Simulation of Magnetically Triggered ${\rm MgB}_{2}$ Switches

Abstract

Superconducting synchronous machines require Direct Current (DC) excitation for their field windings which can be achieved via brushless exciters or by direct connection to current leads. However, the resulting heat loads limit their application. An excitation system consisting of a High-temperature Superconducting (HTS) full wave rectified flux pump eliminates these issues and enables operation at high currents. Rectification is achieved through superconducting magnetic switches, which also allow persistent current operation. Initial experimental results demonstrated that magnetic switching in MgB2 can be achieved without any significant temperature increase, enabling a fast recovery of the switches to the superconducting state. An empirical model has been developed which allows estimating MgB2 switch performance over the operational range needed for rotating machine excitation. The model uses measured critical current densities and n-values of commercially available MgB2 conductor and enables the design of optimized switches for field winding excitation and other applications.