2 March 2017 under-frequency events

The Authority received a report from the system operator that recommended there was no causer of the first 2 March 2017 under-frequency event, and that Meridian Energy was the causer of the second event on that day. The Authority’s draft determinations agreed with the system operator’s recommendation on the second event, and recommended that Transpower New Zealand Limited, as the grid owner, is the causer of the first event.

We received one submission, from Meridian Energy, that agreed with the draft determinations and contained a question regarding the calculation of the MW lost which will be passed on to the system operator for consideration. Accordingly, the Authority’s final determination is that Transpower, as grid owner, was the causer of the first under-frequency event on 2 March 2017 at 11.21am.

The Authority’s reasons for this final determination are:

• the first UFE was triggered during a planned outage of the Livingston-Naseby circuit, when the two Clyde-Twizel 220 kV transmission circuits disconnected from the grid in quick succession, causing a reduction of energy into the North Island at the HVDC injection point
• as the grid owner that owns the Clyde-Twizel circuits, Transpower meets the definition of “causer” in Part 1 of the Code.

In accordance with clause 8.65 of the Code, the clearing manager rebates the event charge to relevant participants. The charge advised in the system operator’s report to the Authority was $145,637.50.

The Authority’s final determination is that Meridian Energy was the causer of the second under-frequency event on 2 March 2017 at 11.24am.
The Authority’s reasons for this final determination are:

• the interruption or reduction of electricity on 2 March 2017 occurred at the Aviemore power station, which belongs to Meridian
• no other asset was identified as having caused or potentially caused this UFE 
• in a reply to a system operator letter, Meridian accepted that it was the causer of this UFE.

The system operator’s report advised there would be no charge for this event.