NewsletterVOLUME 1, NO. 3DECEMBER 2006 EDITION

ElectroMagnetic Transients Program

Software NewsIMPORTANT CHANGES IN THE MARKETING AND SUPPORT OF THE EMTP PRODUCT LINE

We would like to announce exciting changes in the marketing and support of the EMTP product line. As of December 1, 2006, all marketing and support are being adopted by CEA Technologies Inc. (CEATI). CEATI brings to the table over 30 years of experience in technology development in power systems. In addition, the existing EMTP-RV technical team, with their knowledge and years of experi-ence, remain devoted to product development and support. Our goal with these changes is to ensure a seamless transition, the best possible support for our customers and ongoing product development.

Starting immediately, all administrative and sales inquiries relating to EMTP-RV can be made directly to CEATI. emtp@ceatech.ca • (514) 904-5546

Product technical support contact information will remain the same:

Phone 1-800-451-4453 Email tech@emtpsupport.com Web www.emtp.com

LOOKING AHEAD TO EMTP-RV VERSION 2.1

NEXT VERSION: V2.1 - COMING SOON!

The next version of EMTP-RV, 2.1, will be released in the first quarter of 2007, with beta testing at the end of January 2007. Important improvements include:

1. DLL (dynamic link library capability). V2.1 will allow complete DLL capability for programming user-defined models. The DLL can be written in any computer language, but must follow the DLL interfacing rules and designa-tion. Any device created by the user can have a DLL specification. The DLL can be placed in the design folder or located in specific editable search paths. One or more DLLs can coexist in the same design. All EMTP-RV device modeling objects and methods become available to the user for entering model equations and even iterating within the iterative loops for nonlinear functions. We believe that this new feature will open the door for building complex user-defined models and allow us to pursue our efforts in the delivery of a complete open-architecture software. The combination of DLL with the available scripting methods will allow users to build not only models, but complete simulation tools with specific interfaces with networks assembled on the EMTP side. (continued...)

SOFTWARE NEWS 1 Important Changes in the Marketing and Support of the EMTP Product Line

1 Looking ahead to EMTP-RV Version 2.1

TECHNICAL CORNER 4 Black-Start EMTP-RV Studies for Entergy’s Alternative Power System Restoration Plan

11 Large Network Simulations Using EMTP-RV at Hydro-Québec

20 New Simulation Methodology for Power Systems - Assumption-Free Analysis Entirely Based on Measurement

SUPPORT 28 CEATI Utility Training Solutions

A Word from the Editor

Georgia Johnston, CEATIgeorgia@ceatech.ca

As you will see from our first news item, there will be a number of behind-the-scenes changes with the marketing and support of EMTP-RV.

With regard to the newsletter, you can rest assured that it will continue to be distributed on a regular basis. Apart from small changes to the design, I would also like to introduce myself as the new editor.

I look forward to taking on this challenge and continuing Martine Chartrand’s excellent work.

INSIDE:

Dr. Jean MahseredjianÉcole Polytechnique de Montréal

1155 Metcalfe Street, Suite 1120 Montreal, Quebec, Canada H3B 2V6

www.ceati.com • info@ceati.com

Phone +1 (514) 904-5546Fax +1 (514) 904-5038

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Software News

LOOKING AHEAD TO EMTP-RV VERSION 2.1 (CONTINUED)

2. Parametric study options. V2.1 has added a large collection of functions for performing parametric studies. In addition to already existing features, V2.1 delivers a new set of built-in high-level scripts and protocols allowing users to restart EMTP simulations after performing data changes and to save/replay simulation data. The MPLOT plotting package has been augmented with a number of functions allowing the automation of tasks for plotting through scripting functions and script data files. We have also provided examples demonstrating how to program parametric studies.

3. Error checking. V2.1 has a new collection of functions for improved error messaging and location of faulty devices or other errors. The new status bar showing simulation progress allows error listing as before, but now the device names are hypertexted and clicking on a device name or signal name will move the user to the subnetwork location of the error and highlight the faulty device or signal on the screen. Floating connections or zero pivot messages are also locatable through a single click.

4. New options for the Load-Flow solution. In version 2.1 it will not only be possible to show positive sequence voltage phasors as before, but also individual phase voltages, currents and powers on devices. The refresh procedure of phasors on the screen will become optionally automatic, thus allowing refreshing at the end of a solution without clicking on the refresh button.

5. New scripts. Several new EMTPWorks/JavaScript methods have been added for various object tasks. 6. New models. Several new models, including an arc furnace model have been added. 7. Global data functions. In V2.1 it will be possible to use global data definitions that can be automatically

propagated to devices that are assigned with the reentry option. This option was already available to advanced users, but it has been standardized to simplify usage through a simple checkbox on attribute. If, for example, a device data is dependent upon a global default frequency definition, the device scripts are automatically called to update data when the default frequency is changed.

8. Minor improvements. In addition to the above, V2.1 will benefit from a large list of minor improvements and fixing due to user experience and recommendations in V2.0.2.

VERSION V2.2 HIGHLIGHTS Current plans are to release V2.2 in the third quarter of 2007. Notable new features available in V2.2 will be related to further development of the new DLL interfacing capabilities and addition of new device models. The DLL capability will also allow interfacing with MATLAB®. We have also developed a beta version of a new set of data panels for lines and cables. This will replace the current Line Data and Cable Data functions. They will become fully integrated into the actual models and only large model data files will be saved separately on disk. This will allow minimizing the number of clicks or steps for building and maintaining models. A similar simplification approach has been undertaken for all models requiring external data computation functions. As this feature will be finalized in February 2007 it may become available as a simple patch to V2.1. The DCG has authorized abandoning the data translation features from EMTP-V3 (EMTP96). Only those related to Line Data and Cable Data computation functions will be maintained. The objective is to eliminate a large chunk of code dedicated to this task and to alleviate maintenance efforts. Some improvements to the asynchronous machine initialization functions within load-flow iterations will become available in V2.2. An IEEE paper demonstrating this option has been already published. The current version allows for the use of a transformer with controlled taps. The transformer taps can only be initialized manually. In V2.2 the objective is to find the transformer tap settings automatically from the load-flow solution. A number of new models are currently under development and some of these models should appear in V2.2.

3

ONGOING PROGRAMMING The following programming activities have been undertaken and may appear in 2007 or 2008 versions:

1. Conversion of MPLOT to MATLAB® Release R2006. This will allow users to benefit from several new features for plot functions available in the latest version of MATLAB®. In addition to this, MPLOT will be augmented with several new functions for scripting.

2. Capability to call JavaScript functions at run-time for ‘Math function’ definitions in control boxes. This will provide

unlimited expandability for user-defined functions.

3. A setup for calling dynamic scopes with automatic refresh is currently being tested.

4. Although EMTP-RV has extended initialization capabilities and does not rely on the Snap-Shot option, such an option can become useful in some cases where initialization is not feasible or for saving computer time. The programming of the Snap-Shot option should start in 2007.

CRINOLINE The release of the new CRINOLINE Toolbox for electromagnetic compatibility computations is scheduled for the last quarter of 2007. In addition to its computation options, CRINOLINE will allow for the integration of geographical positioning of transmission lines and cables in EMTPWorks. The CRINOLINE Toolbox was introduced in the November 2005 newsletter.

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Technical Corner

BLACK-START EMTP-RV STUDIES FOR ENTERGY’S ALTERNATIVE POWER SYSTEM RESTORATION PLAN

S. Datta, Entergy Services S. Kolluri, Entergy Services T. He, Entergy Services B. Khodabakhchian, Simtech International

Entergy Corporation is an integrated energy company located in New Orleans, LA. Entergy engages in electric power production and retail electric transmission and distribution operations in the states of Louisiana, Mississippi, Arkansas and Texas. During the recent hurricanes that devastated the Gulf coast, a generating unit that was designated as the black-start unit for the southern Louisiana area was heavily damaged. Studies are underway to devise an alternative black-start plan for the Entergy grid in the southern Louisiana area in the event of yet another system-wide blackout. Of the various options considered, one option is to use an existing 65.9 MVA combustion turbine (CT) unit at Sterlington to start-up larger units at Perryville (up to four 239 MVA) in northern Louisiana to finally bring power into the southern Louisiana area using the existing 200 mile 500 kV transmission line (Fig. 1).

500/115 kVAuto

500/115 kVAuto

Sterlington 115 Sterlington 500

3.9 miles

Perryville 500

Baxter Wilson 500 Grand Gulf 500

Franklin 500

71.4 miles 21.5 miles 43.5 miles

55.6 miles18.13 miles20.8 miles

Willow Glen 500 Coly 500 McKnight 500

Perryville Units

Sterlington unit

2 * 40 MVAr reactors on tertiary+ load on 115 kV system

18 kV239 MVA

18 kV239 MVA

18 kV239 MVA

13.8 kV65.9 MVA

SM12

115/13.8

12

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18

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12

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Np,NqKp,Kq

Z Dist

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Va,Vb,Vc

50/60 Hz

CP +

+

Np,NqKp,Kq

Z Dist

MW,MX,PF

Va,Vb,Vc

50/60 Hz

CP + CP + CP +

CP +CP +CP +

a

Fig. 1: One-line diagram of the black-start cranking path

The drawbacks of connecting generators to long and unloaded 500 kV transmission lines have been well documented. Besides steady state voltage rise due to the Ferranti effect, switching transients, harmonic resonances and possible self-excitation of generating units are of main concerns. This paper discusses portions of results from EMTP-RV simulations performed during the development of the black-start plan. DETERMINING THE MINIMUM NUMBER OF UNITS AT PERRYVILLE GENERATING STATION The 65.9 MVA black-start unit at Sterlington is capable of supplying starting power to the first 239 MVA unit at Perryville. Following the synchronization of these two units, additional Perryville units may be needed to come on line to safely energize the Perryville to Franklin 500 kV line sections (switching transients) and the first 560 MVA autotransformer at Franklin (harmonic resonances).

5

The determination of the required minimum number of units at Perryville must be based on: 1. The total charging of the Perryville – Franklin 500 kV line sections, which is around 190 MVars; 2. The actual Sterlington and Perryville units’ reactive absorption capability, which is conservatively estimated as

50% and 40% of their nominal MVA or 33 and 96 MVars successively; 3. The guaranteed amount of load that can be taken on the 115 kV side of the 600 MVA autotransformer at

Sterlington, which is estimated as being around 150 MW; 4. The acceptable level of temporary overvoltages generated following the large autotransformer switching at

Franklin which is 1.5 pu. Criteria 1, 2 and 3 are easily satisfied with a minimum number of 2 units at Perryville. Satisfying the number 4 criterion is a much less straightforward task and necessitates accurate EMTP-RV simulations and good engineering judgments. In order to study the temporary overvoltage concerns at Franklin, an EMTP-RV model was developed and detailed models for generators and their exciters were included in the model for each of the units. The 500kV transmission lines from the Sterlington substation through the start-up path to the Willow Glen substation were modeled using the wide-band line model. The wide-band line model is a fully general line model that can be used for cables as well as overhead transmission lines. The transformation matrix can be frequency dependant, and the time domain counterparts of the propagation matrix H and the characteristic admittance matrix Yc are obtained from inverse Fourier transform. The 560 MVA, 500/115/13.8 kV, YY• autotransformer was modeled with the HV-LV common winding. A hysteretic reactor and some iron losses were placed in the tertiary. An adequate amount of residual fluxes were also specified on the three phases. Fig. 2 shows typical HV no-load current obtained by simulation.

Fig. 2: HV no-load current of the YY• autotransformer.

Past operational experience of the Sterlington area was used in determining the composition of the load in this study. The 150 MW load was modeled using a combination of frequency and voltage-dependant static loads and induction motors. 20% of the load was modeled using induction motors, representing those found in typical commercial and residential loads in that area. The remainder of the total load was modeled using the frequency and voltage-dependant variable static load model available in the ‘Advanced Library’ of EMTP-RV. An exponential real-power voltage dependence factor (Np) of 1.3 and a reactive-power voltage dependence factor (Nq) of 2.5 were used. For the purpose of conservative but realistic damping effects of the load on temporary overvoltages, a real-power multiplier of 4 for the constant impedance portion (25%) of the composite load model was assumed. For a given load and generator dispatch condition, load flow was first solved in order to initialize machine variables. Next, statistical time-domain simulations were run with the 560 MVA autotransformer switched in. The closing switch was given a statistical Gaussian distribution with a standard deviation of 1 ms spread across the sine wave cycle from 0 to 360 degrees. For the case of 2 units at Perryville, Figure 3 shows the statistical overvoltages generated at the HV side of the Franklin autotransformer through 50 statistical runs.

6

Fig. 3: Statistical overvoltages at Franklin 500 kV bus during autotransformer switching (2 units at Perryville) Fig. 4, showing the maximum harmonic overvoltages at Franklin 500 kV (simulation # 42), demonstrates that a number of peaks may reach much higher values than the 1.5 pu criterion set for a negligible autotransformer loss of life. Therefore, additional statistical runs were executed with the case of 3 units at Perryville.

Fig. 4: Maximum harmonic overvoltage at Franklin 500 kV during autotransformer switching (2 units at Perryville).

Statistical overvoltages at Franklin 500 kV bus V

olta

ge

(pu)

Simulation Number

Max overvoltage 1.78 pu

7

Fig. 5 shows that adding 1 additional unit at Perryville will guarantee that the maximum temporary overvoltages during autotransformer switching at Franklin will present only one crest value exceeding 1.5 pu. Consequently, the minimum number of units that need to be started at Perryville should be set to 3.

Fig. 5: Maximum harmonic overvoltage at Franklin 500 kV during autotransformer switching (3 units at Perryville).

Finally, it should be noted that in order to facilitate the synchronization process at Willow Glen (Ferranti effect), it is adequate to take advantage of the presence of the second 40 MVars reactor at Franklin. EMTP-RV simulations show that no harmful harmonic overvoltages (<1.25 pu) by sympathetic effect of autotransformers’ saturation will be created by the switching of the second transformer at Franklin 500 kV if the established amount of load (150 MW) is taken previously on the 115 kV side of the first energized autotransformer. LINE SWITCHING STUDY Line switching on long EHV lines can cause overvoltages to develop, especially on the open-ended terminal of the line being switched due to switching transients. The same generator and line models as used for the transformer switching study were used in this study. In order to ensure that the transients caused by the switching of the 500 kV lines did not cause unacceptably high voltages at substations in the cranking path, the closing of each line in the black-start path was simulated. Arresters were also modeled at the line ends. Both the voltages at the open-ended side of a line being switched in and the arrester energies were monitored. Fig. 6 shows the maximum switching overvoltages of the 50 statistical runs done for each of the three 500 kV line sections between Perryville and Franklin. Based on the actual 500 kV insulation levels of the 500 kV transmission line, these overvoltages, along with their arrester duties, are well within limits.

8

Fig. 6: Statistical switching overvoltages of the Perryville – Franklin line sections

For the case of line switching studies between Franklin and Willow Glen, a similar 150 MW load at Franklin 115 kV was assumed. The 40 MVar reactor in the tertiary of the autotransformer was assumed to be also in service since it represents a countermeasure to the Ferranti effect of the long transmission line. Fig. 7 shows the maximum switching overvoltages for the three line sections between Franklin and Willow Glen. Again, switching overvoltages and arrester duties were found to be well below the limits.

9

Figure 7: Statistical switching overvoltages of the Franklin – Willow Glen line sections

SELF-EXCITATION AND MACHINE TRIPPING DUE TO NEGATIVE FIELD CURRENTS STUDIES For generators that do not have negative field current capability, self-excitation generally occurs when the machine direct axis reactance (Xd) or the machine quadrature axis (Xq) resonates with the capacitive reactance seen at the machine terminals (Xc). An over-frequency condition during black-start makes this situation worse. When self-excited, the machine time constants governing the flux dynamics in the d and q axis become negative and the field circuit develops positive feedback thus causing the terminal voltage to increase exponentially, limited only by transformer saturation. Avoidance of machine self-excitation or machine tripping due to field currents crossing zero can only be met by limiting the amount of reactive power that the machine has to absorb during normal and contingency conditions. In this case, load-flow under the suggested path of black-start and machine loadings (1 unit at Sterlington, 3 units at Perryville, 2 x 150 MW load and 2 x 40 MVars reactors) shows satisfactory operations far from self-excitation. As for a severe contingency condition, an EMTP-RV simulation was run under the following conditions:

One 40 MVars reactor at Franklin out of service Full 150 MW load rejection at Franklin 115 kV at t=1 s.

The results are shown in Fig. 8. It can be seen that even under such a severe double-contingency condition, no negative field currents nor any self-excitation phenomenon are experienced by the units in the frequency interval of 60 – 63 Hz.

10

Fig. 8: Machines signals during self-excitation contingency conditions.

CONCLUSION Extensive EMTP-RV simulations demonstrate that Entergy’s proposed alternative power system restoration plan to start units in northern Louisiana and bring the power to the New Orleans area is sound and perfectly feasible. Starting an adequate number of generating units in the north along with the taking of some minimum amount of loads in the path represent the main line of defense against the generation of harmful temporary overvoltages and self-excitation and tripping of the generators.

11

LARGE NETWORK SIMULATIONS USING EMTP-RV AT HYDRO-QUÉBEC

L. Gérin-Lajoie, Hydro-Québec TransÉnergie J. Mahseredjian, École Polytechnique de Montréal B. Khodabakhchian, SimTech International

EMTP simulations of large networks have been in practice at Hydro-Québec TransÉnergie since the mid 1990s in various studies related to machine-network interaction phenomena and breaker TRV studies in series compensated networks. The introduction of EMTP-RV in 2003, along with its powerful Graphical User Interface (GUI) EMTPWorks, has greatly facilitated the task of building and maintaining very large networks. EMTPWorks provides an advanced environment for large network visualization and network data management. It is powerful and user-friendly, yet efficient. This paper summarizes the work undertaken in simulating the large Hydro-Québec network in EMTP-RV. It demonstrates some unique EMTP-RV capabilities for very large network problems, in addition to providing validation with a conventional load-flow and transient stability package (PSS/E). The presented network is the largest network ever created and simulated in an EMTP-type simulation tool. NETWORK DATA Two different networks were developed in EMTPWorks. The first very large network represents the complete (100%) Hydro-Québec power grid. The second smaller network is a reduced version of the first network. It does not represent medium and low voltage transmission lines and regroups some loads into large centers. The complete network constitutes a reference for obtaining network frequency dependant equivalents for various study purposes. It is also a unified environment for maintaining and extracting large scale network data. Snapshots taken from this network are presented in Figure 1 to Figure 3. The complete Hydro-Québec network is organized in a 6 page hierarchical design and contains a total of 30700 physical devices and 4700 power signals. The actual number of signals of the entire design is 5570 and counts control signals, 1-phase and 3-phase signals (counted once). The top level list of devices is:

• 1100 transmission lines representing the existing 1560 lines and derivations; • 296 three-phase transformers representing the existing 1500 three-phase units connected in Ynyn, DD, Dyn, Ynd,

Ynynd, Yndd and ZigZag grounding banks. Scripts and various data loading methods available in EMTPWorks were used to simplify data loading tasks from available external libraries or other software.

• 532 load models representing a total of 36000 MW. All medium and high voltage shunt capacitors and inductors were modeled separately.

• 7 SVC (Static Var Compensator) models of 300 Mvars and 600 Mvars. The SVCs have been combined on some buses by creating 600 Mvar models.

• 32 series capacitor MOVs and 303 nonlinear inductances used for high voltage power transformer saturation representation.

• 99 synchronous machines (SM) with associated controls representing 49 power stations and four synchronous compensators. All synchronous machine devices are matched to corresponding load-flow type devices for specifying the PV constraints used for initializing machine phasors at load-flow solution convergence.

The reduced network (second network) was constructed as an alternative to the first network for achieving reduced computer timings in simulations. Most of the UHV studies can be conducted on the reduced network. The validity of this network has been verified using the Frequency Scan feature of EMTP-RV by comparing the input impedance versus frequency plots at several buses. The results shown in Figure 4 indicate clearly that the reduced system may be confidently used in the majority of studies.

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Figure 1 Part of 735 kV series-compensated network representation.

L7060

23

1

T3aT8

23

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T1T2

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LF

lagrande2_b2449

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LFA5aA10

P=2000MWV=14.4kVRMSLLSM:A5aA10

LFA11aA16

P=2000MWV=14.4kVRMSLLSM:A11aA16

LFA1A2

P=665MWV=14.4kVRMSLLSM:A1A2

LFA3A4

P=665MWV=14.4kVRMSLLSM:A3A4

AVR

-exst1-pss1a

(pu)

AVR_A11aA16

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(pu)

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SM

A5aA10

?m

13.8kV2220MVAPVbus:A5aA10

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-exst1-pss1a

(pu)

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AVR

-exst1-pss1a

(pu)

AVR_A3A4

SM

A3A4

?m

13.8kV740MVAPVbus:A3A4

L7061

L7088

L7089

lagrande2_b749

Figure 2 Multi-machine power plant representation.

+ ZnO

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eastmainlasarcelle

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,L]

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,L]L1356_B

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,L]

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montlaurier_b4275

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LF 35.19MW6.48MVAR

ouimet_b8403

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26.58MW6.09MVAR

lannonciation_b8410

LF38.43MW0

stdonat_b8385

LF10MW0

arundel_b8460grandbrule_b770

grandbrule_b1170

ouimet_b8400

Figure 3 Typical 69 kV and 120 kV network with loads.

Figure 4 Frequency response plots for the complete (red) and reduced (blue) networks. Left column plots

show three 735 kV substations between generation and loads. Right column plots show three 735 kV substations near the load.

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SYNCHRONOUS MACHINE INITIALIZATION The initialization process of machines in achieving fast steady-state in the time-domain solution is achieved by applying the following steps to each synchronous machine:

• The converged load-flow solution of EMTP-RV provides the synchronous machine with the terminal voltage phasors. This is an automatic step available in EMTP-RV. Since the synchronous machine is paired with a load-flow device, EMTP-RV is able to retrieve the phasors automatically when the steady-state solution is started from a previously converged load-flow solution.

• The steady-state solution of a machine model is able to initialize all internal electrical and mechanical quantities from terminal voltage phasors. The steady-state solution of the field voltage Efss becomes available as a bundled observable signal used for initializing machine control diagram variables.

• The reference voltage Vref is determined by the Automatic Voltage Regulator (AVR) as shown in Figure 5.

Figure 6 presents the time-domain simulation of the complete network with 99 synchronous machines and their AVRs. The SVCs are disconnected for this simulation. It demonstrates that the system stays in the equilibrium state dictated by the load-flow solution. The power flow solutions computed by PSS/E are compared favorably to the ones calculated by EMTP-RV for both the complete and reduced networks. In EMTP-RV some measuring devices have a normal settling delay of one period, which is why some power measurements shown in Figure 6 have an initialization delay and appear pulsed.

11 rsT+

1f

f

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dynamics

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Vaux

Vaux

Vm_rms

Vm_rms

Efd_ic

Vref

Vref

Vin

Vin Vr EfdVe Ve_lim Vef

Vf

Figure 5 Initialization and dynamic blocks in an EXST1 exciter model in EMTPWorks

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Figure 6 Network initialization. Column 1: bus voltages in pu. Column 2: line transit in MW. Column 3: power

generation in MW. Column 4: power plant field voltage (pu). Green: PSS/E waveforms. Blue: EMTP-RV complete network. Red: EMTP-RV reduced network.

The AVR blocks are based on the IEEE 421.5 standard. Developed AVR and power system stabilizer models (Figure 7) are available on the support website (www.emtpsupport.com).

AVR

-ieeet5(pu)

AVR

-ieeex1

(pu)

AVR

-exst1-pss1a

(pu)

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(pu)

AVR+Gov

-exst1-pss1a-gov ieeeg3

Network frequencyor rotor speed (pu)

(pu)

AVR+Gov

-exst1-pss4b-ieeeg3

Network frequencyor rotor speed (pu)

(pu)

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(pu)

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(pu)

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-expci1-pss2a

(pu)

expci1 partial

AVR

-expic1-pss1a

(pu)

expci1 partial

Figure 7 A library of AVR and AVR/Governor masked subcircuits

Since controller data was initially available in PSS/E, it was manually copied from the dynamic data file of PSS/E to the AVR subcircuit mask of EMTP-RV. The process is simplified by arbitrarily setting the same appearance order of variables in both applications. An example for copying data for EXST1 is shown in Figure 8.

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Figure 8 Copying data from PSS/E to EMTPWorks masks

INITIALIZATION WITH DETAILED SVC MODELS Since power electronics-based components cannot be automatically initialized due to changeable switching patterns, a simple technique was developed to connect the SVCs to the network for minimal perturbations in the time-domain waveforms. Since the SVC is assumed to be initially floating, this is basically done by isolating the SVC during the first 200 ms in parallel with an ideal voltage source giving the expected voltage phasor of the SVC bus (Figure 9). Figure 10 presents the initialization process for the seven SVCs. It is observed that all the SVCs reach their steady-state in less than 800 ms after switching onto the network. Without this technique, the SVC initialization, due to internal controls and related thyristor firings, will delay the network from reaching the steady-state for up to 5 s of simulation time. This is not convenient for the simulation due to the significant CPU time requirement.

+

+3 ph

0+

+3 ph

0+

3x

xfo=660 MXchibougamau_CLC

svc_Topen

svc_Tclose

Figure 9 SVC model initialization circuit

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Figure 10 Network initialization with SVC models

VALIDATION Short-circuit tests along with dynamic simulations were compared to the results provided by PSS/E and excellent matches were observed. Table 1 shows that fault current values evaluated on the complete and reduced networks compare very well with those computed by PSS/E. It is noted here that the fault current in PSS/E is computed as a steady-state phasor using an equivalent d-axis subtransient reactance model, while EMTP-RV computes the exact time-domain waveform with the complete machine model. The comparison is made by filtering the EMTP-RV waveforms and computing the value at fundamental frequency.

EMTP-RV

Name PSS/E Complete Reduced

Boucherville 21,2 21,1 0% 21,1 0%

Duvernay 20,3 20,5 1% 20,5 1%

Levis 21,6 22 2% 22 2%

Micoua 19,8 20 1% 20 1%

Nicolet 18,1 18,5 2% 18,5 2%

Arnaud 15,0 15 0% 15 0%

Montagnais 18,0 18 0% 18 0%

Abitibi 14,2 14,5 2% 14,7 4%

La Vérendrye 24,2 24 -1% 24 -1%

Radisson 15,8 16 1% 15,5 -2%

Table 1 Short-circuit currents compared to PSS/E results

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For dynamic simulation tests, more than one hundred signals of PSS/E and EMTP-RV among 735 kV bus voltages, power system stabilizer signals and power line transits were compared to fully validate the EMTP-RV design data. Figure 11 shows the results corresponding to the case of a three-phase fault followed by the loss of a 735 kV transmission line. Once again the exceptional agreements between various signals are confirming the validity of the large network assembled in EMTP-RV.

Figure 11 Simulation of a 3-phase fault and loss of a 735 kV transmission line. Column 1: bus voltage in pu. Column 2: line transit in MW. Column 3: power plant generation. Green: PSS/E waveforms. Blue: complete

EMTP-RV network. Red: reduced EMTP-RV network. Finally, Table 2 presents computer CPU timing data for both EMTP-RV network simulations. It confirms that simulating ever larger networks in EMTP-RV for lengthy time intervals is feasible. This is a clear extension of EMTP-RV capabilities into the stability time-frame and a first demonstration of simulation of such a large network in the electromagnetic transients domain.

Complete network Reduced network

Time-domain B vector updating 570 47

Time-domain Ax=B solution 27 360 2 200

Solution of control systems 14 480 7 200

Time-domain history updating 2 700 246

Total 47 500 s 10 740 s

Table 2 EMTP-RV CPU timings for a 10 s simulation interval using a t 100 sΔ = μ CONCLUSIONS This paper has presented the simulation of the complete Hydro-Québec power grid in EMTP-RV. Such a simulation encounters many important challenges. The graphical user interface of EMTP-RV (EMTPWorks) allows assembling, visualizing and maintaining extra large networks within a resourceful environment. Network file loading times were found to remain below a record of 15 s and the use of pages and hierarchical blocks have contributed tremendously to the network

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assembly and visualization process effectiveness. The EMTP-RV load-flow and steady-state initialization options have a major impact on the feasibility of the simulations and the computer timings. Since in many utilities original network data is available in the PSS/E format, PSS/E simulations were used to verify the design assemblies in EMTP-RV. PSS/E is used for standard positive sequence computations of load-flow and electromechanical transients. Building and maintaining large networks is also useful for keeping a unique network data set from which engineers can extract smaller networks for performing various simulations. It is also useful for creating and verifying frequency dependent network equivalents. Since EMTP-RV uses wideband models, its designs can be applied in insulation coordination studies, in switching transients, temporary overvoltages and steady-state analysis simulations. The authors wish to thank Sophie Paquette (Hydro-Québec) for providing data and assistance for PSS/E simulations.

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NEW SIMULATION METHODOLOGY FOR POWER SYSTEMS – ASSUMPTION-FREE ANALYSIS ENTIRELY BASED ON MEASUREMENT Martin Tiberg, martin.tiberg@ch.abb.com, ABB Switzerland Ltd, Switzerland Olaf Hoenecke, olaf.hoenecke@zhwin.ch, Zürcher Hochschule Winterthur, Switzerland Christoph Heitz, christoph.heitz@zhwin.ch, Zürcher Hochschule Winterthur, Switzerland Bjørn Gustavsen, bjorn.gustavsen@sintef.no, SINTEF Energy Research, Norway ABSTRACT The SoFT tool measures, models, and analyzes electrical networks so that customers can pinpoint existing problems or unforeseen risks in their electrical systems quickly, and take corrective action fast. A description of the SoFT tool is presented in this paper. The electrical networks of utilities and industries are increasingly subjected to various forms of electrical transients resulting from circuit breaker switching, lightning strikes, network resonances, etc. Such transients can cause insulation failure in motors, transformers and other electrical equipment. Analysis of these transients is fundamental for equipment troubleshooting, and for designing or improving the electrical system protection. To provide the best possible analysis of these power systems, ABB has pioneered a completely new approach to power system simulation. Instead of relying on theoretical assumptions and equivalent circuits, the SoFT method starts by measuring the true and fully frequency-dependent behavior of the electrical equipment. These measurements reveal the interplay between the three phases, the equipment interaction, and system resonances to achieve the most authentic and accurate power system studies possible. The paper presents the necessary steps of assumption-free simulation and simulation model creation entirely based on measurements. It describes the technology necessary to realize this new methodology in the context of modeling a large power transformer. For the first time ever, measurement and modeling results based on this procedure are being published. KEYWORDS SoFT, motor, transformer, measurement, assumption-free modeling, simulation, modal excitation, linear N-port, state-space model, passivity enforcement

SoFT measurements performed on a 3-phase motor

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INTRODUCTION Electrical power systems are everywhere in our society, supplying all our homes, offices, industries and more. After clean water supply, electricity is our most essential infrastructure. To minimize the risk of failure of this infrastructure, utilities and industries always analyze the effect of any larger change to their power systems before they implement them. Equally important is the analysis of the causes of failures that occur despite precautions having been taken. In the tables below, examples of electrical issues and their relevant frequency ranges are listed.

Origin Frequency Range Transformer energization, ferroresonance

(DC) 0.1 Hz – 1 kHz

Load rejection 0.1 Hz – 3 kHz Fault clearing Fault initiation

50 Hz – 3 kHz 50 Hz – 20 kHz

Line energization Line reclosing

50 Hz – 20 kHz (DC) 50 Hz – 20 kHz

Transient recovery voltage Terminal faults Short line faults

50Hz – 20 kHz 50 Hz – 100 kHz

Multiple restrikes of circuit breaker 10 kHz – 1 MHz Lightning surges, Faults in substations

10 kHz – 1 MHz

Disconnector switching and faults in GIS 100 kHz – 50 MHz It is a highly complicated task to analyze power systems with the electrical interaction between cables, transformers, motors, filters, breakers, and all other components that constitute electrical systems. Affordable computing capacity has made power system simulations a common and precise method for electrical system studies. In general, running simulations is an efficient use of resources; one person alone can test alternative system designs, identify power system weaknesses, and remedy these weaknesses for a whole plant or power grid – sometimes even before the electrical system is built – making expensive testing based on trial and error obsolete. Even though simulation software continually becomes more sophisticated and powerful, the underlying models have largely remained unchanged since the early days: equivalent circuits are used to approximate electromagnetic behavior of the power system components. Unfortunately, these equivalent circuits recurrently misrepresent the true electrical equipment, and they do not correctly capture its frequency dependent behavior. Additionally, models generally assume symmetry between the three phases; an assumption that is often incorrect for a large range of frequencies. These shortcomings may weaken or invalidate the simulation results since the simulation output can only be as good as its input. Contrarily, SoFT does not rely on theoretical assumptions and equivalent circuits; instead the true and fully frequency-dependent behavior of the electrical equipment is measured in a wide frequency range from 10 Hz – 10 MHz. These measurements reveal the often highly intricate behavior that results from internal interaction between equipment subsystems as well as frequency dependent effects in metallic parts and insulation materials. Thus, SoFT models make highly authentic and accurate power system studies possible. THE SOFT METHODOLOGY SoFT is a new approach to power system analysis and simulation, which consists of three steps:

1. On-site SoFT measurements. 2. True and fully frequency-dependent modeling of all electrical components. 3. Simulation of the electrical system.

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Existing modeling techniques do not include the first and second steps. Instead, they require estimation or guessing of many important parameters. Such a procedure leads to inaccuracies which may invalidate the simulation results or seriously degrade them. Even if the parameter estimation is done exceptionally well, the validity of the resulting model is usually confined to a narrow frequency range. Although procedures for obtaining models via measurements have been proposed in the past [Gustavsen, 2004], the resulting accuracy is often insufficient since modal excitation is not possible with commercially available measurement hardware. Contrary to this, SoFT builds dynamic and accurate models of electrical linear N-ports (i.e. motors, cables, transformers, busbars, etc.) based on real-world measurements and a unique modal excitation and modeling capability. Below is an example of SoFT measurements performed on March 31, 2006, on a large distribution transformer manufactured by ABB in Guarulhos, Sao Paulo, Brazil.

Guarulhos transformer data

Voltage levels 13.8 / 69 kV

Power 17 MVA

Type Dyn1 (HV-delta, LV-star)

Manufacturing year 2006

SoFT measurement settings for Guarulhos transformer

Measurement frequencies 20 Hz – 2 MHz in 600 steps

Output voltage 8 V

Measurement time 37 min

Channels used 7

Measurement cables BNC, 7 m long

SoFT measurements The colored graphs on the next page show the 7th row of the admittance matrix obtained from the SoFT measurements of the Guarulhos transformer. Rows 1-6 have been omitted in order to not clutter the graphs. These measurements were performed by applying a voltage on each of the 7 terminals of the transformer and representing these voltages by a voltage vector Ui with 7 elements. Concurrently, the current flowing at each terminal was measured and represented by a current vector Ii. This procedure was repeated 7 times with 7 orthogonal voltage vectors yielding a set of 7 measured voltage and current column vectors. This set of vectors completely characterizes the transformer and the information may be stored in its admittance matrix Y, which can be derived from the equation: [I1 … I7] = Y x [U1 … U7]. (1) For the Gaurulhos transformer, the admittance matrix has a 7x7 dimension because 7 measurement channels were used and connected to the transformer terminals as follows:

Measurement channel 1 2 3 4 5 6 7

Transformer terminal H1 H2 H3 LV1 LV2 LV3 NEUTRAL

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7th row of admittance matrix of the measured Guarulhos transformer in logarithmic scale

7th row of admittance matrix of the measured Guarulhos transformer in linear scale

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SoFT modeling The figures above show not only the measurement data, but also a state-space model fitted to the data based on the vector fitting technique. The theory of this modeling approach is complex and the computational requirement for fitting a large data set can be substantial. However, the result is simple: five frequency-independent matrices A-E representing the state-space model:

uEDuCxiBuAxx

&

&

++=+=

(2)

In the frequency domain, the time derivative of a sinusoidal signal can be represented as jω, and straight-forward matrix algebra to eliminate the state vector x yields:

( )[ ]uEjDBAIjCi ωω ++−= −1 (3)

A comparison of equations 1 and 3 identifies the expression within brackets in equation 3 as the admittance matrix computed from the fitted model. The 7th row of this matrix is evaluated at the measured frequencies and plotted as a black dotted line in the figures above together with the measurement data. The sum of the errors for row 7 between the fitted elements of equation 3 and the measured ones of equation 1 is also shown. The error is close to 1% or less over the whole frequency range of 5 decades. Such accuracy by an automated procedure has never before been demonstrated for a power transformer in such a large dynamic range. This example illustrates how a transformer can be modeled highly accurately based on measurements. The whole measurement procedure was automatic and lasted for 37 min without any cable reconnections. The modeling was also performed completely automatic with a few parameter inputs into the algorithm. In this particular example, the modeling was done using 80 poles, a 3 iteration procedure, capacitive compensation for the 7m long measurement cables and a weight of 1/abs(Y). Measurements and modeling of cables, motors, complete busbars, etc., are equally automatic and simple. SoFT simulations SoFT has simple interfaces to commonly used simulation software. The matrices of the state-space-model in equation 2 can be directly imported in EMTP-RV using the State-space equations feature of the program and MATLAB has a ready to use state-space data type in its control toolbox. By importing the SoFT models of various electrical components into simulation programs such as these ones, careful and highly accurate simulation and analysis of the electrical networks containing these components can be carried out. In order to estimate the accuracy gains of the SoFT methodology in electrical network simulation, ABB has an ongoing study to compare:

A. An MV network simulation of switching transients based on built-in cable, breaker and motor models in EMTP-RV, B. The same simulation based on measured SoFT models, and C. Time-domain measurements of the switching transients in the real system built up in the Birr test field of ABB

Electrical Machines/ATM in Switzerland. The belief is that the results of B will much more closely resemble the reality C than the results of A. However, the results of the study are outside the scope of this paper. LIMITATIONS OF THE SOFT METHODOLOGY The SoFT modeling is restricted to passive, linear objects, which do not change state. Additionally, the SoFT measurements are limited to 7 or fewer terminals and objects with off-line availability. These restrictions imply that SoFT measurements and modeling is not possible for:

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A. Active objects such as drive systems in operation; these cannot be measured. B. The transition between different states, such as a breaker in operation; this cannot be measured. C. Non-linear objects such as surge-arrestors; these cannot be modeled accurately.

In these cases, the electrical equipment must be modeled in the traditional theoretical way. ADVANCES TO REALIZE THE SOFT METHODOLOGY In order to realize SoFT, i.e. the creation of simulation models entirely based on measurements, advances and innovations in five fields were performed. 1. Integrated system for data acquisition and model generation for arbitrary N-ports. Before SoFT, no integrated system for both data acquisition and model generation existed. Now, SoFT allows a quick, robust and accurate modeling of arbitrary N-ports (e.g. AC motors and generators, 3-phase cables, transmission/distribution transformers, busbars, RC-filters, capacitor banks) by users that are not necessarily trained engineers. The user interface guides the user through all steps, beginning with the measurement and ending with a simulation model. 2. Fully automatic data acquisition system. To determine the dynamics of an N-port for data driven model generation, measurements with different voltage applications must be performed. Before, only static, one-phase data acquisition equipment existed, whereas SoFT is able to automatically perform multi-phase dynamic measurements needed for feeding a model estimation algorithm for N-ports. 3. Modal approach for excitation. The excitation of individual modes by applying frequency dependent eigenvectors of the dynamical system is known from vibration analysis in mechanical engineering. In the field of electrical N-port characterization, this is an original idea [Niayesh et al 2002], that enables unsurpassed data acquisition accuracy. To realize this mode excitation, the SoFT hardware has the latest technology in signal generation, amplification and data acquisition embedded. The result is an innovative measurement system with seven independent but synchronized signal generators operating over 6 decades of frequencies. 4. Model generation: fitting and passivity enforcement. Four years ago, the SoFT development resulted in a new theory for utilizing modal-based measurements in the modeling of N-ports while retaining the relative accuracy of all modes [Heitz, Steiner, 2002]. Around the same time, a new approach for rational model identification (Vector Fitting) [Gustavsen et al 1999] and passivity enforcement by residue perturbation [Gustavsen et al 2001/2005] was developed. As part of the SoFT development, all three approaches are fused and implemented in software for the first time. 5. Model interface. To be interoperable and compatible with the whole simulation community, a generic SoFT interface has been developed. It uses a state-space representation with five frequency-independent matrices. Recent versions of EMTP-RV, commonly used throughout the power system industry, implement an automated procedure for importing SoFT models. BACKGROUND & ACKNOWLEDGEMENT The development of SoFT started at ABB Corporate Research in Switzerland at the end of the 1990s. In 2004, the technology was transferred to the business unit ABB Electrical Machines in Birr, Switzerland, and it entered into a commercial phase. Thereafter a product was developed incorporating the SoFT technology together with the partners Zürcher Hochschule Winterthur, SINTEF Energy Research, Hydro-Quebec TransÉnergie Technologies, and PI Electronics. In January, SoFT received the Swiss Technology Award 2006.

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The SoFT development team

REFERENCES B. Gustavsen and A. Semlyen, “Rational approximation of frequency domain responses by Vector Fitting”, IEEE Trans. Power Delivery, vol. 14, no. 3, pp. 1052-1061, July 1999. B. Gustavsen and A. Semlyen, “Enforcing passivity for admittance matrices approximated by rational functions”, IEEE Trans. Power Syst., vol. 16, no. 1, pp. 97-104, Feb. 2001. B. Gustavsen, “Wide band modeling of power transformers”, IEEE Trans. Power Delivery, vol. 19, no. 1, pp. 414-422, Jan. 2004. B. Gustavsen, “Computer code for passivity enforcement of rational macromodels”, 9th IEEE Workshop on Signal Propagation on Interconnects, pp. 115-118, 2005. C. Heitz, A. Steiner: Algorithm for an automated modal model generation from measured data for electrical N-ports. Unpublished report, Dec. 2002. K. Niayesh, M. Berth, A. Dahlquist and C. Heitz: Measurement algorithm for optimal characterization of multi-port electrical components and systems, 2002.

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VOLUME 1, NO. 3DECEMBER 2006 EDITION

ElectroMagnetic Transients Program

Support

CEATI UTILITY TRAINING SOLUTIONS - Simulation and Analysis of Power System Transients using EMTP-RV

CEATI is pleased to announce that the ‘Simulation and Analysis of Power System Transients using EMTP-RV’ training course will be offered as part of our new Utility Training Solutions Program.

The objective of this course is to provide beginner and intermediate participants good hands-on experience in the simulation and analy-sis of power systems transients in general. The course is based on the usage of EMTP-RV for demonstrating concepts and teaching through practical problem cases. EMTP-RV, the recently released version of the DCG/EMTP, contributes greatly to the simplification of complex power system studies and to the visualisation and accurate simulation of large systems.

Topics covered include theoretical backgrounds to the simulation of transients, equipment modeling and applications, control systems modeling and applications, practical power system studies, power quality studies and more.

This course is intended for engineering personnel familiar with the basics of electric power system analysis needing greater in-depth practical knowledge of power system transient simulation and analysis in areas such as: Insulation coordination of HV substations and transmission lines; Rotating machines dynamics; Power quality studies; Application of power-electronics-based converters and associ-ated controls in power systems (HVDC, SVC, STATCOM); Wind power generation.

Upcoming SessionsJune 18-21, 2007 - University of Wisconsin-Madison. See http://epdwww.engr.wisc.edu/courses/course.lasso?myCourseChoice=J052 for more information.

An additional session has been tentatively planned for September 2007 (details will be announced at a later date).

Training can also be organized for your organization upon request. For more information, please visit www.utilitytrainingsolutions.com.

1155 Metcalfe Street, Suite 1120 Montreal, Quebec, Canada H3B 2V6

www.ceati.com • info@ceati.com

Phone +1 (514) 904-5546Fax +1 (514) 904-5038