Investigation on Electromagnetic–Thermal–Mechanical Multi-Physics Field Characteristics of GIS Disconnector Under Different Contact Conditions

Gas-insulated switchgear (GIS) disconnectors are subject to repeated mechanical operations during service, which may cause contact degradation and eventually lead to severe equipment faults. However, existing single-parameter detection methods are insufficient for early and comprehensive assessment of contact condition deterioration. To address this issue, this paper investigates the multi-physics field characteristics of a GIS disconnector under different contact states from the perspective of electromagnetic–thermal–mechanical coupling. A 252 kV three-phase separated GIS experimental platform was established, and three contact states—closed, transition, and critical—were simulated by adjusting the insertion depth of the moving contact. Vibration, temperature, ultra-high-frequency (UHF), and ultrasonic signals were synchronously acquired under various current and voltage levels. The evolution laws of each physical quantity with contact degradation were systematically analyzed. The results demonstrate that the vibration signal amplitude increases significantly with contact degradation, and in the critical state, the vibration amplitude at 1200 A is approximately 4.7 times that at 300 A, far exceeding the current increase ratio. The temperature signal exhibits a nonlinear rise with degradation severity, reaching a 5 °C enclosure temperature rise in the critical state at 1200 A after 120 min, while the closed state shows less than 0.5 °C over the same period. Partial discharge signals, including UHF and ultrasonic, are excited only in the critical state when the applied voltage exceeds 140 kV, presenting typical floating potential discharge characteristics: phase-symmetric double-cluster clustering in the PRPD spectrum and a dominant 100 Hz component with a V100 Hz/V50 Hz ratio of approximately 2. The findings reveal that vibration and temperature signals are sensitive to early-stage contact degradation, whereas UHF and ultrasonic signals effectively identify severe-stage discharge defects. The staged response patterns of these multi-physics signals clarify the complementary relationships among different physical quantities, providing a theoretical foundation for developing a comprehensive detection strategy that combines early warning via vibration and temperature with discharge confirmation at severe stages.