Effect of Polarity Reversal on the Partial Discharge Phenomena

In the field of High Voltage Direct Current (HVDC) transmission, the space charge accumulation phenomenon and the Partial Discharges (PD) phenomena are considered the main causes of dielectric ageing. During the years, the degradation effect of both phenomena under constant DC stress has been widely studied by several researchers. In case of polarity reversal, typically carried out to control bi-directional power flow between interconnected High Voltage transmission systems, the space charge movement may not synchronously follow the electric field polarity. This could make the moment of reversing polarity a very critical one, where space charge injected during preceding polarity produces high local electric field in the insulation. This, in turn, could promote the trigger of PDs and therefore reduce the cable lifetime. Based on this, the aim of the present work is to evaluate the PD activity in a specimen containing an air void subjected to the polarity reversal DC voltage. In addition the effect of the polarity reversal operation has also been evaluated in the partial discharges phenomena under AC stress. This has been made by making the partial discharge measurement after and before the polarity reversal cycles.