Electrical and optical measurements investigation of the pre-breakdown processes in natural ester oil under different impulse voltage waveforms

A study of pre-breakdown processes in natural ester oil is realised in the present study. A point-to-plane electrode configuration was used and the oil was subjected to lightning and switching impulse (SI) voltage stress. The inter-electrode gap distance was set to 1 and 2 cm long. Hence, electrical and optical measurements, concerning breakdown voltage, gap current, and light emission were acquired. Experimental data shows significant differences between the pre-breakdown processes taking place under the application of lightning 1.2/50 μs and switching 250/2500 μs impulse voltage. Ionisation/excitation activity, prior to breakdown, clearly occurs mainly under the application of SI voltage. This activity is mirrored on the optical emission signal while gap current measurements prior to breakdown were negligible in all cases. Furthermore, secondary-reverse streamers are detected during the SI voltage.