Flashover at Haywards substation cuts power to 94,000 Wellington homes

During routine maintenance switching at the Haywards substation in Lower Hutt, incorrect earthing was applied, causing an electrical arc flashover reported initially as an explosion, with a loud bang and smoke. Transpower stated no equipment caught fire and nothing physically exploded, while a Fire and Emergency spokeswoman said there had been a small explosion in the switchyard. Protection systems automatically cut supply. The fault caused a widespread outage across the Hutt Valley, Wairarapa and parts of Wellington, affecting about 94,000 properties. Train services on the Hutt line were suspended, traffic signals failed on State Highway 2, and water and wastewater utilities activated backup generators while asking residents to conserve water. Power was restored within roughly two hours, with restoration work completed by mid-morning. No injuries were reported. Transpower said the cause was believed to be human error during the switching procedure.

Incorrect earthing applied during routine maintenance switching at the substation, attributed by the operator to human error.

1. Switching and earthing procedures during substation maintenance require rigorous verification steps to prevent human error causing arc flashovers.
2. A single transmission substation fault can cascade into widespread regional disruption affecting transport, traffic control and water utilities, so dependent critical infrastructure needs resilient backup supplies.
3. Rapid activation of on-site and mobile generators at water and wastewater facilities can limit the secondary impacts of a grid outage.

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