GROUND FAULT SENSING CIRCUIT

• US 3,621,334 A
• Filed: 01/21/1970
• Issued: 11/16/1971
• Est. Priority Date: 01/21/1970
• Status: Expired due to Term

• Current Assignee: Hubbell, Inc.
• Original Assignee: Edward P. Burns, Sung C. Lee
• Inventors: Edward, P. Burns, Sung, C. Lee
• Primary Examiner(s): James D. Trammell
• Application Number:
  US05/004,676
• Time in Patent Office: 664 Days
• Field of Search: 317/18A,18D,18,27 310/DIG.3 307/309
• US Class Current: 361/45
• CPC Class Codes: H02H 1/0007 concerning the detecting means in general G01R or other subclasses of G01; reed switches H01H71/2445
• CPC Class Codes: H02H 3/332 with means responsive to dc component in the fault current

Abstract

There is disclosed a ground fault sensing circuit usable with either AC or DC circuits. It includes a closed loop magnetic core having a gap. Two windings are disposed on the core in series, respectively, with the different conductors supplying the load. The windings are arranged in such a manner that, when the currents in the conductors are equal, there is no magnetic flux produced in the core and gap. Positioned in the gap is a solid state magnetic field sensitive element such as a Hall effect device or magnetic transistor. Underground fault conditions, a magnetic field appears across the gap and an output signal is generated by the solid state device. This signal is amplified and trips a circuit breaker in series with the load.

Claims

1. A ground fault sensing circuit which is frequency insensitive and responsive to DC leakage currents comprising:

a magnetically permeable core defining an airgap therein;

first and second windings on said core;

means for connecting each of said windings in series with a different conductor supplying a load from an electrical power source, said connecting means and windings being disposed to generate equal and opposite magnetic fluxes in said core when the currents in said conductors are equal;

solid state magnetic field responsive means adjacent said airgap for producing an output signal responsive to a magnetic field in said airgap; and

means for receiving said output signal and indicating the presence of a ground fault producing such magnetic field.

2. The circuit of claim 1 wherein said magnetic field responsive means comprises a Hall effect device.

3. The circuit of claim 2 wherein said magnetic field responsive means comprises means for supplying a selectively adjustable control current to said Hall effect device.

4. The circuit of claim 1 wherein said means for receiving said output signal comprises:

circuit breaker means in at least one of said conductors including a tripping coil; and

current-switching means in series with the coil of said circuit breaker and closable in response to said output signal.

5. The circuit of claim 4 wherein said current-switching means is a reed switch.

6. The circuit of claim 4 wherein said current-switching means is a solid state switch.

7. The circuit of claim 6 wherein said solid-state switch is a controlled rectifier.

8. The circuit of claim 1 wherein said magnetic field responsive means comprises a madistor.

9. The circuit of claim 8 wherein said means for receiving said output signal comprises:

circuit breaker means in at least one of said conductors including a tripping coil; and

current switching means in series with the coil of said circuit breaker and closable in response to said output signal.

10. The circuit of claim 9 wherein said current-switching means is a reed switch.

11. The circuit of claim 1 wherein said core defines two airgaps therein, a different magnetic field responsive means being adjacent each gap.

12. The circuit of claim 1 wherein said core includes shaped pole pieces adjacent said gap to concentrate the magnetic field therein.