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Current transformer initial condition correction

Imported: 23 Feb '17 | Published: 22 Oct '02

Michael S. Tignor

USPTO - Utility Patents

Abstract

A method and apparatus is disclosed herein for protecting a power circuit within a first cycle after power up using a current transformer to sense current and an electronic trip unit having a first trip threshold value at power up and a second trip threshold value for the reference value at about the first half cycle of the first cycle after power up. The first and second trip threshold values are threshold values used to determine an over-current condition at different preselected times after powering up is initiated.

Description

BRIEF DESCRIPTION OF DRAWINGS

Referring now to the drawings wherein like elements are numbered alike in the several Figures:

FIG. 1 is a schematic diagram of an electrical distribution system including a circuit breaker;

FIG. 2 is a diagrammatic representation of the electronic components interfacing the current transformer within the circuit breaker of FIG. 1;

FIG. 3 is an illustration of initial and steady state magnetization curves for the current transformer in FIG. 2;

FIG. 4 is an illustration of an output current signal from the current transformer in FIG. 3 depicting current vs. time; and

FIG. 5 shows a flow chart for operation of a trip unit of an exemplary embodiment.

Claims

1. A method of protecting a power circuit, including within a first cycle after powering up, using an electronic trip unit and a current transformer to sense current, the method comprising:

2. The method set forth in claim 1 wherein said sensing comprises:

3. The method set forth in claim 1 wherein said sensing comprises:

4. The method set forth in claim 1 wherein said accepting said first and second trip threshold values comprises;

5. The method set forth in claim 1 wherein said first trip threshold value is about half of said second trip threshold value.

6. The method set forth in claim 1 wherein said generating a trip signal comprises annunciating said trip condition including illuminating an LED for communicating that a trip condition occurred and the type of trip condition that occurred.

7. The method set forth in claim 6 wherein said annunciating comprises displaying a message for communicating that a trip condition occurred and the type of trip condition that occurred.

8. The method set forth in claim 6 wherein said annunciating includes visually communicating to an operator that a fault condition occurred and the type of fault condition that occurred.

9. The method set forth in claim 6 wherein said annunciating comprises making said annunciation at a remote monitoring location.

10. The method set forth in claim 1 wherein said second trip threshold value is accepted at about completion of said first cycle after power up.

11. A trip unit for determining a trip condition within about a half cycle after power up using a current sensor to sense current comprising:

12. The trip unit set forth in claim 11 wherein said output trip signal comprises a transmission of a signal to a remote monitoring location.

13. The trip unit set forth in claim 11 wherein said output trip signal is directed towards a display unit for displaying the trip condition.

14. The trip unit set forth in claim 11 wherein said output trip signal is directed to a trip module to actuate a separation of contacts.

15. The trip unit set forth in claim 11 wherein said first and second trip threshold values are operator selectable.

16. The trip unit set forth in claim 11 wherein said first and second trip threshold values are stored in nonvolatile memory.

17. The trip unit set forth in claim 11 wherein said second trip threshold value is about twice the value of said first trip threshold value.

18. The trip unit set forth in claim 11 wherein said second trip threshold value is accepted after about a first half cycle of a first cycle after power up.

19. The trip unit set forth in claim 11 wherein said second trip threshold value is substituted for said first trip threshold value at about the first cycle after power up.

20. The trip unit set forth in claim 11 wherein said second trip threshold value is a nominal instantaneous trip value setting.

21. The trip unit set forth in claim 11 wherein said current transformer includes:

22. The trip unit set forth in claim 21 wherein the metal core is in the shape of a toroid.

23. The tip unit set forth in claim 21 further comprises a load strap that connects with an external electrical distribution circuit, wherein the load strap functions as the primary winding.

24. A circuit breaker comprising:

25. The circuit breaker set forth in claim 24 wherein said output trip signal comprises a transmission of a signal to a remote monitoring location.

26. The circuit breaker set forth in claim 24 wherein said output trip signal is directed towards a display unit for displaying the trip condition.

27. The circuit breaker set forth in claim 24 wherein said output trip signal is directed to a trip module to actuate a separation of contacts.

28. The circuit breaker set forth in claim 24 wherein said first and second trip threshold values are operator selectable.

29. The circuit breaker set forth in claim 24 wherein said first and second trip threshold values are stored in nonvolatile memory.

30. The circuit breaker set forth in claim 24 wherein said second trip threshold value is about twice the value of said first trip threshold value.

31. The circuit breaker set forth in claim 24 wherein said second trip threshold value is accepted after about a first half cycle of a first cycle after power up.

32. The circuit breaker set forth in claim 24 wherein said second trip threshold value is substituted for said first trip threshold value at about the first cycle after power up.

33. The circuit breaker set forth in claim 24 wherein said second trip threshold value is a nominal instantaneous trip value setting.

34. The circuit breaker set forth in claim 24 wherein said current transformer includes:

35. The circuit breaker set forth in claim 34 wherein the metal core is in the shape of a toroid.

36. The circuit breaker set forth in claim 34 further comprises a load strap that connects with an external electrical distribution circuit, wherein the load strap functions as the primary winding.