Transpower has canceled a grid emergency in New Zealand after Cyclone Gabrielle flooded the Redclyffe Substation on Feb. 14, halting power supply to local lines run by Eastland Network in Tairāwhiti and Unison Networks in Hawke's Bay. Transpower completed the next stage of partial restoration of the substation, enabling an additional 220-kV line to connect to Unison Network’s local lines network, increasing capacity and improving reliability.
“The flood damage to the Redclyffe substation was unlike anything I have seen,” Transpower General Manager Mark Ryall said. “It has taken a massive effort from our people working with service providers and the wider community to first restore as much power to the region as possible and then to work around Redclyffe to stabilize supply to the region."
Transpower successfully reinvigorated a certain amount of power supply via Redclyffe as a switchboard and control room at the site were renovated in 2013 in line with the company’s new build standards. This benefited Unison’s 33kV network. This standard offers more protection from floods when compared to past standards.
“There is still a lot to do over coming weeks to continue to add additional resilience into the regional network, as well as assessing long-term options to fully restore or relocate Redclyffe,” said Ryall,. “But the work we completed Friday maximizes supply into the region and provides a measure of stability to our local lines company partners and their customers.”
The region remains on "reduced security" until Redclyffe is fully restored, meaning there is a higher risk of power cuts – and the potential for another grid emergency to be called – if faults happen on the system.
Meanwhile, more rain has delayed work on two transmission towers impacted by a slip to the southwest of Wellsford. The slip has impacted one tower on the Henderson to Maungatapere 110-kV line and another on the Henderson to Marsden 220-kV line. The slip is positioned in an area where the two lines intersect and where they are diverted toward supplying power to Northland.
Transpower is simultaneously working on a permanent solution for the 110kV line, which has been taken out of service because it is closest to the slip and at the biggest risk of falling if it moved further, potentially pulling down the 220kV line with it.
“While there is still a very small risk of an extended outage due to the slip advancing, an outage during the construction of the temporary bypass would most likely be caused by lightning or other equipment failure,” Ryall said. “Depending on the cause, we would expect to be able to restore power relatively quickly, from a few minutes to a matter of hours.”
In the unlikely case a tower was to fail due to the slip, Ryall said that Transpower and its service providers would work hard to restore supply as soon as possible, likely within 48-72 hours.