Solid state transfer switches and current interruptors for mission-critical shipboard power systems

This paper describes operation and application of SABT in mission-critical applications on board navy ships. Typically, static automatic bus transfer switches (SABT) use silicon-controlled rectifier (SCR) power-switching elements to transfer critical loads from a primary power source to an alternate power source in the event of interruption or abnormal conditions. Since switching occurs in less than four milliseconds (4/1000th of a second), infinitely faster than electromechanical switches, it appears seamless to even the most sophisticated weapon systems. SABT facilitate maintenance by incorporating modular construction down to the LRU level. Self-diagnostic testing and remote monitoring and control features are included. Over 500 SABT successfully installed on US Navy destroyers, submarines and aircraft carriers. The paper also describes the novel solid state dual-function switch (DFS) that acts as a solid-state auto-bus transfer switch (SABT) or as a solid-state current interrupter (SSCI), depending upon whether a source fault or a load fault detected. Various types of semiconductors (thyristor, IGBT, and MCT) were compared. This combined function further reduces the cost, dimensions, and weight of the power system.