On-line partial discharge analysis for improving availability and maintenance of hydroelectric generators

Abstract

This thesis presents the results of an on line partial discharge measurment on hydroelectric generator. Test data were compiled, analyzed and interpreted. The objective is to apply the interpreted test data into maintenance program in order to increase efficiency of maintenance activities and generator availability. The activity starts from a study of generator structure at critical parts such as stator winding and insulation system. Study on the phenomena of partial discharge within stator winding insulation, which is a sign of insulation deterioration. The study also deepened into how to measure partial discharge activity without shutdown generator, method of analysis and test data interpretation under theoretical and experiences accumlated by specialist's papers. The four conditions of generator operation are recommended to apply measurement procedure, i.e. no load cold, full load cold, full load hot and no load hot respectively. The test data are interpreted, analyzed and compared to sign of some damaged or deteriorated parts of winding such as surface discharge due to coil surface deterioration, internal discharge due to delaminating within main ground wall insulation, slot discharge due to poor semi-conductor coating and loose wedging. The study of on line partial discharge analysis was set up at generator unit 2 of Sirikit Hydro power plant. Some special couplers were installed into each of parallel path in each phase of winding, then the measurement was taken, and all test data were complied, analyzed and interpreted. The results showed some deteriorated parts as surface deterioration, internal main ground wall delaminating and high partial discharge activities occurred within the whole part of winding. All interpreted data were applied in planning of next minor inspection of generator unit 2. When period of inspection was started up, visual inspection was done and found some deterioration as defined on testing at the first stage. The suitable repairing method and material required could be prepared in advance, resulting in keeping schedule and efficient maintenance of generator. The result of this study was put into the maintenance program of all generators of EGAT's Hydro power plants.