Safety Analysis of Inner Capacitive Coupling Partial Discharge Sensor for 10kV Cable Joints under Lightning Impulse

The inner capacitive coupling partial discharge sensor for cable joints is of high sensitivity and wide detecting bandwidth, but can be coupled to a dangerously high voltage under lightning impulse with lots of high frequency components. In this paper, an equivalent circuit model was built up to simulate the coupling potential of sensor under lightning impulse. Subsequently, an inner capacitive coupling sensor applied for partial discharge detection in 10kV cable joints was developed and installed; a lightning impulse was applied to the test cable. But the measured voltage was quite different from the simulated one in peak value and time to crest, so a correction for circuit simulation was made to give a result much more similar to the measured voltage. Finally, the effects of impulse front time and the resistivity of outer semicon layer on the coupling voltage were investigated, and this analysis indicates that the coupling voltage under lightning impulse can be dangerous when the resistivity of outer semicon is large enough. Hence, it is necessary to measure the resistivity of outer semicon or carry out lightning-impulse test to check out whether the capacitive sensor meets the security requirements before engineering application. The findings contribute to a better understanding of safety issue regarding the capacitive coupler and promoting its engineering application.