Improvement of AMF distribution in the inter-contact gap of VCB

Abstract

Nowadays, many manufacturers of vacuum circuit breakers (VCB) apply the axial magnetic field (AMF) to stabilise the electric arc diffusion during current breaking process. In many papers, various designs of contacts are proposed to improve the AMF distribution between circuit breaker’s contacts. In the present paper, some methodological aspects of AMF investigations have been presented and discussed. In the beginning, a short explanation of AMF influence on arc behaviour has been presented. A simplified physical model of phenomena considered has been applied for this purpose. The above analysis indicates that special attention should be paid to reach possibly high value of the axial magnetic field density especially in the peripheral electrode region. An own laboratory stand for AMF measurements has been described. Measurement and computational results of AMF distribution have been compared. The computations have been done with a commercial software package Maxwell (Ansoft) based on the finite element method (FEM). Good convergence of the results compared indicates that AMF can be investigated in experimental as well as in theoretical way. The numerical analysis presented enabled to select the contact configuration which ensures more stable arc behaviour during the circuit breaking process. Images of arc behaviour registered with a high speed camera for a new contact construction as well as contacts known from industrial practice have been presented.