Karápiro Power Station
One of the country’s oldest hydro power plants is undergoing a multimillion-dollar refurbishment. Reporter Lawrence Gullery and visual journalist Tom Lee take a tour of the Kara¯piro Power Station with Mercury Energy.
‘‘Some of the kit we have inside is from the 1940s. The generator has run for 72 years and the technology of the engineering was such a good standard, it has been able to last that long.’’
Matt Kedian Mercury hydro generation manager
Art deco architecture timestamps the Kara¯ piro Power Station, reminding visitors it has helped supply electricity to the nation for more than 70 years.
A $75 million investment from its current owner, Mercury Energy, for its refurbishment will ensure it can power along for another 70 years or more.
Stepping inside the plant’s main building, there are still remnants of its art deco origins.
The symmetrical patterns of the ceiling light system in the main control room, created many years in the past, still manage to create a distinctive, futuristic feel.
The dials, buttons and flashing lights on the wall control panel remain as functional today as they were when they were fitted.
The Kara¯ piro Power Station is one of eight hydroelectric plants constructed in the 1940s and 1950s as part of a Government programme to firm up electricity resources for a national power grid.
There was a national power shortage looming and intense political pressure to see new generation schemes developed quickly.
Construction of the Kara¯ piro dam, on the Waikato River, to feed the hydroelectric station started in 1940.
It was scheduled to take three years to build.
But resources were hard to come by during World War II, with the best steel, for example, used to build tanks, weapons and other machinery.
Labour was also short as people were put to work for the war effort.
It meant it took longer for materials to arrive from overseas but the Kara¯ piro plant was eventually completed in 1946 and commissioned in 1947.
The construction workforce peaked at about 1136 people in 1946 as the project was completed.
More than 25,000 people came to watch the lake fill with water when the dam was flooded in April 1947.
Seven years later, the Queen and Prince Philip added the power station to the schedule of their royal tour of New Zealand in 1953-1954.
A photo of the royal couple being shown through the control room hangs on the wall in the same control room today.
Looking at the photo, not a lot has changed in the room since the couple visited 67 years ago.
In fact, many of the plant’s components remain in service today, which Mercury hydro generation manager Matt Kedian said was testament to the engineers and labour force who constructed the power station.
‘‘Some of the kit we have inside is from the 1940s. The generator has run for 72 years and the technology of the engineering was such a good standard, it has been able to last that long.
‘‘They would not have had the modelling we have today to predict how long things last. I suspect they designed it to last forever and it has almost done that.’’
Kedian is based in Rotorua but regularly visits Mercury’s network of power generators, from Taup to Hamilton.
The company takes care of nine hydro stations on the Waikato River.
Arapuni is the oldest, built in 1929; and then Kara¯ piro (1947); Maraetai I and II (1952, 1970); Whakamaru (1956); Ätiamuri (1958); Öhakuri (1961); Waipa¯ pa (1961); and Aratiatia (1964).
Kedian said the refurbishment at Kara¯ piro was part of a wider project to upgrade Mercury’s hydro power stations to ensure they could remain operating for future generations.
Extensive work has already been completed at O¯ hakuri, Arapuni, Ätiamuri and Whakamaru.
Kara¯ piro was constructed to generate 96MW and the upgrade will increase that output by 17 per cent, or 16.5MW, to 112.5MW.
It will be enough to power about 19,000 New Zealand homes and the plant’s average energy production will increase by 32GWh to 537GWh per year.
The Kara¯ piro upgrade is a sixyear project which started in 2019 and is scheduled for completion in 2025.
Andritz Hydro has completed detailed turbine hydraulic and generator designs over the past year.
Components are being manufactured in factories across Europe, China and Mexico, and shipped to the Port of Napier for transport to Waikato.
Some parts will be assembled on site at the power station from this month.
Key components include three identical Kaplan turbines, which will replace the original Kaplan units installed in the 1940s.
The propeller-type water turbine is widely used in hydroelectric power stations around the world and the more modern versions coming to Kara¯ piro will feature six blades, whereas the originals have five.
New head gates that control the flow of water from the dam into the turbines will also be installed as will generators and governor systems. Mercury senior production technician Magnus Adlam said the turbines were like ‘‘a ship propeller which has been turned vertically’’.
In a sub-floor of the main engine room, Adlam demonstrates how the water is fed into the turbine chamber by a spiral casing.
A series of guide vanes around the propeller can open or close, like a venetian blind, to control the flow of water hitting the turbine. A governor system controls the guide vanes to ensure the propellers are rotating at the required speed. ‘‘Think of it as if you are driving a car and you want to maintain 100kmh. If you are going up a hill, you need to use more fuel.
‘‘If you are going down a hill, you apply the brake.
‘‘That is what the governor does, it can provide more flow to the turbine or reduce water to slow it down.’’
On the ground level of the engine room, three generators sit on the floor, channelling the power made by each of the turbines below them.
Up above is the original twoperson crane which would have been used to install the turbines in the 1940s.
It has been modified so it operates as one unit, when previously two people had to use it in tandem. It will be used to remove the original turbines and install the new ones.
One turbine will be removed and replaced each year from this year to 2024.
It will mean there will be one outage per year to install the new equipment, scheduled over summer months to lower the impact of reduced power generation at the station.