Research on the Statistical Characteristics of the Discharge Inception Electric Field Strength of Gap Defect in Insulation pressboard Based on Three-parameter Weibull Model

Partial discharge (PD) has been paid much attention as an essential factor of insulation deterioration of various large equipment in power system. Partial discharges are prone to occur when there are air gaps in insulation pressboard. Based on different sizes of air-gap of air-gap discharge models, this paper proposes a three-parameter Weibull distribution to describe the probability distribution of partial discharge onset field strength in the air-gap model. The results show that the internal air-gap discharge of the pressboard has an obvious size effect. When the air gap diameter increases, the position parameter E 0 and the scale parameter a decrease due to increased inhomogeneity and area effect, while the initial voltage data concentration increases and shape parameter $\beta$ increases. When the separation of the gap defect inside the insulation pressboard is small, the separation of the gap defect is not the main factor affecting the partial discharge. The cross-sectional area of the air gap in the direction perpendicular to the electric field largely determines the initial field strength of the air gap.