Grid emergency resolved

23 June 2022

As a result of unexpected losses of electricity generation this morning Transpower called a grid emergency to enable it to maintain grid security.

The grid emergency allowed the System Operator to work with lines companies to remove controllable load like hot water systems until the peak morning electricity demand began easing around 9am. Hot water systems are switched on and off regularly during winter and New Zealanders will not have noticed any impact.

With additional generation coming online shortly before 9am and with demand falling the System Operator was able to start working with lines companies to restore controllable load. This was completed by 9.25am and the grid emergency ended.

Transpower CEO Alison Andrew said that Transpower worked quickly to maintain system security during the grid emergency.

“We have a grid emergency system in place for exactly this type of situation,” Ms Andrew said.

“Lines companies knew what was expected of them and they moved quickly to manage controllable load and reduce demand to get us through the emergency.”

“No one was disconnected, and the system stayed stable throughout.”

Transpower is currently working with industry to ensure there is sufficient generation to cover this evening’s peak. 

The affected generation included:

  • Contact Energy’s 105MW Stratford Peaker failed to start 
  • One of Genesis Energy’s Huntly Rankine Units had to temporarily reduce output by 150MW 
  • Wind generation dropped from a forecast of 90MW to 30MW. 


Transpower’s role

Transpower, as the electricity System Operator, is responsible for managing the real-time power system and operating the wholesale electricity market. Transpower does not own or operate any electricity generation.

Hot water ripple control

Traditional hot water cylinders around the country have separate meters which allow local electricity lines companies to turn them on and off. An average hot water cylinder contains approximately one day’s hot water usage and needs approximately 3-4 hours of heating per day to recharge. This means if it is turned off for a short period you are unlikely to see any impact on your hot water supply.

Every winter electricity lines company use hot water ripple control to manage load on the network to ensure it is not overloaded, during network issues and during maintenance.



Nathan Green, Principal Communications Advisor

021 328 643