Magnetic and gas dynamic effects on arc motion in miniature circuit breakers

This paper presents new results on the magnetic and atmospheric environment in the arc chamber of a miniature circuit breaker under short circuit conditions. Finite element magnetic field calculations provide data on the flux density in the arc chamber and the effects of steel plates placed around the arc chamber. The magnetic calculations are used with a one-dimensional flow model to assess the influence of the magnetic environment on the arc dynamics. The results are compared with new experimental data on arc dynamics obtained using an optical fibre imaging system in a production miniature circuit breaker. Additional information on the environment within the arc chamber is supplied by pressure and conductance measurements. Results show that the presence of steel in the sides of the arc chamber has a large effect on the magnetic field and the arc dynamics. Plasma jet and pressure wave formation have a significant effect on atmospheric conditions in the arc chamber.