Electrical ground fault protection circuit

• US 6,437,951 B1
• Filed: 06/17/1999
• Issued: 08/20/2002
• Est. Priority Date: 06/19/1998
• Status: Expired due to Fees

• Current Assignee: Dennis R. Robbins, Michael R. Ahlstrom
• Original Assignee: Dennis R. Robbins, Michael R. Ahlstrom
• Inventors: Ahlstrom, Michael R., Robbins, Dennis R.
• Primary Examiner(s): Leja, Ronald W.
• Application Number:
  US09/335,259
• Time in Patent Office: 1,160 Days
• Field of Search: 361/42-50
• US Class Current: 361/42
• CPC Class Codes: B23K 9/10 Other electric circuits therefor; Protective circuits; Remote controls
• CPC Class Codes: H01H 2071/006 Provisions for user interfaces for electrical protection devices
• CPC Class Codes: H02H 11/001 in case of incorrect or interrupted earth connection disconnection by breaking of earth connection H02H5/105
• CPC Class Codes: H02H 3/083 for three-phase systems
• CPC Class Codes: H02H 3/338 also responsive to wiring error, e.g. loss of neutral, break

Abstract

The electrical ground fault protection circuit (10) includes power and ground LINE connections (12) that are connectable to power (18a, 18b, 18c) and ground lines of an electrical distribution system. They also include power and ground LOAD connections (14) that are connectable to a load (29). Power and ground paths extend from the power and ground LINE connections to the power and ground LOAD connections and include an interrupter (72) having a connect position in which it allows current flow from the LINE connections to the LOAD connections and a disconnect position in which it interrupts such current flow. A ground line monitor (64) detects the presence or absence of a fault condition in the ground line (20). In response to the presence of a fault condition, the circuit switches the interrupter from its connect position to its disconnect position. The power path monitor (66) detects the presence or absence of a fault condition in the power path (18a, 18b, 18c). In response to the presence of a fault condition in the power path, the circuit switches the interrupter from its connect to its disconnect position. The circuit (10) includes a ground path and plural power paths extending from the power and ground LINE connections to the power and ground LOAD connections (18a, 18b, 18c). A voltage monitor (VM₁₂, VM₂₁, VM₃) is interconnected between each power path and the ground path (20). The monitors detect the presence or absence of a voltage drop in the power path. In response to the presence of a voltage drop of a predetermined amount, the circuit switches the interrupter from its connect position to its disconnect position.

Claims

1. An electrical ground fault protection circuit, comprising:

at least one power LINE connection and a ground LINE connection, said power and ground LINE connections being connectable to power and ground lines of an electrical distribution system;

at least one power LOAD connection and a ground LOAD connection, said power and ground LOAD connections being connectable to a load;

a power path extending from said power LINE connection to said power LOAD connection, and a ground path extending from the ground LINE connection to the ground LOAD connection;

an interrupter in the power path and in the ground path, having a connect position in which it allows current flow through the path and a disconnect position in which it interrupts such current flow;

a ground line monitor for detecting the presence or absence of a ground fault condition in the ground path, and in response to the presence of a such a condition, switching the interrupter from its connect position to its disconnect position; and

a power path monitor for detecting the presence or absence of a ground fault condition in the power path, and in, response to the presence of such a fault condition, switching the interrupter from its connect position to its disconnect position, said power path monitor including a voltage drop monitor interconnected between the power path and the ground path, for detecting a voltage drop in the power path, and in response to the presence of a voltage drop of a predetermined amount, switching the interrupter from its connect position to its disconnect position.

2. The electrical fault protection circuit of claim 1, wherein the voltage drop monitor includes a voltage sensor.

3. The electrical fault protection circuit of claim 1, wherein the power path monitor includes a current leakage monitor.

4. The electrical fault protection circuit of claim 1, further comprising a ground continuity monitor for detecting the ground continuity of the circuit.

5. The electrical fault protection circuit of claim 1, further comprising an elevated voltage monitor for detecting an elevated voltage that is above a predetermined voltage and in response to such an elevated voltage will switch the interrupter from its connect position to its disconnect position.

6. An electrical ground fault protection circuit, comprising:

a plurality of power LINE connections and a ground LINE connection, said power and ground LINE connections being connectable to power and ground lines of an electrical distribution system;

a power LOAD connection for each power LINE connection and a ground LOAD connection, said power and ground LOAD connections being connectable to a load;

a separate power path extending from each power LINE connection to a related power LOAD connection, and a ground path extending from the ground LINE connection to the ground LOAD connection;

an interrupter in each power path and in the ground path, having a connect position in which it allows current flow through the path and a disconnect position in which it interrupts such current flow;

a ground line monitor for detecting the presence or absence of a ground fault condition in the ground path, and in response to the presence of such a condition, switching the interrupter from its connect position to its disconnect position; and

a power path monitor for detecting the presence or absence of a ground fault condition in a power path, and in response to the presence of such a fault condition, switching the interrupter from its connect position to its disconnect position, said power path monitor including a voltage drop monitor interconnected between each power path and the ground path, for detecting a voltage drop in the power path and, in response to the presence of a voltage drop of a predetermined amount, switching the interrupter from its connect position to its disconnect position.

7. The electrical fault protection circuit of claim 6, comprising a transformer connected to receive power from the power paths and to supply power to the voltage drop monitors.

8. The electrical fault protection circuit of claim 6, connectable to an electrical distribution system that includes three primary legs and a primary ground, wherein said circuit includes three power paths, one for each primary leg, each connected to a separate one of the primary legs, and a ground path connected to the primary ground.

9. The electrical fault protection circuit of claim 8, comprising a voltage sensor interconnected between each power path and the ground path, for detecting a voltage drop in the power path, and in response to the presence of a voltage drop of a predetermined value, switching the interrupter from its connect position to its disconnect position.

10. The electrical fault protection circuit of claim 9, comprising a transformer connected to receive power from the power paths and to supply power to the voltage sensors.

11. The electrical fault protection circuit of claim 6, wherein the power path monitor detects current leakage in any one of the primary legs, and the ground line monitor detects the presence of a current in the ground path.

12. The electrical fault protection circuit of claim 11, further including the ground path extending from the ground LINE connection to the ground LOAD connection, and wherein the interrupter when in its connect position provides a ground path from the ground LINE connection to the ground LOAD connection, and in its disconnect position opens the ground path.

13. An electrical ground fault protection circuit, comprising:

power and ground LINE connections that are connectable to an electrical distribution system that includes primary legs and a primary ground;

power and ground LOAD connections that are connectable to a load;

power and ground paths extending from the power and ground LINE connections to the power and ground LOAD connections and including a power path for each primary leg and a ground path, and an interrupter having a connect position in which it allows current flow from the LINE connections to the LOAD connections and a disconnect position in which it interrupts such current flow;

a voltage drop monitor interconnected between each power path and the ground path, for detecting a voltage drop in the power path, and in response to the presence of a voltage drop of a predetermined amount, switching the interrupter from its connect position to its disconnect position; and

a ground line monitor for detecting the presence or absence of a ground fault condition in the ground path, and in response to the presence of such condition, switching the interrupter from its connect position to its disconnect position.

14. The electrical fault protection circuit of claim 13, comprising a transformer connected to receive power from the power paths and to supply power to the voltage drop monitors.

15. In a building having a building ground, an electric welding machine including an electrode, an electrode lead, a work table and a work table lead, and an electrical fault protection circuit, comprising:

at least one power LINE connection and a ground line connection, said power and ground line connections being connectable to power and ground lines of an electrical distribution system;

at least one power LOAD connection and ground LOAD connection, said power and ground LOAD connections being connectable to the electrode lead and the work table lead of the welding machine;

a power path extending from said power line connection to said power LOAD connection, and a ground path extending from the ground LINE connection to the ground load connection;

a power path interrupter in the power path having a connect position in which it allows current flow through the power path and a disconnect position in which it interrupts such current flow;

a ground path interrupter in the ground path having a connect position in which it allows current flow through the ground path and a disconnect position in which it interrupts such current flow;

a ground line monitor for detecting the presence or absence of a fault condition in the ground line, and in response to the presence of such a condition, switching the interrupter from its connect position to its disconnect position; and

a power path monitor for detecting the presence or absence of a fault condition in the power path and in response to the presence of such a fault condition switching the power path interrupter from its connect to its disconnect position, said power monitor including a voltage drop monitor interconnected between the power path and the ground path, for detecting a voltage drop in the power path and, in response to the presence of a voltage drop of a predetermined amount, switching the interrupter from its connect position to its disconnect position.

16. The electrical fault protection circuit of claim 15, comprising said ground path and a plurality of power paths extending from the power and ground LINE connections to the power and ground LOAD connections, and a voltage drop monitor including a voltage sensor interconnected between each power path and the ground path, for detecting a voltage drop in the power path, and in response to the presence of a voltage drop of a predetermined amount, switching the interrupter from its connect position to its disconnect position.

17. The electrical fault protection circuit of claim 16, comprising a transformer connected to receive power from the power paths and to supply power to the voltage sensors.

18. The electrical fault protection circuit of claim 15, connectable to an electrical distribution system that includes three primary legs and a primary ground, wherein said circuit includes three power paths, one for each primary leg, each connected to a separate one of the primary legs, and a ground path connected to the primary ground.

19. The electrical fault protection circuit of claim 18, comprising a voltage drop monitor including a voltage sensor interconnected between each power path and the ground path, for detecting a voltage drop in the power path, and in response to the presence of a voltage drop of a predetermined value, switching the interrupter from its connect position to its disconnect position.

20. The electrical fault protection circuit of claim 19, comprising a transformer connected to receive power from the power paths and to supply power to the voltage sensors.

21. The electrical fault protection circuit of claim 15, wherein the power path monitor includes a current leakage monitor.

22. The electrical fault protection circuit of claim 15, further comprising a ground continuity monitor for detecting the ground continuity of the circuit.

23. The electrical fault protection circuit of claim 15, further comprising an elevated voltage monitor for detecting an elevated voltage at the load that is above a predetermined voltage and in response to the presence of such an elevated voltage will switch the interrupter from its connect position to its disconnect position.