Concentrated discharges and dry bands on polluted outdoor insulators

This paper describes concentrated discharges on polluted insulators in the laboratory and in the field. The authors have observed the concentrated discharges at the high-voltage laboratories in Stuttgart, Zittau, and Mannheim, Germany, and Wroclaw, Poland. The concentrated discharges were also documented under natural conditions. These discharges are very dangerous especially for high-voltage apparatus, bushings, and polymer insulators. It has been shown that due to uneven voltage distribution at very low surface conductivity, the concentrated discharges can ignite even under uniformly polluted and uniformly wetted insulators.