Partial Discharge Characteristics During Electrical Tree Growth in LDPE

Partial discharge (PD) measurements were performed during an electrical treeing process in a classical needle-plane low density polyethylene sample under AC voltage. This treeing process features an evolution from the propagation of a non-conducting electrical tree to the generation of a conducting electrical tree. PD characteristics are discussed with regard to different treeing stages during the process. It is found that changes in PD characteristics occur before transitions in the visual aspect of treeing development. In particular, statistical parameters obtained from measurements reveal a polarity dependence in PD patterns in the AC cycle. In general, during non-conducting tree growth, positive and negative discharges are not symmetric in magnitude or phase of occurrence. Positive discharge patterns are more stable in time than negative discharge patterns. The discharge frequency and magnitude seems to have an inverse relationship for negative discharges. Negative PD patterns were found to change during periods of fast tree growth. This was not the case for positive PD patterns.