Nonstationary behaviour of partial dischargesin agenerator stator conductor due to voltage conditioningeffects

Often partial discharge measurements on generators are taken immediately after the application of a test voltage. From measurements on a full-sized bitumen–mica generator conductor, it was observed that partial discharges go through a transient phase immediately after the application of a voltage or after the voltage has been changed. Parameter values derived during this time are therefore subject to variations and do not adequately reflect the true static condition of the insulation. After the transient phase, however, partial discharges behave in a statistically stable manner and repeatable measurements can be obtained even for long durations. The paper describes the long-duration measurement method used to observe the partial discharges and discusses some of the features relevant to computerised partial discharge measurements. A vector representation of the partial discharge data and analytical methods are described that may be used to screen nonstationary data in an automated partial discharge data acquisition environment.