Transpower cautions electricity supply looking tight again this evening

Tuesday, 28 June 2022

Notice issued by Transpower means available supply should still exceed demand, unless something unexpected were to happen.

Transpower has called for power companies to increase their generation to reduce the risk of power cuts this evening.

The electricity system operator issued a notice shortly before 4pm advising that there was less than 200 megawatts (MW) of slack in the system between 5pm and 7.30pm.

The notice reflects the risk that there could be insufficient power during peak evening demand if unexpected events were to reduce supply.

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The notice from Transpower is two steps short of the “grid emergency” it declared on Thursday after mechanical and electrical failures at two power stations and a sudden drop in wind speeds resulted in a bigger scare.

But Transpower nevertheless advised that power cuts were again a possibility if generators did not respond adequately.

Transpower spokesperson Rachael Drummond said it decided to issue the notice to power companies after it saw higher demand and that wind power generation was not as high as it had been forecasting.

Chief executive Alison Andrew said in an update at about 5pm that it had seen additional generation being offered into the market as a result of its notice.

“At this stage we do not anticipate any disruption to consumers' electricity supply,” she said.

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The next step if the situation did worsen would be for Transpower to issue a “warning” notice and then if required to declare another grid emergency.

Power demand usually peaks at about 6800MW during winter mornings and evenings.

One of the biggest single risks often hanging over the power system during periods of tight supply is that one of the five turbines at Genesis’ Huntly Power Station might fail.

Most of those turbines have a peak output of about 250MW.

Thursday’s grid emergency was caused by a mechanical failure at Contact’s Stratford power station which prevented one of its two gas turbines from starting as expected, a fan failure which halved the output from one of the Huntly turbines and a sudden drop in wind speeds which meant low forecast wind generation came in even lower than expected.

Together those three issues prevented about 315MW of expected generation from being fed into the grid.

The country last experienced power cuts last August, when 34,000 homes in the central North Island were disconnected due to a shortage of generation.

That shortfall was primarily caused by a polar storm which sent temperatures plunging and pushed up demand for power to an unexpected level and which also stirred up weeds on a lake, blocking a water intake and preventing generation at Genesis Energy’s 240MW Tokaanu hydro power station on the Tongariro River.

Transpower is forecasting several more days between now and early August when there would be a risk of power cuts if multiple adverse events that it models for were to occur.