3D finite element analysis modelling of the arc chamber of a current limiting miniature circuit breaker

This paper presents the initial stage of a 3D finite element (FE) model of the electromagnetic field in the arc chamber of a current limiting miniature circuit breaker (MCB). The final objective of the model is to compute the magnetic forces on the arc, and predict the position of the arc at a series of discrete time steps. The trajectory of the arc calculated from the model will then be compared with experimental data recorded by a high speed arc imaging system (AIS) on a flexible test apparatus (FTA) designed to simulate the operation of a commercial MCB under laboratory conditions. By comparing the FE model of the arc behaviour with the actual arc images generated from the AIS an insight into the factors governing the motion of the arc can be gained. In particular the relative importance of the average flux density across the arc chamber is compared with the local flux density distribution at the arc roots. An understanding of the influence of the magnetic flux distribution can then be used to improve the magnetic design of the MCB to promote low immobility times and effective current limiting operation.