30 July and 7 October 2022 under-frequency events

The normal frequency band in New Zealand is between 49.8 and 50.2 Hz. An under-frequency event (UFE) occurred on 30 July 2022 and 7 October 2022, when the frequency fell below 49.25 Hz because of a loss of more than 60 megawatts injected into the grid.

The system operator recommended that:

• the causer of the 30 July 2022 UFE was Genesis Energy Limited, as the generator that owns Unit 5 of Huntly power station
• the causer of the 7 October 2022 UFE was Transpower New Zealand Limited, as the grid owner that owns the Haywards HVDC.

Our draft determinations agree with the system operator’s recommendations.

Final determination

One submission was received. The submission supported the draft determination on the 7 October 2022 UFE and provided no comment on the 30 July 2022 UFE. Accordingly, the Electricity Authority's final determinations under clause 8.61 of the Code are that:

• Genesis Energy Limited, as the generator that owns Huntly Unit 5, was the causer of the UFE on 30 July 2022 at 6:13am
• Transpower New Zealand Limited, as the grid owner that owns the Haywards HVDC, was the causer of the UFE on 7 October 2022 at 5:36am.

The Electricity Authority's reasons for the 30 July 2022 final determination are:

(a) A UFE occurred on 30 July 2022 at 6:13am when frequency dropped to 49.21Hz in the North Island.

(b) The interruption/reduction of electricity occurred at the grid injection point for Huntly Unit 5, which belong to Genesis.

(c) No other asset was identified as having caused or potentially caused the UFE.

(d) The system operator and Genesis agree that Genesis was the causer of the UFE.

The Electricity Authority's reasons for the 7 October 2022 final determination are:

(a) A UFE occurred on 7 October 2022 at 5:36am when frequency dropped to 49.16Hz in the North Island.

(b) The interruption/reduction of electricity occurred at the grid injection point for Haywards HVDC, which injects energy into the North Island HVDC injection point and belongs to the grid owner.

(c) No other asset was identified as having caused or potentially caused the UFE.

(d) The system operator and the grid owner agree that the grid owner was the causer of the UFE.

The charge advised in the system operator's reports to the Electricity Authority was $245,125 for 7 October 2022 and $105,625 for 30 July 2022. In accordance with clause 8.65 of the Code, the clearing manager will identify the relevant participants and the portion of the charges payable to each.