Influence of Contact Plate Parameters and Eddy Currents on Residual Flux Decay in AMF-Type Vacuum Interrupters

The axial magnetic field (AMF)-type contact is utilized in vacuum interrupters (VIs) due to its effectiveness in current interruption. This paper deals with the study of the eddy current phenomenon occurring in the AMF VIs. The residual AMF beyond current zero is directly the result of eddy currents in the contact plate and, thus, is dependent on the contact plate geometry. Considering that the contact plate is analogous to a disk winding, an analytical formulation is developed to compute the eddy current decay constant as a function of contact plate parameters. The analytical predictions are verified using finite-element method (FEM) simulations of the step response of a circular plate placed in a uniform magnetic field. A linear relationship is established between the contact plate parameters and the eddy current decay constant. The analytical formulation is then used to predict the residual flux decay constant in the context of AMF contact model simulations. A coil-type AMF contact is analyzed using FEM simulations, and parametric studies are carried out to study the effect of the contact opening velocity and radial slots on distribution of the contact gap AMF. The results reported in this work will enable VI engineers to improve the contact design by better control of contact plate parameters.