Voltage distribution of a string insulator under DC voltages

The variation of voltage distribution across an insulator string consisting of four porcelain disk insulators has been studied under ambient conditions, for 12 h on any given working day, for relative humidity conditions varying from 19% to 70%, stretching over a period of about one year. The voltage distribution across the string measured over a period of about half an hour clearly shows a nonlinearity in the distribution. Peaks in the voltage across the insulators were observed in the initial 3-h period when the initial relative humidity was >60%. The variation in the voltage across a given insulator over a period of time seems to depend on the processes of charge accumulation and draining at the cap and pin of the middle two insulators, while it seems to depend on the accumulation and draining of charges at the cap of the line end insulator and at the pin of the ground end insulator. The variation in the voltage displayed by the insulators has a large spread