Meridian Energy may have to adjust some turbines at the country's biggest wind farm near Wellington because of the power of "Formula One" type winds.

During inspections, the state-owned enterprise has identified a number of bearing faults and has had blades patched at the West Wind farm at Makara.

The farm's 62 turbines are covered by a warranty and Meridian was carrying out inspections before it ran out.

Wind maintenance manager Russell Thomas said of the 27 turbines inspected, six had bearing problems.

"We're not freaking out, put it that way. This is standard for any site, that's why you have a warranty."

The company - in line to be partly sold if a National Government is re-elected - would assess long-term maintenance issues during the next two years and might have to change the angle at which some blades face the wind, he said.

"We won't have to take any down but what we might find is that under certain wind conditions we have to de-rate the machines to take some of the stress out of it."

Thomas has worked in Britain and the United States for seven years and said turbines had to be re-calibrated at some projects.

Seven turbines at West Wind were generating above 50 per cent capacity. The worst-performing machine was operating at 25 per cent, which would be considered "average to good" in Europe.

"I wouldn't say we're putting too much stress on the machines. What we'll find over the next couple of years is that we'll see some parts wear quicker than others."

Operating and maintenance costs for wind farms using large turbines were up to 4 per cent of the project price, he said. Project West Wind cost $440 million, meaning the running costs would be over $17 million a year.

Thomas said the site at Makara was exposed to "Formula One" wind.

"It's never cheap to run a Formula One car and if you're running it at the top of the game there's always a benefit," he said.

"But we're not just pouring money into the site. It's a business and we're looking at it on a machine-by-machine basis and if we do identify that we have got machines costing us more than others we'll identify those, understand why and then act accordingly."

While the project was commissioned just two years ago, some machines had done the equivalent of four years' operation, he said.

A 600-tonne-capacity crane was being used for the bearing repairs. Some of the 28-tonne gearboxes had been lifted down but repairs were now being done at the top of the 70m towers.

Some spot repairs were also being done to turbine blades because of faulty fibreglassing when they were made in Denmark.