Arc fault circuit breaker apparatus and related methods

[0002] This invention relates generally to circuit breakers and more particularly to arc fault detecting circuit interrupters.

[0003] An arc fault circuit interrupter protects against electrical discharge characterized by low and erratic current resulting, for example, from a damaged extension cord or an improperly installed wall receptacle. Arc fault interrupters are commonly configured in one-pole and two-pole circuits that utilize current transformers and current sensors to detect arc faults and over-currents. When such a hazard is detected, a trip device is activated to open the circuit.

[0004] Bimetal thermal trip devices typically include a bimetal current sensor in a two-pole circuit breaker. A ground fault detecting current transformer is associated with one of the two poles. If the breaker trips when no power is sensed on a side of the current transformer, and if the bimetal current sensor is at a potential equal to that of the pole conductor associated with the transformer, a large spurious signal may enter an over-current sensor circuit and cause the breaker to work incorrectly.

[0005] One-pole arc fault circuits have been adapted to two-pole breaker circuit configurations. Such circuits typically are complex, particularly where powered from a pole not associated with the transformer. Thus, for example, one known two-pole configuration references three separate ground potentials and includes two opto-couplers. A ground reference for each over-current sensor is referenced to the bimetal resistor at its associated pole potential, and power for each sensor circuit is derived from a neutral conductor. The trip circuit contains a ground leakage detection circuit and is powered by a full-wave power supply. Over-current trip signals are relayed to the trip circuit by the two opto-couplers. As the above described circuit illustrates, prevention of spurious trip signals has entailed additional power supply circuitry and use of opto-couplers or other devices capable of transferring a signal across high voltages.

[0006] In an exemplary embodiment, a circuit for detecting arc faults and over-currents includes a ground fault circuit and two over-current detection circuits. Each over-current detection circuit includes a Hall effect current sensor configured to determine a current in a corresponding pole conductor. The ground fault and over-current detection circuits are referenced to a single ground and configured to receive power from a single power supply. In operation, a current signal is sensed by a Hall effect sensor with reference to the single ground and without a metallic connection between the sensor and the pole conductor.

[0007] The above described circuit allows a two-pole breaker circuit to be configured in a form similar to a one-pole circuit and also eliminates tripping caused by spurious signals from bimetal sensors.

[0008] FIG. 1 is a diagram of an electrical power circuit utilizing a breaker circuit; and

[0009] FIG. 2 is a circuit diagram of a two-pole arc fault breaker circuit.

[0010] FIG. 1 illustrates a typical electrical power circuit or system 10 for distributing power from a power source 12 to e.g. machinery or appliances 14 in a residence or other location. A breaker circuit 16 is utilized to protect against arc faults and over-currents in e.g. wiring or outlets associated with use of appliances 14. Breaker circuit 16 includes a detection circuit 18, a trip device or circuit 20 and a breaker 22. When circuit 18 detects an arc fault or over-current, it signals trip device 20. Trip device 20 triggers breaker 22, which breaks an electrical connection between power source 12 and appliances 14. Power circuit 10 as shown in FIG. 1 is exemplary only, and embodiments of the present invention are practiced in connection with many other power circuit configurations.

[0011] Referring to FIG. 2, system 10 includes a plurality of pole conductors 26, e.g. two conductors L1 and L2, and a neutral conductor 28. Circuit 16 for detecting arc faults and over-currents includes a ground fault detection circuit 30 and two over-current detection circuits 32 and 34. Ground fault detection circuit 30 includes a current transformer 36 surrounding pole conductors 26 and neutral conductor 28. A sensor coil 38 receives a signal from transformer 36 representing a differential value of combined currents through conductors 26 and 28. An operational amplifier 40 passes the sensed signal to trip circuit 20, which trips breaker 22 (shown in FIG. 1) for circuit 10 if the amplified signal reaches a predetermined trip magnitude.

[0012] Over-current detection circuit 32 includes a Hall effect semiconductor current sensor 50 corresponding to a pole conductor 26, e.g. L1. Similarly, over-current detection circuit 34 includes a Hall effect semiconductor current sensor 52 corresponding e.g. to pole conductor L2. No metallic connections exist between sensors 50 and 52 and respective corresponding pole conductors 26. Sensors 50 and 52 are electrically connected via operational amplifiers 54 and 56 to trip circuit 20.

[0013] Ground fault detection circuit 30 and over-current detection circuits 32 and 34 each receive power from a single power supply 60, e.g. a full wave power supply of 26 volts DC. Circuits 30, 32 and 34 also are referenced to a single analog ground potential, e.g. to a potential of neutral line 28 in the embodiment shown in FIG. 2. Thus, in the embodiment shown in FIG. 2, a negative rail 62 of power supply 60 is at a neutral potential while a positive rail 64 of power supply 60 supplies power to circuits 30, 32 and 34.

[0014] In operation, sensors 50 and 52 sense current signals in pole conductors L1 and L2 respectively. Operational amplifiers 54 and 56 pass the signals sensed respectively by sensors 50 and 52 to trip circuit 20, which trips breaker 22 (shown in FIG. 1) for circuit 10 if the amplified signal reaches a predetermined trip magnitude. Because there is no metallic connection and very little capacitance between a Hall effect sensor and a conductor from which current is being sensed, sensor circuits 32 and 34 receive very little spurious signal.

[0015] A solenoid 70 referenced to a line 72 connecting sensor circuits 32 and 34 activates trip circuit 20 when a combination of clipped signals from pole conductors 26 exceed a predetermined trip magnitude. A Zener diode 74 and a capacitor 76 clamp the voltage difference between power supply 60 and neutral conductor 28 at e.g. 26 volts.

[0016] Other configurations are within the scope of the present invention. For example, in another embodiment in which two additional diodes are utilized, a full wave bridge power supply is used with a negative rail utilized as an analog ground. Such an embodiment responds to a fault during a first half-cycle after the fault has become detectable. In yet another embodiment, a half-wave bridge power supply is used in which a positive rail is at a neutral potential, and analog ground is referenced to a power supply negative rail.

[0017] The above described circuits thus are exemplary embodiments of a method for detecting arc faults and over-currents in system 10. Such method includes the step of determining a current in a pole conductor using a sensor not in contact with the pole conductor, e.g. using Hall sensor 50 corresponding to conductor L1 and sensor 52 corresponding to conductor L2. Because sensors 50 and 52 do not contact corresponding pole conductors 26, sensor circuits 32 and 34 receive very little spurious signal. Thus tripping caused by spurious signals is reduced or eliminated.

[0018] While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.