Planned maintenance work on HVDC link from 22 - 27 November

22 November 2018

Transpower is undertaking some planned maintenance work on the HVDC link- the transmission line running between North and South Island. The HVDC link includes 570 km (around 530 km in the South and 40 km in the North) of transmission line, plus 40 km of undersea cables, and equipment at Haywards and Benmore substation.

What are we doing?

Every year we undertake maintenance on our HVDC equipment (consisting of Pole 2 and Pole 3 circuits and connected assets), to ensure reliability is maintained throughout the year, and to avoid unexpected outages.

This annual work is important maintenance on one of the most critical parts of our power system. We are taking the opportunity to do extra work, involving a large team of people, some of who are overseas, to service this complex equipment.

Over six days, we plan to take each circuit and connected assets out of service one at a time, with two circuits planned to be out over the weekend. This means there will be reduced capacity over the week-days and a shut down over the weekend.

We are not expecting this work to impact consumers electricity supply.

The plan has been thoroughly tested and well-thought through over a period of six months.

What happened this morning?

Prior to the outage Transpower as system operator was constantly monitoring system security. The situation this morning was assessed as tight but manageable, so the grid owner went ahead with the outage as planned. However, due to higher than expected demand and low wind generation available, Transpower as

system operator assessed that system security was an issue and issued the North Island (NI) generation warning notice. That led to Transpower as the system operator requesting the grid owner return the HVDC to service on short notice.

Impact to the market

This outage has been signalled to the market since July 2018, and Transpower, as the system operator, will be managing the power through the network to ensure that security is maintained. If security of supply becomes an issue again, then Transpower, as system operator, will once again take steps to ensure security of supply is maintained over the shutdown.

Due to the restriction of gas in the market, prices may be higher in the North Island over the outage period.

The work is expected to be complete and the HVDC returned to full capability late on Tuesday 27 November.

For further information, please contact:

Kerri Osborne, Corporate Communications Manager, 021 195 8613 or 04 590 7479.