The Benmore - Haywards HVDC Link Benmore - Haywards HVDC Link ... • MAV’s require reasonable...
Transcript of The Benmore - Haywards HVDC Link Benmore - Haywards HVDC Link ... • MAV’s require reasonable...
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The Benmore - Haywards HVDC Link
National Historic Heritage Workshop- Engineering Heritage
3 to 5 August 2004
Wellington
Marshall ClarkTranspower New Zealand
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Milestones1950 Bill Latta forecasts NZ supply and demand1950 ASEA awarded contract for world’s first undersea HVDC link
to Swedish island of Gotland1954 Gotland HVDC link commissioned1956 BICC reports on viability of Cook Strait crossing1958 Trial length of cable laid off Oteranga Bay1960 Construction of Benmore dam commences1961 HVDC link approved1964 Cable laying commences1965 First full power transmitted – 1 April 19651965 Official opening – 15 May 19651976 Link modified to allow power to be transmitted south1992-1993
Upgraded HVDC link commissioned with addition of 700 MWthyristor converters
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International Context
• Only 12 HVDC mercury arc valve transmission schemes were ever commissioned
• The New Zealand scheme was notable for its high voltage and long length of submarine cable
• By end 2005, there will only be one other HVDC scheme still operating with mercury arc valves
Transpower currently plans to maintain its mercury arc valves until at least 2010
5Scheme was controversial
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Cook Strait Cable Cross Section1. Hollow duct - N2 filled
2. Copper conductor
3. Conductor screen
4. Dielectric - paper tape
5. Dielectric screen -copper tape
6. Lead sheath
7. Reinforcement bedding
8. Reinforcement - steel tape
9. Armour bedding tape
10. Bend restricting armour
11. Anti-corrosion serving
12. Anti-teredo protection - brass
13. Armour bedding
14. Steel wire armour
15. Serving - jute string
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N2 filled hollow duct
Copper conductor
Dielectric - paper tape
Lead sheath
Reinforcement - steel tape
Bend restricting armour
Anti-teredo protection - brass
Steel wire armour
Serving - jute string
Cook Strait Cable
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9Cook Strait Cable
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Fighting Bay Cable Terminal Station
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HVDC line
12Line insulators replaced live
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Overview Single Line Diagram
14Haywards
15Benmore
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Mercury Arc Valve
17Mercury arc valve group
18Mercury arc valve hall
19Mercury arc valve workshop
20Clean workshop
21Haywards DC switchyard
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Smoothing reactor
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Valve Damping Resistor
24Base isolation scheme
25Haywards AC harmonic filters
26Haywards resistor-reactor units
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How the HVDC link is now used
• Mix of hydro/thermal generation• South Island hydro capacity exceeds demand in that island• HVDC transfer is determined by market dispatch tools based on
solving on priced half-hourly offers for generation• HVDC transfer can vary rapidly with market conditions• variability of transfer is unprecedented in 39 year history of
HVDC in New Zealand
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South Island Generation
DC Transfer (-)
Mid Waitaki
Manapouri
Clutha
Upper Waitaki
-1200.0 -1000.0 -800.0 -600.0 -400.0 -200.0
0.0200.0400.0600.0800.0
1000.01200.01400.01600.01800.02000.02200.02400.02600.02800.0
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1/07/99 p1
1/07/99 p13
1/07/99 p25
1/07/99 p37
2/07/99 p1
2/07/99 p13
2/07/99 p25
2/07/99 p37
3/07/99 p1
3/07/99 p13
3/07/99 p25
3/07/99 p37
4/07/99 p1
4/07/99 p13
4/07/99 p25
4/07/99 p37
Day
Average (Period) M
W
Upper Waitaki
Clutha
Manapouri
Other SI Hydro
Mid Waitaki
DC Transfer (-)
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Mercury Arc Valve Performance
• MAV’s require reasonable thermal stability• frequent start/stops, rapid rates of change of load and
inverter/rectifier mode changes increase rate of valve disturbances– commutation failures– arc backs– arc-throughs
• disturbances lead to increasing internal deterioration• increasing risk of valve faults and consequential failures• some constraints have been imposed on dispatch patterns to
preserve remaining life
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Scheduled Energy Unavailability
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4
6
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1993 1995 1997 1999 2001 2003
Year
SEU
(%)
MAV
Thyristor
Forced Energy Unavailability
00.20.40.60.8
11.21.4
1993 1995 1997 1999 2001 2003
Year
FEU
(%)
MAV
Thyristor
Operational Performance
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Forced Outage Count
010203040506070
1993 1995 1997 1999 2001 2003
Year
FOC MAV
Thyristor
Mercury arc valves inherently suffer more operational performance problems than the modern thyristor replacement
Operational Performance
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Risks of ownership
• Mercury presents an on-going safety and environmental hazard, although it is well controlled at present
• There is a rapidly diminishing pool of international expertise in the maintenance of mercury arc valves (support from the manufacturer ceased in 1970 !)
• Much of the equipment is unique and spares are very limited• Custom made solutions are required for failures of some
components - this carries its own risk• The equipment does not have the same seismic strength as
modern equipment• The operational performance is less than the modern equivalent
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Planning for replacement
• Transpower is preparing plans for replacement of the mercury arc valves and associated converter station equipment
• These plans will form part of a major Grid Upgrade Plan to be submitted to the Electricity Commission next year
• Following consultation, if approval is given, a major project will be launched to replace the mercury arc valve converter stations by around 2010
• The original converter stations will remain in service until thecompletion of the commissioning of the new equipment
• A lengthy period of decommissioning and decontamination is likely to be required
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Preservation for the Future
• The New Zealand HVDC scheme has been an extremely important part of our electricity system since 1965
• The scheme represented world-leading technology in its time, and involved very challenging engineering work
• The history is well documented in the books:– People, Politics & Power Stations– White Diamonds North
• The mercury arc valves themselves are the icons of this scheme• Efforts should be made to preserve at least one• An Electricity Transmission Heritage Society has been formed
with industry support• Plans must be made for some suitable memorial
351990 Engineering Heritage Plaque