The Shed Hole Influence on the Electrical Performance of Composite Insulator

In recent years, shed holes appeared on the surface of in-service composite insulators have been observed in transmission lines in the southern and middle regions of China. Their presence can shorten the insulator creepage distance and therefore may impair the composite insulator's electrical performance. In this paper, extensive experiments were carried out to study the influence of shed hole (shed hole diameter, shed hole arrangement, shed hole percentage) on the electrical performance including pollution flashover voltage, pollution-rain flashover voltage, dry flashover voltage, wet flashover voltage, and lightning impulse voltage. The experimental results showed that the presence of shed hole had insignificant impact on the dry flashover voltage, wet flashover voltage, and lightning impulse when the shed diameter was 1.0 mm. However, the shed hole influence on the pollution flashover and pollution-rain flashover performance was appreciable. When the shed hole diameter is 1.0 mm, both the pollution flashover voltage and the pollution-rain flashover voltage are higher with alternating arrangement than that with straight-line arrangement. With the same shed hole diameter and pollution degree, the electrical performance of pollution-rain flashover is better than the pollution flashover. It is also found that the diameter of shed hole is increased by 3% to 60% after the pollution flashover test.