Measurement of partial discharges ( PDs) current pulses is found to be one of the most efficient methods to evaluate the high voltage electrical equipment insulation condition. Generators, transformers, cables and transmission lines are especially tested for the presence of PDs. In AC, the solution is well known. Phase-resolved method can be used to detect and determine partial discharge activities. Although phase-resolved method works well under AC voltage; due to lack of a cyclic variation in DC voltage and current this cannot be used when studying partial discharges in DC voltage systems. Therefore, other methods are employed to interpret the partial discharge in DC. For this purpose, the discharge magnitude q, discharge intervals and their repetition rate are measured and employed for comparison. Based on above three basic parameters, some distributions are extracted and used to differentiate the source of related partial discharge patterns. To develop the required data base for comparison, it is needed to experimentally model various defect types. This paper describes the DC voltage partial discharge characteristics for different sources such as: void discharge, corona discharge, surface discharge and discharge in oil. Additionally, some features of these DC related PDs has been classified.
