Surge arrester with insulative support bracket

Abstract

 A surge arrester for use in connection with a high voltage electric power distribution system includes a housing, a plurality of metal oxide varistor blocks disposed within the housing, a ground lead disconnector, and a conductive stud which electrically couples the ground lead disconnector to the varistor blocks. The surge arrester has a metal support arm disposed between the housing and the ground lead disconnector, and isolating members for electrically isolating the metal support arm from the conductive stud. The isolating members comprise a first insulative member disposed between the metal support arm and the housing, and a second insulative member disposed between the metal support arm and the ground lead disconnector. In the case of arrester failure, the isolating members prevent high voltage from being provided to the metal support arm.

Description

Technical Field of the Invention

[0001] The present invention relates to an insulative support bracket for mounting a high voltage surge arrester and, more particularly, to an insulative support bracket for preventing short circuits between the surge arrester and the structure to which the surge arrester is mounted.

Background of the Invention

[0002] High voltage electric power distribution systems carry electric power having a voltage in the range, for example, of approximately 3,000 volts to 35,000 volts or higher, and are used to provide electric power for the electrical equipment of residential, commercial, and industrial electric power users. Destructive voltage surges, such as those produced by lightning strikes, can propagate along these distribution systems and, if not arrested, can damage not only the electrical equipment of residential, commercial, and industrial electric power users, but also the transformers and other equipment of the electric power distribution systems. Therefore, surge arresters are commonly used in these high voltage electric power distribution systems in order to shunt such overvoltage surges to ground.

[0003] A surge arrester typically used in such distribution systems includes a plurality of series-connected metal oxide varistor blocks provided in either a porcelain or a polymer housing. The metal oxide varistor blocks are connected at one end to a high voltage conductor of a high voltage electrical power distribution system and at another end to ground through a ground lead. Normally, the varistor blocks are in a high impedance condition so that the flow of current therethrough is small (on the order of one milliampere); however, when a relatively large voltage, e.g. due to an overvoltage surge, is impressed across the varistor blocks, they conduct high current (amperes to thousands of amperes) to thereby shunt the excess voltage to ground.

[0004] If a metal oxide varistor fails, it typically fails in a runaway condition in which its temperature increases. This temperature increase decreases the resistance of the metal oxide varistor, which increases the current flowing therethrough, which further increases its temperature, and so on. If the surge arrester has a ceramic housing, such a failure may take the form of an explosion in which the surge arrester fragments and the metal oxide varistor blocks are expelled. If the surge arrester has a polymeric housing, however, failure of the arrester may only result in the rupture of a portion of the housing, with the other elements of the surge arrester remaining intact. If so, a sustained ground fault results because the final resistance of the failed series-connected metal oxide varistor blocks is essentially zero.

[0005] Accordingly, a high voltage surge arrester is typically provided with a ground lead disconnector which, upon a failure of the surge arrester, separates the ground lead from the ground end of the surge arrester in order to prevent a sustained ground fault on the distribution system and to signal that the surge arrester has failed. Care must be taken, however, in mounting the surge arrester because otherwise the mounting arrangement could provide a ground path for the surge arrester and thus negate the benefit of the ground lead disconnector. Therefore, it has been the practice of many electric utilities to mount a high voltage surge arrester with an insulative support bracket. Thus, even if the surge arrester fails, the high voltage of the electrical distribution system is prevented from being shorted to ground through the arrester.

[0006] Examples of such insulative devices are disclosed in U.S. Patent Nos. 4,972,291, 4,991,053, and 5,237,482. In those patents, the insulative devices are in the form of insulative support brackets. These brackets are connected between the arrester and the metal support bracket, and have a plurality of baffles formed thereon to increase the creepage path along the bracket. While surge arresters incorporating such insulative brackets operate satisfactorily, these types of insulative brackets are relatively expensive to manufacture.

[0007] Another surge arrester having a support bracket is disclosed in U.S. Patent No. 4,851,955 to Doone, et al. That surge arrester has a metal support bracket which is connected to a metal end cap provided on the bottom end of the arrester. The metal end cap is fitted to the end of the arrester with a silicone rubber or like sealant which fills the space between the interior of the end cap and the arrester core. If the mounting structure of the Doone, et al. patent were used for a surge arrester with an elastomeric housing, an undesirable short circuit between the arrester elements and the metal mounting bracket might occur upon rupture of the elastomeric housing at a point adjacent the metal mounting bracket.

Summary of the Invention

[0008] Accordingly, in one aspect of the present invention, a surge arrester for use in connection with a high voltage electric power distribution system has a housing, an arrester element disposed within the housing, a ground lead disconnector, and a conductive stud which electrically couples the ground lead disconnector to the arrester element. An insulative support bracket is provided for supporting the arrester. The support bracket has a support arm disposed adjacent the conductive stud, and the support arm is electrically isolated from the conductive stud. Thus, in the case of arrester failure, the high voltage of the electric power distribution system to which the arrester is connected is prevented from being shunted to the support arm.

[0009] In another aspect of the present invention, a surge arrester for use in connection with a high voltage electric power distribution system, includes a housing, at least one metal oxide varistor block disposed within the housing, a ground lead disconnector, and a conductive stud which electrically couples the ground lead disconnector to the at least one metal oxide varistor block. An insulative support bracket supports the housing and includes a metal support arm disposed between the housing and the ground lead disconnector. The metal support arm is electrically isolated from the conductive stud.

[0010] In yet another aspect of the present invention, a surge arrester for use in connection with a high voltage electric power distribution system includes a housing, at least one surge arresting element disposed within the housing, and a conductive stud located at one end of the housing and electrically coupled to the at least one surge arresting element. A metal support arm is disposed at the one end of the housing and is arranged to support the housing. The metal support arm is electrically isolated from the conductive stud by first and second insulative members. The first insulative member is disposed on a first side of the metal support arm between the metal support arm and the housing, and has a flange disposed circumferentially about a portion of the housing. The second insulative member is disposed on a second, opposite side of the metal support arm.

Brief Description of the Drawing

[0011] These and other features and advantages of the present invention will be apparent to those of ordinary skill in the art in view of the detailed description of the preferred embodiments, which is made with reference to the drawing, in which:

Figure 1 is a partial cross-sectional view of one embodiment of a surge arrester having an insulative mounting bracket in accordance with the present invention;

Figure 2 is a partial cross-sectional view of a portion of the surge arrester embodiment shown in Figure 1;

Figure 3 is a partial cross-sectional view of a portion of a second embodiment of a surge arrester in accordance with the present invention;

Figure 4 is a partial cross-sectional view of a portion of a third embodiment of a surge arrester in accordance with the present invention; and,

Figure 5 is a partial cross-sectional view of a portion of a fourth embodiment of a surge arrester in accordance with the present invention.

Detailed Description of the Preferred Embodiments

[0012] One embodiment of a high voltage surge arrester 10 in accordance with the present invention is shown in Figure 1. The surge arrester 10 includes terminal ends 10a and 10b. The terminal end 10a has a conventional clamping device 12, a threaded metal stud 14, and a threaded nut 16 for electrically connecting the arrester 10 to a power line (not shown) of a high voltage electric power distribution system. The terminal end 10b of the arrester 10 has a clamping device 18 and a threaded nut 20 for electrically connecting the arrester 10 to ground through a ground lead (not shown). The arrester 10 also has a body portion 22, and a conventional explosive ground lead disconnector 24 disposed at its terminal end 10b. The body portion 22 of the arrester 10, the disconnector 24, and an insulative support bracket 26 are interconnected firmly together by way of a threaded conductive stud 28.

[0013] The body portion 22 of the arrester 10 includes arrester components 30 enclosed within an insulating housing 32, which may be composed of either an elastomeric or ceramic material, and which includes a plurality of integrally formed weathersheds 32a to increase the creepage path along the arrester housing 32. The arrester components 30 include a pair of spaced-apart metallic spacers 34 and 36 and one or more metal oxide arrester elements 38 disposed between, and in electrical series contact with, the metallic spacers 34 and 36. The arrester components 30 may also include a relatively rigid insulative tube or wrapping 40, firmly attached to the spacers 34 and 36 for retaining the spacers 34 and 36 and the arrester elements 38 together in series electrical contact.

[0014] The spacers 34 and 36 are centrally threaded to receive and engage the threads of the respective threaded studs 14 and 28 which pass through central holes in a pair of metal disks 42 and 44. The bracket 26 is attached to the arrester 10 by the engagement of the stud 28 with the ground lead disconnector 24.

[0015] The insulative support bracket 26 is composed of a metal support arm 46 and an insulating arrangement for electrically isolating the support arm 46 from the other portions of the arrester 10. This insulating arrangement includes a first insulative member 48 disposed between the support arm 46 and the arrester housing 32, and a second insulative member 50 disposed between the support arm 46 and the ground lead disconnector 24. The first insulative member 48 is supported within a circular opening 52 formed in the support arm 46. The insulative members 48 and 50 are preferably composed of any suitable insulating material, such as a thermoplastic, and can be formed in any conventional manner, such as by injection molding.

[0016] The support arm 46, which is preferably composed of steel, has a portion 46a which lies in a direction substantially perpendicular to the central axis of the arrester 10, a portion 46b which lies in a direction substantially parallel to the central axis, and a portion 46c which makes an acute angle with respect to the central axis. The metal support arm 46 has an insulative coating or sleeve 54 which is provided at approximately the same elevation as the ground lead disconnector 24 and the nut 20 to electrically isolate or shield the metallic support arm 46 from those components.

[0017] Referring to Figure 2, the first insulative member 48 has a flat, disk-shaped portion 56 with a central opening provided therein through which the stud 28 passes, a first annular flange 58 formed integrally with the disk-shaped portion 56 and disposed circumferentially about a portion of the arrester housing 32, and a second annular flange 60 formed integrally with the disk-shaped portion 56 and disposed between the support arm 46 (not shown in Figure 2) and the stud 28.

[0018] The second insulative member 50 is generally cup shaped, having a flat, disk-shaped portion 62 and an integrally formed annular flange 64 extending downwardly from the disk-shaped portion 62. The annular flange 64 is disposed circumferentially about the ground lead disconnector 24, and electrically isolates and shields the ground lead disconnector 24 from the support arm 46.

[0019] A portion of a second embodiment of the arrester 10 is shown in Figure 3. The arrester components of Figure 3 are the same as in Figure 1, except that the insulative members 48 and 50 of Figure 1 are provided as a unitary insulative member 70, and except that the metal support arm 46, instead of having a circular opening completely surrounded by the metal support arm 46, has an opening in the form of a slot 72 so that the unitary insulative member 70 can be inserted into the slot 72 laterally with respect to the metal support arm 46.

[0020] A portion of a third embodiment of the invention is shown in Figure 4. In the embodiment of Figure 4, the arrester 10 includes a first insulative member 80 and a second insulative member 82. The first insulative member 80 has a flat, disk-shaped portion 84 with a central opening provided therein through which the stud 28 passes, a first annular flange 86 formed integrally with the disk-shaped portion 84 and disposed circumferentially about a portion of the arrester housing 32, and a second annular flange 88 formed integrally with the disk-shaped portion 84 and disposed between the support arm 46 and the stud 28.

[0021] The second insulative member 82 is generally cup shaped, having a flat, disk-shaped portion 90, a first annular flange 92 formed integrally with the disk-shaped portion 90 and extending downwardly from the disk-shaped portion 90, and a second annular flange 94 formed integrally with the disk-shaped portion 90, extending upwardly from the disk-shaped portion 90, and disposed adjacent the stud 28. The annular flange 92 is disposed circumferentially about the ground lead disconnector 24, and electrically isolates and shields the ground lead disconnector 24 from the support arm 46.

[0022] A portion of a fourth embodiment of the invention is shown in Figure 5. Although any of the insulative members shown herein may be used in the embodiment of Figure 5, the specific arrester 10 shown in Figure 5 includes a first insulative member 100 and a second insulative member 102, which are similar to the insulative members 80 and 82 shown in Figure 4. The first insulative member 100 has a flat, disk-shaped portion 104 with a central opening provided therein through which the stud 28 passes, a first annular flange 106 formed integrally with the disk-shaped portion 104 and disposed circumferentially about a portion of the arrester housing 32, and a second annular flange 108 formed integrally with the disk-shaped portion 104 and disposed between a metal support piece 110 and the stud 28.

[0023] The second insulative member 102 is generally cup shaped, having a flat, disk-shaped portion 112, a first annular flange 114 formed integrally with the disk-shaped portion 112 and extending downwardly from the disk-shaped portion 112, and a second annular flange 116 formed integrally with the disk-shaped portion 112, extending upwardly from the disk-shaped portion 112, and disposed adjacent the stud 28. The first annular flange 114 is disposed circumferentially about the ground lead disconnector 24, and electrically isolates and shields the ground lead disconnector 24 from the metal support piece 110 and a metal mounting bracket 118.

[0024] The metal support piece 110 has a first hole 120 therethrough to accommodate the first insulative member 100, the second insulative member 102, and the stud 28. Accordingly, in a manner similar to the above embodiments, the arrester 10 is fastened to the metal support piece 110 by way of the first hole 120. The metal support piece 110 also has a second hole 122 therethrough. The metal mounting bracket 118 has a hole 124 therethrough. A bolt 128, which extends through the second hole 122 in the metal support piece 110 and the hole 124 in the metal mounting bracket 118, and a nut 130 threaded onto the bolt 128 fastens the metal support piece 110 and the metal mounting bracket 118 together so that the arrester 10 is supported by the metal mounting bracket 118.

[0025] The metal support piece 110 permits a more versatile mounting arrangement for the arrester 10 so that the arrester 10 can be mounted on any shaped metal mounting bracket.

[0026] Further details of the arrester 10 are described in U.S. Patent No. 4,161,012 to Cunningham, in U.S. Patent No. 4,972,291 to Cunningham, in U.S Patent No. 4,991,053 to Cunningham, and in U.S. Patent No. 5,237,482 to Osterhout, et al., the disclosures of which are incorporated herein by reference.

[0027] With reference to Figure 1, when the arrester 10 is placed in service, the terminal end 10a of the arrester 10 is connected to a high voltage power line (not shown) of an electric power distribution system via the clamp 12, and the terminal end 10b is connected to ground via a ground lead (not shown) electrically connected to the terminal end 10b of the arrester 10 by way of the clamp 18. The metal support arm 46 may also be electrically grounded.

[0028] As is well known, overvoltage surges on the power line to which the arrester 10 is connected will be shunted through the arrester 10 to ground via the terminal end 10b. If the arrester 10 fails, the ground lead disconnector 24 explosively separates the ground lead from the arrester 10, thereby interrupting the current carrying conductive path to system ground and signalling that the arrester 10 has failed.

[0029] In at least some cases of arrester failure, the arrester 10 may remain relatively intact, with a short circuit through the arrester element 38, so that the high voltage of the high voltage power line connected to the terminal end 10a of the arrester 10 is present at the terminal end 10b. In such a case, the insulating members 48 and 50 advantageously electrically isolate and shield the metal support arm 46, which might be connected to ground, from the high voltage present at the terminal end 10b in order to prevent the high voltage of the power distribution system from being provided to the grounded metal support arm 46. The insulative sleeve 54 provided on the support arm 46 and the flange 64 (Figure 2) of the second insulative member 50 also electrically isolates any high voltage that might be present on remaining portions of the ground lead disconnector 24 from the metal support arm 46.

[0030] The insulating members 48 and 50 (and analogous components 70, 80, 82 of Figures 3 and 4) are relatively inexpensive to manufacture. Also, the metal support arm 46 provides a relatively strong support for the arrester 10, and the support arm 46 is relatively compact.

[0031] Modifications and alternative embodiments of the invention will be apparent to those skilled in the art in view of the foregoing description. This description is to be construed as illustrative only, and is for the purpose of teaching those skilled in the art the best mode of carrying out the present invention. The details of the structure and method may be varied substantially without departing from the spirit of the invention.

Claims

1. A surge arrester for use in connection with a high voltage electric power distribution system, the surge arrester comprising:
   a housing (22);
   an arrester element (30) disposed within the housing (22);
   a ground lead disconnector (24);
   a conductive stud (28) which electrically couples the ground lead disconnector (24) to the arrester element (30); and
   an insulative support bracket (26) for supporting the surge arrester, the insulative support bracket (26) comprising:
      a support arm (46) disposed adjacent the conductive stud (28); and
      isolating means (48,50) for electrically isolating the support arm (46) from the conductive stud (28), the ground lead disconnector (24) clamping the isolating means (48,50) to the housing (22).

2. A surge arrester as defined in claim 1,
   wherein the support arm (46) has a first portion (46a) which lies in a direction substantially perpendicular to a central axis of the surge arrester, and a second portion (46b) which lies in a direction which makes an angle with respect to the first portion (46a) of the support arm, the second portion of the support arm being disposed relatively near the ground lead disconnector, and
   wherein an insulative sleeve (54) is disposed on the second portion (46b) of the support arm (46) electrically to isolate the second portion (46b) of the support arm (46) from the ground lead disconnector (24).

3. A surge arrester as defined in claim 2 wherein the second portion (46b) of the support arm (46) is substantially parallel to the central axis.

4. A surge arrester as defined in any preceding claim, wherein the isolating means (48,50) comprises an insulative member (48) provided between the support arm (46) and the housing (22).

5. A surge arrester as defined in claim 4,
   wherein the support arm (46) has an opening (52) provided therein,
   wherein a portion of the conductive stud (28) is disposed within the opening (52), and
   wherein the insulative member (48) has a flange (60) disposed between the support arm (46) and the portion of the conductive stud (28) disposed within the opening (52).

6. A surge arrester as defined in claim 5, wherein the opening (52) provided in the support arm (46) is circular and wherein the flange (60) of the insulative member (48) is annular.

7. A surge arrester as defined in claim 5 or claim 6,
   wherein the insulative member (48) has a second flange (58), the second flange (58) being disposed circumferentially about a portion of the housing.

8. A surge arrester as defined in any of claims 3 to 7, wherein the isolating means (48,50) further comprises a second insulative member (50), disposed between the support arm (46) and the ground lead disconnector (24).

9. A surge arrester as defined in claim 8,
   wherein the second insulative member (50) has a flange (64) disposed circumferentially about the ground lead disconnector (24).

10. A surge arrester according to any preceding claim, wherein the support arm (46) is made of metal.

11. A surge arrester as defined in any preceding claim, wherein the support arm (46) has a first hole (120) for receiving a portion of the conductive stud (28) and a second hole (122) for attaching the support arm (46) to a mounting bracket (118).

12. A surge arrester for use in connection with a high voltage electric power distribution system, the surge arrester comprising:
   a housing (22);
   at least one surge arresting element (30) disposed within the housing (22);
   a conductive stud (28) at one end of the housing and electrically coupled to the at least one surge arresting element (30);
   a metal support arm (46) being disposed at the one end of the housing (22) and being arranged to support the housing (22); and,
   isolating means (48,50) for electrically isolating the metal support arm (46) from the conductive stud (28), the isolating means comprising:
      a first insulative member (48) disposed on a first side of the metal support arm (46) between the metal support arm (46) and the housing (22), the first insulative member (48) having a flange (58) disposed circumferentially about a portion of the housing (22); and,
      a second insulative member (50) disposed on a second, opposite side of the metal support arm (46).

Drawing