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-cooled turbine generators, dielectric strength drops steeply due to wet heat deterioration. To ensure operational reliability, it is essential to know whether or not water has permeated the insulation, and if so, to determine accurately the degree of deterioration. We have developed a capacitance measuring robot which enables measurement near the stator core end without removing the rotor, and confirmed good results in the field. The robot travelling along the retaining ring can be accurately positioned, and measured capacitances are stable and reproducible. The robot minimizes the extent of disassembly and reassembly, thus greatly reducing the out-of-operation period. Further, because the insulation condition can be accurately determined through its periodical use, we believe that it will contribute to both preventing accidents and assuring generators with high reliability.