AUTOMATIC GROUND FAULT CIRCUIT INTERRUPTER

• US 3,558,980 A
• Filed: 05/29/1969
• Issued: 01/26/1971
• Est. Priority Date: 05/29/1969
• Status: Expired due to Term

• Current Assignee: Douglas A. Florance, Foldes Stephen, Lloyd P. Nordholm
• Original Assignee: Douglas A. Florance, Foldes Stephen, Lloyd P. Nordholm
• Inventors: Florance, Douglas A., Nordholm, Lloyd P., FOLDES STEPHEN
• Application Number:
  US04/828,836
• Time in Patent Office: 607 Days
• US Class Current: 361/45
• CPC Class Codes: H02H 3/33 using summation current transformers H02H3/347 takes precedence

Abstract

A power distribution system with automatic protection of ground fault is described. In series with both conductors of a power line are primary windings of a transformer connected in opposite phase relation. A secondary winding is energized by virtue of a predetermined reference current through one of the primary windings. A control circuit or the holding coil of a circuit breaker is energized from the secondary winding. The induced electromotive force due to reference current is canceled by ground fault leakage current which must flow through the out-ofphase primary winding effecting disconnection of the live conductor.

D R A W I N G

Claims

1. In a power distribution system including at least two load current carrying conductors receiving power from a supply circuit at the feed end and delivering power at the delivery end, one of said conductors, termed the neutral, being grounded at said feed end and the other conductor, termed the live conductor, being above ground potential, means for protecting said live conductor from current leakage to ground due to a fault creating a conductive path which bypasses said neutral conductor comprising:

a. a first circuit means establishing a predeterMined reference current flow between said conductors;

b. sensing means responsive to said reference current;

c. switching means in series with said live conductor operable to be placed in conductive and nonconductive modes;

d. control means responsive to said sensing means for maintaining said switching means in conductive mode, whereby said conductors may deliver current to a load at said delivery end; and

e. means responsive to current flow in said live conductor through a path to ground, bypassing said neutral conductor, said last-mentioned means being operable to cancel the response of said control means, placing said switching means in nonconductive mode, thereby disrupting current flow to said delivery end.

2. A power distribution system in accordance with claim 1, including:

a. a shunt circuit across said switching means; and

b. means in said shunt circuit operable, upon cessation of current flow, for disabling the operation of said sensing means, whereby said switching means is held in nonconductive mode until current flow ceases through said path to ground.

3. A power distribution system in accordance with claim 1 wherein said first circuit means, establishing a predetermined reference current, includes a resistance between said live conductor in series with a first current coil of a transformer, said current coil being in series with said neutral conductor.

4. A power distribution system in accordance with claim 1 wherein said sensing means comprises the secondary winding of a transformer having a first current coil in series with said neutral conductor.

5. A power distribution system in accordance with claim 1 wherein said switching means comprises a pair of silicon-controlled rectifiers connected back-to-back, in series, with said live conductor.

6. A power distribution system in accordance with claim 1 wherein said control means comprises an oscillator energizing the gate electrodes of said rectifiers.

7. A power distribution system in accordance with claim 1 wherein said means responsive to current flow in said live conductor having a ground path comprises a second current coil of a transformer in series with said live conductor, said transformer having a first current coil in series with said neutral conductor.

8. A power distribution system in accordance with claim 7 wherein said current coils of said transformer are connected in bucking phase relation.

9. In a power distribution system including at least two load current carrying conductors receiving power from a supply circuit at the feed end and delivering power at the delivery end, one of said conductors, termed the neutral, being grounded at said feed end and the other conductor, termed the live conductor, being above ground potential, means for protecting said live conductor from current leakage to ground due to a fault creating a conductive path which bypasses said neutral conductor comprising:

a. a transformer having a first primary winding in series with said neutral conductor and a second primary winding in series with said live conductor, said primary windings being connected in opposing phase relation;

b. a secondary winding coupled to said primary windings;

c. an impedance element connected between said live conductor and said neutral conductor, including, in series, said first primary winding, thereby establishing a predetermined reference current inducing a voltage in said secondary winding;

d. a circuit breaker for said live conductor having a holding coil; and

e. circuit means interconnecting said holding coil with said secondary winding, whereby said circuit breaker is held in operating position for maintaining said live conductor in current supplying condition at said feed end until current flow in said second primary winding, due to a path between said line conductor and ground, cancels said induced voltage, thereby effecting the tripping of said circuit breaker.