Abstract
Dynamics of melting and welding of closed electrical contacts is analyzed for ac current half-wave. It is shown that in the range of low current and contact load the spherical model introduced by R. Holm describes satisfactorily the contact heating. The special attention is focused on the influence of softening of contact material on the current density and temperature field. All consecutive stages of contact heating including pre-softening, softening, melting and welding processes are described by the mathematical model based on the Stefan free boundary problems for the spherical heat equation. The relationship between current, contact load, parameters of the contact material and the radius of contact welded zone is obtained, discussed and compared with experimental data. It was found that for the certain range of contact parameters the influence of contact softening is very important and should be taken into account.