| The DC high voltage test is not suitable for the test of XLPE cable, because the DC high voltage test will produce space charge which may damage the XLPE cable when the test is completed. The AC high voltage test can be applied to the test of XLPE cable, but the equipment power is large and heavy, which makes it difficult to be widely used in XLPE cable voltage test. To solve these problems, a new polarity transition ultra-low AC voltage test system is proposed in this paper. The operating frequency is only0.1Hz which is1/500of the power frequency in this new system, which makes the capacity of the equipment smaller than that of the AC high voltage test system. In addition, the new system is equal to AC high voltage test of50Hz and the DC high voltage test in effectiveness. The output of the test circuit can reach30KV and it can be applied to high-voltage capacitive load test of10KV and below.The paper mainly completes the design of the main circuit and the control system. The main circuit includes uncontrollable rectifier circuit, the DC chopper circuit, inverter circuit, high-powered voltage rectifier circuit and polarity conversion circuit. Control system includes the chopper control circuit, the polarity transformation test circuit control, the protecting current holding circuit, and so on.In the system main circuit,Uncontrollable rectifier circuit uses full-bridge diode rectifier circuit, the boost circuit uses BOOST circuit and high-powered voltage rectifier circuit and polarity test circuit uses the design of a high voltage switch and GTO combination. In the control circuit, using the difference between the output voltage and input voltage of the chopper circuit generates pulses to control the chopper, using the cycles for the0.0014s pulse controls the square wave inverter circuit, using the cycles for10s pulse control polarity conversion test circuit, and the PI closed-loop control is used in the regulator process, making output voltage adjustable and polarity transition ultra-low frequency voltage automated.Finally, the PSIM simulation result show that the voltage fluctuation range is not greater than0.04%and the time of polarity conversion is less than5ms, which can well meet the standard of the ultra-low frequency high voltage generator test. In addition, the system uses the modern power electronics inverter technology, so it has the advantages of small size, light weight, convenience and flexible. |
