Dormant oscillator ground to neutral protection for ground fault interrupters

Abstract

Ground to neutral fault protection employing dormant oscillators which are only energized and function on the .[.occurance.]. .Iadd.occurrence .Iaddend.of such type of a ground fault. Combined with known types of two and three wire single phase AC ground fault interrupters to provide circuit interruption regardless of which wire is faulted to ground.

We claim: 
     
       1. In a ground fault interrupter for an alternating current distribution circuit which has a neutral electrically grounded conductor and at least one electrified conductor, of an electro-responsive circuit breaker having contacts for connection between each electrified conductor of an alternating circuit supply source and corresponding conductors of said distribution circuit, normally dormant means responsive to a low resistive fault between said neutral conductor and ground to initiate generation of a high frequency oscillatory potential and means responsive to the resulting oscillatory, current to effect energization of said electro-responsive circuit breaker. 
     
     
       2. The combination according to claim 1 wherein said normally dormant means comprises amplifying means and two differential transformers each having cores through which the conductors of said distribution circuit pass and a secondary winding in circuit with said amplifying means. 
     
     
       3. The combination according to claim 2 wherein said amplifying means includes an operational amplifier, wherein secondary winding of one of said transformers has a capacitor connected thereacross and is connected to the input terminals of said amplifier, and wherein the secondary winding of the other of said transformers has a capacitor connected thereacross and is in circuit with the output of said operational amplifier. 
     
     
       4. The combination according to claim 3 wherein the inductance of said secondaries and the capacitance of the capacitors connected thereacross provide a pair of high frequency resonant tank circuits that are insensitive to normal distribution circuit frequencies. 
     
     
       5. The combination according to claim 3 together with a third differential transformer having a core through which the conductors of said distribution circuit pass and a secondary winding in circuit with the input terminals of said operational amplifier and a capacitor connected across the last mentioned secondary winding, said last mentioned secondary winding and capacitor having inductance and capacitance values such that an alternating potential will be generated in their parallel combination when a fault occurs between any electrified line and ground at the distribution circuit frequency. 
     
     
       6. The combination according to claim 3 wherein the cores and secondary windings of said transformers upon .[.occurance.]. .Iadd.occurrence .Iaddend.of a neutral conductor to ground fault are thereby effectively coupled by said neutral conductor and the fault established ground return path to initiate and sustain the generation of said high frequency oscillatory current, and wherein the gain of the circuit inclusive of said coupled secondary windings of said transformers and said amplifier is equal to or greater than unity. .Iadd. 7. A protective system for use in an electrical system having at least a first conductor and a second conductor extending from a source of alternating current to a load, said protective system comprising: a transformer having a core, a primary on said core and a secondary formed by said at least first and second conductors;   an amplifier;   means to couple the output of said amplifier to said primary of said transformer; and   means including said transformer for causing said amplifier to break into self-sustained oscillations upon the occurrence of a given event relating to said at least first and second conductors. .Iaddend..Iadd. 8. A protective system as defined in claim 7 wherein said given event is the establishing of a parallel conductive shorting path across at least one of said at least first and second conductors. .Iaddend..Iadd. 9. A protective system as defined in claim 7 wherein one of said at least first and second conductors is a neutral conductor grounded at the source side of said electrical system and said given event is the establishment of a low impedance to ground in said neutral conductor on the load side of said electrical system. .Iaddend..Iadd. 10. A protective system as defined in claim 8 wherein said means for causing said amplifier to break into self-sustained oscillations also includes a differential transformer having a core, a primary formed by said at least first and second conductors and a secondary on said core, said secondary being coupled to the input of said amplifier. .Iaddend. .Iadd. 11. A protective system as defined in claim 9 wherein said means for causing said amplifier to break into self-sustained oscillations also includes a differential transformer having a core, a primary formed by said at least first and second conductors and a secondary on said core, said secondary being coupled to the input of said amplifier. .Iaddend..Iadd. 12. A protective system as defined in claim 8 wherein responsive means is coupled to the output of said amplifier, said responsive means responding to the voltage developed at the output of said amplifier when said amplifier breaks into self-sustained oscillations. .Iaddend..Iadd.13. A protective system as defined in claim 12 wherein said responsive means is a circuit breaker coil coupled to the output of said amplifier. .Iaddend..Iadd. 14. A protective system as defined in claim 9 wherein responsive means is coupled to the output of said amplifier, said responsive means responding to the voltage developed at the output of said amplifier when said amplifier breaks into self-sustained oscillations. .Iaddend..Iadd. 15. A protective system as defined in claim 14 wherein said responsive means is a circuit breaker coil coupled to the output of said amplifier..Iaddend.