Evaluation of Flashover Voltage and Proposal of Management Criteria Based on Critical Pollution Level for Indoor Switchgear Post Insulators

Indoor switchgear is generally considered low-risk for pollution; however, dust and salt can accumulate on insulator surfaces during long-term operation, raising flashover risk under humid conditions. This study evaluated soluble and non-soluble pollution effects on 12 kV-class epoxy post insulators under Type A pollution. Soluble pollution was varied through the equivalent salt deposit density (ESDD), and non-soluble pollution through the kaolin content and resulting non-soluble deposit density (NSDD). Relative to the clean condition, flashover voltage decreased by about 30% and 44% at ESDD levels of 0.05 and 0.1 mg/cm², respectively; these are proposed as critical pollution levels for the action and urgent management criteria. Using environment-specific accumulation rates for five service scenarios, the urgent criterion was reached after about 120 months in clean environments but only 3.2 months in coastal and offshore environments, supporting differentiated maintenance intervals.