The in situ repair of the bottom cover of a 300MW pump turbine at Dinorwig power station

Dinorwig Power Station commissioned in 1983 is among the largest pumped storage power stations in Europe. It was specifically designed to meet sudden increases in electricity demand and can generate up to 1320MW output within approximately 12 seconds. This paper describes the following activities: i) How a leak in a spiral casing cover joint of a large pump turbine deteriorated with time to such an extent that a major stripdown of the machine became necessary. ii) Methods adopted to try and address the problem i.e. with different types of sealing compounds and the methodology involved. iii) The development phase of the project, and how a full scale replica of the bottom casing of the Pump Turbine, was built which helped with the development and utilisation of new and existing insitu machining equipment, enabling the work to be carried out within a very limited space available. iv) In order to reduce the down time of a major stripdown the suction cone at the turbine was cut into pieces to allow for a bottom dismantling, instead of a more conventional approach which required upwards and sideways removal. v) The bottom cover had to be lowered with special lifting and handling equipment, access tools had to be designed to transport and handle the heavy components. A special machining device was installed to carry out the repair. vi) Planning, risk analysis, safety assessment and staff training were a major contribution to the success of the project.