An Approach to Monitor Medium Voltage Switchgear Plum Contact Connections Based on Temperature Rise Index

Withdrawable circuit breakers (CBs) rely on plum contacts in medium-voltage switchgears, but loose connections during insertion can cause fires or explosions at the making moment. Although loose connections lead to rising temperatures, traditional steady-state temperature measurement cannot effectively address this issue due to the slow response and susceptibility to ambient temperature. This article presents a temperature rise index (TRI)-based thermal monitoring method for switchgears, aiming for fast detection, straightforward implementation, reliability enhancement, and cost efficiency. To reach that a COMSOL multiphysics simulation with electromagnetic-thermal-fluid coupling has been established for a real plum contact connection configuration. This simulation identifies a criterion that exhibits independence from the ambient temperature variations and enables rapid detection of loose connections within the plum contact. TRI-based thermal monitoring method eliminates the ambient temperature sensors and utilizes only the temperature sensors of the plum contact connections and the current feedback from each phase. The method has been implemented in experiments on a 24 kV switchgear to clarify the feasibility and applicability of the approach. Simulations and experiments confirm TRI's sensitivity to plum contact connection states and electrical current. This agreement validates the simulations and positions TRI as a reliable monitoring tool. In addition, this information helps us to identify the impact of current on TRI and determines the best reference point.