Positive streamer propagation in natural ester and mineral oil under lightning impulse voltage

Summary

This article describes the comparative experimental studies on streamer propagation in natural ester and mineral oil under high voltage positive lightning impulse voltage. These studies were concentrated around the small electrode gaps (5 and 20 mm) and the point-plane electrode arrangement. The spatial shapes of the developing streamers, light emission and propagation velocity were analyzed and compared between the two dielectric liquids: natural ester and mineral oil. In both of them two streamer propagation modes were registered during the studies performed. Propagation of slow 2nd mode streamers took place below the so-called acceleration voltage while fast 3rd mode streamers developed at acceleration voltage and above. Comparing the streamer shapes corresponding to a given voltage polarity, no visible differences were observed between the liquids tested. Concerning the light emission, higher frequencies of light pulses were registered in the case of natural ester. For 20 mm gap the significant differences between both liquids were noticed in the value of the acceleration voltage estimated. In natural ester streamers started to develop as 3rd mode at much lower value of testing voltage than in the case of mineral oil. For 5 mm gap observation of streamer propagation was more difficult because breakdowns occurred even in the presence of pressboard plate placed on the grounded electrode. However, the fundamental conclusion from the results concerning both the gaps considered is that natural ester may have a lower ability of preventing the development of fast and energetic 3rd mode streamers, even at small electrode gaps.

Additional informations

Authors

Sakamoto Yo, Isaka Katsuo