Corona Discharge under Non-Sinusoidal Voltage Excitation at Very Low Frequency

For condition assessment of electrical insulation, high-voltage testing at very-low-frequency (typically 0.1 Hz or lower) has been widely used in recent years as an alternative to normal testing at power frequency (50/60 Hz). In this paper, an experimental study of AC corona discharge under the application of sinusoidal and non-sinusoidal (rectangular and sawtooth) waveforms is presented. Here, a comparative study at both frequencies is reported based on the phase-resolved discharge patterns and various IEC 60270 integrated parameters such as discharge magnitude, repetition rates, current, etc. Measurement results reveal that these diagnostic characteristics are strongly dependent on the excitation frequency as well as the shape of voltage waveform. In particular, for the same applied peak voltage, very low frequency excitation yields larger discharge magnitude and higher repetition rate and the phase range of discharge activities correlates with the maximum voltage slew rate.