The Whakamaru to Brownhill Road transmission line is a double-circuit 400 kV-capable transmission line constructed by Transpower to increase the capacity of the National Grid between the southern Waikato and the city of Auckland. The line runs from the Whakamaru sub-station near the Whakamaru Power Station, over a distance of to the new Brownhill Road substation near Whitford in southeastern Auckland. The line will initially be operated at 220 kV. From Brownhill Road, 220 kV underground cables connect the line to the Pakuranga sub-station in eastern Auckland. The project was the subject of considerable controversy and protest during the planning and approval stages. Construction of the line started in February 2010, and the line was commissioned on 30 October 2012. The transmission line forms the major part of a wider North Island Grid Upgrade project with a forecast cost to completion of $894 million.
Overview The line was a major enhancement to the National Grid and was designed to increase electrical supply and security to Auckland and Northland. The line provides more transmission capacity between the Waikato River hydro stations and Auckland, and takes load off the existing 220 kV lines. Prior to the commissioning of the new line, all existing major transmission lines into Auckland converged on the Ōtāhuhu substation, creating a concentration of risk to the security of supply to Auckland and Northland. The new line was terminated at the Pakuranga substation instead, creating diversity of electricity supply to Auckland.
The line was designed and built for 400 kV operation, but has operated since commissioning at 220 kV. In future, possibly by 2030, the installation of 220/400 kV transformers at Whakamaru and Brownhill Road would allow the transmission line to be operated at 400 kV, but the high cost of the required 400 kV transformers are unlikely to make that upgrade feasible. If upgraded to 400 kV operation, additional underground cables would be needed to connect Brownhill Road directly to Ōtāhuhu substation.
Background
There are very few electricity generating stations north of Auckland, which means that the electricity requirements for Auckland city and Northland must be supplied from the south - especially from the hydroelectric power stations on the Waikato River and the dual-fuelled Huntly Power Station.
Prior to the commissioning of this new transmission line, there were six lines running north into Auckland:
A double-circuit 220 kV line from Ohinewai (near Huntly) to Ōtāhuhu via Huntly and Takanini, with one circuit also going via Drury. A double-circuit 220 kV line from Whakamaru to Ōtāhuhu via Ohinewai, with one circuit also going via Hamilton. Two single-circuit 220 kV lines from Whakamaru to Ōtāhuhu direct. A double-circuit 110 kV line from Arapuni to Ōtāhuhu, via Hamilton, Bombay and Wiri. A single-circuit 110 kV line from Arapuni to Bombay direct
The Ohinewai-Huntly-Ōtāhuhu line was the last of these transmission lines to be built into Auckland, commissioned in the late 1970s to export electricity out of the then under-construction Huntly Power Station. Since then, the population of the upper North Island has more than doubled, and electricity use has trebled.
Power supply to the Upper North Island is dependent largely on two major factors: the generation from Huntly and the transmission capacity between Huntly and Ōtāhuhu; and generation from Whakamaru and south of Whakamaru, and the transmission capacity between Whakamaru and Ōtāhuhu. For the transmission system as at 2010, issues that could arise during periods of high demand and low generation in the Auckland area included: an outage of a Huntly–Ōtāhuhu circuit may overload the other Huntly–Otahuhu circuit an outage of a Huntly–Ohinewai circuit may overload the other Huntly–Ohinewai circuit the two 220 kV Whakamaru-Ōtāhuhu circuits may overload during a contingency an outage of the Whakamaru-Hamilton circuit may overload the two 110 kV Arapuni–Hamilton regional circuits an outage of the Hamilton–Ohinewai circuit may cause low voltage at the Hamilton 220 kV bus.
The North Island Grid Upgrade (NIGU) project, including the Whakamaru to Brownhill transmission line, was intended to address these issues, although forecasts predict the last issue (Hamilton–Ohinewai outage causing low voltage at Hamilton) will reappear towards 2025. The project also increases the power transfer capacity into Auckland, and reduces the loading on the existing 220 kV Whakamaru-Ōtāhuhu and Huntly–Ōtāhuhu circuits, with a consequential reduction in the reactive support needed in the Upper North Island.
Project Timeline Key milestones in the history of the project are: 2004 – Transpower announced its intention to build 400kV line from Whakamaru to Auckland, but open for input on minor variations on exact route. Estimated cost $500 million.Future of the national grid: transmission plan summary. Transpower. Alexander Turnbull Library Wellington Accession:PamBox q11622 Barcode 74444000120913 July 2004 – Founding and incorporation of New Era Energy Inc, an organization opposed to the 400 kV design and seeking less intrusive, and less costly transmission line alternatives May 2005 – Transpower submitted an Investment Proposal for a 400 kV line from Whakamaru to Ōtāhuhu to the Electricity Commission, under transitional provisions of the Electricity Governance Regulations 2003, which didn't provide the financial detail required by the Electricity Commission 30 September 2005 - Transpower submitted a Grid Upgrade Plan to the Electricity Commission, including several investment proposals, one of which was a revised version of the proposal for a 400 kV line from Whakamaru to Ōtāhuhu 27 April 2006 - Electricity Commission announced a draft decision to not approve the Transpower Grid Upgrade Plan proposal for a 400 kV line from Whakamaru to Ōtāhuhu (because it considered there were other lower cost alternatives) 20 October 2006 - Transpower submitted another revised proposal, for a 400 kV capable transmission line that would be initially operated at 220 kV, terminating south of Auckland, with 220 kV underground cables to Pakuranga substation 31 December 2006 - Roy Hemmingway departed Electricity Commission after his contract not renewed 31 January 2007 - The Electricity Commission issued a notice of its intention to approve the proposal but agreed to hold a public conference. The public conference was held in May. 27 May 2007 – Transpower lodged “Notices of Requirement” under the Resource Management Act 1991, with seven affected local councils 5 July 2007 – The Electricity Commission announced its final decision to approval the proposal August 2007 – New Era Energy announced it intends to file an application with the High Court in Wellington for a Judicial Review of the Electricity Commission decision to approve the Transpower revised proposal for a 400 kV capable transmission line. 9 August 2007 - Cabinet Minister Pete Hodgson announced he would use powers under the Resource Management Act to "call in" Transpower's proposal to build the electricity transmission line from Waikato to Auckland, because of its national significance, and establish a Board of Inquiry to consider the designations and resource consents required for the project 19 October 2007 - Ralph Craven departed Transpower, with $350,000 golden handshake.Fisher, David (May 16, 2008)Danger High Voltage NZ Listener Retrieved February 2, 2020 25 March 2008 - Ministry for the Environment (MfE) Board of Inquiry commenced hearings of the Notices of Requirement and applications for resource consent 31 October 2008 – MfE Board of Inquiry hearings concluded 4 May 2009 – The High Court New Era Energy Inc. v Electricity Commission NZRMA 63 [HC] finds against New Era Energy's application for a Judicial Review of the Electricity Commission's approval of the project 27 May 2009 – MfE Board of Inquiry released its draft report and decision to approve the designations and consents required for the project under the Resource Management Act. 18 September 2009 – MfE Board of Inquiry released its final report and decision approving the designations and consents required for the project 4 May 2010 - First of the new transmission towers constructed 27 October 2011 - Stringing of conductor commenced 18 May 2012 - Transpower announced a $30M increase in the forecast cost of the project, taking the total to $894 M. The increase was attributed to increased costs of construction and costs of acquiring property rights. 20 May 2012 - Stringing reaches the single-circuit Karapiro to Hinerua 110 kV line north of Lake Karapiro. Supply to Hinerua substation is cut for seven hours, affecting Tīrau, Putāruru and parts of Matamata, while a structure is erected to protect the 110 kV line during stringing. 30 October 2012 - The line is commissioned, operating at 220 kV. Final cost $894 million.
The route
The line commences at a newly constructed substation, Whakamaru North (also known as Whakamaru B), just outside the Whakamaru village. The new substation is 800 metres north of the existing main Whakamaru substation (Whakamaru A). A short tie-line connects the two substations. The double-circuit 220 kV Wairakei to Whakamaru C line, under construction and expected to be commissioned in 2013, will have one circuit connect to each substation, with the circuit passing via Te Mihi connecting to the Whakamaru A switchyard and the direct circuit connecting to the Whakamaru North switchyard.
From Whakamaru, the line travels approximately 186 km north-north-west through the South Waikato, Waipa, Matamata-Piako (passing just west of Morrinsville), Waikato and the Franklin ward of Auckland. The overhead line terminates at a new substation at Brownhill Road, near Whitford, close to the south east Auckland urban boundary. From there, two sets of underground cables connect to Pakuranga substation, which despite the name is near Botany Town Centre in eastern Auckland (the suburb of Pakuranga is 5 km east of the substation). Each cable circuit has a continuous rating of around 660 MVA.
The underground cable route from Brownhill to Pakuranga is 11 km long, and follows Brownhill Road, Sandstone Road and Caldwells Road, weaving through the suburban streets of Dannemora to Te Irirangi Drive until the final approaches to Pakuranga substation.
Sites Whakamaru (main) substation: Lake Karapiro/State Highway 1 crossing: State Highway 26 crossing: State Highway 2 crossing: Brownhill Road substation: Pakuranga substation:
Technical description
The transmission line is a double circuit line, supported mostly on steel lattice towers. The route length is and there are 426 structures. The average height of the towers is 60 metres, with some up to 70 metres tall. The average span length between towers is 437 metres, with a maximum span length of 824 metres.
Almost all of the transmission structures are steel lattice towers, but there are seven monopole structures in the Lake Karapiro area (three on the north bank, and four on the south bank). This area had been classified as a Special Landscape Character Area in the Waipa District Plan. The final report of the Board of Inquiry accepted Transpower's proposal to use monopoles instead of lattice towers in this area, and this became a requirement as part of the resource consent conditions for the project.