Analysis of the effects of induced fields from sliding electrical contacts

Sliding electrical contact surfaces are encountered in many applications, including current-collection brushes in generators, armatures sliding between rails, and circuit breakers. The speeds of relative motion between the two contact surfaces vary according to application; in the first two, speeds on the order of 1 km/s are not uncommon. Prediction of speed and the effects of fields on speed have traditionally been made using finite element codes. Here, an alternative semianalytic method is investigated. A rectangular armature sliding between a pair of rails is studied, with a typical current profile based on published data as input for the problem. A model analytical field consistent with the total current input is used. Forces and speeds are computed, and the effects of induced fields due to motion on the speed and the current are analyzed and compared to typical experimental data.