An Improved Variable-Frequency Series Resonant System for PD Detection of MV Power Cables Based on DAC Technology

Medium voltage (MV) Power cables is gaining an important role in distribution power grids. However, potential defects and faults in the cables pose a great threat to the power system. Partial discharge (PD), which can reveal the potential defects and faults, is worldwide accepted as an indicator for insulation condition of MV power cables. Nowadays, the variable-frequency series resonant (ACRF) system can only be used for the withstand test, due to the disturbance produced by the inverter. Besides, the commercial damped AC system for PD detection is expensive because of the high voltage switches. This paper presents an improved ACRF system, which is a combination of the ACRF system and the damped AC (DAC) system. The system uses the ACRF method to excite high voltage on the test cables, and uses a relative low voltage bidirectional solid-state switch to obtain the pure DAC voltage. An implementation of the system was established for PD detection of a 200m faulty cable. The experimental results verify the feasibility of the system.