Investigation on electro-dynamic repulsion force in molded case circuit breakers taking into account current constriction between contacts

With 3-D finite element nonlinear analysis, according to the equations among current-magnetic field-repulsion force and taking into account the ferromagnet, two methods for calculating the Holm force due to current constriction between contacts, Holm formula and introducing cylinder bridge model, are compared. It shows that the error of the force results is within 10 percent though the current density and magnetic flux density distribution are distinct when the current is less than 10kA. Measuring the repulsion force with a quartz force transducer, it demonstrates and verifies that the calculation method and results are reliable.