Structure

A road runs along the crest of Arapuni's concrete gravity arch dam, which diverts the river into the intake and down through eight steel penstocks to the powerhouse at the base of the gorge. The intake is located more than 1 km down the headrace from the dam and the powerhouse is below it in the gorge.

The building is a reinforced concrete structure and because of extensions to house the four additional generators, is about twice its original size. These installations, which began in 1934, took three and a half years to complete. The seventh and eighth generators were added to keep pace with increasing demand for power during World War II.

Continuous improvement and refurbishment of the station's generating plant ensure that Arapuni, despite being the oldest operating power station on the river, remains an efficient, key component of the Waikato hydro system.

For 1 MW of electricity to be generated at Arapuni, 2.16 tonnes of water every second is required. All power in the Waikato system is generated at 11,000 volts. Most stations use transformers to step the voltage up to 220,000 volts for transmission onto the national grid. However, at Arapuni and Karapiro, the voltage is stepped up to 110,000 volts.

Like all the power stations on the Waikato River Arapuni is remotely operated from our control room in Hamilton which monitors, controls and co-ordinates the output of each station on the river.

Role

With eight generating units, Arapuni has the largest single capacity of any of the stations in the Waikato hydro system.

Due to its close proximity to Hamilton's urban centre, Arapuni provides a voltage support role for power transmissions to the area. Recent upgrades to the station have enhanced its capability in this area. This station is occasionally used for frequency keeping.