Cavity discharge behaviors under trapezoid-based voltage at very low frequency

As Very Low Frequency (VLF) diagnostic testing is becoming more widely used in assessing electrical insulation degradation, it is important to investigate partial discharge behaviors in insulation defects under VLF excitation. This paper is an experimental study of discharges in an air-filled void bounded by solid dielectric under different trapezoidal-shape voltage waveforms at 0.1 Hz. Measurement results show that discharge characteristics are strongly dependent on the rate of change of voltage rather than the applied frequency. The rise time of voltage also affects the inception of discharges in the cavity as it influences the local electric field causing discharges. Comparing between VLF and 50 Hz, the accumulated charge decay rate in the cavity surface contributes to differences in discharge magnitudes.