Partial discharges characteristics during load transients in an HVDC model cable

The occurrence of Partial Discharges (PD) in HVAC cables is widespread considered as one of the most important concerns for the stability of the insulation. To date, the role of PD in the ageing and definitive fault of HVDC cables has been poorly investigated. This is mainly due to some practical difficulties in the performing of the measurements. Compared to the PDs occurring under AC stress, the higher inception voltages and the lower repetition rates, obtainable under DC voltage, make the exclusion of the measurement noise more difficult. This paper is focused on the study of the characteristics of the PDs occurring in an artificial defect located in proximity of the outer dielectric' surface of an HVDC model cable. The main purpose of this research is to evaluate the PD characteristics during load transients in the proposed experimental setup. The investigation on the PD activity in an artificially defected HVDC model cable has been experimentally performed on a segment of cable 6 m long jointed and heated up by means of a current transformer. The PD activity has been measured by means of an antenna sensor during all the duration of the experiment. After a period during which no PD are detected, a PD repetition rate increasing over time has been found, attributable to the rising of the electric field intensity in proximity of the outer dielectric surface.