Karapiro Power Station
Encyclopedia
The Karapiro Power Station is a hydroelectric power station on Waikato River
, in the North Island
of New Zealand
. The power station station lies on Lake Karapiro
, 30 kilometres (18.6 mi) upstream from the city of Hamilton
. Karapiro is the last of the eight hydroelectric power stations on the Waikato River.
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 state-owned electricity generator Mighty River Power.
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.
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 turbine
s. Each turbine turns a generator, outputting 32 megawatts of electricity each at 11,000 volts. Around 3770 litres (7,967.4 US pt) of water every second is required to run through the turbines to generate 1 MW of electricity.
Karapiro is controlled remotely by Mighty River Power's Waikato River control room in Hamilton.
, 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).
Waikato River
The Waikato River is the longest river in New Zealand. In the North Island, it runs for 425 kilometres from the eastern slopes of Mount Ruapehu, joining the Tongariro River system and emptying into Lake Taupo, New Zealand's largest lake. It drains Taupo at the lake's northeastern edge, creates the...
, in the North Island
North Island
The North Island is one of the two main islands of New Zealand, separated from the much less populous South Island by Cook Strait. The island is in area, making it the world's 14th-largest island...
of New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
. The power station station lies on Lake Karapiro
Lake Karapiro
Lake Karapiro is an artificial reservoir lake on the Waikato River in the North Island of New Zealand. The lake, near Cambridge and some south-east of the city of Hamilton, was created in 1947 to store water for the Karapiro Power Station, the last of the eight hydroelectric power stations on the...
, 30 kilometres (18.6 mi) upstream from the city of Hamilton
Hamilton, New Zealand
Hamilton is the centre of New Zealand's fourth largest urban area, and Hamilton City is the country's fourth largest territorial authority. Hamilton is in the Waikato Region of the North Island, approximately south of Auckland...
. Karapiro is the last of the eight hydroelectric power stations on the Waikato River.
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 state-owned electricity generator Mighty River Power.
History
Karapiro was the second power station built of the Waikato hydro scheme. Construction of the dam and power station began in 1940, but material and labour shortage due to World War IIWorld War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
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
Horahora Power Station
Horahora Power Station was an early hydroelectric power station on the Waikato River in New Zealand. It was the country’s first large-scale power station, completed in 1913. Initially built to service a gold mine, the power station was expanded to supply a significant part of the North Island...
, 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 damArch dam
An arch dam is a type of dam that is curved and commonly built with concrete. The arch dam is a structure that is designed to curve upstream so that the force of the water against it, known as hydrostatic pressure, presses against the arch, compressing and strengthening the structure as it pushes...
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 turbine
Kaplan turbine
The Kaplan turbine is a propeller-type water turbine which has adjustable blades. It was developed in 1913 by the Austrian professor Viktor Kaplan, who combined automatically adjusted propeller blades with automatically adjusted wicket gates to achieve efficiency over a wide range of flow and...
s. Each turbine turns a generator, outputting 32 megawatts of electricity each at 11,000 volts. Around 3770 litres (7,967.4 US pt) of water every second is required to run through the turbines to generate 1 MW of electricity.
Karapiro is controlled remotely by Mighty River Power'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 ArapuniArapuni
Arapuni is a rural town centre on the Waikato river in the South Waikato District of New Zealand. The population on census night 2006 was 2,145 usual residents, slightly down from 2,163 in 2001 and 2,211 in 1996. The town sits next to a hydroelectric dam at Lake Arapuni, one of six in the South...
, 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
Cambridge, New Zealand
Cambridge is a town in the Waikato region of the North Island of New Zealand. Situated 24 kilometres southeast of Hamilton, on the banks of the Waikato River, Cambridge is known as "The Town of Trees & Champions".In the 1840s Cambridge had a Maori population but in the 1850's missionaries and...
, where Karapiro's electricity is distributed to Hamilton, northern Waikato, and Auckland
Auckland
The Auckland metropolitan area , in the North Island of New Zealand, is the largest and most populous urban area in the country with residents, percent of the country's population. Auckland also has the largest Polynesian population of any city in the world...
. Electricity from Karapiro is also distributed via two single-circuit 110 kV lines to Te Awamutu
Te Awamutu
Te Awamutu is a town in the Waikato in the North Island of New Zealand. It is the council seat of the Waipa District and serves as a service town for the farming communities which surround it...
(KPO-TMU-A) and Hinerua, near Matamata
Matamata
Matamata is a rural Waikato town in New Zealand with a population of around 12,000 . It is located near the base of the Kaimai Ranges, and is a thriving farming area known for Thoroughbred horse breeding and training pursuits...
(HIN-KPO-A).