Partial Discharge Characteristics of Cable Terminations with Stress Cone Misalignment Defects Under AC-Superimposed Switching Impulse Voltage

This study investigates the partial discharge (PD) behavior of a 10 kV XLPE cable termination with a controlled stress cone misalignment defect under AC-superimposed switching impulse voltage. A test platform was developed to apply positive- or negative-polarity switching impulses at specified AC phase angles. Repeated measurements showed that the impulse could initiate PD at the defect and that PD activity could persist for several AC cycles after the impulse decayed. The PD pulse count and maximum sensor-output amplitude during the subsequent AC stage depended strongly on the superposition phase angle. Under positive-polarity impulse superposition, both parameters showed an approximately sinusoidal phase dependence. Under negative-polarity impulse superposition, detectable post-impulse PD was strongest when the impulse was applied during the negative AC half-cycle and reached its maximum for 270° superposition. Overall, positive-polarity impulse superposition produced stronger PD signals than negative-polarity impulse superposition. These observations are consistent with the combined influence of the instantaneous local field during the impulse and the field associated with residual interfacial charge during subsequent AC cycles. The results provide experimental evidence for assessing cable-termination defects under switching-overvoltage conditions.