Source Phase Sensitive Transfer Method and Apparatus

A method of transferring AC electrical power to a load from a first power source to a second power source, each of the power sources producing a voltage waveform, comprising the steps of:

• sensing the phase of the voltage waveform from the first power source;
• sensing the phase of the voltage waveform from the second power source;
• determining the difference between the phase sensed in steps a and b;
• calculating a time delay corresponding to the difference determined in step c;
• monitoring the voltage supplied by the first power source;
• initiating a transfer from the first power source to the second power source in response to an unacceptable condition in voltage from the first power source monitored in step e by interrupting the supply of power from the first power source to the load;
• and
• connecting the second power source after waiting for a period of time corresponding to the time delay calculated in step d.

Apparatus for controlled switching of power supplied to a load from a first AC power source to a AC second power source, comprising:

• a first set of solid state switches coupled to a junction;
• a second set solid state switches coupled to the junction;
• monitoring circuits for monitoring a current state through the switches for the first and second sets of switches;
• a controller connected to the first and second switches for activating the switches, and connected to the monitoring circuit, the controller comprising a stored program for sensing the phase of the voltage waveform from first power source, sensing the phase of the voltage waveform from the second power source, determining the difference between the phase of the voltage wave form from the first power source and the phase of the voltage wave form from the second power source, calculating a time delay corresponding to the difference, initiating the first set of switches from the first power source to the second power source by interrupting the supply of power from the first power source.