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

We began refurbishment of Maraetai II in January 2026.

It involves removing and then refurbishing existing turbines, generators, and water intake gates for each of its five generation units. 

We are investing $29.6m in the four-year upgrade project which will improve the hydro station’s operational reliability and extend its life by 20 years.

The work will be completed by hydro specialists ANDRITZ, staged over four years to 2029. 

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 generation unit will take about six months to refurbish. 

Project milestones

2026

• 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