Electrical load transfer control system

Claim 1

For use in an electrical power system having two power sources, where the first power source is an ordinarily available aternating current source and the second power source is an inverter having an output synchronized to said first power source, and where the load is an alternating current load which is normally connected to the output of said second power source; a control system for providing an essentially uninterrupted power flow to said load in the event of failure of said second power source by transferring said load to said first power source, and for isolating said second power source from said first power source when said first power source is connected to said load, comprising: first controllable and normally open switch means having a first operating period to close, and being connected to said first power source and to said load; second controllable and normally closed switch means having a second operating period to open, and being connected to said second power source and to said load; each of said first and second switches being such that the respective power source is both current and voltage isolated from said load when that switch is open; fault sensing means connected to said second power source for sensing any fault therein while said second power source is connected through said second switch means to said load; said fault sensing means being connected to said first switch means so as to emit a first control signal to cause said first switch means to close when a fault in second power source is sensed, and being connected to said second switch means so as to emit a second control signal simultaneously with said first control signal to cause said second switch means to open; and a ferroresonant circuit having an energy storage element connected between said second power source and said load so as to be connected to said load even after any failure of said second power source for at least the length of time of said second operating period;