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When your power demand is a long way from the source of generation, then your transmission infrastructure better be very good, which ours isn’t, and the reason Transpower is investing $5 billion on the national grid over the next seven years.
For the first half of the last century the national grid slowly displaced coal stations in major cities and then expanded quickly in the1950s and 1960s as new power stations were built in the lower South Island and upper North Island. However, investment in new transmission had slowed down to a trickle by the turn of the century when, after a series of dramatic blackouts in Auckland, it was obvious that serious re-investment in the national grid was overdue. The grid is a high voltage AC transmission network that supplies most of the major load centres in New Zealand, made up of a backbone grid of 220 kV transmission lines stretching nearly the full length of each island. Generation on each island is linked by a high-voltage direct current (HVDC) system. The original network of 110kV lines runs roughly parallel to the 220kV network that is primarily used for transmission to regions that do not have 220 kV, or for sub-transmission to substations within a region. Transpower, the state-owned enterprise tasked with owning and operating the country’s gird and substations, is now involved with the largest transmission project to be undertaken in New Zealand since 1960s – replacing, repairing and upgrading infrastructure and assets for a more energy secure (and renewable) future. Made up of a number of individual, large-scale projects, some $3.8 billion is being spent of this grid upgrade over a five year period and has taken many years of planning and approval. Because Transpower’s transmission network is a natural monopoly, these huge investments had to pass by the industry regulator, the Electricity Commission (which will be replaced by a leaner and more independent Electricity Authority in October), while costs had to be approved by the Commerce Commission. Each major project in the overall grid upgrade had to pass the Grid Investment Test (GIT) overseen by the Electricity Commission to make sure they promoted economic and energy efficiency in transmission and provided a net benefit to the wholesale and consumer markets. The HVDC upgrade
North Island grid upgradeThe largest of the line upgrades is the North Auckland and Northland (NAaN) project to meet the growing electricity demand in this region and improve security of supply. It will also assist the viability of new generation, such as wind farm and geothermal projects in the centre North Island. This project has three major components: A new overhead transmission line, new substations, and new underground cables. The overhead transmission line comes under the North Island Grid Upgrade Project (NIGUP), with a scheduled commissioning date of 2012, and involves a new 186 kilometre, 400kV overhead transmission line (initially operated at 220 kV) between a new substation at Whakamaru in the lower Waikato and a new switching station at Brown Hill Road in south-east Auckland. The capacity for the project in its final 400kV configuration is given as 5500MW. This was the most controversial of the grid projects as it involves massive pylons to be built on private, crown and Maori land. The 400kV overhead lines will stop at the new switching station in South Auckland and, from there, two underground 220kV cable circuits will run to a new substation at the existing substation Pakuranga site and, at a later date, two more circuits will run to the new Otahuhu substation located closer to the Auckland city centre. Otahuhu completed
A third of New Zealand’s power supply and nearly all of Auckland and Northland’s power is currently supplied through this one site and now incoming power is spilt to both new and old substations, so if one of them trips, the power still gets through. The project, brought forward following the outage at the Otahuhu substation in 2006, involved over 300 people and over 300,000 work hours without any lost time injuries. It is the first completed of around $1.7 billion worth of transmission projects Transpower has underway to reinforce its network into and across Auckland – that also includes the new 400kV line into Pakuranga from the south, and an underground cable circuit between Pakuranga and Albany. Second circuit for AucklandAn underground 220 kV cable connection is being laid between Penrose and Albany (via the Auckland Harbour Bridge), that will provide an alternate electricity supply route to the North Auckland and Northland regions, which currently rely on just one, 220kV high capacity line strung between Otahuhu and Henderson to the city’s west. Transpower paid out $53 million to lay this high-voltage cable through Vector’s nine kilometre long, three-metre wide tunnel from Penrose to Hobson Street in Auckland and its North Shore transmission corridor. The tunnel was built in 2001 to accommodate 110kV and 33kV cables to improve security of supply into the Auckland CBD. The one-off payment, paid in two installments, is for the use of the tunnel, which is a better alternative to digging up Auckland’s streets. Tactical projects
This $20 million project involved connecting two 220kV transmission circuits between Huntly and Otahuhu that pass over the substation site (with expansion for a further circuit in the future), which allows better load sharing between the existing circuits and improved security in the event of the loss of one or more transmission circuits. Getting the juice out of WairakeiIn the centre of the North Island, Transpower is building a new double circuit 220kV transmission line between Wairakei and Whakamaru to help connect more geothermal generation being built in the area. As part of this project, the existing Wairakei to Whakamaru B line (via Poihipi Rd) will be decommissioned and removed. It took Transpower a while to figure out its preferred route, which will be about 500 metres wide and in general vicinity of the existing lines, but deviating to the north. This route, it says, is the least visible and avoids (as much as possible anyway) existing dwellings, reduces impacts on surrounding communities, and ties in well for further geothermal generation development at Mokai and Te Mihi. South Island grid upgrade
This project, worth up to $170 million, involves releasing extra capacity from Transpower’s existing transmission lines between Roxburgh and the Waitaki Valley, and will transport electricity from planned or potential new generation in the lower South Island region (like the planned wind farm near Lake Mahinerangi). Additionally, during dry years, this project will help improve supply security to Southland. Most of the work involves replacing the conductor (wire) on these lines. It is expected that the work will be undertaken progressively from 2012 to 2015. The work will not change the basic line; however, some towers and tower foundations may require strengthening. Top of the South IslandIn May this year, Transpower submitted a Grid Upgrade Plan to the Electricity Commission seeking approval for work on its transmission network supplying the upper South Island (north of the Waitaki Valley). Initially, Transpower thought such investment would not be required until 2017, but reopened its investigations due to increasing irrigation and changing land uses, changing peak load periods and planning for high impact-low probability events, among other reasons. This is a provisional investment project, it says, and if an investment is required, Transpower anticipates seeking approval from the regulator for the first stage of the project in early 2012. Static synchronous compensatorsAlso in May this year, Transpower submitted grid upgrade plan involving ‘dynamic reactive support’ in the Auckland/Northland region that involves a package of investments including two static synchronous compensators (STATCOMs), a reactive power controller to control these devices, monitoring equipment, software upgrades and load control initiatives. These investments (in conjunction with the NIGUP currently under construction) will relieve the existing voltage stability issues in the upper North Island until 2015. Dynamic reactive support maintains voltage within acceptable limits in the milliseconds following unexpected outages and helps avoid the possibility of cascade failure which would result in widespread loss of supply. “Although more reactive support will be needed in the future, we have only sought approval for the investment required until 2015. Although we are studying options for the period beyond 2015, further investment will be deferred if new confirmed generation emerges in the meantime,” says Transpower.
Energy NZ Vol.4 No.5 September-October 2010 |
Most of the country’s electricity is generated in large, centralised power stations a long way from where the power is used; only five percent of our electricity comes from distributed generation.
Generation in the south (all hydro and a little wind) is connected to generation in the north – hydro, thermal, combined cycle gas, co-generation and geothermal – via a 575 kilometre long high-voltage direct current (HVDC) line that runs from Benmore substation in the South Island to Haywards substation near Wellington. This project is featured in detail on page 18.
The second substation at Otahuhu was officially opened as this magazine was being put together, marking the completion of the $100 million ‘Otahuhu 220 kV substation diversity project’, which will provide greater diversity of power supply to the Auckland and Northland regions. The project involved the construction of a new 220 kV substation, in addition to the existing one at Otahuhu, featuring a combination of gas insulated switchgear (GIS) and an outdoor switchyard.
The Auckland upgrade has also involved a suite of tactical projects designed to get as much as possible out of Transpower’s existing assets before the new 400kV line from Whakamaru is built and commissioned. One of these was a new switching station at Drury, south of Auckland (commissioned October 2010). This provides up to 150MW more from existing transmission assets (or about seven percent of Auckland’s peak winter load), which is important given that commissioning of the complete North Island Grid Upgrade is still about two years away.
Transpower has received final approval from the Electricity Commission for its Lower South Island Facilitating Renewables project.