The North Auckland and Northland project delivered the first extra high-voltage underground circuit for New Zealand’s biggest city. It was completed four months early, $70 million below budget and constructed relatively “under the radar”.
The project had to overcome a range of diverse challenges including working in motorway corridors and rail tunnels, and solving the technical complexities of fixing rigid cables on a flexible structure – the Auckland Harbour Bridge.
It now provides substantial benefits of resilience, flexibility and diversity to the Auckland region, Northland and the overall New Zealand economy. Electricity consumers have also benefited from savings as a result of the project being under the $494 million budget.
Before this project, the only electricity supply to West Auckland, the North Shore and Northland (the NAaN area) was through one 31-kilometre double-circuit line from Otahuhu to Henderson. Now there is a parallel route that creates a high capacity ring around the main Auckland isthmus and two new direct grid connections into the Vector distribution network.
Transpower says the value of the resilience and diversity the new circuit provides was demonstrated during the Penrose substation fire in October which interrupted supply to parts of Auckland.
The northern section of the NAaN cable provided Vector with options to manage supply. Transpower estimates this prevented an immediate 25 MWh of lost supply over three hours and an overall economic benefit of approximately $1.5 million.
The redundancy and extra capacity provided by the cable also improves operational flexibility and allows the company to safely remove circuits on the Otahuhu to Henderson line from service for maintenance.
The project involved the installation of a new 220 kV single underground circuit comprising three cables from Pakuranga to Albany via the Penrose substation, the construction of two new substations at Hobson Street and Wairau Road and fixing the cable to the Auckland Harbour Bridge. An eight- kilometre transmission line between the Pakuranga to Penrose substations was also dismantled.
Transpower says the scale and complexity of the project required fresh approaches across a range of issues.
Regular risk workshops were undertaken throughout the project to record, score and incorporate all risks into a master schedule. The project was completed while maintaining reliable and continuous supply to Auckland and Northland.
Early development of a procurement strategy was also key to the project’s delivery. One positive outcome was the early definition of the framework for the four cable supply contracts worth around $200 million. That early decision resulted in a strong tender response when earlier indications suggested there was limited interest.
At the more technical level, Transpower bought and modified specialised equipment to ‘pull’ cables weighing more 40 kilograms per metre. New techniques were also developed to pull 1.4 kilometre cable lengths up the harbour bridge and then prevent “runaway” on the other side.
Transpower also signed a unique partnering agreement with Vector for all the works at the confined Hobson Street substation site. The team was tasked with considering the entire site as a single development, resulting in an optimised solution for both parties and the best value from money.
The Energy Project of the Year award category is sponsored by ITL