KEY POINTS:
Transpower is looking to push part of its ageing inter-island link back into service to act as insurance against power supply shortages next winter.
The national grid operator says with existing generation and transmission available there is "medium confidence" the country will get through winter.
But it concedes there could be problems at peak times if there was a failure of major generating machinery.
A report by industry specialists assessing next winter's risks has found there would be demand shedding if a large North Island generator was lost and no provision had been made to expand inter-island transmission.
Transpower's chief executive Patrick Strange said the report reflected an industry view that the system could meet peak winter demand if all generation is available - excluding Contact Energy's station at New Plymouth, which is out and not expected to return to service.
He said the supply and transmission outlook was "tighter" than what was ideal, especially for North Island consumers.
"You never say never but with all the steps being taken I'm reasonably confident we should not have an issue. We're just tighter than we'd like to be."
He said it was "very unlikely" there would be brownouts, where power is cut in stages.
A power industry veteran, Strange said an average of one in three years would be tight and next year would be one of those.
"When we've had the dry year risks like 2003 they're very hard to deal with - this is somewhat easier to address as if all the worst things happen you're only having outages early in the evening if it's cold and we'd do everything to avoid it."
Transpower took the 40-year-old Pole One out of service at short notice in September because of the fire and earthquake risk. This halved capacity to shift power between the islands.
Yesterday it announced it would permanently decommission half of the pole but look at reconfiguring the remaining half pole to be kept on "warm standby" so that it could be used from next winter.
The remaining half pole would only be available for critical situations where the power system was becoming too constrained due to high demand for electricity or insufficient supply from generators in the North Island.
Strange said Transpower was confident it could move transformers and other equipment around to get the link back into a steady state, just running south to north.
"It's not so much a patchup but a different mode of operation.
"In the very unlikely event we lose a big plant in May then the margins would get very tight if we didn't do anything about it."
Strange said Transpower favoured a complete replacement of Pole One, which would cost more than $800 million but could last another 40 years.
Reconfiguring the undersea cables, which increases Pole Two's capacity from 500 to 700 MW, was completed earlier this week.
Genesis Energy's chief executive Murray Jackson, who has raised concerns about power security next winter, said anything to minimise transmission constraints would help - even if it meant employing "the No 8 wire" approach.
POWER PROBLEMS
THE ISSUE
* Generation in North Island is down.
* Inter-island transmission capacity is down by about half.
TRANSPOWER'S SOLUTION
* Restore around a quarter of transmission capacity.
