North Auckland and Northland grid upgrade project

It added new 220 kV transmission capacity to the National Grid by providing 37 km of underground cable between the Pakuranga, Penrose, and Albany substations.

The Penrose to Albany section included connections to the zone substations owned by Vector at Hobson Street in the Auckland CBD, and Wairau Road in the North Shore, and established new grid exit points at both of those locations.

The main electricity load centres in the region are the North Auckland urban areas, Whangārei, and the Marsden Point Oil Refinery.

Since the Auckland Harbour Bridge opened in 1959, the North Shore alone has expanded nearly five-fold, from a population of 50,000 in the late 1950s to 229,000 in June 2011.

[5] Prior to the commissioning of the NAaN project, the main route for electricity transmission into the North Auckland and Northland region was through the double-circuit 220 kV Henderson to Otahuhu via Southdown line.

However, these lines are of relatively low capacity and on their own could support only a very small proportion of the total load north of Mount Roskill.

[5] Therefore, the Henderson-Otahuhu double circuit 220 kV line represented a single mode of failure for the supply of electricity to the entire North Auckland and Northland region.

A study of the High Impact, Low Probability (HILP) risks associated with the Henderson to Otahuhu 220 kV transmission line was included as one of the submissions made by Transpower to the Electricity Commission in early 2009, in support of the need for the NAan project.

The vulnerability of the transmission line was subsequently shown on 30 October 2009 at around 8:00am, when power was cut to the whole of Northland and most of the northern half of Auckland, affecting 280,000 consumers (14.5% of the country).

[7] Key milestones in the history of the project are: The 9 km long route of the underground cables between Pakuranga and Penrose is mainly in the road carriageway of Ti Rakau Drive and the South Eastern Highway.

[21] Vector has three existing 110 kV overhead line circuits connecting Albany to Wairau Valley to provide redundancy on this section.