Transpower has increased its profits: the national electricity grid operator made almost $136 million in the year until June, compared with $107.7 million in the previous year.
The company attributes the rise to a rise in revenue from higher transmission prices and to lower costs from technical problems.
However, company managers say the increase could have been much greater.
Transpower says it needed to put aside $27.5 million more than anticipated, to secure reserves of electricity to back up the Cook Strait cable in case of failure.
The company says these costs are beyond its control.
It is not paying a dividend to the Government, so it can pay for a $3 billion development programme.