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

What happened

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.

Contributing factors

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

Lessons learned

1. Incorrect earthing during substation switching can trigger an arc flashover, so operators must add independent verification of earth connections before energising.
2. A substation fault can cut power to 94,000 properties and disrupt trains, traffic signals and water utilities, so critical infrastructure needs tested backup supplies.

More lessons on worker safety and safe systems of work, outages, backup supply and restoration, from every incident on the register.

Not yet known

• Exact sequence of the human error
• Switchgear model and age
• Cost of the outage and damage

This entry is updated when these are reported. Get an alert for the next one like it.

Source

nzherald.co.nz