Top Energy workers at Kaikohe substation. Photo: RNZ / Peter de Graaf
Far North business leaders say it's ironic the district has faced a second power outage, a week after Top Energy gave assurances that the supply was reliable.
Power was cut to more than 23,000 homes and businesses just after 5.20pm on Thursday, with the outage covering the entire southern part of the district, including the Bay of Islands, Kaikohe, South Hokianga and Whangaroa.
Lines company Top Energy said it had progressively restored power to all households by midnight.
However, people are still being urged to conserve power with it running on reduced supply after another massive outage.
Top Energy will be assessing the full extent of damage to a switchboard on Friday morning.
The area is now running on its smallest transformer at Kaikohe, and Top Energy can't guarantee supply.
It says repairs may be needed and its suppliers will be with it on site this morning.
It says it needs to confirm how long it will take and what equipment it needs.
There'll be diesel generation to support the southern part of the network at Omanaia.
Top Energy believes it's extremely unlikely the cut is related to another big one in the same area last week.
Two outages since assurance
Kaikohe Business Association chairperson Mike Shaw said a Top Energy spokesperson gave assurances that the supply was reliable at a business breakfast last Friday, but there had now been two major outages since then.
Top Energy said last week's failure isn't believed to be related to Thursday's outage, but a cause was yet to be identified.
According to its outage centre, the fault was on a sub-transmission feeder. Investigations showed half of the 33-kilovolt switchboard was damaged and could not be returned to service on Thursday night.
However, the other half of the switchboard had been salvaged and power restored. Top Energy said capacity was reduced as it was running on its smallest transformer at Kaikohe, meaning it could not guarantee full security of supply until repairs were completed.
"The damaged 33kV switchboard is approximately 10 years old, they have a normal life of about 50 years," the company said.
"We need to confirm repair timelines and what replacement equipment may be required."
Kaikohe substation provides power to much of the Far North. Photo: RNZ / Peter de Graaf
A Kaikohe woman living near the substation said she heard a loud boom about 5.20pm.
She went outside to investigate and saw the doors to a building at the substation appeared to have blown open.
Smoke or water vapour was coming out of the doors.
No one was present at the substation so she called 111.
FENZ sent volunteer fire crews from Kaikohe and Ōkaihau.
She said three firefighters entered the building wearing protective clothing and breathing apparatus.
There was no sign of fire that she could see.
The fire crews had left but Top Energy workers continued to come and go from the substation on the outskirts of Kaikohe.
It's exactly the same area that was affected by a huge outage last Friday, just six days earlier.
In that case, the cause was a tree falling on a 33-kilovolt line near Mount Pokaka, south of Kerikeri, but it was not clear why that caused the Kaikohe substation to shut down, cutting power to more than half the district.
The northern part of the district, including Doubtless Bay, Kaitaia, the Aupouri Peninsula and North Hokianga, did not lose its connection, in an apparent re-run of last week's outage.
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