Patent ID: 7816815

Claim:
A system for transferring a load between a preferred power source and an alternate power source, the system comprising: a power scheme for switching the load between the preferred power source and the alternate power source; a plurality of phase voltage sensors for measuring and outputting phase voltages of the preferred power source; a memory for storing and outputting a sense time value and a voltage unbalance threshold value; a preferred power source voltage sensing timer that expires upon counting to the sense time value; a processor that receives the phase voltages and the memory output, determines a voltage unbalance from the phase voltages, and outputs a switch control to the power scheme, such that if the voltage unbalance exceeds the voltage unbalance threshold value, the processor reacts by: directing the power scheme to disconnect the load from the preferred power source; determining whether a regenerated voltage condition exists; and inhibiting the power scheme from retransferring the load to the preferred power source if the regenerated voltage condition exists further comprising a retransfer delay timer that expires upon counting to a retransfer delay value, wherein the memory further stores and outputs a retransfer delay value, and wherein inhibiting the power scheme from retransferring back to the preferred power source comprises: initiating a retransfer delay timer; and directing the power scheme to remain disconnected from the preferred power source until after the retransfer delay timer has expired, and further comprising a second plurality of phase voltage sensors for measuring and outputting phase voltages of the alternate power source, wherein if the voltage unbalance exceeds the voltage unbalance threshold value, the processor further reacts by directing the power scheme to connect to the alternate power source, and wherein the retransfer delay timer expires if the second plurality of phase voltage sensors indicates a failure of the alternate power source.