Transpower has officially opened the $100 million upgraded Otahuhu substation, which it says will bolster the security of power supply to the upper North Island.
A fault at the substation in Auckland in 2006 cut power for several hours to hundreds of thousands of people.
The national grid operator is hoping the upgrade will prevent a repeat of the power cut, which caused hospitals to reduce their services and caused businesses to lose money.
Half the transmission lines pass through the site's old system and half through the one opened on Thursday, so if there's a fault with one, the other can handle the power needs.
The upgrade has cost $100 million and uses world-leading technology.