Grid upgrade no cure for repeat of blackout

Workers try to restore power to Auckland at the Otahuhu Substation. Picture / Richard Robinson

Planned national grid upgrades will not protect Auckland from power failures like yesterday's, though they will limit the extent of disruption, Transpower has warned.

However, business groups and lobbyists angered at such a failure said it illustrated the importance of ensuring the country's largest city had a secure supply of power.

They say the national grid - many parts of which are reaching the end of their life - is limiting economic development, and they support a controversial plan to build a new 400kV line through the Waikato to Auckland.

Transpower systems operations general manager Kieran Devine said the outage, caused by the failure of equipment designed to protect substations from lightning strikes, was a freak occurrence - the first of its type for almost 20 years.

So-called "earth wires" overlaying the Otahuhu substation broke away early yesterday morning. One fell on to - and then short-circuited - switching gear at the substation, while another flicked up and short-circuited overhead transmission lines.

The extent of the disruption reflects the importance of the Otahuhu substation as the main power corridor into Auckland.

Planned upgrades will increase the number of circuits to distribute power into the city, limiting the effects of such failures.

The failure disrupted power in the affected part of the substation and interrupted supply from the Otahuhu B and Southdown power stations.

One power conductor was damaged during the failure and remained in service but will be repaired over the next few days.

Transpower is to thoroughly analyse the failure over the next few days.

The Electricity Commission agreed that new lines into Auckland would not have prevented the outage.

It wants Transpower to give it a detailed explanation for the failure and identify ways of ensuring it will not happen again.

"A large volume of power comes into Auckland through one substation. That is something that concerns the commission," said chairman Roy Hemmingway.

The Employers & Manufacturers Association (Northern) said the failure would have cost Auckland business and the public as much as $50 million in lost work, unused production capacity and overheads, and inconvenience.

"That a break on a 110kV line can take out Auckland shows the need for reinforcing the power supply into the city," said chief executive Alasdair Thompson.

Brook Asset Management chairman Simon Botherway said: "It is major for this country. How can corporates make investment decisions if there is an unreliable supply of power into this country's largest city?"

But Walker Capital Management's Steve Walker noted such failures had also occurred recently in London and New York.

"This happens everywhere really," he said. "I do not think it's particularly bad for the country's reputation."