Power-cut threat for two years

Transpower's photo of one of the corroded D-shackles.

Auckland will remain vulnerable to power cuts for at least another two years as Transpower works on ways to reduce the city's dependence on one electricity substation.

Three options to improve the reliability of Auckland's power supply were given yesterday in a report about the blackout which affected much of the city just over two weeks ago.

But each of the options - including a new cable to Pakuranga - would take up to two years to complete.

Energy Minister David Parker yesterday released three reports supplied by Transpower which confirm that Auckland's blackout was triggered by the failure of two severely corroded D-shackles at the Otahuhu sub-station.

Photographs clearly show the shackles were in poor condition, but that was not noticed in the most recent equipment inspection, made in late 2003.

While discussion about Transpower's maintenance plan is continuing, the national grid operator is also looking at ways to reduce the city's dependence on a single gateway for its electricity.

Mr Parker yesterday conceded that Auckland would have to rely on Otahuhu for some time yet.

"It's more than months. It would be close to two years, I think, before there would be a substantial rebuild of the Transpower facility at Otahuhu if that was the interim solution pursued," he said.

"But, short of that, I'm sure there will be a lot more attention to minimising the risk of repetition of events like this in the intervening period."

One option Transpower is considering is whether to fast-track construction of a new substation on the same Otahuhu site.

A second option involves running a new cable link between Penrose and Albany, and reinforcing supplies to Penrose.

Transpower's third option - which it hasn't put forward before - is to bring a new cable to Pakuranga from Waikato.

That would effectively give Auckland a separate power supply line, and would be in line with ideas mentioned by the Government to improve Auckland's power reliability.

Transpower spokesman Chris Roberts said yesterday a route for the cable had not been decided yet because the proposal was in the early stages.

"It's just an idea at the moment - we have no route yet.

"We would have to consult on possible routes before choosing the best one."

The Pakuranga cable would be underground for about the final 10km, and would go mainly under roads.

It would be part of Transpower's existing controversial plan to bring a line from Waikato to Otahuhu, and would simply add Pakuranga as an end location for the line.

Transpower said it felt the option was "desirable", but Mr Roberts said it would cost hundreds of millions of dollars.

He said the national grid operator had previously shied away from the Pakuranga option because of costs and because the location was in a residential area.

"I am sure there will be resource consent issues to manage," he said.

A switchyard would also have to be built in Pakuranga.

Transpower is to continue to work on the three options, and Mr Parker said he expected to see firmer information on a favoured proposal in about a month.

A spokeswoman said the minister was gathering information at this stage and did not favour any option.

While the Government wanted to move quickly to remedy the situation, Mr Parker said any proposal would have to be assessed by the Electricity Commission.

"I will certainly be making sure it happens as fast as it practically can. Some of these things take a while to build."


Inspector missed corrosion

Shackles holding an earthing wire at Otahuhu substation were severely corroded before they broke and triggered the power blackout across Auckland almost two weeks ago.

Two D-shackles failed in winds of 86 km/h, despite expectations that they were designed to withstand gusts of up to 140 km/h.

Electrix, a power maintenance contractor, last inspected the shackles in October 2003 but it did not identify a problem with the condition of the shackles.

A report by engineering consultants Sinclair Knight Merz following the blackout says both shackles are in similar condition and show significant metal loss and corrosion.

"While the first failure was triggered by the high wind, the failure occurred because of the poor condition of the shackle."

The report, released by Energy Minister David Parker yesterday, says Transpower is following its maintenance plan and the contractor is "generally following" the plan.

However Electrix was not able to provide field records of the assessment.

Transpower said it would review its maintenance schedule and added that it did not intend to end its relationship with the contractor because of one mistake by a person who no longer worked at the company.

Mr Parker said he believed the blackout was preventable.

Newmarket Business Association general manager Cameron Brewer said if that were the case, "someone hasn't done their job, and so clearly someone's head has got to roll".