Electricity Authority
Electricity Authority
08/03/2026 | News release | Distributed by Public on 08/02/2026 15:14
Seeking feedback on 23 October 2025 under-frequency event
The Electricity Authority Te Mana Hiko is seeking feedback from electricity market participants who may have been substantially affected by an under-frequency event on 23 October 2025.
An under-frequency event occurs when the system frequency falls below 49.25Hz.
On 23 October 2025, at approximately 5.42pm, circuit breaker 662 at Wairakei was closed, energising circuit TAB-WRK-1. Circuit breaker 662 (CB662) at Tauhara was then closed. Within seconds, the Tauhara geothermal unit (TAB G1) and Te Huka 3 geothermal unit (TAC G1) both tripped. The resulting imbalance between generation and demand caused the North Island frequency to fall to a minimum of 49.2Hz. Automatic reserves responded and rebalanced the power system, returning frequency to the normal operating band by 5.43pm.
The Authority's draft determination is that the System Operator caused this under-frequency event. Our reasons are outlined in this draft determination paper.
Feedback is welcomed on our draft determination by 5pm, 31 August 2026 to [email protected]
We will consider all submissions before making our final decision.
Electricity Authority published this content on August 03, 2026, and is solely responsible for the information contained herein. Distributed via Public Technologies (PUBT), unedited and unaltered, on August 02, 2026 at 21:14 UTC. If you believe the information included in the content is inaccurate or outdated and requires editing or removal, please contact us at [email protected]