Transpower cold on special care for critical sites

Transpower is unhappy at suggestions that its maintenance schedule should give special treatment to sites where failures would have the biggest impact.

The suggestion is contained in an independent review of Transpower's reports about the power failure which crippled much of Auckland on June 12.

The review, conducted by consultants Connell Wagner at the request of Energy Minister David Parker, found that the Otahuhu substation was an "absolutely critical" element of the national grid.

"But we have found no evidence that Transpower has any special inspection and maintenance process to recognise that criticality," Connell Wagner said.

Transpower's maintenance programme has been in the spotlight since the blackout, which was triggered by the failure of two severely corroded D-shackles at the Otahuhu substation.

The shackles' poor condition was not noticed in the most recent equipment inspection, made in late 2003.

Connell Wagner said nobody had produced "conclusive evidence" that the shackles were closely inspected in 2003. If they had been, "their poor condition would have been obvious".

The consultants said the blackout was avoidable and suggested Transpower implement an Otahuhu maintenance and inspection regime "above and beyond" what would be applied to similar system elements in "normal" situations.

The regime could involve more frequent climbing inspections, perhaps annually, in combination with "rigorous" management to ensure the inspections were carried out, Connell Wagner said.

But Transpower expressed concern yesterday at the idea it should treat the Otahuhu substation differently to other parts of its grid.

"Our approach has been that we apply the same high standards to all of our locations, as they're all critical to some degree or another," said spokesman Chris Roberts.

"We wouldn't want to be seen to deliberately treat some areas of New Zealand's electricity supply as non-critical."

But the suggestion has caught the eye of the Energy Minister, who has written to Transpower to ask if it will adopt a tiered maintenance scheme.

Mr Parker requested that Transpower reply by July 21 and also asked for information identifying the highest risk points on the national grid.

Other suggestions made by Connell Wagner and followed up in the minister's letter are:

* That Transpower electrically bond earthwire connections at Otahuhu, reducing the rate of corrosion and cutting the risk of heat-induced failure.

* That existing 220kv line entries which cross over other equipment be put underground.

* That all conductors and earthwires that cross over items called busbars be removed.

The underground option would come at a significant cost, although Transpower was unable yesterday to say how much.

The national grid operator was already planning such work as part of its controversial proposal to build a line of pylons into Otahuhu from the Waikato in a few years.

But Transpower is now developing a separate proposal to get the work done in two years. It had increased its supervision of inspections at Otahuhu, removed earthwires at the site and was reviewing its policy around bonding connections.

Connell Wagner found the Otahuhu substation had major and minor design deficiencies, which Transpower had previously acknowledged.