Decision on 4 February 2026 under-frequency event

An under‑frequency event occurred at approximately 8.29pm on 4 February 2026 when HVDC Pole 3 suddenly ramped down, reducing North Island frequency to 49.20Hz.

The Electricity Authority’s final determination (under clause 8.61 of the Electricity Industry Participation Code 2010) is that Transpower New Zealand Limited, as the grid owner, was the causer of this under-frequency event.

Our reasons for this determination are:

• An under‑frequency event occurred at approximately 8.29pm on 4 February 2026 when HVDC Pole 3 suddenly ramped down, reducing North Island frequency to 49.20Hz
• The grid owner is the owner of the HVDC asset
• A power supply issue caused incorrect cooling status of the HVDC equipment to be recorded at the HVDC control system and consequently applied a current limit to the transfer capability of Pole 3
• No other generation tripped at the time.

The clearing manager will rebate the event charges to the relevant participants, in accordance with clause 8.65 of the Code. The event charge calculated in the System Operator’s report to the Authority is $187,962.50.

Any participant who is substantially affected by this determination may dispute it by contacting registrar@electricityrulingspanel.nz by 5pm, 30 July 2026.

The Authority did not consult on this event as it is no longer required to publicly consult when the alleged causer accepts it was the causer of the event (clause 8.61(2A) of the Code).

The System Operator’s causation report is below.