Power cut to 11,500 explained

Power went off for about 40 minutes in Dunedin and Palmerston yesterday. Photo from ODT / Peter McIntosh

Human error was to blame for a widespread but short power outage in Otago yesterday, national power company Transpower says.

Power went off at 2.30pm in Dunedin, including in the CBD, and at Palmerston.

It was reinstated about 40 minutes later.

Derek Todd, of Delta, speaking on behalf of Aurora Energy, said 11,500 customers were affected.

The outage followed a failure to ''isolate protection mechanisms'' during ongoing work at the Halfway Bush power substation, Transpower communications manager Rebecca Wilson said.

Aurora and OtagoNet rely on the substation to provide power to their customers in Dunedin and Palmerston respectively.

OtagoNet reported 3272 of its customers lost power as a result of yesterday's outage.

Ms Wilson said the work at the Halfway Bush substation was ''quite a big project'' to replace old transformers.

''We were doing some testing, and our provider failed to isolate protection mechanisms, and that caused an outage.''

Transpower was ''definitely taking [the outage] seriously'', she said.

''And we apologise for the inconvenience.''

The outage was not related to strong winds about Dunedin and Otago yesterday. As a result of the power cut, electricity was cut to the Dunedin City Council offices and the neighbouring Municipal Chambers, temporarily halting yesterday's council meeting.

Deliberations resumed when power was restored about 40 minutes later.

Mr Todd said the outage was a ''relatively unusual event'', and he was not aware of a similar incident in the recent past.

Ms Wilson said Transpower would carry out an investigation into why the isolation did not happen, which would take a week or two.

It was definitely a case of human error, she said.