More than 30 turbines on the Tararua wind farm were still not spinning today, two days after vandals broke in and caused hundreds-of-thousands of dollars of damage to the farm's transformers.
TrustPower said it hoped to have the problem fixed by tonight.
Thieves broke into the site's transformer yard before 1am on Monday, cutting up copper earthing wire in an attempt to steal it, and draining oil from two transformers into catchment reservoirs underneath.
It is estimated about 20,000 litres of oil was drained from the two transformers.
New oil can only be pumped back into the machines at a rate of about 1000 litres an hour, and after that a number of checks have to be carried out before they can be turned on.
The turbines have not been spinning since the break-in, at a cost to the company of up to $7000 for each hour of lost operation.
The smaller Te Rere Hau wind farm is powered by the Tararua transformer and is also not working.
Ashhurst Police constable Darrell Cowan said they have some leads they are following up.
"Basically, it was a straight, clear-cut breaking and entering.
"We are looking at a few things and we're working on a few lines of inquiry but at this stage we're not appealing for any sightings," Mr Cowan said.
TrustPower spokesman Graeme Purches said the cost of repairing the damage and the loss of power to the grid could be substantial.
"Our general equation in terms of power lost is one megawatt hour is worth about $80," Mr Purches said.
"At the moment, we're sitting at about $75,000 in terms of lost production, plus there's the cost of replacing the oil and the men working to fix it so we're not completely sure yet.
"It will probably be well into six digits," Mr Purches said.
At full capacity, Tararua wind farm can feed more than 93 megawatts of power into the national grid, and its 31 turbines can produce up to three megawatts of power each.
Te Rere Hau wind farm can produce up to 48.5 megawatts of power when operating at full capacity.
The outage was big enough to cause a "frequency disturbance" in the national grid, but Mr Purches said the damage would not affect power to people's homes.
The company was reviewing whether security cameras should be installed in the transformer yard, he said.
The transformers, which hold tens of thousands of litres of oil each, have protection switches that disconnect if the oil gets below a certain level.
TrustPower said both farms can run on just one transformer, and they were working to get at least one up and running yesterday afternoon, without success.
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