Inter‐correlations between emitted lights and corresponding currents associated to different energy level spark discharges in mineral oil submitted to high‐voltage direct current stresses

The present work is devoted to the analysis of currents and emitted lights associated to electrical spark discharges in mineral oil in a point–plane electrode system under high‐voltage direct current stress. A systematic survey has been led on currents and emitted lights that characterise both positive and negative events through large applied field levels. On the other hand, interrelationships have been established between the currents and their corresponding emitted lights for all types of discharges. A particular attention will be accorded to the inter‐correlation function between the recorded currents and light emissions and between their corresponding fast Fourier transforms. In spite of the similar shapes, major differences have been found between the spectral behaviours between currents corresponding to low‐energy level discharges and those corresponding to high‐energy level ones. On the other hand, photonic signals are found to be more accurate and expressive than the recorded current ones to investigate the physicochemical processes involved in the degradation of the insulating properties of the oil. The total energies of all types of discharges are of comparable magnitudes for both polarities. Their derivatives, i.e. powers, dissipated along the propagation are more expressive of the nature of discharge.