The PD pulse behaviour in rotating machine stator windings

The acquisition, storage and processing of partial discharge (PD) signals is widely used as a condition monitoring tool to determine the integrity of the solid insulating systems of high power plants. Despite the advances in the instrumentation available for this purpose, the ability of partial discharge data to provide the necessary information to enable accurate assessments to be made is compromised in rotating machines by the modification which partial discharge pulses undergo in their passage from their site(s) of origin to the point where detection instrumentation is connected. Calibration strategies in general use with such instrumentation do not address this problem. This paper presents results of an experimental investigation into pulse propagation in induction motor stator windings. In particular, the paper focuses on the mechanisms of pulse propagation, i.e. series mode propagation through the windings and capacitive coupling and on the factors influencing their relative effects