17 September 2024 under-frequency event

The Electricity Authority's final determination under clause 8.61 of the Electricity Industry Participation Code is that Genesis, as the generator that owns Huntly Unit 5, was the causer of the under-frequency event (UFE) at 2.04pm on 17 September 2024.

The Authority's reasons for the determination are:

• A UFE occurred at 2.04pm on 17 September 2024 when frequency dropped to 49.16Hz in the North Island.
• The interruption or reduction of electricity occurred at the grid injection point for Huntly Unit 5, which belongs to Genesis.
• No other asset was identified as having caused or potentially caused the UFE.
• Genesis agreed with the system operator’s assessment that Genesis was the causer of the UFE.
• We had no feedback from other industry participants. We are not required to consult with non-industry participants.
• We received feedback from one non-industry participant which mainly related to other issues.

In accordance with clause 8.65 of the Code, the clearing manager will rebate the event charge to the relevant participants. The event charge calculated in the system operator’s report to the Authority was $224,040.41.

Any participant who is substantially affected by this determination may dispute the determination by referring the matter to the Rulings Panel in accordance with clause 8.62 of the Code by 5pm, 24 April 2025.

This consultation sought feedback from generators, the grid owner and other market participants who may have been substantially affected by a UFE on 17 September 2024.

At 2:04pm on 17 September 2024 a UFE occurred when 239.232MW of generation injection was lost at the Huntly grid connection point. This resulted in a drop of frequency to 49.16Hz in the North Island.

The Authority’s draft determination is that Genesis Energy was the causer of the 17 September 2024 UFE because:

• the interruption of energy injected into the grid occurred at Unit 5 of the Huntly power station, which belongs to Genesis
• no other asset was identified as having caused or potentially caused the UFE
• in the system operator’s view, Genesis was the causer of the UFE
• Genesis has accepted that it was the causer.

We welcomed feedback on the draft determination and the system operator’s calculation of the megawatts of power lost during the event.