Abb Power Td & Company

Per A Danfors

Vinod N Bapat

John G Reckleff

Methods and apparatus for switching a load between first and second sources is shown to include first and second solid state switches connected to the load. First and second mechanical breakers are connected between the switches and the sources so that each source is connected to the load through a circuit breaker and solid state switch. A controller is connected to sense the voltage from the first and second sources. The controller is connected to the first and second switches and the first and second mechanical breakers. The controller senses the phase difference between the voltages from the first and second sources. The controller causes the first and second mechanical breakers to open and close in response to sensing the phase difference between the sources. The first and second mechanical breakers can include medium voltage vacuum breakers. In a preferred embodiment, when the controller senses that the phase difference between sources is more than 30 degrees out of phase, the controller will open the circuit breaker connected to the alternate source. In this manner voltage stress on the solid state switching devices is minimized.

Growing community of inventors

Elm Grove, WI, United States of America

Per A Danfors