The Influence of Voltage Grading and Insulation Length on Contamination Performance

The results of experiments made to determine the effect of voltage distributions on the ac contamination performance of insulators are described. By using both internal and external capacitive grading, the voltage distributions on long insulator strings were varied from highly uniform to highly nonuniform. Results of contamination tests made on these insulators with clean fog are presented, and the impact for insulation design is discussed. Additional contamination test data on long post-type insulators are given. An analysis of these results shows that a potentially severe design problem exists for such insulators if large diameter columns are used for supports or on apparatus in substations located in contaminated areas.