PRECISION, TEMPERATURE-COMPENSATED, SHIELDED CURRENT MEASUREMENT DEVICE

• US 20080007249A1
• Filed: 07/06/2006
• Published: 01/10/2008
• Est. Priority Date: 07/06/2006
• Status: Active Grant

• Current Assignee: Schweitzer Engineering Laboratories, Incorporated
• Original Assignee: Schweitzer Engineering Laboratories, Incorporated
• Inventors: Kesler, James, Wilkerson, Donovan, Skendzic, Veselin
• Granted Patent: US 7,545,138 B2
• Time in Patent Office: Days
• US Class Current: 324/127
• CPC Class Codes: G01R 15/181 using coils without a magnetic core, e.g. Rogowski coils

Abstract

A current measurement device using a Rogowski coil having a generally toroidally shaped core with flattened faces, a first winding in one direction, a second winding forming a return loop, and a temperature compensation and scaling network coupled to the coil. The core has concentric cavities and a rough surface to restrain movement of the coil winding A Faraday shield is wrapped over the coil. One shield is “serpentine,” having staggered (offset) lateral extensions from a central region An alternate shield has a generally circular central region with extensions in generally radial directions. The shield is formed of three layers comprising a non-ferromagnetic metal central layer surrounded by insulative layers. At an end tab of the shield, the metal layer is exposed for collection to a ground lug or other connector. An insulative housing envelops the coil and electrical network An output wire terminates in an industrial connector A resistive network may be implemented with the current measurement device. The resistive network may be balanced or unbalanced The resistive network may be capable of signal attenuation of an output, capable of calibration of an output, or provide temperature compensation of an output

Claims

1. An electric current measuring device of the type using a coil and comprising:

a core comprising a plurality of concentric cavities;

a conductive coil wound about the core to form a first winding in a first direction and a second winding constituting a return winding, and

a Faraday shield extending around the core, outside of the coil.

2. The electric current measuring device of claim 1 further comprising a coating layer securing the position of the coil.

3. The electric current measuring device of claim 1 wherein the core is made of a non-magnetic insulating material.

4. The electric current measuring device of claim 1 wherein the core is generally toroidally-shaped.

5. The electric current measuring device of claim 1 wherein the core is generally toroidally-shaped, having flattened side faces and includes an inside annular face having a first radius from a center point and an outside annular face having a second radius from the center point, the second radius being larger than the first radius.

6. The electric current measuring device of claim 5 wherein the core further comprises rounded corners between the annular faces and the side faces.

7. The electric current measuring device of claim 1, wherein the conductive coil comprises magnet wire.

8. The electric current measuring device of claim 1 wherein the return winding has substantially the same number of turns as the first winding.

9. The electric current measuring device of claim 1 further comprising a resistive network electrically coupled to the conductive coil.

10. The electric current measuring device of claim 1, wherein the second winding comprises a return winding wrapped on top of the first winding coil in a reverse direction of advancement as the first winding.

11. The electric current measuring device of claim 5 wherein the a flattened side faces comprise the plurality of cavities.

12. The electric current measuring device of claim 1 wherein the Faraday shield comprises a central region with first and second lateral extensions extending in opposite lateral directions from the central region.

13. The electric current measuring device of claim 12 wherein the first and second lateral extensions are offset from one another so that they generally have a serpentine orientation when flat.

14. The electric current measuring device of claim 1 wherein the Faraday shield comprises a first insulation layer and a non-ferromagnetic metal layer.

15. The electric current measuring device of claim 14 wherein the Faraday shield further comprises a second insulation layer, wherein the metal layer is positioned between the first and second insulation layers.

16. The electric current measuring device of claim 15 further comprising an adhesive positioned at lower faces of each of the first and second insulation layers and the metal layer.

17. The electric current measuring device of claim 1 wherein the Faraday shield has a portion coupled electrically to an electric grounding terminal.

18. The electric current measuring device of claim 1 further comprising a coil attenuation, calibration, and temperature compensation circuit using a resistive network electrically coupled to the first winding and the second winding of the coil.

19. The electric current measuring device of claim 18, wherein the resistive network comprises a balanced resistive network.

20. The electric current measuring device of claim 19, wherein the balanced resistive network includes first and second output nodes, and comprises:

first and second nodes coupled to ends of the first and second windings;

first, second, third, and fourth resistors;

wherein the first resistor is coupled between the first and second nodes;

wherein the second resistor is coupled between the first node and the first output node;

wherein the third resistor is coupled between the first and second output nodes; and

wherein the fourth resistor is coupled between the second node and the second output node.

21. The electric current measuring device of claim 18, wherein the resistive network comprises an unbalanced resistive network.

22. The electric current measuring device of claim 21, wherein the unbalanced resistive network includes first and second output nodes, and comprises:

first and second nodes coupled to ends of the first and second windings;

first and second resistors;

wherein the first resistor is coupled between the first node and the first output node; and

wherein the second resistor is coupled between the first and second output nodes, and coupled to the second node.

23. The electric current measuring device of claim 1 further including an insulated housing surrounding and supporting the coil and the Faraday shield.

24. The electric current measuring device of claim 23 further including an interface cable and wherein the housing includes an aperture receiving the interface cable.

25. The electric current measuring device of claim 1 wherein at least a portion of the core has a rough surface.

26. The electric current measuring device of claim 1 wherein the core is injection molded.

27. The electric current measuring device of claim 1 wherein the core is machined.

28. The electric current measuring device of claim 1 wherein the first and second windings are generally helically wrapped substantially around the full perimeter of the core.

29. A Faraday shield for a generally toroidally-shaped coil comprising:

a central region;

a plurality of first extensions extending in a first direction from the central region;

a plurality of second extensions extending in a second direction from the central region, the second direction being opposite from the first direction;

wherein the size of the central region generally corresponds to a size of a face of the coil,

wherein the extensions are sized and configured to wrap around other faces of the coil.

30. The shield of claim 29 wherein the first and second extensions are offset from one another so that they generally have a serpentine orientation when flat.

31. The shield of claim 29 wherein the shield comprises an electrically conductive material and is covered substantially with an electric insulator.

32. The shield of claim 29, further comprising an end tab which extends laterally from the central region.

33. The shield of claim 32 wherein the shield comprises an electrically conductive material and is covered substantially with an electric insulator and wherein the end tab has a face that is not covered by the insulator.

34. The shield of claim 32 wherein the end tab extends further laterally from the central region than other ones of the extensions.

35. The shield of claim 29 wherein the Faraday shield comprises a first insulation layer and a non-ferromagnetic metal layer.

36. The shield of claim 35 further comprising a second insulation layer,

wherein the metal layer is positioned between the first and second insulation layers.

37. The shield of claim 36 further comprising an adhesive positioned at lower faces of each of the first and second insulation layers and the metal layer.

38. The shield of claim 29, wherein the central region is substantially circular in shape.

39. The shield of claim 38, wherein the first direction is outward from the central region, and the second direction is inward from the central region.

40. A core for a coil comprising:

a core made of a non-magnetic material configured in a geometric shape;

a plurality of cavities extending from an outer surface of the core into the core, the cavities being concentric with the core.

41. The core according to claim 40, wherein the core is generally toroidally shaped.

42. The core according to claim 40, wherein the core has a circular plan view.

43. The core according to claim 40, further comprising a structural rib.

44. An electric current measuring device of the type using a coil and comprising:

a core;

a conductive coil wound about the core to form a first winding in a first direction and a second winding constituting a return winding, and

a resistive network coupled to the coil.

45. The electric current measuring device of claim 44, wherein the resistive network provides temperature compensation of an output of the current measuring device.

46. The electric current measuring device of claim 44, wherein the resistive network is capable of signal attenuation of an output of the current measuring device.

47. The electric current measuring device of claim 44, wherein the resistive network is capable of calibration of an output of the current measuring device

48. The electric current measuring device of claim 44, wherein the resistive network is balanced.

49. The electric current measuring device of claim 48, wherein the balanced resistive network includes first and second output nodes, and comprises:

first and second nodes coupled to ends of the first and second windings;

first, second, third, and fourth resistors;

wherein the first resistor is coupled between the first and second nodes;

wherein the second resistor is coupled between the first node and the first output node;

wherein the third resistor is coupled between the first and second output nodes; and

wherein the, fourth resistor is coupled between the second node and the second output node.

50. The electric current measuring device of claim 44, wherein the resistive network is unbalanced.

51. The electric current measuring device of claim 50, wherein the unbalanced resistive network includes first and second output nodes, and comprises:

first and second nodes coupled to ends of the first and second windings;

first and second resistors;

wherein the first resistor is coupled between the first node and the first output node; and

,

wherein the second resistor is coupled between the first and second output nodes, and coupled to the second node.