Country New Zealand Opening date May 1948 (May 1948) Impounds Waikato River Opened May 1948 Owner Mercury Energy Spillway 4 | Status Operational Type of dam Arch dam Height 52 m Create Lake Karapiro Construction began 1940 | |
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Location near Cambridge, Waikato Address Karapiro 3496, New Zealand Similar Maraetai Power Station, Arapuni Power Station, Waipapa Power Station, Horahora Power Station, Jones Landing | ||
The Karapiro Power Station is a hydroelectric power station on Waikato River, in the North Island of New Zealand. The power station lies on Lake Karapiro, a major rowing regatta venue. Karapiro is 30 kilometres (19 mi) upstream from the city of Hamilton and is the last of the eight hydroelectric power stations on the Waikato River.
Contents
Karapiro is a baseload power station, as it is required to maintain water flow in the lower Waikato River even during low inflows to the catchment and during low electricity demand. Only two turbines are required to keep the river flow at a reasonable level, with the third turbine being available for peak generation and maintenance on one of the other turbines.
Like all of the hydroelectric power stations on the Waikato River, Karapiro is operated by electricity generator Mercury Energy.
History
Karapiro was the second power station built in the Waikato hydro scheme. Construction of the dam and power station began in 1940, but a materials and labour shortage due to World War II meant progress was slow. The station was completed in 1947, four years behind schedule.
The creation of Lake Karapiro behind the dam flooded the Horahora Power Station, the first power station built on the Waikato River.
The bridge over the spillway is the only road access to the turbine hall. The first bridge had a supporting column in the center of the bridge. The bridge was destroyed by the water running through the spillway in a significant flood event (Source: Mighty River Photo archives). The replacement bridge is as you see today with no supporting column.
To the left of the four spillway gates are three siphon tubes. These were designed for the management of the lake level under normal river flow and the spillway gates were to be used in only extreme conditions. The design of the siphon tubes was faulty: The flow of water was supposed to be stopped by a blast of air, but this never worked properly - resulting in the spillway gates to be used for lake level control.
Generation
Karapiro's powerhouse is located on the northern bank of the river, with a diversion tunnel and spillway also on the northern bank. The river is dammed by a concrete arch dam south of the powerhouse, with the electricity substation on the southern bank of the river.
Water from Lake Karapiro runs through the penstocks to three Kaplan turbines. Each turbine turns a generator, outputting 32 megawatts of electricity each at 11,000 volts. Around 3,770 litres (830 imp gal; 1,000 US gal) of water every second is required to run through the turbines to generate 1 MW of electricity.
Karapiro is controlled remotely by Mercury Energy's Waikato River control room in Hamilton.
Transmission
Electricity generated by Karapiro is stepped-up at the powerhouse to 110 kV, and then is sent across the dam to the Karapiro substation on the other side. Karapiro, along with Arapuni, connect to the 110 kV grid, rather than the 220 kV grid like other stations on the Waikato River.
From Karapiro, electricity is transmitted by a twin-circuit 110 kV line (HAM-KPO-A) to Hamilton, via Cambridge, where Karapiro's electricity is distributed to Hamilton, northern Waikato, and Auckland. Electricity from Karapiro is also distributed via two single-circuit 110 kV lines to Te Awamutu (KPO-TMU-A) and Hinerua, near Matamata (HIN-KPO-A).