figure below.

Results show that the AC system voltage is less vulnerable in case of faults if the converter control is designed to inject reactive current into the AC distribution system. Conclusion A distributed system with CPL as load has been modeled in EMTDC/PSCAD and simulations where run under fault conditions for different voltage drop levels. The results shows that a converter control that allows the load to support the AC distribution system with reactive current increases the system stability compared to a passive load without this ability.

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Splicing and Coil Winding of MgB2 Superconductors

Student: Frode Sætre Faglærer: Magne Eystein Runde Veileder:

Description Splicing and Coil Winding of MgB2 Superconductors Aluminium extrusion billets (massive Al cylinders) are preheated to around 500 C before they are extruded to profiles. The heating is usually accomplished by using electromagnetic induction heaters operating at 50/60 Hz. SINTEF Energy Research is leading an EU sponsored project where the goal is to build a full scale induction heater with superconducting (i.e. lossless) coils. Two coils with an inner diameter of more than 1 m and each consisting of around 9 km of MgB2 superconductors are crucial parts of this device and will be designed and built at SINTEF. A semi-automatic system for putting on electric insulation on the superconducting tape and winding the tape into coils has been designed. A “wet-winding” technique is used, i.e. the epoxy impregnation is applied during the winding process. Each coil is built by stacking and joining 16 discs or “double pancake” sub-coils. Making reliable and low loss electrical joints between the superconductors of each of these discs is crucial in keeping the operating temperature sufficiently low. The student should take part in the project work, and will get the main responsibility for matters related to the joints, and will also take part in developing and modifying the procedures and techniques used for the coil winding. Hence, the assignment includes a number of primarily experimental tasks: - A study of superconductors in general, and in particular of the electrical and mechanical properties of MgB2 tapes and their use in the induction heater application. - Design, development and testing of tools and procedures for making low-loss electrical joints between MgB2 conductors. - Improving and streamlining the set-up for insulation and wet-winding of MgB2 tapes, and applying this for making the sub-coils.

Abstract Conventional induction heaters for extrusion purposes have an efficiency of only 55 – 60 %

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due to the resistive losses in the copper coils putting up the magnetic field. By using superconductor and DC current these losses can be minimized and the overall efficiency can be increased to as much as 90 %. DC current requires a new design of the induction heater were the billet has to rotate with the magnetic field perpendicular into the billet. A 200 kW induction heater is to be build by using the superconductor MgB2 which was discovered in 2001. The heater consists of two coils with 16 discs in each coil. Each disc has 75 turns inwards and 75 turns outwards with a total length of 550 metres wound in two layers. The operating temperature in the coils is 20 – 22 K and the current is 200 A. The discs in the coils have to be joined together in a resistive overlap joint. The joints will generate heat which must be cooled away and will decrease the critical current (highest current the superconductor can conduct). It is important that the joints have low resistance and can be made in fairly reproducible way. A tool to make these joints was therefore made and tested. The overlap joints had a length of 10 cm and had a resistance of maximum 71 nΩ. When increased the force pressing the conductors together the highest resistance was 48 nΩ which will generate 2 mW of heat each if a operating current is 200 A. The critical current was decreased due to the joints. The critical current was found to be 238 A at 30 K and approximately zero magnetic field density. The expected critical current for the joints are approximately 400 A at 25 K. With an expected reduction in critical current of 15 % due to the magnetic field in the joints can still conduct the operating current of 200 A with a large safety limit. To be able to determine the performance of the joints the temperature has to be measured with a certain degree of accuracy. This was a problem in the work with testing the joints and the accuracy of the thermometer itself had to be carried out. The thermometer was the temperature dependency of the resistance in a 0.1 mm copper wire. The deviation from the given resistance ratio increased at lower temperatures and caused a misreading of as much as 5 degrees at 21 K. It was determined that the thermometers are not recommended to use at temperatures below 35 K and that they need a calibration before use at higher temperatures if high accuracy is required. The superconducting tapes are insulated in polyimide film before they are wet-wound in an epoxy with high thermal conductivity. The insulation and winding of these discs have been going on in parallel with the joint testing and the process is described in this report.

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Expert system for hydropower stations developed in Volve Knowledge Tools Student : Erlend Timberlid Supervisor : Lars Norum Contact : Øyvind Holm, Frode Sørmo Collaboration : Voith Siemens, Volve AS Problem description Despite the fact that hydropower stations are equipped with the latest technology in both regulation and remote control, it is not enough to replace the traditional machine expert. The machine expert was a person stationed in the power plant. He had the responsibility for the running and maintenance of the station. This person’s experience and human senses made him crucial for the surveillance of the station. Since the machine expert has now been replaced by electronics and newer technology, there are still areas of his expertise that are to be made. Today’s facilities are highly sophisticated and contain the latest technology, but there are still situations that the surveillance system may fail to intercept. These situations could for instance be the beginning of an fault in an component. To help the surveillance system detect these situations, the idea is to implement an expert system. In this way the control system can match the machine expert’s skills. Øystein Fjellheim has already done extensive work in finding a suitable development kit. He explored several software packages looking for one to use for this purpose. The result was the program Volve Knowledge Tools, and the purpose of this report is to further test this program for use in expert systems. This testing considers more advanced and intelligent forms of reading raw data, such as mean calculation, derivation and integration. It also includes testing of how the program learns and uses existing knowledge to solve problems. The Task The intention of this report is to investigate if Volve Knowledge Tools is capable of performing the functions required of an expert system. This investigation is about exploring the software and mapping the features it possesses. To explore the software a program has been developed and tested through simulations. Since hydropower plants can be constructed in so many ways, it is almost impossible to make an expert system that can include all varieties. One solution is to narrow down the system to a reference system. This system consists of defined components that are common in today’s facilities. Despite this narrowing there are still many processes in a hydropower station that need to be monitored. Voith Siemens has promoted that thermal surveillance is desirable. The reason is that, when performing thermal surveillance, the rest of the system would be indirectly monitored as well. A good example of this would be to monitor the bearings. To detect the condition of a bearing, one has to compare several parameters, of which temperature is the most essential. Two conditions of the bearing are simulated, defective bearing and water in the bearing oil. To create a program in Volve Knowledge Tools it is necessary to go through three steps: creating an ontology model, a causal model and a case model. To these three models

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information about the process is added. When all three steps are accomplished, the program has extensive information about the process. The models consist of information about which process the program will modulate. It also knows how the components work together, how the system reacts to errors and what errors that may occur. All the models that have been created, are constructed in such a way that it is easy to expend them, and by this, easy to continue with. In this report three simulations have been performed, one for each case. The cases contain two ways of detecting a defective bearing, and the final simulation concern detecting water in bearing oil. All detections of error states are based on comparing parameters. The symptoms of a defective bearing are mainly that the temperature in the bearing segments increases and vibrations are detected. These two parameters are compared with the position of the cooling water valve, the produced effect and the oil level. If vibrations are detected, the temperature in the segments is increasing, the cooling water valve’s position is 100%, the aggregates are not running on overload and the oil level is normal, it can be said with great certainty that a bearing is defective. This way of detecting a defective bearing represents Case 1. Case 1 contains the integration part. Sometimes when a bearing is defective the temperature increases very fast. Today’s surveillance does not include this form of monitoring, but only observes the maximum level of the absolute temperature. When the temperature increases rapidly in a hydropower station today, nothing is triggered until the temperature reaches its pre-warning level. By the time the temperature reaches its critical value, the aggregate goes to emergency stop. This scenario represents case 2 and contains derivations. The final case is detecting if there is water in the bearing oil. To do this, the oil level in the bearing will be considered. Since it is normal that the oil level is varying during operation, the mean value of it is considered. As a comparison with this parameter the running time of the reserve bilge pump and the temperature in the bearings are monitored. The reason for monitoring the reserve bilge pump is to detect if the water in the bilge sump is increasing, which would be a result of a water leakage. The parameters are compared with the produced power. The simulations have proved that Volve Knowledge Tools can predict faults at an early stage, and therefore see to that the aggregates can be driven more efficient way. The program has also proved it self to be user friendly and is an important user support for a human operator. Conclusion By developing a simple expert system in Volve Knowledge Tools and using this program for simulations, I gathered a lot of information about how the program operates and functions. After considering advantages versus disadvantages, and the suitability of the program for developing expert systems, I concluded that: Volve Knowledge Tools fulfils the demands that the development an expert system entails. I therefore recommend by Volve Knowledge Tools as the development kit for evolving an expert system in continuing work.

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Energiforsyning til sykehus i Sudan basert på solenergi

Student: Camilla Bakken Torp Faglærer: Per Finden Veileder: Øystein Ulleberg, Institutt for energiteknikk Oppgavetekst Normeca as er et norsk selskap som i 2007 bygget et modulbasert sykehus til Sudan. Normeca arbeider nå videre med tilbud på ytterligere leveranser av flere sykehus. Sykehusene er i dag basert på energiforsyning fra aggregater drevet med fossilt brensel (diesel), men de arbeider med planer om i fremtiden å kunne levere sykehus med teknologi som i størst mulig grad bruker fornybar energi. Oppgaven består i å gjennomføre en analyse av ulike konsept som belyser hvordan solenergi konkret kan dekke energibehovet til varmt tappevann, oppvarming, kjøling, og elektrisitet til utstyr og belysning. Det skal legges vekt på hvordan man på en optimal måte kan fase inn solenergi for å dekke disse energibehovene. Kjøling ved hjelp av absorpsjonskjølere drevet på varme fra termiske solfangere skal være i fokus. Oppgaven skal utføres ved å modellere systemene og bruke simuleringsverktøy for optimalisering. I tillegg skal det gjøres beregninger av kostnader knyttet til de ulike alternative løsninger.

Sammendrag Denne masteroppgaven er gjennomfort ved Institutt for Energiteknikk på Kjeller (IFE) i samarbeid med Normeca A/S, varen 2008. Rapporten tar for seg ulike energisystemer basert på solenergi til bruk i feltsykehus i deler av verden med høy temperatur og stor tilgang på sol. Sykehusene har hoyt kjolebehov, ingen muligheter for tilknytning til elektrisitetsnett og er ofte plassert uten for sentrale veinett. Utgangspunktet for oppgaven er en forespørsel fra Normeca AS, en leverandor av feltsykehus, til Institutt for energiteknikk (IFE) om a se på energiforsyningssystemet til deres prefabrikkerte mobile feltsykehus. Ettersom sykehusene har stor tilgang pa sol er det ønskelig a ta i bruk energisystemer drevet på solenergi. Det høye kjolebehov i kombinasjon med den gode sol tilgangen gjør det ekstra interessant a se på kjolesystemer drevet med solenergi. Energiforsyningen er i dag basert på strømproduserende dieselaggregater. Ved hjelp av et modelleringsprogram skal ulike alternative energiforsyningssystemer, i hovedsak basert på solenergi, modelleres. Simuleringer og lønnsomhetsanalyser skal gjøres for a finne kunne anbefale et mulig solenergibasert energisystem for sykehusene. Første del av rapporten er en teoridel som beskriver solenergisystemene som skal brukes, samt dataverktøy og metoder for lønnsomhet. En termisk solfanger er en enhet som tar imot innstrålt solenergi og konverterer det til varme. Varmen avvis til et varmelager via en varmebærende krets. Varmelageret lagrer varmen til den trengs pa forbruksstedet. De finnes i hovedsak tre typer termiske solfangere; plane vaskesolfangere, vakuum solfangere og konsentrerende solfangere. For energisystemet i oppgaven er det valgt å bruke vakuumsolfangere som gir høy temperatur og god

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virkningsgrad til en fornuftig pris, samtidig som den kan monteres som en integrert del av en bygning. Solenergi produsert med termiske solfangere og som brukes til a produsere kjoling i absorpsjonskjølere har fokus i oppgaven. En absorpsjonskjolemaskin er en innretning som bruker varme til å produsere kjøling. Grunnprinsippet er det samme som for en vanlig kompresjonsmaskin (for eksempel en luft – luft kjolepumpe) som bruker en vaskes evne til å kondensere og fordampe ved ulik temperatur bestemt av metningstrykket til a flytte varme fra et sted til et annet. I stedet for å bruke mye elektrisk energi i en kompressor til å heve trykket på den fordampede vasken, bruker absorpsjonskjolemaskinen drivkraften fra en kjemisk reaksjon mellom to medier som gjør at det ene mediet absorberer det andre, og en vaskepumpe til å øke trykket. Varmen som er drivkraften i syklusen, brukes til igjen å fordampe det ene mediet ut av det andre slik at syklusen fortsetter. Varme produsert av termiske solfangere kan brukes som drivkraft i prosessen. En solcelle er en enhet kan gjøre om sollys direkte til elektrisk energi. Det er ikke lagt spesielt fokus på beskrivelse av solcelleteknologien i oppgaven ettersom det er solfangerne og absorpsjonskjøleren som har hovedfokus. Modelleringsprogrammet som brukes er Trnsys, et fleksibelt simuleringsverktøy brukt til å gjøre dynamiske simuleringer av ulike energisystemer. Programmet baserer seg på at brukeren lager modeller av energisystemene ut fra alle komponentene systemet skal besta av. Det finnes over 400 tilgjenglige komponenter tilgjenglig for å beskrive systemene. Modellene brukes til å gjøre simuleringer på energi produsert og forbrukt og inneholder klimadata for a teste systemene over hele verden. Lønnsomheten til de ulike energiforsyningssystemene er vurdert ut fra en sammenlikning av systemenes årskostnad. Årskostnadene er beregnet med årskostnadsmetoden som gar ut på å regne sammen alle de forventede inntekten og utgiftene til energisystemet til like store årlige beløp. Beregningene tar utgangspunkt i en kalkulasjonsrente pa 4,5 % og en levetid på systemene på 20 ar. Driftskostnadene kostnader til innkjøp av diesel, med en dieselpris oppgitt fra Normeca på 6,43 kr/L eks. mva. For a se på en fremtidig mulig okning i dieselpris er det og gjort lønnsomhetsvurderinger med en dieselpris på 10,0 kr/L. Normeca signerte i september 2006 en avtale med myndighetene i Sør- Sudan og helse-departementet om byggingen av 10 semi - permanente statlige sykehus i Sør-Sudan inkludert totalt 50 mobile klinikker og 2 flyende sykehus for Nilen. Det første sykehuset, Katiko Referral Hospital, er levert til en by som heter Kapoeta sørøst i Sør-Sudan. Dette sykehuset består av 150 containere og i tillegg 160 containere til boliger for de ansatte. For utviklingen av det soldrevne energisystemet er Normeca interessert i a se på en mindre enhet som kan leveres alene eller kobles sammen som flere enheter til et sykehus av samme størrelse som Katiko Referral Hospital. Denne mindre enheten er designet av Normeca og kalt en Satellittklinikk. Satellittklinikken består av 22 containere og har et totalt areal på 406 m2. Den skal inneholde alt av nødvendige fasiliteter for a kunne fungere som et komplett helsetilbud på mindre steder. For modellering og utvikling av modeller for energisystem i oppgaven, er det tatt utgangspunkt i Satellittklinikken som bygning og informasjon om dagens energisystem og lokasjon fra Katiko Referral Hospital.

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Dagens energisystem er basert på strømproduserende dieselaggregater. Elektrisk energi brukes til a dekke alt energibehov til utstyr, belysning, oppvarming av varmtvann og kjøling. Bygget har ikke noe romoppvarmingsbehov. Kjølingen produseres med luftkondisjoneringsanlegg plassert på hvert rom, og varmtvann oppvarmes med elektriske varmeelementer ved tappepunktet. Dieselen transporteres totalt 1 600 km for den kan brukes i aggregatene. En estimering av solenergi lokalt over aret i Kapoeta ved hjelp av NASA klimadata gir årlig innfallende stråling på horisontal flate pa 2 014 kWh, til sammenlikning har Norge ca. 1 000 kWh/ar. Dette tyder på gode muligheter for bruk av energisystemer basert pa solenergi. For a kunne utvikle et energisystem for Satellittklinikken var det behov for a vite noe om energibruken i bygningen. Det ideelle hadde vart a ha tilgang på lastkurver for elektrisitetsbruk til alle energikrevende komponenter i bygningen, men siden Satellittklinikken kun foreløpig er på tegnebrettet og Katiko Referral Hospital er betydelig større og heller ikke har noe oversikt over forbruket, er det gjort manuelle estimeringer av energibehovet basert på standard verdier. Standardverdiene er hentet fra Norsk Standard for sykehus og tilpasset forholdene så godt som mulig etter Katiko Referral Hospital. Informasjon i selve bygningskonstruksjonen er oppgitt fra Normeca. Beregninger er gjort i Excel ved hjelp av likninger for energibruk i bygninger. Det er i beregningene tatt utgangspunkt i gjennomsnittlige månedlige verdier for solinnstråling og utetemperaturer for Kapoeta. Årlig energibehov til Satellittklinikken er estimert til 83 903 kWh. Ved hjelp av resultatene fra den manuelle estimeringen, og verdier for brukstid er det laget lastprofiler for forbruket som beskriver effekt per kvadratmeter i løpet av en dag. Ettersom energisystemet som skal modelleres skal bruke solenergi som gir produksjon av energi på bestemte tider av døgnet, er det nødvendig a vite når energien forbrukes. For å modellere dette er det laget en modell i Trnsys som brukes som utgangspunkt for energiforsyningsmodellene og som beskriver de ulike energibehovene i Satellittklinikken time for time over året. Denne modellen er kalt Lastmodellen, og den baserer seg på lastprofilene laget fra den manuelle estimeringen og standard verdiene. Trnsys inneholder ikke klimadata for Kapoeta, så klimadata for nærmeste sted, Kisangani i Demokratiske Republikk Kongo, er blitt brukt i stedet. Kisangani har laveres gjennomsnittstemperatur og solinnstråling enn Kapoeta. Energibehovet estimert med Lastmodellen er 89 377 kWh/ar. Verdien er høyere på grunn av en okning i kjolebehovet pa grunn av at time for time verdiene for solinnstråling i kombinasjon med høye temperaturer gir mye større utslag enn gjennomsnittsverdiene. For det ses på muligheter for bruk av energisystemer basert på fornybar energi er det viktig a redusere energiforbruket til et minimum for a spare investeringskostnader og unødvendig bruk av komponenter (brukes mye energi for å lage komponentene). Det er gitt forslag til en rekke energisparende tiltak som kan brukes i Satellittklinikken, men ettersom det er så lite informasjon tilgjengelig om utstyrsbruken og flere usikkerheter i lastbruken er det ikke kjørt simuleringer på flere enn et av tiltakene. Tiltaket som er testet gikk ut a orientere Satellittklinikken slik at kortsidene på bygningen vendte mot vest og øst, som har størst solinnstråling, og at det kun er vinduer pa langsidene. Målet var a redusere solinnstråling gjennom vinduene som gir okt kjølebehov. Tiltaket reduserte energiforbruket med nesten 3 000 kWh ned til 86 791 kWh/år. Tiltaket ble utfort for videre utvikling av energiforsyningsmodellene.

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For å ha et utgangspunkt a kunne sammenlikne de nyutviklede energisystemene med, ble det laget en modell som beskriver energisystemet til Satellittklinikken ut fra beskrivelsen av energisystemet til Katiko Referral Hospital i Kapoeta. Denne modellen er kalt Dieselmodellen. I Dieselmodellen dekkes alt energiforbruk i Satellittklinikken med elektrisk energi produsert med dieselaggregater, inkludert kjøling med luftkondisjoneringsanlegg. Simulering av Dieselmodellen viste at originalt energiforbruk i Satellittklinikken vil vare 17 746 liter per år. Årskostnaden til anlegget er 128 212 kr med en dieselpris på 6,43 kr/L og 191 566 kr med en dieselpris på 10,0 kr/L. Det ble laget fire nye energiforsyningsmodeller for Satellittklinikken. De tre første, Alternativ 1, 2 og 3 baserer seg p bruk absorpsjonskjolemaskiner til kjøling av bygget i med ulike kombinasjoner med og uten solfangere og solceller. Kjølingen distribueres gjennom bygningens ventilasjonssystem. Den siste, Solcelle- dieselmodellen, implementere solceller i Dieselmodellen og bruker fortsatt luftkondisjoneringsanlegg til å produsere kjøling. Målet med simuleringene av modellene er a finne den losningen som gir størst mulig reduksjon av dieselforbruket og god lønnsomhet sammenliknet med Dieselmodellen. Beste losning skal finnes ut fra lønnsomhets-beregninger med dagens dieselpris på 6,43 kr/L. Lønnsomheten til alternativene med dieselpris på 10,0 kr/L er beregnet for å gi et bilde av lønnsomheten med bruk av solenergi dersom dieselprisen stiger i fremtiden. Alternativ 1 bruker spillvarmen fra dieselaggregatet til a drive en absorpsjonkjolemaskin, og til oppvarming av varmtvann. En dieselfyrt oljekjel sikrer back- up varme. Alternativet gav en reduksjon i dieselforbruket på 2 195 L/år i forhold til originalt forbruk. Systemet vil gi en årlig sparing på 6 900 kr med dieselpris på 6,43 kr og 14 737 kr med dieselpris på 10,0 kr. Alternativ 2 er likt Alternativ 1, men har i tillegg termiske solfangere for å produsere varme til absorpsjonskjøleren slik at det blir mindre behov for energibidrag fra den dieselfyrte oljekjelen. Det ble gjort simuleringer for Alternativ 2 med varierende solfangerareal fra 10 til 120 m2. Beste losning for Alternativ 2 vil ha 60 m2 solfangere. Denne losningen vil redusere dieselforbruket med 5 335 L/ar og gi en årlig sparing på 9 415 kr. Dersom dieselprisen stiger til 10,0 kr/L vil en losning med 70 m2 solfangere gi best lønnsomhet. Denne losningen vil gi en årlig reduksjon i dieselforbruket på 7 458 liter, og en årlig sparing på 28 746 kr. Alternativ 3 er likt Alternativ 2, men har i tillegg solceller som reduserer den elektriske lasten inn på dieselaggregatet og dermed også dieselforbruket i aggregatet. Det ble gjort simuleringer for Alternativ 3 med varierende solfangerareal fra 10 til 120 m2 og solcellesystemer med maksimal effekter fra 1,29 til 11,64 kWp. Beste losning for Alternativ 3 vil ha 70 m2 solfangere og et solcellesystem med maksimal effekt på 9,05 kWp. Denne løsningen vil redusere dieselforbruket med 9 561 L/ar og gi en årlig sparing på 9 824kr. Dersom dieselprisen stiger til 10,0 kr/L vil samme losning som den beste med dieselpris på 6,43 kr/L gi best lønnsomhet. Årlig sparing vil da vare 43 957 kr. Solcelle- dieselmodellen er lik Dieselmodellen, men har i tillegg solceller som reduserer effektbehovet inn på dieselaggregatene ved a dekke deler av lasten. Det ble gjort simuleringer for Solcelle- dieselmodellen med solcellesystemer med maksimal effekter fra 1,29 til 25,8 kWp. Beste losning for Solcelle- dieselmodellen vil ha

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et solcellesystem med maksimal effekt på 23,2 kWp. Denne losningen vil redusere dieselforbruket med 9 731 L/ar og gi en årlig sparing på 1 866kr. Dersom dieselprisen stiger til 10,0 kr/L vil en løsning med et solcellesystem med maksimal effekt på 18,1 kWp gi best lønnsomhet. Denne losningen vil gi en årlig reduksjon i dieselforbruket pa 9 150 liter, og en årlig sparing på 41 257 kr. Ut fra kriteriet om at beste losning vil vare den losningen som gir en høy reduksjon i diesel-forbruket samtidig som den gir god lønnsomhet sammenliknet med Dieselmodellen, anbefaltes Alternativ 3 med 70 m2 solfangere og et solcellesystem med maksimal effekt på 9,05 kWp som det beste energiforsyningssystemet til Satellittklinikken ut fra dagens energipris på 6,43 kr/L. Det er forutsatt at dette energisystemet installeres i forbindelse med byggingen av Satellittklinikken og at det ikke finnes noe energiforsyningssystem på stedet fra for. Dersom et alternativt energiforsyningssystem skal etterinstalleres i et sykehus med et allerede eksisterende energiforsyningssystem tilsvarende Dieselmodellen, vil Solcelle- dieselmodellen anbefales fordi den vil utnytte det eksisterende anlegget best og derfor kreve mindre etter-innstalleringer. Det er i oppgaven vist at det er gode muligheter for Normeca å installere et energisystem basert på solenergi og at det derfor bør gjøres. Dimensjoneringen av systemet krever ny, nøyaktig kartlegging av Satellittklinikkens energibehov dersom de virkelige verdiene varierer sterkt med de verdiene som er brukt i oppgaven.

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Elektrisk Fremdriftsystem for Shell Eco-marathon PureChoice Kjøretøy Beregning av motorstørrelse for drivstoffgjerrig hydrogenkjøretøy

Student: Bjørn Ola Wiik Veileder: Lars Norum

”Shell Eco-marathon Europe” ble første gangen arrangert i 1985 og går ut på at studenter fra

høyskoler og universiteter i Europa konkurrerer om å bygge den mest energieffektive bilen.

NTNU stilte i år med sitt første bidrag i konkurransen i klassen Urban Concept. Studentene som

har stått for byggingen av bilen er tverrfaglig gruppe fra fem institutter og har hatt prosjektet som

masteroppgave våren 2008.

Shell Eco-marathon 2008 ble avholdt "Paul Armagnac Race Circuit" utenfor Nogaro i Sør-

Frankrike. Data for banen er hentet inn, og sammen med PureChoice kjøretøyets parametere ble

det gjort beregninger for effektområdet for elektrisk motor til bruk i fremdriftssystem.

Beregninger viste at det var hensiktsmessig med kraftig akselerasjon ved start, og effektbehovet

her ble dimensjonerende for motorens størrelse.

Ulike motortyper gir ulike muligheter. Etter en del vurderinger rundt teknologier og behov ende

valget på børsteløs likestrømsmotor. Motorer av denne typen er separatmagnetisert ved hjelp av

permanentmagneter og komuterer ved bruk av motordrift med komuteringslogikk og

vekselretterbro. BLDC-motorer har høyt forhold mellom effekt og vekt, noe som var spesielt

gunstig i denne situasjonen.

Testing av fremdriftssystemet i laboratoriet har vist forskjellen i virkemåte for ulike former for

tilbakekobling av rotorposisjon. Både løsning med Hallsensor og metode for måling av mot-

indusert spenning er prøvd ut. Målinger gjort for de ulike motorenes virkningsgrad avgjorde

hvilken modell som ble brukt i fremdriftssystemet.

I løpet av april og mai ble PureChoice kjøretøyet satt sammen og ferdigstilt for deltakelse i Shell

Eco-marathon den 22. til 24. mai 2008. Ved montering av fremdriftssystemet i kjøretøyet ble det

lagt vekt på så enkle løsninger som mulig. Med dette menes at det ikke ble lagt til funksjoner

utover det som var behovet for et funksjonelt fremdriftssystem. Resultatet ble et ryddig og

oversiktlig motorrom som var lett å feilsøke og endre på.

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Virkningsgraden for fremdriftssystemet er avgjørende for hvor langt det er mulig å kjøre på

energiinnholdet i en liter bensin. Illustrasjonen viser tapene som forekommer fra hydrogentank til

bevegelsesenergi ut på hjulet for PureChoice kjøretøyet.

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Kvalitetssikring av polymerisolerte HVDC-kabler ved hjelp av spenningsprøving

Student: Marit Holbø Ytterstad Faglærer: Erling Ildstad Veileder: Erling Ildstad Utføres i samarbeid med: Bedrift/annet lærested Problemstilling På grunn av marked og miljøhensyn er det en økende interesse for storskala utveksling av elektrisk kraft over lange avstander. Norsk industri og E-verk er sentrale aktører i denne utviklingen og flere HVDC kabelforbindelser er under planlegging, blant annet er det aktuelt med flere nye forbindelser til Nederland/Tyskland og til olje/gass installasjoner i Nordsjøen. For systemspenninger over ca 150 kV er det i dag kun oljeimpregnert papir som benyttes som HVDC-kabelisolasjon. Isolasjonssystem basert på ekstruderbare polymerer har i lang tid vært under utvikling, men mange spørsmål er fortsatt ubesvart. En slik aktuell problemstilling er valg av prøvemetodikk for dokumentasjon av produksjonskvalitet og langtidsegenskaper. Den prøveprosedyre som velges må kunne brukes på 10 - 50km lange kabler, være relevant i forhold til driftspåkjenningen og i stand til å detektere de produksjonssvakhetene som vil kunne gi økt sannsynlighet for driftshavari. Denne hovedoppgaven er en del av et NFR- og industristøttet prosjekt der formålet er å utvikle prøveteknikker for kvalitetskontroll og deteksjon av isolasjonssvakheter i HVDC-polymerisolerte kabler. Oppgaven To alternative testmetoder ble vurdert. Den ene metoden gjelder bruk av lavfrekvent (VLF) AC-spenning, mens den andre metoden er å utsette kabelen for DC-spenning en bestemt tid, for deretter å jorde den ene enden og dermed oppnå en rask endring av det påtrykte feltet. Vurderingen av de to testmetodene ble gjort ved å studere effekten av å påtrykke spenning med forskjellige frekvenser på testobjekt med ”kunstige” defekter i form av innesluttede nåler. Kryssbundet polyetylen (PEX) fra en 12kV fordelingskabel ble valgt som isolasjonsmateriale. Først ble det utført levetidsforsøk på 1,20m lange kabelseksjoner. Her ble avstanden mellom nålespissen (50 µm) og den indre halvlederen holdt konstant 1,4mm. Tid til havari ble målt som funksjon av spenningsnivå og frekvens. Videre ble det utført DC-kortslutningstesting med samme type kabelobjekter. Testobjektene ble påtrykt en DC-spenning i omtrent 24 timer før jordingene ble satt i gang med intervaller på 60 sek. Til slutt ble treveksteksperimentet utført ved å stikke akupunkturnåler inn i 2,0mm tykke blokker av PEX-isolasjon. Isolasjonsavstand ble holdt til 1,0mm for alle prøveobjektene. Vekstraten til elektriske trær ble studert under mikroskop for ulike spenningspåtrykk og frekvenser, også her ble DC-kortslutningstesting gjennomført. Modell/målinger Det eksperimentelle oppsettet brukt for levetidsforsøken (50 hz, 0,1 Hz og 0,02 Hz) av kabelobjekt med nål er vist i figuren til venstre. En skisse av oppsettet brukt for kortslutningstestene er vist i figur 2. Et kulegap med en releedrevet jordingsnål sørget for kortslutniger. Dette releet ble digitalt kontrollert av en datamaskin for å sikre lik påkjenningstid og like intervaller mellom jordingsbølgene.

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Figur 1: Eksprimentelt oppsett for levetidsforsøk av PEX-kabelobjekt for 50 Hz, 0,1 Hz og 0,02 Hz.

Figur 2: Eksperimenteltoppsett for DC-påtrykk med påfølgende jording av PEX-kabelobjekt med nål.

Skissen viser det eksperimentelle oppsettet brukt for undersøkelsen av elektrisk trevekst i 2,0 mm tykke PEX-blokker.

Figur 3: Eksperimentelt oppsett for undersøkelse av elektrisk trevekst i PEX-blokker med nål nedsenket i olje. Beregninger Resultatet fra AC-levetids- og DC-kortslutningstesting av kabelobjekt med nål er vist under.

1,00

10,00

100,00

1 100 10000 1000000

1E+08

log antall perioder

log

U [k

V]

50 Hz

0,1 Hz

0,02Hz

DC +jording

Figuren under viser vekstraten og initieringstiden til elektrisk trevekst ved ulike spenningspåtrykk for henholdsvis 50 og 0,1 Hz. Testobjektene brukt her er 2 mm PEX-blokker med nål.

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50 Hz

0

0,20,4

0,60,8

1

0,00 10,00 20,00

[min]

[mm

]

6,25 kV 6,50 kV 8 kV

10 kV 12 kV 6,25 kV

0.1 Hz

00,20,40,60,8

1

0,00 10,00 20,00[min]

[mm

]

12 kV 14 kV 16 kV 18 kV22 kV 14 kV

Konklusjon Følgende hovedkonklusjoner kan trekkes ut fra arbeidet:

• Levetidsforsøkene for kabelobjekt med nål viste at gjennomslag skjer ved skarpe, ledende partikler som et resultat av AC-påtrykk. Resultatene viser at havari inntreffer ved lavere spenning og etter kortere tid ved økende frekvens. Det betyr at man for VLF enten må øke testtiden eller testspenningen sammenlignet med 50 Hz.

• DC-kortslutningstestingen viste en klar reduksjon i DC-holdfastheten som funksjon av raske jordinger med økende spenningsnivå. Disse målingene indikerer at DC-påtrykk etterfulgt av raske jordinger kan bli en effektiv testprosedyre for å avsløre svakheter i polymer HVDC-kabler før installasjon.

• Treveksteksperimentet bekreftet at tiden til gjennomslag reduseres med økt spenningspåtrykk. Vekstraten øker, og initieringstiden avtar med frekvensen. Resultatene fra levetidstestingen og undersøkelsen av elektrisk trevekst for 0,1 og 0,02 Hz indikerer at VLF kan bli en nyttig testmetode for å detektere uregelmessigheter i kabler med polymerisolasjon.

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Korleis nytte fleirmåls beslutningsanalyse og influensdiagram til vedlikehaldsplanlegging av sjøkabelanlegg.

Student: Hans Ørjasæter Faglærer: Eivind Solvang Veileder: Eivind Solvang Utføres i samarbeid med: BKK Nett AS Problemstilling

Problemstillinga i oppgåva er å sjå på korleis fleirmåls beslutningsanalyse (FMBA) og influensdiagram kan brukast ved vedlikehaldsplanlegging av sjøkabel i distribusjonsnettet. For å verte kjend med Netica er delar av prosjektoppgåva ”Vedlikehold og fornyelse i BKK Nett” frå hausten 2007 brukt til å lage ein modell. Denne vart basert på ein lastsituasjon med 4 sjøkablar som forsyning til eit område. Oppgåva har omfatta følgande aktivitetar: 1. Etablere nytteverdimodell i Netica for sjøkablane som vart analysert i prosjektoppgåva. 2. Beskrive aktuelle risikofaktorar og KPIar for sjøkablar hos BKK Nett med hensyn til økonomi, leveringspåliteligheit, personsikkerheit, omdømme, ytre miljø og teknisk tilstand. 3. Gi ein kort oversikt over aktuelle vedlikehaldsstrategiar for sjøkablar i fordelingsnett. 4. Etablere ein risikomodell for sjøkablar med beskrivelse av datagrunnlag, analysemetodar-/verktøy og resultatpresentasjon. 5. Implementere risikomodellen for utvalgte sjøkablar hos BKK Nett, samt analysere/beskrive risikoen for sjøkablane ved hjelp av risikomodellen. Oppgaven

Vedlikehald av sjøkabelanlegg er eit tema som det er lite fokus på i mange nettselskap, og lite feil og statistikkar fører ofte til ein havaristyrt strategi. I denne oppgåva ser ein på korleis fleirmåls beslutningsanalyse og influensdiagram kan brukast til å vurdere tilstanden til sjøkabelanlegg. Dette for at ein på ein betre måte skal kunne sortere ut dei anlegga med dårligast tilstand.

FMBA-verktøyet som er brukt er ein prototyp frå Sintef som er basert på MS Excel og dette har ikkje vore brukt på ei slik problemstilling før. Verktøyet har stort sett vore brukt på få prosjekt med mykje informasjon og tilhøyrande økonomiske analyser, mens det i dette tilfellet er brukt på mange anlegg utan økonomiske analyser. Dette har ført til nokre justeringar for at verktøyet skal fungere best mogeleg for dette formålet.

For å gjennomføre ei slik analyse trengs mykje informasjon om anlegga, og ein del tid har gått med til å strukturere all informasjonen og presentere denne på ein god måte. Mesteparten av arbeidet som er gjort ligg i store tabellar, så det anbefalast å sjå godt på desse. For å gjennomføre ei kvalitativ vurdering må ein definere dei kvalitative faktorane som skal vurderast. I denne analysa er desse faktorane økonomi, leveringspåliteilgheit, personsikkerheit, ytre miljø, omdømme og teknisk tilstand. Desse faktorane er vekta opp i mot kvarandre ved hjelp av AHP-metoden for å bestemme fraksjonen av kor mykje dei ulike faktorane bidreg til det totale resultatet. Dei ulike faktorane vert og delt opp i ei gradering slik at ein ved vurdering av anlegga velger kor stort utslag på skalaen anlegget gir.

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Sjølv om mykje informasjon om anlegga er samla inn vart det vurdert til at datagrunnlaget var for tynt til å gjennomføre ei reell analyse. Vurderingane som er gjort på anlegga er difor fiktive, men graderinga er gjort på grunnlag av dei opplysningane som er kjent rundt anlegget.

Ved å legge inn alle vurderingar i FMBA-verktøyet og modifisere resultatvisninga noko får ein fram ei god oversikt over korleis tilstanden til dei ulike anlegga er. Utifrå desse resultata kan ein for eksempel bestemme kva slags anlegg ein bør sette i gang forebyggande tiltak ved, eller bestemme inspeksjonsintervall for anlegga i ein vedlikehaldsplan. Influensdiagrammet som er laga i Netica er laga som et komplement til FMBA-verktøyet. I dette diagrammet kan ein legge inn vurderinga av eit anlegg for så å forandre på vurderinga og skaleringa av kriteria, og få ut den nye kvalitative verdien. På denne måten slepp ein å legge inn alle data på nytt i FMBA-verktøyet, men ser endringa i kvalitativ verdi umiddelbart.

For å bli kjend med Netica-verktøyet vart det laga ein modell der delar av prosjektoppgåva frå hausten 2007 vart teke i bruk. Den tar for seg korleis KILE vert påvirka av ei eventuell fjerning av ein kabel i nettet, og ein har muligheit til å forandre på parameterar som last og lengde på utetid.

Utifrå det som er erfart i denne oppgåva gir vurdering ved hjelp av FMBA-verktøy ei god framstilling av tilstanden til anlegga. Resultata kan brukast til å legge opp vedlikehaldsplanar, og vedlikehaldsstrategiar kan enkelt knyttast til analysen.

Sidan mykje av denne analysa er basert på antakelsar er det usikkert kor god den er i realiteten, og derfor bør det gjennomførast fleire prosjekt med fokus på dette temaet. Eit steg vidare vil for eksempel vere å teste analysemetoden på eit utvalg av kablar der ein skaffar seg mykje informasjon om kablane og foretek både mekaniske og elektriske undersøkelsar. På denne måten kan ein få ei reell analyse som vil gi betre grunnlag for å vurdere om denne metoden gir eit godt bilde av virkeligheita.

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