20080509_-_High_Voltage_Engineering_for_modern_Transmission_Networks.ppt

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 MUHR
O.Univ.-Prof. Dipl.-Ing. Dr.techn. Dr.h.c.
Graz 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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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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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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Development of Voltage Levels for HVAC
In Discussion: China 1000 kV
Japan 1100 kV
India 1200 kV
Source: SIEMENS

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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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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
i1
w/o PST
X1
X2
UPST
~
itotal
i2-Δi
i1+Δi with PST
X1
X2

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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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4. Future Trends
Costs of a high voltage transmission system
Source: SIEMENS PTD SE NC - 2002

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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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Transmission Line Systems
AC DC
Maximum voltage
in operation
kV 800 +/- 600
Maximum voltage
under development
kV 1000 +/- 800
Maximum power
per line in
operation
MW 2000 3150
Maximum power
per line under
development
MW 4000 6400

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Prof. S. Gubanski / Chalmers University of Technology

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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 Line
5. Transmission Lines
 Liberalisation of the Electricity Market
 Renewable Energy is on the rise
 Increased environmental awareness
Possibilities for
Transmission Lines
in High Voltage Networks:
Decision Criteria
Cable Line Gas Insulated Line

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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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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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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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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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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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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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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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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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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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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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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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Structural Elements of Mono-Core Power Cable

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Structural Elements of 3-in-1 Power Cable

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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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Nanotechnology

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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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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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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

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 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
42
High Voltage Engineering For Modern Transmission Networks
Thank you for your attention!

20080509_-_High_Voltage_Engineering_for_modern_Transmission_Networks.ppt

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