Investigation of the Electromagnetic Force and Contact Spring in Rotational Ultrafast Disconnector in Railway DC Circuit Breaker

The ultrafast disconnector (UFD) is a critical component in hybrid dc circuit breakers (DCCBs), facilitating a low-loss current path. The UFD’s operation speed directly impacts the overall interruption time of the DCCB. Compared with linear UFD designs, rotational UFD architectures demonstrate reduced energy requirements within the driver circuit to actuate the moving contact. A strong connection between fixed and moving contacts is crucial to minimize electrical resistance and counteract electromagnetic repulsion force caused by current flow. The contact spring mechanism reduces the electromagnetic repulsion force and ensures a strong connection between the contacts when the UFD is in a closed position. However, this spring pressure also increases the operation time of the UFD. Therefore, it is essential to investigate the impact of the contact spring on the driving mechanism of the UFD and the economic cost of the driver circuit design. This study uses the Comsol Multiphysics software and finite element method (FEM) to analyze the electromagnetic forces exerted on the contacts of a rotational UFD. This UFD is incorporated into a hybrid DCCB designed for a rated voltage of 1.5 kV, a rated current of 1 kA, and a short-circuit current of 7 kA. This article presents the design of a spring optimized through an analysis of contact compression and increased connection points. Simulation results are validated by comparing established equations for electromagnetic repulsive force in vacuum breakers and experimental measurements on a rotational UFD prototype.