Benmore Dam - Transmission

Transmission

Benmore is a major switching point in the New Zealand national grid and one of two major switching stations in the Waitaki Valley (the other being Twizel sub-station). The importance is largely due to the location at Benmore of the southern terminal station of the HVDC Inter-Island link.

The main AC switching station is on the east bank of the tailrace, and electricity generated at Benmore Power Station is injected into the national grid here. Three major 220 kV lines containing five circuits run from the Benmore substation. Clockwise from south, they are:

• A double-circuit line to the Twizel sub-station, with one circuit going via Ohau C power station and one circuit going via Ohau B power station.
• A single-circuit line to Islington sub-station in Christchurch, via Twizel sub-station and Tekapo B power station.
• A double-circuit line to Aviemore Dam

The HVDC converter stations are located on the west side of the tailrace, connected to the AC switching station by lines over the tailrace. The +270 kV mercury-arc Pole 1 has its valve hall on the north side of the site, near the powerhouse. The -350 kV thyristor Pole 2 has its valve hall on the south side of the site. A new +350 kV thyristor Pole 3 is currently under construction to replace the ageing Pole 1, and its valve hall is located adjacent to the existing Pole 2 valve hall.