Prediction Method of Breakdown Voltage Probability Distribution Considering Area Effect for Shield Gaps in Vacuum Interrupter

The objective of this article is to propose a method considering the area effect for quantitatively predicting the breakdown (BD) voltage probability distribution of the shield gaps in vacuum interrupter. In this method, the area effect was evaluated by a strong electric field area of cathode ${S}_{\text {se}}$ . According to the distribution of vacuum BD position, ${S}_{\text {se}}$ was defined as the region where the geometry field strength exceeded 60% of its maximum. Through the dielectric tests under a lightning impulse voltage (LIV), the results reveal that the BD voltage of shield vacuum gap (VG) had a significant area effect. Under a fixed gap distance of 1 mm, as the shield diameter increased from 40 to 80 mm, ${S}_{\text {se}}$ increased from 330 to 627 mm2 and the 50% BD voltage of shield VG decreased from 167.8 to 141.6 kV, decreased by 16%. By the proposed method, the predicted BD probability distributions of shield VGs with various diameters and gap distances could well agree with the experimental ones. The prediction error was within 11% in the whole range of BD probabilities. This method can be used to predict the insulation performance between the multiple shields with large sizes in the high-voltage vacuum interrupter.