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Transpower has applied for Government approval to spend more than half a billion dollars on an underground cable to bolster electricity supply through Auckland to Northland.
The national grid operator announced yesterday that it had submitted an investment proposal to the Electricity Commission to spend $521 million on a high-voltage cable running underground for 37km between Pakuranga and Albany via Penrose and Auckland Harbour Bridge.
It is already spending $50 million to $60 million on ducts under Fanshawe St and the Northern Busway, for a 220,000-volt cable to be installed by 2013 and with enough room for a duplicate version to follow at some undetermined date.
Auckland energy consultant Bryan Leyland wants both cables laid at the same time, to reduce Northland's reliance on transmission towers through Onehunga and Mt Roskill, seven of which rise out of the Manukau Harbour.
He said that if one of those fell over, a single underground cable carrying a maximum of 680 megawatts would not be enough to service Northland for the several weeks it would take to repair the severed link.
But Transpower grid investment general manager Tim George said although electricity demand north of the harbour bridge would grow by up to 21 per cent in the next six years, laying both cables together could not be justified on economic grounds.
He said there had never been a double-circuit failure on the overhead link through Onehunga, which is capable of carrying at least 900 megawatts, subject to the resolution of likely appeals to the Environment Court against an Auckland City planning decision allowing extra current to be pumped through it.
Mr George said Transpower considered alternative options for the new link to Albany, including building more overhead lines, but ruled these out because of the cost of buying property rights through densely populated urban areas.
An underground cable through road or rail corridors would be $41 million cheaper to install than any other option.
Although negotiations were continuing for the use of lines company Vector's $70 million electricity supply tunnel between Penrose and central Auckland, Mr George said Transpower's proposal did not depend on access to that facility.
He said a cable could be laid instead under the Southern Motorway corridor or beside the main railway line.
Onehunga Enhancement Society chairman Jim Jackson, who is preparing appeals against the decision by Auckland City planning commissioners allowing Transpower to boost supply through overhead lines running above his electricity manufacturing business, said the grid operator should not wait until 2013 to complete the new link.
He said Transpower should follow its own precedent of using the Northern Busway for an underground cable, by laying ducts under State Highway 20 motorway projects as a first step towards dismantling the overhead lines, reducing risks of health problems for those living or working near them.
Mr George said building the new link before it became necessary to service demand would impose an unjustifiable annual cost of about $30 million on Transpower's customers.
