Maximum Permissible Value Correction for Dielectric Loss Tangent of 110 kV Air-Tight Bushing Basic Insulation Subject to Operational Factors Impact

The paper presents a maximum permissible value determination technique for dielectric loss tangent $(\mathrm {t}\mathrm {g}\delta _{1})$ of high-voltage bushing basic insulation with application of a minimum risk method. A statistical data processing procedure under insufficient measurement data is applied to results of periodic monitoring of the equipment insulation condition. Dielectric loss tangent distribution is analyzed for operational and faulty bushings. Maximum permissible values of dielectric loss tangent are specified to ensure minimum risk. Factors affecting maximum permissible values of $\mathrm {t}\mathrm {g}\delta_{1}$ are analyzed.