Electrical arc furnace protection system

• US 6,810,069 B2
• Filed: 03/24/2003
• Issued: 10/26/2004
• Est. Priority Date: 07/12/2002
• Status: Expired due to Term

• Current Assignee: Eaton Intelligent Power Limited (Eaton Corporation PLC.)
• Original Assignee: Mcgraw-Edison Company (Eaton Corporation PLC.)
• Inventors: Bishop, Martin T., Kojovic, Ljubomir A.
• Primary Examiner(s): Hoang, Tu Ba
• Application Number:
  US10/394,661
• Publication Number:
  US 20040012901A1
• Time in Patent Office: 582 Days
• Field of Search: 373/2, 373/60, 373/102, 373/104, 219/482, 219/490, 219/497, 219/503, 324/117.R, 324/127, 361/62, 75/101.2, 266/80, 266/81
• US Class Current: 373/60
• 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 3/10 additionally responsive to some other abnormal electrical conditions
• CPC Class Codes: H02H 3/28 involving comparison of the voltage or current values at two spaced portions of a single system, e.g. at opposite ends of one line, at input and output of apparatus for transformers H02H7/045
• CPC Class Codes: H02H 7/045 Differential protection of transformers

Abstract

Protection systems are described for electrical systems such as electrical arc furnaces. The protection systems may be designed and used to detect and clear faults that may occur within the electric arc furnace. For example, a pair of Rogowski coils may be used to detect current at their respective locations along a conductors, and output corresponding signals to a multi-function, differential relay having multiple voltage and current inputs. By comparing the signals from the Rogowski coils, the differential relay may determine whether a fault exists at some point along the conductors and between the pair of Rogowski coils. Further, the relay may then, in response to the fault, trip a circuit breaker or other network protection device, so that the fault may be corrected.

Claims

1. An electrical protection system comprising:

a first Rogowski coil positioned along a first conductor and operable to measure a first current in the first conductor and output a first signal, where the first conductor is part of an electric arc furnace (EAF) system; and

a protection device operable to use the first signal in determining that a fault exists in the EAF system.

2. The system of claim 1 wherein the first conductor is associated with a primary winding of a transformer of the EAF system.

3. The system of claim 2 wherein the first Rogowski coil is located outside of a vault housing the transformer.

4. The system of claim 1 wherein the first conductor is associated with a secondary winding of a transformer of the EAF system.

5. The system of claim 4 wherein the first current is output from the secondary winding.

6. The system of claim 4 wherein the first Rogowski coil is located within a vault housing the transformer.

7. The system of claim 4 wherein the first conductor includes a conducting arm attached to an electrode of the EAF system.

8. The system of claim 1 further comprising a second Rogowski coil positioned along a second conductor of the EAF system and operable to measure a second current in the second conductor and output a second signal.

9. The system of claim 8 wherein the first conductor is associated with a primary winding of a transformer of the EAF system and the second conductor is associated with a secondary winding of the transformer.

10. The system of claim 8 wherein the protection device includes a differential relay.

11. The system of claim 10 wherein the differential relay determines that the fault exists based on the first signal and the second signal.

12. The system of claim 10 wherein the differential relay determines that the fault exists between the first Rogowski coil and the second coil.

13. The system of claim 10 further comprising a third Rogowski coil positioned along a third conductor of the EAF system and operable to measure a third current in the third conductor and output a third signal.

14. The system of claim 13 wherein the differential relay determines that the fault exists between the second Rogowski coil and the third Rogowski coil.

15. The system of claim 13 wherein the differential relay determines that the fault exists between the first Rogowski coil and the third Rogowski coil.

16. The system of claim 1 further comprising a table containing a first winding ratio of a transformer of the EAF system at a first position of an operating tap of the transformer and a second winding ratio of the transformer at a second position of the operating tap.

17. The system of claim 16 wherein the protection device is operable to determine whether the first winding ratio or the second winding ratio is associated with a present position of the operating tap, and is further operable to scale a magnitude of the first signal based on the present position.

18. A method of detecting a fault in an electrical system, the method comprising:

measuring a first current in a first conductor using a first Rogowski coil, where the first conductor is part of an electric arc furnace (EAF) system;

outputting a first signal from the first Rogowski coil;

inputting the first signal at a protection device; and

determining that the fault exists in the EAF system based on the first signal.

19. The method of claim 18 further comprising:

measuring a second current in a second conductor of the EAF system using a second Rogowski coil;

outputting a second signal from the second Rogowski coil; and

inputting the second signal at the protection device.

20. The method of claim 19 further comprising determining that the fault exists in the EAF system between the first Rogowski coil and the second Rogowski coil based on the first signal and the second signal.

21. The method of claim 19 further comprising:

measuring a third current in a third conductor of the EAF system using a third Rogowski coil;

outputting a third signal from the third Rogowski coil; and

inputting the third signal at the protection device.

22. The method of claim 21 further comprising determining that the fault exists in the EAF system between the second Rogowski coil and the third Rogowski coil based on the second signal and the third signal.

23. The method of claim 21 further comprising determining that the fault exists in the EAF system between the first Rogowski coil and the third Rogowski coil based on the first signal and the third signal.

24. The system of claim 23 wherein the first conductor is associated with a primary winding of a transformer of the EAF system, and the second conductor and the third conductor are associated with a secondary winding of the transformer.

25. The system of claim 18 wherein the protection device includes a differential relay.

26. An electrical protection system comprising:

a first Rogowski coil positioned to measure a first current at a first location of an electrical arc furnace (EAF) system and output a first signal;

a second Rogowski coil positioned to measure a second current at a second location of the EAF system and output a second signal; and

a protection device operable to input the first signal and the second signal and determine that a fault exists within the EAF system based on the first signal and the second signal.

27. The system of claim 26 wherein the protection device includes a differential relay.

28. The system of claim 26 wherein the protection device is further operable to open a circuit breaker associated with the EAF system upon determination of the fault.