Phase sequence detector for three-phase ac power system

Abstract From the Canadian patent

The phase sequence of the phase currents supplied by a three-phase AC power supply to a phasesensitive load (such as a three-phase AC motor( is monitored by developing three phase-displaced rectangular, shaped logic signals, respectively representing the three phase currents, and applying these logic signals to respective ones of the J, C and K inputs of a J-K flip-flop. When the load is correctly connected to the power supply the phase relationship of the three logic signals will be appropriate to trigger the flip-flop to its set operating state. Any other sequence actuates the flip-flop to its reset state which, in turn, disconnects the load from the power supply.