HVDC Inter-Island
Encyclopedia
The HVDC Inter-Island link is a high-capacity, bipolar high-voltage direct current
(HVDC) transmission system connecting the electricity transmission networks of New Zealand's two main islands to form the National Grid
. The HVDC link is owned and operated by state-owned transmission company Transpower New Zealand
. The link is commonly referred to as the Cook Strait cable. This is somewhat of a misnomer
, because there are actually three submarine HVDC power cables across Cook Strait
in current use (with other cables still on the floor of the strait from previous use), the cables make up only a small proportion of the total route length, and the complete link includes long overhead transmission lines and large converter stations at each end. However, the term Cook Strait cable is commonly used in the media and press releases.
The 610 km link starts at the Benmore Hydroelectric Power Station
, on the Waitaki River in Canterbury, and travels 534 km on an overhead transmission line through inland Canterbury and Marlborough to Fighting Bay in the Marlborough Sounds. From Fighting Bay, the link travels 40 km via submarine cables across Cook Strait to Oteranga Bay, near Wellington
, before travelling the final 37 km to Haywards
transmission sub-station in the Hutt Valley.
The HVDC link was first commissioned in April 1965, originally as a bipolar 600 MW link with mercury arc valves. The original equipment was paralleled onto a single pole (Pole 1) in 1992, and a new thyristor-based pole (Pole 2) was commissioned alongside it. The mercury-arc pole was partially decommissioned in 2007. Work is underway to completely replace the mercury-arc valve converters with a new thyristor pole, with work expected to be completed in 2012.
The HVDC link is an important component of the transmission system in New Zealand. It connects the transmission grids of the two islands, and is used as an energy-balancing system, helping to match energy availability and demand in the two islands.
The two islands are geographically different – the South Island is 33% larger than the North Island, but the North Island has 3.2 times the population of the South Island. As a consequence, the North Island has a substantially larger energy demand. However, the South Island loads include the Tiwai Point Aluminium Smelter, which at a peak demand of 640 MW is New Zealand's largest single electricity user, and the second largest load centre after the city of Auckland. In total, around 32.5% of the total electricity generated was consumed in the South Island, while 67.5% was consumed in the North Island.
The South Island is more mountainous than the North Island, containing 38 of the 40 New Zealand peaks over 2500 m, creating larger resources for hydroelectricity. However, the North Island has numerous natural gas reserves, geothermal areas, and suitable coalfields to support thermal generation (South Island coal is generally harder and more suitable for steel manufacture than electricity generation). Both islands are suited for wind generation, although the North Island has more wind generators currently than the South Island. The South Island has a total generating capacity of 3582 MW (37.8%) – of which 98% is hydroelectricity. The North Island's generating capacity is 5905 MW (62.2%) – of which 31.6% is hydro, 29.6% is gas, 16.0% is coal, 10.8% is geothermal, 7.4% is wind, and 4.6% is other fuels.
Although both islands normally have enough generating capacity to power themselves in the short term without the connection between the two islands, the HVDC link provides benefits for both South Island and North Island energy markets:
The link plays an important role in the New Zealand electricity market
and facilitates competition. Deregulation of the electricity industry that occurred the 1990s led to the breakup of the generation previously owned by the Electricity Corporation of New Zealand
. With the exception of Contact Energy
, the split up of the Electricity Corporation generators was carried out geographically. As a result, two generating companies (Genesis Power and Mighty River Power) were based solely in the North Island, and one (Meridian
) solely in the South Island. Contact Energy owned stations in both islands. If the HVDC link didn't exist, or in the event of a failure, wholesale electricity prices could rise from a shortfall in capacity and reduced competition.
The link is designed to be able to transmit electricity in both northwards and southwards directions, but the design of the transmission system in the lower North Island restricts the amount of electricity that can be transmitted southwards. The North Island's electricity system has most of its generation in the centre of the island, while the two major load centres, Auckland
and Wellington
, are located north and south of the main generation resources. The HVDC Inter-Island link connects to the North Island AC transmission system at Haywards in Wellington. The Wellington region is a major load centre with a regional peak demand of approximately 780 MW and local generation of only around one-fifth of that. During periods of northwards power flow on the HVDC link, the energy from the South Island is largely used in the Wellington region, and any surplus flows along four 220 kV transmission circuits to points further north. However, during periods of southwards HVDC flow, the 220 kV circuits into Wellington must transmit electricity from the North Island grid for both Wellington and the HVDC link. Southwards HVDC power transfer is limited by the capacity of the lower North Island 220 kV transmission circuits, and by the risk of voltage disturbances in the Wellington region in the event of a sudden disruption to HVDC transfer. Large southwards transfers on the HVDC link are not generally required except during period of prolonged low inflows to South Island hydro lakes, and the limited southbound capacity is not a major constraint.
The inter-island transmission system was designed as HVDC, despite the cost of the conversion from AC to DC and back, to suit the requirements of a long transmission line and a sea crossing. The link crosses Cook Strait
, between the two islands, using submarine power cable
s laid along the sea floor. HVDC is more suitable than AC for transmission over long distances, and particularly where cable transmission is required, because it typically has lower energy losses. See High-voltage direct current
.
and British Insulated Callender's Cables
. The original Cook Strait cables were installed in 1964, from the cable laying ship Photinia.
The HVDC Inter-Island link was built with large mercury-arc rectifiers and inverters
– 1960s technology. When it was completed, the HVDC Inter-Island link was the world's longest with the highest power rating, and the largest undersea power cables.
Until it was upgraded in 1993, the HVDC Inter-Island link was a bi-pole HVDC transmission line with normal operating voltages of plus and minus 250 kilovolts, and a maximum power transmission capacity of about 600 megawatts (MW).
The HVDC transmission line that connects the rectifier/inverter (converter) station at the Benmore Dam
hydroelectric plant in the southern half of the South Island with the converter station at Haywards
on the North Island has an overall length of 610 kilometres. The overhead transmission line is supported by 1649 transmission tower
s and has a total route length of 570 km. The submarine cables across Cook Strait
are 40 km long.
technology. The existing mercury arc valve converters were re-configured to operate in parallel at each station (they had previously operated with opposite electrical polarity
). The reconfigured mercury arc valve converters were designated as Pole 1, and the new thyristor converters were designated as Pole 2. The operating voltage of the new converters was 350 kV. The project scope included the laying of three new new submarine cables across Cook Strait, and re-insulation of the overhead HVDC line to accommodate the increased operating voltage. The three new power cables were installed in 1991 by the specialist cable laying vessel Skagerrak.
Transpower also announced in November 2007 that by December 2007, it would increase the power transmission capacity from south to north of Pole 2 from 500 MW to 700 MW. This was done by reconfiguring the three operational submarine cables by moving one of the two cables of Pole 1 to Pole 2.
On 13 March 2008, Transpower announced that work had been completed to restore 50% of the capacity of Pole 1 to service at times when the demand for power on the North Island peaked. Several mercury arc rectifiers were salvaged from the Konti-Skan
link between Denmark and Sweden for this restoration.
The energy transfer on Pole 1 has been strictly limited to the northbound direction, to reduce the stress and strain on the aged converter system.
In May 2009 Transpower placed Pole 1 back into service at a limited capacity of 200 MW in response to a temporary loss of capacity on Pole 2.
Planned outages of the link are required occasionally to carry out maintenance that is not possible while the system is live. Maintenance outages are planned well in advance to minimise the effects – they are usually carried out in summer when inter-island electricity demand is at its lowest, and usually on one pole at a time, while the other pole remains in operation with earth electrodes providing a path for return current through the ground.
Notable faults and outages on the HVDC Inter-Island:-
for the replacement of the old mercury arc valve Pole 1 converter stations with new thyristor converter stations.
In July 2008, the Electricity Commission announced its intention to approve the project .
turned the first sod, with the new converter stations scheduled for commissioning in April 2012.
Work involved in the replacement of Pole 1 with the new Pole 3 converter stations includes:
The decommissioning of Pole 1 is scheduled for July 2012, allowing works to switch the existing lines over Pole 3 and to test the new pole to occur during the summer months where electricity demand and therefore inter-island electricity transfer is low. Pole 3 is planned to be commissioned for operation in December 2012.
The new pole will initially be limited to 500 MW northbound transfer (1000 MW total transfer with Pole 2) due to inadequate voltage support at Haywards.
After a new static synchronous compensator
(STATCOM) at Haywards is commissioned, planned for January 2014, Pole 3 will be able to operate at its full 700 MW capacity (1200 MW total transfer with Pole 2).
If new cables are laid (taking the total usable cables on the floor of the strait to 4 or 5) then the link will be capable of 1400 MW (700MW on each pole). Pole 2 was originally built to handle 700MW transfer.
One of the many proposals to alleviate this issue includes a tap into the HVDC Inter-Island and an inverter/rectifier station where it meets the two 220kV Islington to Kikiwa lines near Waipara in northern Canterbury. This would allow another route for electricity into Christchurch and the Upper South Island, and create redundancy in the network. However, it is unlikely for such a tap to be built before 2021.
High-voltage direct current
A high-voltage, direct current electric power transmission system uses direct current for the bulk transmission of electrical power, in contrast with the more common alternating current systems. For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses...
(HVDC) transmission system connecting the electricity transmission networks of New Zealand's two main islands to form the National Grid
National Grid (New Zealand)
The National Grid is the nationwide system of electric power transmission in New Zealand. The grid is owned and operated by Transpower New Zealand Limited, a State owned enterprise.- Transmission :- Existing :...
. The HVDC link is owned and operated by state-owned transmission company Transpower New Zealand
Transpower New Zealand Limited
Transpower New Zealand Limited is the state-owned enterprise responsible for electric power transmission in New Zealand. Transpower performs two major functions in the New Zealand Electricity Market...
. The link is commonly referred to as the Cook Strait cable. This is somewhat of a misnomer
Misnomer
A misnomer is a term which suggests an interpretation that is known to be untrue. Such incorrect terms sometimes derive their names because of the form, action, or origin of the subject becoming named popularly or widely referenced—long before their true natures were known.- Sources of misnomers...
, because there are actually three submarine HVDC power cables across Cook Strait
Cook Strait
Cook Strait is the strait between the North and South Islands of New Zealand. It connects the Tasman Sea on the west with the South Pacific Ocean on the east....
in current use (with other cables still on the floor of the strait from previous use), the cables make up only a small proportion of the total route length, and the complete link includes long overhead transmission lines and large converter stations at each end. However, the term Cook Strait cable is commonly used in the media and press releases.
The 610 km link starts at the Benmore Hydroelectric Power Station
Benmore Dam
Benmore Dam is the largest dam within the Waitaki power scheme, located in the Canterbury Region of New Zealand's South Island. There are eight other power stations in the valley....
, on the Waitaki River in Canterbury, and travels 534 km on an overhead transmission line through inland Canterbury and Marlborough to Fighting Bay in the Marlborough Sounds. From Fighting Bay, the link travels 40 km via submarine cables across Cook Strait to Oteranga Bay, near Wellington
Wellington
Wellington is the capital city and third most populous urban area of New Zealand, although it is likely to have surpassed Christchurch due to the exodus following the Canterbury Earthquake. It is at the southwestern tip of the North Island, between Cook Strait and the Rimutaka Range...
, before travelling the final 37 km to Haywards
Haywards
Haywards is the location in Wellington, New Zealand, where the North Island's static inverter plant of the HVDC Inter-Island transmission line is located. Suburbs and towns near Haywards include Belmont, Judgeford, Silverstream, Trentham and Taita....
transmission sub-station in the Hutt Valley.
The HVDC link was first commissioned in April 1965, originally as a bipolar 600 MW link with mercury arc valves. The original equipment was paralleled onto a single pole (Pole 1) in 1992, and a new thyristor-based pole (Pole 2) was commissioned alongside it. The mercury-arc pole was partially decommissioned in 2007. Work is underway to completely replace the mercury-arc valve converters with a new thyristor pole, with work expected to be completed in 2012.
Background
The two islands are geographically different – the South Island is 33% larger than the North Island, but the North Island has 3.2 times the population of the South Island. As a consequence, the North Island has a substantially larger energy demand. However, the South Island loads include the Tiwai Point Aluminium Smelter, which at a peak demand of 640 MW is New Zealand's largest single electricity user, and the second largest load centre after the city of Auckland. In total, around 32.5% of the total electricity generated was consumed in the South Island, while 67.5% was consumed in the North Island.
The South Island is more mountainous than the North Island, containing 38 of the 40 New Zealand peaks over 2500 m, creating larger resources for hydroelectricity. However, the North Island has numerous natural gas reserves, geothermal areas, and suitable coalfields to support thermal generation (South Island coal is generally harder and more suitable for steel manufacture than electricity generation). Both islands are suited for wind generation, although the North Island has more wind generators currently than the South Island. The South Island has a total generating capacity of 3582 MW (37.8%) – of which 98% is hydroelectricity. The North Island's generating capacity is 5905 MW (62.2%) – of which 31.6% is hydro, 29.6% is gas, 16.0% is coal, 10.8% is geothermal, 7.4% is wind, and 4.6% is other fuels.
Although both islands normally have enough generating capacity to power themselves in the short term without the connection between the two islands, the HVDC link provides benefits for both South Island and North Island energy markets:
- The link provides the South Island consumers with access to the North Island’s gas and coal generation resources that can support the South Island demand during times of low hydro storage levels and low inflows to South Island hydro lakes
- The link provides North Island consumers with access to the South Island’s large hydro generation resources that can support the North Island demand at times of peak load.
The link plays an important role in the New Zealand electricity market
New Zealand Electricity Market
New Zealand's electricity market is regulated by the Electricity Industry Participation Code administered by the Electricity Authority . The Authority was established in November 2010 to replace the Electricity Commission and its publication explains how the market works.- Overview :Until 1987,...
and facilitates competition. Deregulation of the electricity industry that occurred the 1990s led to the breakup of the generation previously owned by the Electricity Corporation of New Zealand
Electricity Corporation of New Zealand
The Electricity Corporation of New Zealand Ltd is a New Zealand state-owned enterprise formed on 1 April 1987, as a transition entity in the process of deregulating the New Zealand electricity market...
. With the exception of Contact Energy
Contact Energy
Contact Energy Limited is a New Zealand electricity generator, natural gas wholesaler and electricity, natural gas, and LPG retailer.The company is the second-largest electricity generator in New Zealand , generating 24 percent of New Zealand's electricity in the year ending 31 December 2009, and...
, the split up of the Electricity Corporation generators was carried out geographically. As a result, two generating companies (Genesis Power and Mighty River Power) were based solely in the North Island, and one (Meridian
Meridian Energy
Meridian Energy Limited is a New Zealand state-owned electricity generator and retailer. The company generates the largest proportion of New Zealand's electricity, generating 32 percent of the country's electricity in the year ending 31 December 2009, and is the fourth-equal largest retailer, with...
) solely in the South Island. Contact Energy owned stations in both islands. If the HVDC link didn't exist, or in the event of a failure, wholesale electricity prices could rise from a shortfall in capacity and reduced competition.
The link is designed to be able to transmit electricity in both northwards and southwards directions, but the design of the transmission system in the lower North Island restricts the amount of electricity that can be transmitted southwards. The North Island's electricity system has most of its generation in the centre of the island, while the two major load centres, Auckland
Auckland
The Auckland metropolitan area , in the North Island of New Zealand, is the largest and most populous urban area in the country with residents, percent of the country's population. Auckland also has the largest Polynesian population of any city in the world...
and Wellington
Wellington
Wellington is the capital city and third most populous urban area of New Zealand, although it is likely to have surpassed Christchurch due to the exodus following the Canterbury Earthquake. It is at the southwestern tip of the North Island, between Cook Strait and the Rimutaka Range...
, are located north and south of the main generation resources. The HVDC Inter-Island link connects to the North Island AC transmission system at Haywards in Wellington. The Wellington region is a major load centre with a regional peak demand of approximately 780 MW and local generation of only around one-fifth of that. During periods of northwards power flow on the HVDC link, the energy from the South Island is largely used in the Wellington region, and any surplus flows along four 220 kV transmission circuits to points further north. However, during periods of southwards HVDC flow, the 220 kV circuits into Wellington must transmit electricity from the North Island grid for both Wellington and the HVDC link. Southwards HVDC power transfer is limited by the capacity of the lower North Island 220 kV transmission circuits, and by the risk of voltage disturbances in the Wellington region in the event of a sudden disruption to HVDC transfer. Large southwards transfers on the HVDC link are not generally required except during period of prolonged low inflows to South Island hydro lakes, and the limited southbound capacity is not a major constraint.
The inter-island transmission system was designed as HVDC, despite the cost of the conversion from AC to DC and back, to suit the requirements of a long transmission line and a sea crossing. The link crosses Cook Strait
Cook Strait
Cook Strait is the strait between the North and South Islands of New Zealand. It connects the Tasman Sea on the west with the South Pacific Ocean on the east....
, between the two islands, using submarine power cable
Submarine power cable
Submarine power cables are major transmission cables for carrying electric power below the surface of the water. These are called "submarine" because they usually carry electric power beneath salt water but it is also possible to use submarine power cables beneath fresh water...
s laid along the sea floor. HVDC is more suitable than AC for transmission over long distances, and particularly where cable transmission is required, because it typically has lower energy losses. See High-voltage direct current
High-voltage direct current
A high-voltage, direct current electric power transmission system uses direct current for the bulk transmission of electrical power, in contrast with the more common alternating current systems. For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses...
.
History
The HVDC inter-island link was designed and built between 1965 for the New Zealand Electricity Department. The major equipment suppliers were Asea Brown BoveriAsea Brown Boveri
ABB is a Swiss-Swedish multinational corporation headquartered in Zürich, Switzerland, and best known for its robotics. ABB operates mainly in the power and automation technology areas. It ranked 143rd in Forbes Ranking ....
and British Insulated Callender's Cables
British Insulated Callender's Cables
British Insulated Callender's Cables was a 20th century British cable manufacturer and construction company, now renamed after former subsidiary Balfour Beatty.-History:...
. The original Cook Strait cables were installed in 1964, from the cable laying ship Photinia.
The HVDC Inter-Island link was built with large mercury-arc rectifiers and inverters
Mercury arc valve
A mercury-arc valve is a type of electrical rectifier used for converting high-voltage or high-current alternating current into direct current . Rectifiers of this type were used to provide power for industrial motors, electric railways, streetcars, and electric locomotives, as well as for...
– 1960s technology. When it was completed, the HVDC Inter-Island link was the world's longest with the highest power rating, and the largest undersea power cables.
Until it was upgraded in 1993, the HVDC Inter-Island link was a bi-pole HVDC transmission line with normal operating voltages of plus and minus 250 kilovolts, and a maximum power transmission capacity of about 600 megawatts (MW).
The HVDC transmission line that connects the rectifier/inverter (converter) station at the Benmore Dam
Benmore Dam
Benmore Dam is the largest dam within the Waitaki power scheme, located in the Canterbury Region of New Zealand's South Island. There are eight other power stations in the valley....
hydroelectric plant in the southern half of the South Island with the converter station at Haywards
Haywards
Haywards is the location in Wellington, New Zealand, where the North Island's static inverter plant of the HVDC Inter-Island transmission line is located. Suburbs and towns near Haywards include Belmont, Judgeford, Silverstream, Trentham and Taita....
on the North Island has an overall length of 610 kilometres. The overhead transmission line is supported by 1649 transmission tower
Transmission tower
A transmission tower is a tall structure, usually a steel lattice tower, used to support an overhead power line. They are used in high-voltage AC and DC systems, and come in a wide variety of shapes and sizes...
s and has a total route length of 570 km. The submarine cables across Cook Strait
Cook Strait
Cook Strait is the strait between the North and South Islands of New Zealand. It connects the Tasman Sea on the west with the South Pacific Ocean on the east....
are 40 km long.
Pole 2 Upgrade Project
Between 1991 and 1993, the inter-island power transmission system was upgraded with the addition of new HVDC converter stations at each end of the link. These new HVDC converter stations used solid state thyristorThyristor
A thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. They act as bistable switches, conducting when their gate receives a current trigger, and continue to conduct while they are forward biased .Some sources define silicon controlled rectifiers and...
technology. The existing mercury arc valve converters were re-configured to operate in parallel at each station (they had previously operated with opposite electrical polarity
Electrical polarity
Electrical polarity is present in every electrical circuit. Electrons flow from the negative pole to the positive pole. In a direct current circuit, one pole is always negative, the other pole is always positive and the electrons flow in one direction only...
). The reconfigured mercury arc valve converters were designated as Pole 1, and the new thyristor converters were designated as Pole 2. The operating voltage of the new converters was 350 kV. The project scope included the laying of three new new submarine cables across Cook Strait, and re-insulation of the overhead HVDC line to accommodate the increased operating voltage. The three new power cables were installed in 1991 by the specialist cable laying vessel Skagerrak.
De-commissioning of Pole 1
, the part of Pole 1 of the inter-island link that still used the original mercury-arc rectifiers and inverters was shut down "indefinitely". However, in December 2007, Transpower announced that one-half of the capacity of Pole 1 would be returned to "warm standby" service before the winter of 2008 in order to meet the demand for power on the North Island if needed. The remaining half-pole equipment of Pole 1 was to be decommissioned.Transpower also announced in November 2007 that by December 2007, it would increase the power transmission capacity from south to north of Pole 2 from 500 MW to 700 MW. This was done by reconfiguring the three operational submarine cables by moving one of the two cables of Pole 1 to Pole 2.
On 13 March 2008, Transpower announced that work had been completed to restore 50% of the capacity of Pole 1 to service at times when the demand for power on the North Island peaked. Several mercury arc rectifiers were salvaged from the Konti-Skan
Konti-Skan
Konti–Skan is the name of high-voltage direct-current transmission line between Denmark and Sweden.-Technical description:...
link between Denmark and Sweden for this restoration.
The energy transfer on Pole 1 has been strictly limited to the northbound direction, to reduce the stress and strain on the aged converter system.
In May 2009 Transpower placed Pole 1 back into service at a limited capacity of 200 MW in response to a temporary loss of capacity on Pole 2.
Transmission faults and outages
Like all transmission systems, the HVDC Inter-Island link is not immune to failures. The importance of the link means that an unplanned outage can have major implications for the whole of the New Zealand electricity system, potentially causing nationwide electricity shortages and a spike in wholesale electricity prices.Planned outages of the link are required occasionally to carry out maintenance that is not possible while the system is live. Maintenance outages are planned well in advance to minimise the effects – they are usually carried out in summer when inter-island electricity demand is at its lowest, and usually on one pole at a time, while the other pole remains in operation with earth electrodes providing a path for return current through the ground.
Notable faults and outages on the HVDC Inter-Island:-
- 1973 – Burning paper insulation caused an electrical fault in Cable 1's Fighting Bay shore joint.
- August 1975 – A strong wind storm caused a string of seven transmission towerTransmission towerA transmission tower is a tall structure, usually a steel lattice tower, used to support an overhead power line. They are used in high-voltage AC and DC systems, and come in a wide variety of shapes and sizes...
s to collapse and damage the line. The link took five days to repair. - 1976 – A fault occurred at the Cable 1 undersea joint, 15.5 km from the South Island end at a depth of 120 metres. The joint was repaired in 1977.
- 1980 – Cable 3 failed at the Fighting Bay shore joint.
- 1981 – A gas leak on Cable 1 occurred at Oteranga Bay. It was repaired in the 1982/83 summer.
- 1988 – Cable 2's Oteranga Bay end joint exploded, spilling insulating oil into the switchyard.
- 2004 – In January, three HVDC towers collapsed as a result of extreme winds, and in August the line voltage had to be reduced for long periods because of insulation flashovers caused by severe salt pollution at the cable station at Oteranga bay. In October, a fault occurred in one of three Cook Strait cables that reduced the Pole 1 capacity from 540 MW to 386 MW. Repairs took almost six months.
- 19 June 2006 – The link experienced an unplanned outage just before the evening peak period on one of the coldest days of the year. With four North Island power stations out for service and an outage of Tauranga's ripple load control equipment, even with the reserve Whirinaki Power Station called upon, the North Island experienced electricity shortages and Transpower subsequently declared a nationwide Grid Emergency at 5:34 pm. The link was restored shortly after the emergency was declared.
- 28 August 2008 – A transmission towerTransmission towerA transmission tower is a tall structure, usually a steel lattice tower, used to support an overhead power line. They are used in high-voltage AC and DC systems, and come in a wide variety of shapes and sizes...
in the Marlborough Sounds was found buckled after its foundations slipped. The tower was reinforced with steel guy ropes until it could be replaced, as the link couldn't be shut down without causing widespread power shortages in the South Island.
Replacement of Pole 1
In May 2008, Transpower submitted an investment proposal to the Electricity CommissionElectricity Commission (NZ)
The New Zealand Electricity Commission was a government authority set up in 2003 to regulate the Electricity sector in New Zealand.The Commission was established under the Electricity Act to regulate the operation of the electricity industry and markets in accordance government energy policy...
for the replacement of the old mercury arc valve Pole 1 converter stations with new thyristor converter stations.
In July 2008, the Electricity Commission announced its intention to approve the project .
The Pole 3 Project
The new converter stations are to be known as Pole 3, and will operate at 350 kV, matching the existing Pole 2. Site works on the $672 million project were formally commenced on 19 April 2010, when Minister of Energy Gerry BrownleeGerry Brownlee
Gerard Anthony "Gerry" Brownlee is a New Zealand politician. He served from 17 November 2003 to 27 November 2006 as deputy-leader of the National Party – during that period the second-largest party in the New Zealand Parliament, and thus forming the core of the Opposition...
turned the first sod, with the new converter stations scheduled for commissioning in April 2012.
Work involved in the replacement of Pole 1 with the new Pole 3 converter stations includes:
- New valve halls adjacent to the Pole 2 valve halls at both Benmore and Haywards, each containing the thyristors converters.
- New transformers connecting the valve halls to the 220 kV buses at both Benmore and Haywards
- Connecting the Pole 3 thyristors to the existing Pole 1 lines at both Benmore and Haywards
- Connecting the Pole 3 thyristors to the existing electrode lines at both Benmore and Haywards.
- Switching the number 5 Cook Strait cable back to the Pole 1/3 line.
- New 220 kV filtersElectronic filterElectronic filters are electronic circuits which perform signal processing functions, specifically to remove unwanted frequency components from the signal, to enhance wanted ones, or both...
on the 220 kV buses at both Benmore and Haywards. - New transformers connecting the four synchronous condenserSynchronous condenserIn electrical engineering, a synchronous condenser is adevice identical to a synchronous motor, whose shaft is not connected to anything but spins freely. Its purpose is not to convert electric power to mechanical power or vice versa, but to adjust conditions on the electric power transmission grid...
s C7 to C10 to the 110 kV bus at Haywards - New 5th and 7th harmonic filters connecting to the 110 kV bus at Haywards
- Removal of the existing converter transformers connecting the Pole 1 mercury arc valves to the 110 kV bus at Haywards
- Removal of all remaining mercury arc valve Pole 1 equipment at both Benmore and Haywards.
The decommissioning of Pole 1 is scheduled for July 2012, allowing works to switch the existing lines over Pole 3 and to test the new pole to occur during the summer months where electricity demand and therefore inter-island electricity transfer is low. Pole 3 is planned to be commissioned for operation in December 2012.
The new pole will initially be limited to 500 MW northbound transfer (1000 MW total transfer with Pole 2) due to inadequate voltage support at Haywards.
After a new static synchronous compensator
STATCOM
A static synchronous compensator is a regulating device used on alternating current electricity transmission networks. It is based on a power electronics voltage-source converter and can act as either a source or sink of reactive AC power to an electricity network. If connected to a source of...
(STATCOM) at Haywards is commissioned, planned for January 2014, Pole 3 will be able to operate at its full 700 MW capacity (1200 MW total transfer with Pole 2).
If new cables are laid (taking the total usable cables on the floor of the strait to 4 or 5) then the link will be capable of 1400 MW (700MW on each pole). Pole 2 was originally built to handle 700MW transfer.
Line maintenance
During the Pole 1 replacement, work is also underway to carry out maintenance and remedial work on some sections of the transmission line. Work includes:- Replacing around 100 transmission towerTransmission towerA transmission tower is a tall structure, usually a steel lattice tower, used to support an overhead power line. They are used in high-voltage AC and DC systems, and come in a wide variety of shapes and sizes...
s in the South Island to fix clearance issues - Replacing some conductor lengths in the North Island as they approach the end of their useful life
- Reinforcing some North Island transmission towers.
Fourth Cook Strait cable
There are proposals to install a fourth cable across the Cook Strait (Cable 7), connecting to Pole 2, to allow the HVDC link to increase to 1400 MW. In addition to a fourth cable, new filters would also be installed at Benmore and Haywards, and a new STATCOM at Haywards. The project is unlikely to be completed before 2016.North Canterbury tap
The Upper South Island north of the Waitaki Valley is generation-poor, yet has many large demand centres, especially Christchurch, Nelson, Ashburton and Timaru-Temuka. Almost all of the electricity has to be imported from the Waitaki Valley, via three major lines carrying between them four 220kV circuits. Increasing demand means that these lines are fast approaching capacity, and because they all converge on Islington sub-station in western Christchurch, a major fault at the sub-station could potentially interrupt the electricity supply to the entire South Island north of Christchurch.One of the many proposals to alleviate this issue includes a tap into the HVDC Inter-Island and an inverter/rectifier station where it meets the two 220kV Islington to Kikiwa lines near Waipara in northern Canterbury. This would allow another route for electricity into Christchurch and the Upper South Island, and create redundancy in the network. However, it is unlikely for such a tap to be built before 2021.
Eastern route
Transpower formerly operated two 110kV circuits from Halfway Bush substation in Dunedin north through Palmerston and Oamaru to South Canterbury. However, the lines between Oamaru and Palmerston were removed in 1993 due to low utilisation (there is little demand in this area). Had this route been kept, it would have provided an alternative to the central 220kV lines.Sites
- Haywards Pole 1 valve hall: 41.15143°N 174.98006°W
- Haywards Pole 2/3 valve hall: 41.151446°N 174.981691°W
- Branch of North Island electrode line: 41.234167°N 174.758611°W
- Terminal Electrode line in the North Island: 41°12′28"S 174°43′11"E
- Cable Terminal in the North Island: 41°17′37"S 174°37′48"E
- Cable Terminal in the South Island: 41°18′35"S 174°12′5"E
- Benmore Converter Station: 44°33′55"S 170°11′24"E
- Electrode on the South Island: 44°34′06"S 170°07′52"E
See also
- National Grid (New Zealand)National Grid (New Zealand)The National Grid is the nationwide system of electric power transmission in New Zealand. The grid is owned and operated by Transpower New Zealand Limited, a State owned enterprise.- Transmission :- Existing :...
- High-voltage direct currentHigh-voltage direct currentA high-voltage, direct current electric power transmission system uses direct current for the bulk transmission of electrical power, in contrast with the more common alternating current systems. For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses...
- List of HVDC projects
- Electricity sector in New ZealandElectricity sector in New ZealandThe electricity sector in New Zealand uses mainly renewable energy sources such as hydropower, geothermal power and increasingly wind energy. The 70% share of renewable energy sources makes New Zealand one of the lowest carbon dioxide emitting countries in terms of electricity generation....
External links
- New Zealand's HVDC Link
- New Zealand HVDC – the interisland link (from the ABB website)
- http://web.archive.org/web/20050526185217/www.transmission.bpa.gov/cigresc14/Compendium/NEW-ZEAL.htm
- http://web.archive.org/web/20050526185217/www.transmission.bpa.gov/cigresc14/Compendium/New-zeal%20Pictures.pdf