Nonstationary behavior of partial discharge during insulation aging

There are two purposes for this work. The first is to present an example of a case where a pulsating partial-discharge (PD) phenomenon exhibits non-stationary behavior associated with discharge-induced "aging" of a dielectric material. The observed nonstationary behavior, which manifests itself by a time-dependence in the statistical characteristics of PD pulses, illustrates the difficulties to be encountered in defining meaningful PD pulse "patterns" that can be used for reliable defect site identification. The second purpose is to point out possible difficulties in relating measured PD pulse-height distributions to measured average PD current which are relevant to the calibration of PD measurement systems.