Highbank Power Station

The Highbank Power Station was constructed as part of the Rangitata Diversion Race (RDR) irrigation scheme by the Public Works Department. The primary purpose of the RDR scheme was for the irrigation of farmland, not the generation of electricity. This irrigation diversion race is the source of the water for the Highbank Power Station. When agricultural demand for water is low the water is used by the station to generate electricity, this is typically during the winter months. The outbreak of World War II saw the project delayed due to manufacturing, material, and manpower shortages. The project's completion in June 1945 followed the completion of the RDR in September 1944. An unfortunate event was the sinking by enemy action of the ship which was carrying to New Zealand the stator for the generator at Highbank. Power house Construction began in 1939, with the power house structure finished in 1942. The modern reinforced concrete structure is some long and wide. The height of approximately allowed for the installation of both the 90-ton crane, and 10-ton auxiliary hoist. ==Generation equipment==

Generator and turbine Both the generator and turbine were manufactured by English Electric and installed from 1942 until the commissioning in 1945. The generator installed was the largest single generating unit in New Zealand at the time of its installation. The single vertical shaft generator is driven by a Francis turbine. The English Electric generator is a 20pole unit rated for 26.5 MW output with a synchronous speed of 300 rpm. Transmission Power is generated at 11 kV and stepped up at the station to 66 kV for transmission via a 66 kV spur line to Methven connecting to the rest of the EA Networks 66 kV system at Methven Substation. ==Upgrades==

Early years In the 1970s the station generation capacity had reduced to approximately 65% of the original rated capacity due to sediment build-up and wear on mechanical components. This led to the turbine runner being replaced along with improvements in sediment control at the canal intake and ongoing removal of sediments to reinstate the original performance. Pump station In 2010, TrustPower (now Manawa Energy) installed a river intake, fish screening, and pumping facilities to deliver the water from the Rakaia River to the RDR using some of the existing Highbank Power Station facilities. The Highbank Power Station site has been equipped with an array of six 1.5 MW pumps that allow it to take water from the Rakaia River and pump it up the power station penstock into the RDR. The water is then available for irrigators to use. TrustPower (now Manawa Energy) generation manager Mike Kedian believed pumping water back through the penstock was a New Zealand first. Pumping water up hill is not without its challenges, and one of these is the volume and pressure of the water contained in the pipeline when being pumped. In order to protect the penstock from pressure fluctuations an air-chamber has been installed adjacent to the pump station to maintain pipeline pressure within acceptable bounds. Generator and turbine replacement The original generation equipment was replaced in a project that commenced in November 2024 and is expected to be complete in May 2026. The original turbine and its scroll case were removed from the power house and a new 29 MW turbine and generator were installed. Replacement of both generator and turbine enables more efficient generation of electricity using the available water, and is expected to increase output by 8 GWh per year. The project was estimated by Manawa Energy to cost NZ$30.5M. Along with the generator and turbine, other mechanical and electrical equipment on the site was replaced. During the outage for the replacement of the main units, the pump station for the Barrhill-Chertsey irrigation scheme was modified so that when not required for irrigation, the pumps could be used for generation, providing 5.8MW of generating output. Highbank Power Station is potentially exposed to a risk of out-of-phase synchronisation resulting from manual or automatic switching on the 66kV network. To manage this risk, the historic practice of EA Networks has been to avoid the use of automatic reclose on the 66kV network, and to ensure that the Highbank generator is disconnected before manually closing circuit breakers. These precautions add complexity to network operations and can delay restoration of circuits after a fault. EA Networks plans to install phasor measurement units (or synchrophasors) on their 66kV network in 2025 to enable automatic re-closing of 66kV circuit breakers if the conditions for closure are suitable and will not produce an unacceptable out-of-phase synchronisation. ==See also==