E.G. Psarros, A.D. Polykrati, C.G. Karagiannopoulos, and P.D. Bourkas (Greece)
Partial discharges, sparks, external partial discharges, crossarm ignition energy.
The conditions that are necessary for the appearance of sparks on insulators or partial discharges or surface breakdown or flashover, are: the existence of extended humidity (steam overlays the insulators) and contaminated environment (sea water salt, dust and smut are deposited on the insulators). For this reason, this phenomenon appears on the medium and high voltage lines, mostly early at the morning during the autumn (October, November) when the rain is absent (otherwise the insulators would be clean) and the humidity is high and in areas where the contamination is extended. As a consequence, the appearance of sparks occur on power lines near the sea (great probability of sea salt deposits on insulators), or near contaminated industrial areas. Partial discharges are a common phenomenon on the power lines of the electrical network. This paper presents the occurrence of sparks and external partial discharges on insulators and the conditions under which they take place. Furthermore, it is investigated the probability of the appearance of sparks on bare conductors of low and medium voltage and the external factors, as humidity and pollution, which affect this phenomenon. Finally, it is estimated that the thermal stress of a wooden crossarm on a pylon of medium voltage could not lead to the ignition of the crossarm. For its ignition, overextended humidity and a very contaminated environment is required. In a simplified model for sparks and external partial discharges, sparks are light radiation and sound (mainly because of the electron flow on the anode), and external partial discharges are the leakage on the insulator due to the ohmic resistance of the combination “pollution humidity”. The first case refers to dry bands and the second to wet bands on the insulator [1-3].
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