Turbine case and guide vane assembly ready to receive runner.

The team at Green Highland Renewables (GHR), experienced turbine engineers, were thrilled to be selected by Quartzelec, an independent electrical engineering group, to work on the Unit 1 turbine at the Maentwrog Hydroelectric Power Station in North Wales. Operated and managed by Nuclear Restoration Services (NRS), a subsidiary of the Nuclear Decommissioning Authority, this project allowed GHR to apply its specialized skills to a critical component of this historic hydroelectric facility.

Strip-down

The strip-down of Unit 1 at Maentwrog took eight days. The work began with a fingerprint test carried out at different machine loads, including temperature and vibration checks.

During the turbine strip-down, all parts, including the surface conditions, were visually checked. Any signs of wear or damage were documented, and, where needed, the parts were sized up for repair. This detailed data gathering is vital in enabling ongoing cross-referencing of previous and future maintenance work, helping prevent unplanned outages in the future and ensuring maximum performance.

The team knew that the generator had an overhung shaft, which meant the turbine and runner assembly had to be stripped down, to unthread the rotor

Two locking elements secured the runner onto the shaft, which was then drawn off with a mandrel and jacking assembly. The turbine was then stripped down to its bare spiral casing.

Before stripping down, both the lower and upper chamber alignments were checked. These were reviewed, and the results influenced the rotor position and then the runner-to-casing alignment.

During the strip down all guide vanes were dismantled and removed. The guide vanes and the runner were non-destructive tested by a dye penetrant. A specialist sub-contractor was brought in by Quartzelec to carry out this work. This method highlights any cracks in a structure, joint or weld.

All relevant parts were sized using a range of precise and calibrated measuring equipment to ensure that all the clearances were correct.

Reassembly

Once everything had been maintained, measured, and documented, the team rebuilt Maentwrog unit 1 turbine, which took another eight days. During the turbine rebuild, the runner radial and angular alignments were carried out and documented. The guide vanes were refitted, and the end float and squeeze were measured. Prior to fitting the runner, a full movement check was also carried out to ensure the correct operation seal when in the closed position. Following all of this work, the spiral casing was pressurised to ensure all sealing faces were correct.

Based on assessments made during the disassembly the team made several recommendations, including adjusting the shimming of the bearings to better align the rotating assembly to the turbine casing, which were all applied.

NRS operated the machine for GHR to conduct a recommissioning fingerprint test of the turbine. The results were then compared to the initial test results to ensure optimum performance. The tests also showed lower vibration in the drive end bearing than what was first recorded in the initial test.

Collaboration

The team worked closely with NRS and Quartzelec at Maentwrog and were delighted to be able to welcome two of NRS’s apprentices to the project to learn more about this fantastic source of clean power.

Members of the Voith Hydro team were on-site and vital to the process. The team worked closely to help verify measurements and findings during disassembly and rebuilding. Given their experience working on these types of power stations around the world, they were able to provide their world-leading expertise and resources throughout the whole process.

Following the full ten-year maintenance overhaul of unit 1 Turbine, it has consistently delivered clean electricity since September 2024.