Stator slot wedge testing of large pumped storage generator motors

First Hydro Company, which is part of Edison Mission Energy, operates two large pumped storage power stations in North Wales. Dinorwig, which was commissioned between 1982 and 1984 is equipped with six 330 MVA GMs (generator motors) and is one of the largest pumped storage power stations in Europe. Ffestiniog, commissioned in the early 1960s, is equipped with four 95 MVA GMs. Pumped storage plant has to be flexible in operation and provide a fast response to changing load. This leads to high thermal and mechanical stresses within the GMs. High quality maintenance is therefore essential to ensure a high level of availability, but to reduce costs outage times must be kept to a minimum. Semi-automatic equipment has been developed by FHC and IDB to measure the tightness of the stator slot wedging at both Dinorwig and Ffestiniog Power Stations. Plant outage times and labour costs have been reduced and the equipment is providing consistent measurements which are being trended against time to plan major maintenance on the GMs.