Mechanical–electrical decoupled failure in glass insulators: Interface and residual strength analysis

This study identifies a new failure mechanism in glass insulators caused by a manufacturing defect: a missing internal thread structure. This defect results in a “mechanical–electrical decoupled failure,” where electrical performance remains intact while mechanical strength is severely reduced. Analysis of a failed insulator from a 220 kV transmission line, together with laboratory tests on 17 units, showed that insulators without threads pass standard electrical tests but retain less than 10% of their strength after failure, compared to over 75% for normal units. Finite element simulations confirmed that electric field distributions stay within safe limits, supporting the decoupling concept. The presence of multiple defective units in the same production batch indicates a quality control problem. Current acceptance tests are unable to detect this hidden defect. Mechanical tests further revealed an unusual failure mode where the steel pin pulls out, rather than the glass breaking. This defect cannot be detected by current factory acceptance procedures, indicating a need to revise mechanical verification protocols and implement enhanced quality control measures for batch-produced glass insulators.