Investigation of morning fog flashover problem for contaminated insulators of a 230 kV transmission line

During the last few years, there have been several flashover reports for cap and pin glass insulators on an important 230 kV transmission line of the national grid of Iran. This type of flashover was reported especially during the spring and in the early morning, so it was named morning fog flashover. The paper shows the result of an investigation to solve the problem. Various fog tests were modeled in the HV lab of the University of Tehran to simulate field conditions. Sprayed water was used to simulate field fog condition. The paper recommends some solutions for solving the problems associated with the existing string of cap and pin insulators. The results show that adding two anti-fog cap and pin insulators to the 230 kV string increases the FOV (flashover voltage) by about 25 kV to 30 kV, depending on the amount of humidity.