Amethyst Hydro Scheme
The 7.7 MW Amethyst Hydro Power Station was successfully commissioned by Westpower in June 2013 and marks the return to the generation business after a hiatus of some 14 years. Amethyst Hydro Ltd, which owns the station, is a joint venture between Westpower (88% ownership) and Harihari Hydro Ltd (12% ownership).
The station is situated some 5 km East of Harihari adjacent to State Highway 6 near the Wanganui River bridge. Water is taken from a stream bed intake high up in the Amethyst River and transported to the powerhouse via a tunnel and penstock with a total length of 2.5 km.
It is expected that the station will produce 45 GWh of energy per annum, significantly reducing losses in transporting electricity to the West Coast. Additionally, the station is able to run isolated from the grid to supply the entire South Westland load, greatly improving the security of supply to South Westland.
Interestingly, the original 250 kW Amethyst Power Station, which was developed to supply the Harihari area in the 1950s, took water from the same river and was situated approximately 1 km upstream from the current site.
From a technical perspective, the turbine is a 6 jet vertical Pelton unit with a shaft speed of 750 rpm and and design flow capacity of 2100 litres per second. This turbine was designed and constructed in New Zealand and is of a very high quality with efficiency figures as good as anything available in the world today of a similar size. The turbine is coupled to a 9250 kVA, 11 kV synchronous generator with full static excitation. The output from the station is stepped up to 33 kV via a small substation for connection into the nearby Westpower 33 kV sub transmission network.
The majority of the scheme has been constructed in public land administered by the Department of Conservation and particular attention has been paid to minimising the environmental footprint, which is also in line with Westpower's commitment to the environment. No dam is involved in the scheme, with a low level weir used to abstract the water from the Amethyst River. This weir had to be constructed solely by helicopter access as the terrain precluded the installation of any roadway, which presented some difficult engineering challenges.
The Amethyst Power Scheme will provide benefits to South Westland electricity consumers for many years to come and demonstrates Westpower's ability to develop small, efficient run-of-the-river hydro schemes in an environmentally sensitive manner.