Road salt on outdoor insulators

Road salt spread on highways during the winter months can be a major source of contamination for insulators. Once the salt is spread on the highway, it becomes airborne through vehicle traffic and wind. The wind may then deposit the salt onto nearby electrical apparatus increasing the risk of flashover. The standard method of assessing contamination on insulators is the equivalent salt deposit density (ESDD) measurement. To determine ESDD and its relation to distance from the highway, strings of suspension insulators were hung from power poles along a distribution line perpendicular to the road before the first snowfall and retrieved before the first rain in the spring; the retrieved insulators were then washed and the ESDD determined. According to an empirical formula, ESDD is a function of wind speed and direction, the amount of road salt spread on the highway and, as confirmed by the present experiment, the inverse distance from the highway. The data from the experiment were used to estimate the minimum distance between a proposed highway and a switching station to prevent excessive flashovers.