13 Mar 2023
The completion of the next stage of a partial restoration of Transpower’s cyclone damaged Redclyffe substation has enabled the System Operator to conclude the grid emergency for Hawke’s Bay and Tairāwhiti.
Work completed Friday has enabled an additional 220kV line into the region to connect to Unison Network’s local lines network, increasing capacity and improving reliability. Unison was able to take the additional supply following work early Sunday morning.
Transpower General Manager Mark Ryall said that a huge effort had gone into restoring supply into the region after Cyclone Gabrielle flooded the critical Redclyffe substation on the morning of 14 February, cutting off supply to local lines networks managed by Unison Networks in Hawke's Bay and Eastland Network in Tairāwhiti.
“The flood damage to the Redclyffe substation was unlike anything I have seen,” he 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 stabilise supply to the region.
“Along with local lines company Unison and our service provider partners, we achieved in a matter of days or weeks what would normally take months to deliver.”
Transpower was able to re-liven some supply through Redclyffe because a control room and switchboard feeding Unison Network’s 33kV network was built in 2013 to Transpower’s new build standards. This standard provides additional protection against flooding compared to the standards in place when the substation was built in 1927 and redeveloped in the 1970s.
“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,” Mr Ryall said. “But the work we completed Friday maximises supply into the region and provides a measure of stability to our local lines company partners and their customers.”
System Operator says region still on reduced security
The grid emergency was concluded by the System Operator, an independent Transpower function that runs the wholesale electricity market and operates the power system.
Speaking for the System Operator, Operations General Manager Dr Stephen Jay said that the ending of the grid emergency reflects that the region is now in a stable configuration until a permanent solution for Redclyffe is in place.
“A grid emergency provides the System Operator with a range of tools to manage power system security in an emergency," he said. “Now that the grid owner has returned the transmission grid to a stable, albeit interim configuration, these tools are no longer needed.”
However, he said that 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.
“We will continue to pay close attention to the region and are doing everything we can to manage the risk and keep the lights on,” he said.
The System Operator’s independence from Transpower as the owner of the national electricity transmission grid ensures that it treats the grid owner the same as it would any other participant in the electricity market.
Progress slowed on Northland tower fix due to rain
Meanwhile, further rain has slowed work to address two transmission towers affected by a slip southwest of Wellsford. The slip affects one tower on the Henderson to Marsden 220kV line and one tower on the Henderson to Maungatapere 110kV line at a point where the two lines that supply Northland cross.
Mr Ryall said that crews had completed over 4km of access tracks into the area to bring in equipment and had installed two of the three temporary towers required to create the 220kV bypass for both circuits. Further rain late last week had delayed work as for safety reasons crews were unable to climb the towers for 48 hours after rain.
“However, the slip remained stable, increasing confidence that we will be able to finish the bypass for the 220kV line without a significant power outage in the region,” he said.
“This is a challenging operation because of the remote location of the slip and that it impacts two lines where they cross, but we are working as quickly as we can to restore full security to the region.
“The risk of power outages remains low and the safety of our people and our service providers has to come first.”
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,” Mr 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, Mr Ryall said that Transpower and its service providers would work hard to restore supply as soon as possible, likely within 48-72 hours.
“However small this risk, we continue to encourage residents in the region to be prepared for an extended outage,” he said.
“We are grateful to our lines company partners Top Energy, Northpower and Vector, as well as key stakeholders like Civil Defence Northland and the wider community for their continued patience and support while we complete the work.”
