A diagnosis of the electrical insulation of a power plant generator by space charge measurements

In this work, we have studied the electrical properties evolution of a stator bar sample of a 180 MW combined cycle gas turbine plant generator by space charge measurements using the thermal step method (TSM). This sample has been subjected to an ac electrical and thermal ageing. We have built an electrical properties evolution scale related to the applied ageing conditions by measuring space charges step by step during the ageing. The aim is to correlate the space charge density and the ageing of the insulation. Conventional diagnostic measurements have not proved particularly effective in detecting insulation problems at a sufficiently early stage. Therefore, it is already scheduled to apply TSM directly on a 180 MW generator of a combined cycle gas turbine plant. The results obtained will be transposed on this "space charge scale" and should allow assessment of the electrical state of the generator insulation.