Partial discharges of artificial defects in cable joints under high DC voltage

Inhalt:
With an increasing amount of extruded DC cable systems in operation, the interest in partial discharge (PD) measurements under DC voltage as a potential diagnostic tool for the detection of defects in the insulation has increased. However, it is often reported that PD occur less frequent under DC than under AC, which can reduce the effectiveness of the PD measurement. In this paper the PD repetition rates of artificial defects in MV-AC cable joints assembled on non-commercial DC-XLPE cables under DC voltage up to ±180 kV are presented, including the strong influence of the cable temperature and the DC voltage magnitude. As an alternative to constant DC voltage a repeatedly in- and decreasing DC voltage (unipolar repetitive DC ramp voltage) was applied to the cables, too. This resulted in higher PD repetition rates than under constant DC voltage. However, as the PD repetition rates are comparatively low under both constant DC voltage and unipolar repetitive DC ramp voltage it is very likely that detecting defects under DC voltage is much more challenging compared to PD measurements under AC voltages, even at higher DC voltage magnitudes.