MARAETAI II HYDRO STATION REFURBISHMENT PROJECT

The refurbishment at Maraetai II will improve the station's reliability and extend its life by 20 years.

Maraetai II

Maraetai II was commissioned in 1972. It has five generation units, and each has an installed capacity of 36MW.

Water for Maraetai II is drawn through a concrete-lined 12m deep and 550m long, 12m wide inlet canal cut into the left riverbank.

Electricity from Maraetai I and II hydro stations is sent to the Maraetai switchyard, between the two powerhouses. Electricity from the downstream Waipapa Hydro Station links into Maraetai via a single circuit 220kV line.  

The station is used for reserves and frequency keeping and is contracted for black start capability.

Refurbishment project

The project involves removing and refurbishing the turbines, generators and water intake gates across each of the station’s five generation units.

The first unit, Unit 10, was returned to service in September 2026 following seven and a half months of work. The next stage will begin with Unit 6 in late September 2026.

We are investing $29.6 million in the four-year project, which will improve the station’s reliability and extend its operational life by around 20 years. The work will be completed by hydro specialists ANDRITZ (Generators) and MB Century (Gates), staged over three years to 2028.

The project is part of our ongoing hydro rehabilitation programme, which involves incrementally upgrading each of the nine hydro stations in the Waikato Hydro System.

From 2029, we are planning a major rehabilitation upgrade of three hydro stations; Maraetai I, Ōhākurī and Ātiamuri. 

Maraetai II project timeline

Each generating unit will be taken out of service in turn for refurbishment, allowing the rest of the station to continue generating electricity. Work on each unit is expected to take approximately six to eight months.

Watch this timelapse video of Unit 10 refurbishment.

Project milestones

2026

• In September, Unit 10 was returned to service following a seven-and-a-half-month refurbishment involving 23,641 hours of work.
• In July, we began testing and commissioning the refurbished Unit 10. Pre-commission began in July with testing and water on commissioning planned for August.
• In July, the refurbished intake gate was reinstalled at the intake gate slot.
• In June we began reinstalling the refurbishment components (rotor, runner, head cover, thrust bearing assembly).
• From May, we focused on upgrading the brush gear system; installing a high-pressure jacking system to make the unit easier and safer to start and operate; modifying the air admission system to improve turbine performance and operating flexibility.
• From March onwards, the unit’s head cover and thrust bearing assembly were removed, inspected, and sent away for refurbishment.
• In February, Unit 10’s rotor was removed and moved to the loading bay for inspection and refurbishment.
• We removed the intake gate for refurbishment in January.
• In January, we began disassembly of the first of the station’s five generation units (Unit 10).
  

Watch this page for further updates on the upgrade project.  

For community and media inquiries on this project: mercurycommunications@mercury.co.nz