Zero voltage crossover detector for polyphase systems

A zero voltage crossover detector for a three phase power system, having A, B and C voltage phase inputs, comprising:

• a first transformer having a first primary coil connected between said A voltage phase input and a common node, and further having a first secondary coil with a first terminal at a first end having a positive voltage when said A voltage phase is positive, a second terminal at an opposed second end having a negative voltage when said A voltage phase is positive, and a center tap connected to ground potential;
• a second transformer having a second primary coil connected between said B voltage phase input and said common node, and further having a second secondary coil with a first terminal at a first end having a positive voltage when said B voltage phase is positive, a second terminal at an opposed second end having a negative voltage when said B voltage phase is positive, and a center tap connected to ground potential;
• a third transformer having a third primary coil connected between said C voltage phase input and said common node, and further having a third secondary coil with a first terminal at a first end having a positive voltage when said C voltage phase is positive, a second terminal at an opposed second end having a negative voltage when said C voltage phase is positive, and a center tap connected to ground potential;
• a first voltage comparator means having a first input connected to said second terminal of said second secondary coil and having a second input connected to said first terminal of said third secondary coil, for generating a first output signal when said first input thereof has a voltage substantially equal in magnitude and opposite in polarity from a voltage on said second input thereof, indicating a zero voltage crossover event for said A phase;
• a second voltage comparator means having a first input connected to said second terminal of said third secondary coil and having a second input connected to said first terminal of said first secondary coil, for generating a second output signal when said first input thereof has a voltage substantially equal in magnitude and opposite in polarity from a voltage on said second input thereof, indicating a zero voltage crossover event for said B phase;
• a third voltage comparator means having a first input connected to said second terminal of said first secondary coil and having a second input connected to said first terminal of said second secondary coil, for generating a third output signal when said first input thereof has a voltage substantially equal in magnitude and opposite in polarity from a voltage on said second input thereof, indicting a zero voltage crossover event for said C phase.