Development of a capacitance measuring robot for the water-cooled stator winding of turbine generators

When water permeates the winding insulation in large-scale direct water-coo led turbine generators, dielectric strength drops steeply due to wet heat d eterioration. To ensure operational reliability, it is essential to know wh ether or not water has permeated the insulation, and if so, to determine ac curately the degree of deterioration We have developed a capacitance measur ing robot which enables measurement near the stator core end without removi ng the rotor, and confirmed good results in the field. The robot travelling along the retaining ring can be accurately positioned, and measured capaci tances are stable and reproducible. The robot minimizes the extent of disas sembly and reassembly, thus greatly reducing the out-of-operation period. F urther, because the insulation condition can be accurately determined throu gh its periodical use, we believe that it will contribute to both preventin g accidents and assuring generators with high reliability.