michael muhr 1 high voltage engineering for modern transmission networks institute for high-voltage...
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Michael MUHR
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High Voltage Engineering For Modern Transmission Networks
Institute for High-Voltage Engineering and Systems Management
High Voltage Engineering For Modern Transmission Networks
Michael MUHRO.Univ.-Prof. Dipl.-Ing. Dr.techn. Dr.h.c.O.Univ.-Prof. Dipl.-Ing. Dr.techn. Dr.h.c.
Institute for High-Voltage Engineering and Systems ManagementGraz University of Technology
Austria
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
Content
1. Introduction
2. High Voltage AC Transmission (HVAC)
3. High Voltage DC Transmission (HVDC)
4. Future Developments & Trends
5. Transmission Lines
6. Overhead Lines
7. Cable Lines
8. Gas-Insulated Lines
9. Technical Developments
10. Summary
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1. Introduction
Essential changes in the framework:
Liberalisation of the electricity market
Increasing of electricity transportation / transit
Renewable Energies are on the rise
Maintenance and modernisation / replacement
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
Development of the world population and the power consumption between 1980 and 2020
Source: IEA; UN; Siemens PG CS4 - 08/2002
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
2. High Voltage AC Transmission (HVAC)
Economical environmentally friendly and low-losses only with the usage of high voltage
Voltage levels for HVAC in Austria and major parts of Europe: 110 kV, 220 kV and 380 kV
Advantage: Easy transformation of energy between the different voltage levels, convenient and safe handling (application)
Unfavourable: Transmission and compensation of reactive power, stability problems, frequency effects can cause voltage differences and load angle issues at long lines
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
Development of Voltage Levels for HVAC
In Discussion: China 1000 kVJapan 1100 kVIndia 1200 kV
In Discussion: China 1000 kVJapan 1100 kVIndia 1200 kV
Source: SIEMENS
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
Control of active power flow
Phase Shifter Transformer (PST)
Flexible AC Transmission Systems (FACTS)
FACTS – Elements:
Elements controllable with power electronics System is more flexible and is able to react fast to changes
in the grid Control of power flow and compensation of reactive power
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
Phase shift transformers (PST) Distribution of current depends on Impedances only Unequal distribution Implementation of additional voltage
sources
Control of active power flow Additional voltage with 90° shift of phase voltage PST implements a well-defined phase-shift between
primary and secondary part of the transformer
itotal
i2
i1w/o PST
X1
X2
UPST
~itotal
i2-Δi
i1+Δi with PSTX1
X2
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
3. High Voltage DC Transmission (HVDC)
Transmission of high amounts of electrical power over long lines (> 1000 km)
Sub-sea power links (submarine cables)No compensation of reactive power necessary
Coupling of grids with different network frequency
Asynchronous operation
Low couple - power
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Advantages of HVDC No (capacitive) charging currents Grid coupling (without rise of short-circuit current) No stability problems (frequency) Higher power transfer No inductive voltage drop No Skin-Effect High flexibility and controllability
Disadvantages of HVDC Additional costs for converter station and filters Harmonics requires reactive power Expensive circuit breakers Low overload capability
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
4. Future Trends
Costs of a high voltage transmission system
Source: SIEMENS PTD SE NC - 2002
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
Possibilities for Transmission Systems for high power
Hybrid Connection
Alternating Current (AC)
Direct Current (DC)
Hybrid AC / DC - Connection
Source: SIEMENS
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
Transmission Line SystemsAC DC
Maximum voltagein operation
kV 800 +/- 600
Maximum voltageunder development
kV 1000 +/- 800
Maximum powerper line in operation
MW 2000 3150
Maximum powerper line under development
MW 4000 6400
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
Prof. S. Gubanski / Chalmers University of Technology
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
Network Stability
Separation of large and heavy meshed networks to prevent mutual influences and stability issues
Usage of HVDC close couplings
Fast control of frequency and transfer power possible
Limitation of short-circuit power
Improvement of transient network stability
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Overhead LineOverhead Line
5. Transmission Lines
Liberalisation of the Electricity Market Renewable Energy is on the rise Increased environmental awareness
Liberalisation of the Electricity Market Renewable Energy is on the rise Increased environmental awareness
Possibilities forTransmission Lines
in High Voltage Networks:
Possibilities forTransmission Lines
in High Voltage Networks:
Decision CriteriaDecision Criteria
Cable LineCable Line Gas Insulated LineGas Insulated Line
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
Framework
Economic necessity
Transmission capacity
Voltage level
Comply with (n-1) – criteria
Reliability of supply
Operational conditions
Environmental requirements
(Civil) engineering feasibility
Economics
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
6. Overhead Lines
Insulating Material: Air
High voltages are easy to handle with sufficient distances/clearances and lengths
Permitted phase wire temperature of phase wires is determined by mechanical strength
Overhead lines are defined by their natural power PNat
Thermal Power limit is a multiple of PNat
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
6. Overhead Lines – Advantages
Simple and straightforward layout
(Relatively) easy and fast to erect and to repair
Good operating behaviour
Long physical life
Large load capacity and overload capability
Lowest (capacitive) reactive power of all systems
Longest operational experience
Lowest unavailability
Lowest investment costs
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
6. Overhead Lines – Disadvantages
High failure rate (most failure are arc failures without consequences)
Impairment of landscape (visibility)
Low electromagnetic fields can be achieved through distances and arrangements
Highest losses
Highest operational costs because of current-dependent losses
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
7. Cable Lines Insulating Materials
Plastics/Synthetics (PE, XLPE) Oil – Paper Polypropylene Laminated Paper (PPLP): reduced power loss and higher electrical
strength than oil-paper cables
Synthetic cables are environmental friendly, dielectrics undergo an ageing process, voltage levels are currently limited to about 500 kV
Cables have a high capacitance large capacitive currents limits maximum (cable) line length compensation
Transferable power is limited by: permitted temperature of the dielectric high thermal resistances of accessories & auxiliary equipment soil condition
Thermal Power Stherm is essential for continuous rating/operation
High voltage cables have a much higher Pnat than Stherm (of about 2...6)
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
7. Cable Lines – Advantages
Large load capacity possible with thermal foundation and cross-bonding
Lower impedances per unit length when compared to overhead lines
Lower failure rate than overhead lines
No electrical field on the outside
Losses are only 50% of an overhead line
Operational costs (including losses) are about half of the costs of an overhead line
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
7. Cable Lines - Disadvantages
High requirements to purity of synthetic insulation and water- tightness
Overload only temporary possible influences lifespan of insulation
High reactive power, compensation necessary PD-Monitoring on bushings, temperature monitoring Unavailability is notable higher when compared to overhead
lines (high repairing efforts) Lifespan: 30 to 40 years (assumed) Extensive demand of space, drying out of soil, only very limited
usage of line route possible threshold value for the magnetic field (100 µT) can be exceeded 3-6 times investment costs compared to overhead lines
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
8. Gas-Insulated Lines (GIL)
Insulating Material: SF6 and N2: Currently 80% N2 and 20 % SF6; pressure: 3 to 6 bar
Currently no buried lines; laying only in tunnels or openly Many flanges necessary Compensation of (axial) thermal expansion of ducts SF6: Environmental compatibility ? Gas monitoring Easy conversion from other line systems to GIL High transmission capacity large overload capability Minimal dielectric losses Low mutual capacitance low charging current / power Good heat dissipation to the environment
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
8. Gas-Insulated Lines – Advantages
Large transmission capacity High load capacity High overload capability Lower impedance per unit length than overhead lines Low failure rates High lifespan expected (Experience with GIS) No ageing Lowest electro-magnetically fields Lower losses than cables Lower operational costs (including losses) than cable lines
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
8. Gas-Insulated Lines – Disadvantages
High Requirements to purity and gas-tightness Higher reactive power than overhead lines Gas monitoring, failure location, PD-monitoring Higher unavailability than cables because of long period of
repair Short operational experience, only short distances in
operation Large sections necessary, only limited usage of soil
possible, issues with SF6
Investment costs 7-12 times higher when compared to overhead lines
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
9. Technical Development
High Temperature Superconductivity (HTS)
Cable Technology: New developments are applied to medium voltage networks
Reduced losses Reduced weight Compact systems Temperature currently 138 K (- 135 °C)
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
Structural Elements of Mono-Core Power Cable
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
Structural Elements of 3-in-1 Power Cable
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
Nanotechnology
Nanotechnology for cables for medium and high voltage
applications (voltage level up to about 500 kV)
Advantages:
Reduction of space charge
Improved partial discharge behaviour
Increase of the electric field strength for the dielectric breakdown
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
Nanotechnology
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
10. Summary – Energy Transmission
Energy Losses Joule Effect – Heating of conductors Magnetic losses – Energy in the magnetic field Dielectric losses – Energy in the insulating materials
Remedies Transformers with reduced losses Transformers with superconductivity High temperature superconductivity (HTS) - Cables Nanotechnology Direct Current Transmission (HVDC) Ultra High Voltage (UHV)
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
Transmission Systems (1)
Alternating Current Transmission (HVAC)
All 3 Systems possible
Overhead lines up to 1500 kV (multiple conductor wires)
Cable lines up to 500 kV
GIL currently up to 550 kV, higher voltages possible
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
Direct Current Transmission (HVDC)
Overhead lines up to 1000 kV possible
Oil-Paper cables up to 500 kV
Cables with synthetic materials up to 200 kV (space charges), with nanotechnology higher values are possible (~ 500 kV)
GIL is currently under research
Transmission Systems (2)
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Michael MUHR High Voltage Engineering For Modern Transmission Networks
Transmission Systems (3)
In general, overhead-, cable- and gas-insulated lines are suitable for alternating current transmission systems
Cables and GIL are currently only applied for short lengths specifically for example in urban areas, tunnels, under- crossings, etc. Therefore no operational experience nor actual costs can be given for long sections
In a macro-economical point of view, overhead lines are the most favourable system (the capital value of cables 2 to 3 times and GIL 4 to 6 higher)
Currently overhead lines are from the technical and economical point of view the best solution
Michael MUHR
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High Voltage Engineering For Modern Transmission Networks
Institute for High-Voltage Engineering and Systems Management
Thank you for your attention!