Mercury reaches key repowering milestone for Waikato hydro system

$75 million modernisation project for Karapiro power station to be the fifth of a nine-station investment programme spanning close to two decades.

29 January 2019 - Securing the inter-generational future of a critical part of New Zealand’s renewable electricity system and getting more power from the same amount of water are the outcomes targeted by Mercury as it confirms capital expenditure of around $75 million to modernise the Karapiro power station, 8km south-east of Cambridge.

The project to upgrade Karapiro station is part of Mercury’s multi-year, multi-million dollar investment across the nine power stations of the Waikato Hydro System.

The hydro power stations are a permanent part of the Waikato River landscape, and they renewably deliver around 10% of the country’s electricity.

“Mercury is privileged to own, maintain and operate these large and complex facilities, the oldest of which (Arapuni) dates back to 1929,” says Mercury’s executive general manager, Hydro and Wholesale, Phil Gibson.

“Our reinvestment for their long-term future builds on our great respect for the Kiwi women and men who created these wonders many decades ago.

“Our modernisation programme brings the best of new design and manufacturing practices to these stations, in many cases replacing machinery that has operating for more than half a century,” Mr Gibson says.

“Careful planning will deliver even more renewable electricity from the gravity we harness from the flowing water, which is otherwise unchanged on its journey to the Tasman Sea.  The station will lift its peak capacity by 17%, the increase sufficient to charge more than 6000 electric vehicles simultaneously. 

“The project will also benefit the regional economy with an increase in personnel living near and working at Karapiro through various stages of the modernisation,” Mr Gibson says.

The Karapiro modernisation will be undertaken by Andritz Hydro, with a milestone contract signing expected to take place on Wednesday (30 January) in Hamilton.

The contract follows two years of scoping. It will take six years to complete, and will be undertaken in stages to minimise any disruption to renewable electricity generation.

Karapiro programme in numbers
  • Six-year project from signing to completion (2019 – 2024)

  • Project will increase overall peak station capacity by 17%, or 16.5MW, to 112.5MW (enough to power approximately 19,000 New Zealand homes) and average energy production by 32GWh to 537GWh per annum.

  • Stages:
    • Feb 2019 to Jan 2020 – Andritz engineers undertake detailed turbine hydraulic and generator designs; turbine scale model and prototype generator stator bars manufactured and tested.
    • Jan 2020 – After designs and tests are accepted, manufacturing of components commences in factories across Europe and Asia.
    • Completed parts shipped to Karapiro, some as component parts to be assembled on site from March 2021 (first generator assembly).
    • Aug 2021 to May 2024 – One unit outage per year to install the new equipment.

  • Note: Unit outages will be scheduled over summer months to lessen impact on the market of reduced generation at the station. Mercury’s Whakamaru and Aratiatia modernisation projects will be complete and all units back on line by this time, meaning limited impact to overall output from the Waikato hydro scheme.
 
Karapiro hydro station and project background

Construction of the Karapiro power station commenced in 1940 (during the Second World War). Progress was impacted by war-related labour and materials shortages. It was completed in 1947 and commissioned in 1948.

Lake Karapiro was formed behind the dam. It is now a well-utilised lake for recreational purposes and home of Rowing New Zealand’s high performance centre.

The Karapiro station comprises three identical Kaplan turbine generating units with a combined output of 96MW.

Work carried out in 2015 contributed to a plan for rehabilitation of major parts of the Karapiro station. The aim is to ensure station’s integrity is maintained, efficiency and generation capacity is enhanced and Karapiro’s place as an important contributor of renewable electricity generation to New Zealand’s national electricity grid can continue long into the future.

Major areas involving plant replacement include the turbines, generators and governor systems. As a part of concurrent work to future proof the station, other items are also being addressed due to either age-related issues (by-pass valves and associated works) or legacy performance challenges (hydro intake gates and operating mechanisms, stoplogs).

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