Rehabilitation and Repair

Mercury provides update on status of Karapiro hydropower station upgrade

Mercury provides update on status of Karapiro hydropower station upgrade
(photo courtesy Mercury)

Mercury in New Zealand said it has reached a major milestone in its three-year upgrade of the Karapiro Hydro Power Station on the Waikato River, where it is about to commission the second of three new turbine-generator units.

This $90 million upgrade project will result in an additional 5W of capacity per unit when completed, increasing total capacity to 112.4 MW from 96 MW, providing total annual generation of 32 GWh annually, according to Stew Hamilton, Mercury executive general manager generation.

This is the first time the generation units have been replaced since the powerhouse was commissioned in 1948. They will enable Karapiro to continue generating electricity for another 50 years, Mercury said.

As part of this work, Mercury is replacing all three water intake gates at the top of the dam, which have reached the end of their life after more than 75 years of operation.

As reported on Hydro Review in 2017, the Karapiro hydro plant is the last in a series of nine power stations on the Waikato River on the North Island of New Zealand. The facility houses three vertical Kaplan turbine-generator units and has a net head of 30 m. The dam is a 52-m-tall, 335-m-long concrete arch structure, with a spillway located on the right abutment.

The spillway has four gates, each of which is 6.1 m wide and rated to pass 3.77 cubic meters per second of water. The gates are of the Stoney roller design and were originally operated one-at-a-time by a gantry crane until 1979, when a dedicated winch system was installed, allowing the four gates to be opened simultaneously. In 1998, the staunching bars were replaced with music note seals and the gates were reinforced for seismic events.

In late 2014, Gate 2 was removed from service for installation of bird netting. After removing the gate, personnel with Mercury determined that the lower section had undergone permanent deformation. Corrosion was also reported on the gate’s internal and external surfaces, prompting an FFS assessment.

Full installation and commissioning of all generating units is expected by August 2025.

Mercury is working with project partner ANDRITZ Hydropower “to ensure the generation units are installed efficiently and seamlessly.”

“Maintenance and enhancement of our hydro stations is important as we work towards helping the country move towards greater use of renewable energy,” Hamilton said.

Mercury generates electricity from 100% renewable sources: hydro, geothermal and wind.