A New Type of VLF Sinusoidal Waveform Generator Used for AC Withstand Voltage Testing of Power Cables

Power cables play an important role in power grid, among which XLPE cables are widely used. Meanwhile, insulation failures of cables have become a severe safety hazard. AC withstand voltage testing is an effective method to assess the overall insulation level of power cables before they are put into operation. The very low frequency (VLF) testing equipment has been popular in recent years used for ac withstand voltage testing due to its portability. This paper presents a new type of VLF sinusoidal waveform generator which can generate a sinusoidal waveform at 0.1 Hz. Compared with other conventional VLF generators, the proposed design benefits at simple structure and novel control. The equipment consists of a bipolar charging circuit, a discharging circuit, a polarity conversion switch, a resistance voltage divider and the control system, and the key to generate VLF sinusoidal waveform is hysteresis control technology. This paper builds the simulation model of VLF generator using the SIMULINK software to verify the feasibility of system topology and control strategy. The simulation result shows that this design of VLF generator can generate a sinusoidal waveform at 0.1 Hz and its total harmonic distortion (THD) value is less than 5%. In the meantime, this paper studies the effect of some circuit parameters on the output waveform to get their optimal values by the SIMULINK software. In the end, an experiment platform was built in the laboratory to verify the simulation result, and the experimental result shows that this VLF generator can generate a sinusoidal waveform at 0.1 Hz and its THD value can meet the requirement of IEEE 400.2 standard, proving its feasibility and effectiveness.