Surge arrester with shunt gap

• US 4,908,730 A
• Filed: 01/18/1989
• Issued: 03/13/1990
• Est. Priority Date: 10/14/1988
• Status: Expired due to Term

• Current Assignee: Cooper Power Systems Incorporated (Eaton Corporation PLC.)
• Original Assignee: Kearney Co., Inc. (Eaton Corporation PLC.)
• Inventors: Westrom, Arthur C.
• Primary Examiner(s): Jennings, Derek S.
• Application Number:
  US07/298,463
• Time in Patent Office: 419 Days
• Field of Search: 361/117, 361/118, 361/119, 361/120, 361/126, 361/127, 338/20, 338/31
• US Class Current: 361/120
• CPC Class Codes: H01C 7/12 Overvoltage protection resistors series resistors structurally associated with spark gaps H01T1/16
• CPC Class Codes: H01T 1/16 Series resistor structurally associated with spark gap
• CPC Class Codes: H01T 4/12 hermetically sealed

Abstract

A surge arrester of modular form, including a metal oxide varistor disk having a coaxial shunt gap located within the disk. The metal oxide varistor disk has a hole located essentially through the center of the disk and includes top and bottom electrode plates having centrally located projections which protrude inwardly of the disk into the hole of the disk, thereby forming a shunt gap within the disk. The module may be used unhoused in under-oil applications or as a component part of a housed arrester. For under-oil applications, the electrode plates are solder sealed to the disk providing a seal preventing oil or moisture from entering the hole in the shunt gap. As an alternate embodiment the surge arrester module may include a series of two or more of such disks stacked between the top and bottom electrode plates.

Claims

1. An electric surge arrester comprising:

a varistor having top and bottom sides and a hole therethrough, the hole passing through both the top and bottom sides;

a pair of opposed, spaced apart electrodes attached to the top and bottom sides of the varistor at least one of the electrodes having a dimple projecting inwardly into said hole in said varister providing a shunt gap between the pair of opposed electrodes within said varistor; and

a conductive joint attaching each of the electrodes to their associated side of the varistor, the joints sealing the hole in the disk and preventing oil or water outside the disk from entering said hole.

2. An electric surge arrester as defined in claim 1, wherein the electrodes are made of copper.

3. An electric surge arrester as defined in claim 1, wherein the conductive joints are solder joints.

4. An electric surge arrester as defined in claim 1, wherein the varistor is made of a non-linear ceramic device.

5. An electric surge arrester as defined in claim 1, wherein the varistor is a zinc oxide based resistor.

6. An electric surge arrester as defined in claim 1, wherein the shunt gap spacing is adjusted to have a 60 Hz sparkover nominally at least about 50% greater than the duty cycle voltage rating of the varistor without the gap.

7. An electric surge arrester as defined in claim 1, wherein an inert gas is sealed with the hole in the disk.

8. An electric surge arrester as defined in claim 1, wherein the varistor is a stack of two or more varistor disks, said hole passing therethrough.

9. An electric surge arrester comprising:

a varistor having at least two sides and a hole therethrough, the hole passing through at least two of the sides of the varistor; and

a pair of electrodes, one of the electrodes being in electrical communication with one side of the varistor having the hole therethrough and the other electrode being in electrical communication with the second side of the varistor also having the hole therethrough, at least one of the electrodes having a projection protruding inwardly into said hole in said varistor providing a shunt gap between the pair of opposed electrodes within said varistor.

10. An electric surge arrester as defined in claim 9, further including a conductive joint attaching each of the electrodes to their associated side of the varistor, the joints sealing the hole in the disk and preventing oil or water outside the disk from entering said hole.

11. An electric surge arrester as defined in claim 9, wherein the electrodes are made of copper.

12. An electric surge arrester as defined in claim 10, wherein the conductive joints are solder joints.

13. An electric surge arrester as defined in claim 9, wherein the varistor is made of a non-linear ceramic device.

14. An electric surge arrester as defined in claim 9, wherein the varistor is a zinc oxide based resister.

15. An electric surge arrester as defined in claim 9, wherein the shunt gap spacing is adjusted to have a 60 Hz sparkover nominally at least about 50% greater than the duty cycle voltage rating of the varistor without the gap.

16. An electric surge arrester as defined in claim 10, wherein an inert gas is sealed with the hole in the disk.

17. An electric surge arrester as defined in claim 9, wherein the varistor is a stack of two or more varistor disks, said hole passing therethrough.

18. An electric surge arrester module as defined in claim 13, wherein the electrodes are made of copper.

19. In a housed arrester, an electric surge arrester module comprising:

a varistor having at least two sides and a hole therethrough, the hole passing through at least two of the sides; and

a pair of opposed, spaced apart electrodes, each one of said electrodes being in electrical communication with a given one of the two sides of the varistor having said hole passing therethrough, at least one of the electrodes having a projection inwardly projecting into said hole in said varistor providing a shunt gap between the pair of opposed electrodes within said varistor.

20. An electric surge arrester module as defined in claim 19, further including a conductive joint attaching each of the electrodes to its associated side of the varistor, the joints sealing the hole in the disk and preventing oil or water outside the disk from entering said hole.

21. An electric surge arrester module as defined in claim 20, wherein the conductive joints are solder joints.

22. An electric surge arrester module as defined in claim 19, wherein the varistor is made of a non-linear ceramic device.

23. An electric surge arrester module as defined in claim 19, wherein the varistor is a zinc oxide based resistor.

24. An electric surge arrester module as defined in claim 19, wherein the shunt gap spacing is adjusted to have a 60 Hz sparkover nominally at least about 50% greater than the duty cycle voltage rating of the varistor without the gap.

25. An electric surge arrester module as defined in claim 20, wherein an inert gas is sealed with the hole in the disk.

26. An electric surge arrester module as defined in claim 19, wherein the varistor is a stack of two or more varistor disks, said hole passing therethrough.

27. A surge arrester comprising a housing, a metal oxide varistor disk having top and bottom sides and a hole therethrough including the top and bottom sides of the disk, a pair of opposed, spaced apart electrodes, one of the electrodes in electrical communication with the top side of the disk and the other electrode in electrical communication with the bottom side of the disk, at least one of the electrodes having a projection protruding inwardly into said hole in said varistor disk electrically providing a shunt gap between the pair of opposed electrodes within said varistor disk, means for closing the housing, and conducting terminals electrically connected to said metal oxide varistor disks contained within the housing.

28. A surge arrester as defined in claim 27, and at least one solid metal oxide varistor block electrically connected in series within said housing with the metal oxide varistor disk.

29. A surge arrester as defined in claim 27, wherein the metal oxide varistor disk is made of a non-linear ceramic device.

30. A surge arrester as defined in claim 28, wherein the metal oxide varistor disk and block are made of a non-linear ceramic device.

31. A surge arrester as defined in claim 27, wherein the metal oxide varistor disk is made of zinc oxide.

32. A surge arrester as defined in claim 28, wherein the metal oxide varistor disk and block are made of zinc oxide.

33. A surge arrester as defined in claim 27, wherein a conductive joint attaches each of the electrodes to its associated side of the metal oxide varister disk having a hole passing therethrough, the joints sealing the hole in said varistor disk and preventing oil or water outside of said varistor disk from entering said hole.

34. A surge arrestor as defined in claim 27, further including a dessicant capsule within the housing.

35. An electric surge arrester as defined in claim 27, wherein the shunt gap spacing is adjusted to have a 60 Hz sparkover nominally at least about 50% greater than the duty cycle voltage rating of the varistor disk without the gap.

36. In a surge arrester comprising a housing, a plurality of varistors electrically connected in series within said housing, means for closing the housing and conducting terminals electrically connected to said varistors contained within the housing, the improvement comprising,

at least one of said varistors having top and bottom sides and a hole passing therethrough including the top and bottom sides of the disk,

a pair of opposed, spaced apart conducting electrodes, one of the electrodes in electrical communication with the top side of the varistor having the hole therethrough and the other electrode in electrical communication with the bottom side of the varistor having the hole therethrough disk,

at least one of the electrodes having a projection protruding inwardly into said hole providing a shunt gap between the pair of opposed electrodes within said varistor having the hole therethrough.

37. In a surge arrester as defined in claim 36, wherein two or more metal oxide varistors are stacked between said electrodes, each of the varistors in said stack having a hole therethrough, all of the holes in the varistors between said electrodes being in communication in series with each other, said projection providing a shunt gap within the series of holes in the stack of varistors.

38. In a housed arrester, an electric surge arrester module comprising:

a varistor having a top and bottom sides and a hole therethrough, the hole passing through both the top and bottom sides; and

a pair of opposed, spaced apart electrodes in electrical communication with the top and bottom sides of the varistor, at least one of the electrodes having a projection protruding inwardly into said hole in said varistor providing a shunt gap between the pair of opposed plates within said varistor;

said module in its quiescent state when operating at a given duty cycle rating being continuously conducting through said varistor but when subjected to temporary overvoltage said varistor being short circuited by sparkover occuring at the shunt gap.