2018 19 Paper: Manapouri Lower Facing Plate Cavitation

Manapouri’s turbines were upgraded during a half-life refurbishment between 2002 and 2005. Upgrading included a replacement runner, wicket gates (guide vanes), stationary band and crown seals and the upper (head cover) facing plate. A routine inspection of Unit 3 found cavitation on the lower facing plate, which was located under the closed wicket gates position.
The paper discusses the work stream that followed, including the investigation, repair options, repair and ongoing monitoring. The ensuing investigation established that there was a “type” issue allied to the turbine
upgrade and the station’s operating conditions. The repair option chosen involved an innovative in-situ repair method, where the head cover was lifted and supported in the turbine pit. Removal of the cavitation damage and preparation of the lower facing plate required the design and manufacture of portable CNC milling machine which could be introduced into the turbine via the spiral casing. The cause of the cavitation will be discussed and why the original turbine did not exhibit the same characteristics. The paper will conclude with commentary on the success of both the repair methodology and the repair. Comments will discuss on-going trials to optimise the repair solution.

• Author: Steve Taylor
• Exchange: 2018 - Albury AGL
• Company: Meridian Energy
• Topic: Condition Monitoring, Francis, Refurbishment, Turbine
• Key Words: Cavitation, Clearance, Rehabilitation, Shaft Seal, Turbine, Upgrade/Uprate, Weld