Influence of paper insulation on the prebreakdown phenomena in mineral oil under lightning impulse

Comparison of properties of electrical discharges developing in natural and synthetic ester at inception voltage

“…Experimental setup used for investigations is identical with the setup used previously for investigation of the influence of paper insulation on the prebreakdown phenomena in mineral oil but with difference in volume of test cell [14]. This setup is schematically shown in Fig.…”

Streamer Propagation and Breakdown in a Very Small Point-Insulating Plate Gap in Mineral Oil and Ester Liquids at Positive Lightning Impulse Voltage

“…Because intense flash finishing streamer propagation was also observed, the wide light pulse from the oscillograms may be identified solely with this flash. The voltage waveform, however, did not indicate a breakdown (voltage collapse was not observed); thus, it may be supposed that the streamers touched the insulating plate placed on the grounded electrode and that surface discharges started to develop with the creation of a return channel, a result of capacitive coupling between the HV point and the grounded plate [17,24]. The intensity of the processes connected with streamer propagation was, as in the case of the measurements at inception voltage, higher in the case where one of the esters was the liquid under the test.…”

“…This was deduced from the fact that a wide light pulse finishing the streamer development appeared after circa 1 µs, thus at least four times faster than at a voltage equal to 1.2 V i . A simple calculation of the propagation velocity considering gap distance and time to appearance of wide light pulse indicated a minimum 10 mm/µs of propagation velocity, which may allow for the identification of the propagation mode as a propagation of fast streamers in very small gaps [13][14][15][18][19][20][21][22]24]. The appearance of such a phenomenon in synthetic and natural ester was observed for all the cases concerning the inception voltage multipliers equal to 1.8 V i .…”

“…It is assumed, in view of the experience gained during many years of studies, that the light pulses are strictly correlated with current pulses providing knowledge about the possible mode of streamer propagation and the level of ionization of streamer channels [13][14][15][17][18][19]21,23,24]. The choice of photomultiplier as a light detector resulted from the fact that light generated by the streamers is weak and the amount of light that reaches the side window of the test cell is limited by the absorption and dispersion phenomena, and only a photomultiplier (PMT) is a detector that is sensitive enough to register such a weak light.…”

“…The calculations were performed using MOSTAT software where the maximum likelihood method was applied. This software is the authors' tool, which was created at the High Voltage Division of the Institute of Electrical Power Engineering of Lodz University of Technology, Poland, and has been tested from many years, solving both scientific and industry problems [17,24,[29][30][31]. The results of this estimation for the considered gap distance of 10 mm are quoted in Table 2.…”