Transpower says there is no need to increase buffer capacity after a second power shortage warning in six days.
No households experienced power outages due to low generation capacity yesterday. Photo: RNZ / Russell Palmer
In the latest incident, the grid operator was forced to ask suppliers to boost generation because of expected high demand last night.
The lines company warned households faced outages if there was not enough power in the network. The peak period was from 5pm to 7.30pm. In the end there was no loss of power to households.
"Last night we issued a warning to the industry called a consumer advice notice (CAN) letting them know that we had a low level of residual generation for the evening peak last night," Transpower chief executive Alison Andrew told Morning Report.
"Residual generation is the difference between expected demand and generation that's offered into the market - a bit that having reserves in the tank.
"We issue these notices when we have less than 200 megawatts of residual generation, enough power for about 200,000 homes, and the reason we had low residual last night was due to demand for electricity being higher than expected and at the same time less wind generation available into the market."
She said the generators responded well and offered more generation into the system, meaning no consumers had any disruption.
There was enough of a capacity buffer in the event of still, clear cold weather creating generation issues over winter, she added.
Andrew said she had confidence in the system, which worked as it was supposed to in situations like this.
"We've managed to get through by controlling the demand and consumers had not had their supply interrupted." - Transpower chief executive, Alison Andrew
"The number of times we've actually had insufficient generation to meet supply it roughly once every five years and in all those situations, except for the 9 August last year, we've managed to get through by controlling the demand and consumers had not had their supply interrupted."
The emergency alert sent out last week was also related to lost generation capacity.
One of Contact Energy's gas turbine units at Stratford failed to start and Genesis Energy reported a fault at its Huntly plant and the wind dropped from a forecast 170 megawatts to just 30.
"The grid emergency that happened last week was that we actually had an issue on the morning peak on Thursday morning just before 8am and in order for us to maintain adequate security we had a problem because we'd lost generation from three sources," she said.
It was up to the industry and regulators to determine whether that capacity needed increasing, Andrew added.
Outages in the Wellington suburbs of Miramar and Seatoun and Johnsonville, affecting nearly 1000 customers, were not linked, she said.
The Electricity Authority had said last week's power generation emergency was well handled by Transpower.