Thermal Analysis of Overload Protection Relays using Finite Element Method

This paper describes a three-dimensional thermal model of the bimetal releaser from low voltage power circuit breakers. The model can be used to analyse the thermal behaviour of the bimetal strip during both steady-state and transient conditions. The steady-state thermal simulations have been done. The maximum temperature is obtained at the extreme of the movable end terminal of the bimetallic strip. The steady-state conditions are reached after approximate 600 seconds from the initial moment of warming. A similar time evolution can be noticed for trip and force characteristics. To validate the three-dimensional thermal model, some experimental tests both in steady-state and transient conditions have been done. It has been recorded the time evolution of the temperature rises, cooling, trip and force characteristics during transient conditions. There is a good correlation between experimental and simulation results. Hence, the maximum difference between the experimental and simulation values is less than 2.5°C.