Experience with directional couplers for partial discharge measurements on rotating machines in operation

Manitoba Hydro applied directional couplers for on-line partial discharge measurements on selected rotating machines beginning in 1981. With the instrumentation available at that time the measurement was vulnerable to the effects of noise external to the machine. There have been improvements in the available coupling capacitors which have allowed selection of more optimum measuring locations. In addition, new instrumentation has become available which allows some of the more serious noise problems to be overcome. The paper describes these developments as well as some of the stator winding problems which have been detected.