On-line partial discharge diagnosis on large motors

The typical epoxy-mica insulation system of large motors is a ´forgiving´ insulation system. Thus, besides showing mere electrical problems, partial discharge activity further serves as an indicator for other defect mechanisms, such as of mechanical, thermal, or environmental influence. On-line partial discharge diagnosis on large motors is greatly simplified when permanent partial discharge signal couplers are installed. Different cost-effective coupling techniques, such as Rogowski coils or coupling capacitors are discussed. Several examples for the analysis of high-resolution phase resolved partial discharge pattern and the related defect mechanism are discussed. Continuous on-line monitoring of the discharge activity can be advantageous to achieve extended maintenance intervals.