Karāpiro Power Station

Karāpiro was the second power station built in the Waikato hydro scheme, after Arapuni. 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 first generator was commissioned on 10 April 1947, just six days after Horahora was flooded. However, problems with the guide bearing meant full generation didn't start until 21 April 1947. The second generator was commissioned on 21 September 1947. In the first 12 months (to 31 March 1948), the station produced 349,568 megawatt-hours of electricity, just over 20 percent of the North Island's electricity requirements. The third and final generator was commissioned in May 1948. Over the 3 year period 2022-2025, the three original turbines and generators were replaced. The installed capacity was increased from 96 MW to 112.5 MW. The projected annual energy production will increase from an average of 505 GWh to 537 GWh. ==Generation==

Karāpiro'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 behind 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 drives a generator with a rated maximum power output of 37.5 MW, at 11,000 volts. Around of water every second is required to pass through the turbines for every 1 MW of power output. Karāpiro is controlled remotely by Mercury Energy's Waikato River control room in Hamilton. ==Transmission==

As part of the power station's construction, a 110,000 volt double-circuit line was built from the station to Hamilton substation. The line was commissioned on 29 March 1947. This line remains in service today as the main connection from Karāpiro to the rest of the national grid. In addition, 110,000 volt single-circuit lines connect Karāpiro with Te Awamutu and Hinuera substations. The transmission lines are owned and operated by national grid operator Transpower. ==See also==