Structure

Karapiro is a concrete arch dam carrying a single lane, public road along its crest. Three steel penstocks convey water from the intakes to the turbines. The water then flows back into the Waikato River 30km upstream from Hamilton City.

The power station is sited below the dam on the right-hand side along with a spillway and a diversion tunnel that are maintained as part of the dam's emergency management strategy, diverting water in the event of flooding or a dam breach.

When first installed, Karapiro's three generators were the largest in New Zealand. Kaplan turbines drive the generators. For 1 MW of electricity to be generated at this powerhouse, 3.77 tonnes of water every second is required. Each of the three generators produces electricity at 11,000 volts. All power in the Waikato hydro 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, Karapiro is remotely operated from our control room in Hamilton which monitors, controls and co-ordinates the output of each station on the river.

Role

As the last station on the Waikato River, Karapiro is required to release a minimum flow to maintain the water levels in the lower Waikato River. The required minimum flow means that at least two of the three generating units at Karapiro are typically operating at all times.

Transmission lines connect the station with the national grid at Hamilton, as well as supplying sub-stations at Hinuera and Te Awamutu.