Analysis of three-phase partial discharge signals

Power distribution networks represent a dynamic and complex challenge with regard to the issues of maintenance and providing a reliable, high quality supply. Utilities historically used regular off-line testing to inform themselves of the health of their assets. This method is reasonably effective for this purpose but does have certain drawbacks associated with it; customer supply can be interrupted during the testing process and the cable sample is not tested under normal working conditions. The modern approach for understanding the health of medium voltage (MV) distribution systems is to continuously monitor the assets whilst on-line. The analysis of the captured data is then used to inform decisions regarding asset replacement and maintenance strategies. Partial discharge (PD) activity is widely recognized as a symptom linked to the degradation of high voltage plant. EDF Energy Networks sponsored research is being undertaken to investigate the evolution of PD activity within paper insulated lead covered (PILC) cables containing known defects. An experiment has been designed to stress cable sections in a such a manner that is representative of the conditions met by on-line circuits. A cable section containing a defect that is known to lead to the failure of in-service cables has been PD tested over a range of operational temperatures. The experiment utilizes three-phase energization and thermal cycling to replicate the daily load pattern experienced by circuits in the field.