Characteristics of noise and interphasal PD pulses in operating stator windings

Online partial discharge measurement in machines requires effective electrical noise suppression to reduce the risk of false indications of stator winding insulation problems. Many noise suppression techniques have been proposed and implemented over the years. This paper examines the method of suppressing noise using 3 phase synchronous (i.e. simultaneous) detection. Known noise pulses were recorded on three phases and they were contrasted with pulses from phase-to-ground PD in the stator slot or phase-to-phase PD between coils in the stator endwinding. Experiments indicated that interphasal PD produces strong pulses on 2 of the 3 phases. In contrast, phase-to-ground PD and noise caused by sparking in one phase of a generator output bus create a dominant pulse in one phase only. With all three types of situations, there may be significant cross-coupling to the other phase(s).