US3715626A

US3715626A - Spring plate contact and support for a lightning arrester sparkgap assembly and associated grading resistors

Info

Publication number: US3715626A
Application number: US00230733A
Authority: US
Inventors: A Olsen
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1972-03-01
Filing date: 1972-03-01
Publication date: 1973-02-06
Anticipated expiration: 1990-02-06
Also published as: CA960746A

Abstract

A lightning arrester having a self-supporting column of sparkgap assemblies and non-linear resistor valve elements, as well as a plurality of load-bearing grading resistors, is provided with a spring plate that is effective to form part of the series discharge circuit through the arrester while at the same time affording a resilient support for the column of arrester components, thereby to maintain the column of arrester components in spaced-apart relationship with respect to the inner walls of the insulating housing of the arrester.

Description

Stetson....; ..315/36 United States Patent 1191 [111 3,715,626 Olsen Feb. 6, 1973 54 SPRING PLATE CONTACT AND 2,825,008 2/1958 Kalb ..317/70 SUPPORT FOR A LIGHTNING 2,640,096 5/1953 Kalb ..317/68 ARRESTER KG ASSEMBLY (SDheadeI ggg ggggg GRADING 2:62am 12,1952 K521i:11:3:1113;111:313:1113;111:1131;13/268 75 Inventor: Arthur A. Olsen, Pittsfield, Mass. j y i fi gg l ssistant xaminer arvey en e man [73] Assrgnee: General Electric Company AttorneywFrancis Doyle et a1 [22] ,Filed: March 1, 1972 57 ABSTRACT [21] Appl. No.2 230,733 I 1 A lightning arrester having a self-supporting column of sparkgap assemblies and non-linear resistor valve ele- [52] US. Cl. ..3l7/68, 317/70, 3311747386 mems, as we as a plurality ofload bearing grading 1 sistors, is provided with a spring plate that is effective [51] Int. Cl. 9/080 to form part of the Series discharge circuit through the [58] new of Search I 1 2 21 arrester while at the same time affording a resilient 315/36 313/1) 3 l support for the column of arrester components,

thereby to maintain the column of arrester com- [56] References C'ted ponents in spaced-apart relationship with respect to UNITED STATES'PATENTS thet inner walls of the insulating housing of the ar- 2 res er. 3,152,279 I 10/1964 Misare ..3l3/231 3,671,800 6/1972 10 Claims, 4 Drawing Figures SPRING PLATE CONTACT AND SUPPORT FOR A LIGHTNING ARRESTER SPARKGAP ASSEMBLY AND ASSOCIATED GRADING RESISTORS BACKGROUND OF THE INVENTION The present invention relates to the internal discharge circuit and mechanical supporting structure of a surge voltage arrester, such as a lightning arrester, and more particularly relates to a spring plate contact device that is operable to maintain a self-supporting column of lightning arrester components in a desired predetermined position within a lightning arrester insulating housing.

' arc-generated gases to escape from the insulating housing, eitherone or both ends of the housing are often sealed with rupturable diaphragms, and substantial spacing is. provided between the stacked column of arrester components and the internal walls of the housing -to provide a generally clear vent passageway for such gasesalong the inner walls of the insulating'housing.

Because of the need for such relatively unrestricted vent passageways around the active arrester components stacked within an arrester housing, it is necessary in the design of such arresters to make some provision for mechanically stabilizing the stacked components. Such stabilizing means are necessary both to assure proper operation of the arrester by maintaining good electrical contact between the respective parts of the discharge circuit, and also to prevent damage to the active components of the arrester due to vibration of the arrester housing during normal shipping and handling of the assembled unit.

' 'One known method of improving the mechanical stability of a self-supporting column of active arrester components is to form the grading resistors for the sparkgap assemblies as segments of annuli which partially surround the sparkgap assemblies to which they are electrically connected. In such arrangements, the grading resistors are stacked upon one another and are arranged in a self-supporting column with blocks of non-linear resistance valve material so that the weight of the column of resistors and non-linear valves is entirely supported by these components, rather than by the sparkgap assemblies, which are positioned within the grading resistors. An arrester assembly of this prior art type is illustrated and described in co-pending US. Patent application Ser. No. 105,724, which was filed on Jan. 11, 1971 and is entitled Self-Supporting Load resters. Accordingly, normal manufacturing tolerances encountered in the fabrication of such arresters are sufficient to cause an appreciable difference in length between the axial length of a sparkgap assembly and a column of self-supporting molded grading resistors surrounding the assembly in the type of prior art surge voltage arrester described above. Therefore, it is usual, in the manufacture of such arresters, to position a compression spring shunted by a conductive strap, between Bearing Voltage Grading Resistors for a Lightning Ar.-

rester, and is assigned to the assignee of the invention described herein.-

At the present time, nonlinear resistance valves for I lightning arresters are commonly formed by a molding operation, and it is also a frequent practice to mold the insulating plates of sparkgap assemblies for such arthe end plate of a sparkgap assembly and the end plate of an adjacent sparkgap assembly, or an adjacent block of non-linear resistance valve material, in order to assure a firm electrical contact between these components of the discharge circuit. In addition, various spacing mechanisms were necessarily mounted in the arrester housing to maintain a proper spacing between the active components of the discharge circuit and the interior surface of the insulating housing. These additional spacing components often were in the form of numerous additional insulating parts that had to be separately assembled to the column of active arrester components. Thus, it will be appreciated that such prior art arrester structures, while completely adequate from a functional viewpoint, possess the disadvantage of being relatively expensive to manufacture, and at the same time undesirably increase the possibility of malfunction due to improper assembly or inadvertent omission of one or more of the numerous parts discharge circuit of the arrester.

SUMMARY OF THE INVENTION In one preferred embodiment of the invention disclosed herein, a self-supporting column of semi-annular grading resistors and blocks of non-linear resistance valve elements are positioned within the generally cylindrical insulating housing of a surge voltage arrester, with the semi-annular grading resistors positioned around one or more sparkgap assemblies. Pursuant to the present invention, a unique spring plate is positioned on top of each sparkgap assembly in a manner such that resilient fingers on the spring plate form a part of the discharge circuit and at the same time resiliently bias the individual electrodes of each spark-gap assembly toward their operating position. In addition, the spring plates are provided with a plurality of confining tab portions that extend beyond the outer circumference of the self-supporting column sothat they may engage the inner walls of the insulating housing with which they can cooperate, to hold the column of 'active arrester components in spaced-apart relationship with respect to the housing. The outer ends of the resilient tabs are covered with insulating means so that electric current is not allowed to pass between the spring plate and the inner walls of the insulating housing, thereby preventing the generation of undesirable radio noise under some conditions of operation.

OBJECTS OF THE INVENTION bled less expensively than prior art contact shunted springs and supporting devices for such arresters.

A further object of the invention is to provide a onepiece resilient contact plate and lateral support mechanism that is operable to maintain a self-supporting column of grading resistors and valve elements in spaced-apart relationship with respect to the interior walls of an arrester insulating housing, while at the same time being operable to bias the separate electrodes of a sparkgap assembly into their desired operating relationship.

Additional objects and advantages of the invention will become apparent to those skilled in the art from the description of it that follows taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation view, partly in cross section, of a surge voltage arrester that is constructed pursuant to the teaching of the present invention.

FIG. 2 is a top plan view of a spring plate, such as one of the spring plates used in the arrester of FIG. 1, which is constructed pursuant to the present invention.

FIG. 3 is a side elevation view, in cross section along the plane 33 of the spring plate shown in FIG. 2.

FIG. 4 is a top perspective view of a partial assembly of a spring plate, a part of a sparkgap assembly, and

part of a semi-annular grading resistor column, similar to the equivalent elements illustrated in FIG. 1 of the drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 of the drawing, it will be seen that there is shown a lightning arrester 1 that includes a generally cylindrically shaped insulating housing 2,.which is shown in cross-section along a plane taken through its longitudinal axis. The insulating housing 2 may be formed of any conventional material such as a suitable ceramic. A pair of

electric terminals

3 and 4 are mounted respectively on opposite ends of the housing 2 and'are shaped to define pressure release apertures 3a and 4a through which arc-generated gas may be exhausted from the interior of the housing 2, if a discharge current produces gases that rupture a pressure-sensitive lead diaphragm 5 at the top of the housing 2m causes aburn-through aluminum diaphragm 6 at the bottom of the housing 2 to rupture, in a manner well known in the prior art. Of course, the

terminals

3 and 4 may be formedof any suitable electrically conductive material such as steel. In order to form a fluidtight seal around the ends of the insulating housing 2, a pair of

resilient rubber gaskets

7 and 8 are positioned respectively between the diaphragms 5 and 6 and the opposite ends of housing 2. Also, bodies of sulfur cement 9 and 10 are poured into the axially deflected edges of

terminals

3 and 4 to further insure a liquid and gas tight seal between these terminals and the insulating housing 2.

The active components of the discharge circuit of arrester l comprise four nonlinear resistance valve units 11 12, 13 and 14, a pair of multi-gap sparkgap assemblies l5 and 16 and a pair of self-supporting columns of semi-annular grading resistors 17 and 18; as well as a compression spring 19, a spring-shunting strap 19a, and

a plurality of spring plates 20 and 21, which are constructed pursuant to the teaching of the present invention and will be described in greater detail below.

Except for the spring plates 20 and 21, the abovereferred to components of the arrester 1 may all be relatively conventional in construction; therefore, none of these components will be described in great detail. However, it can be understood that the sparkgap assemblies l5 and 16 may be constructed, for example, in the manner described in U.S. Pat. No. 3,576,459 Sakshaug et al, which issued Apr. 27, 1971 and is assigned to the assignee of the present invention. Moreover, the columns of grading resistors 17 and 18 may be constructed in a manner described in the above-referenced co-pending Stetson patent application. Thus, it will be understood that, as is conventional, each of the

sparkgap assemblies

15 and 16 include a plurality of separate, series connected sparkgap electrodes and a pair of

contact plates

15a, 15b and 16a, 16b, respectively mounted on the opposite ends of the two sparkgap assemblies.

Before proceeding with a more detailed description of the spring plates 20 and 21, it should be understood that in the preferred form of the invention each selfsupporting column of grading resistors 17 and 18 comprises a plurality of semi-annular grading resistors formed of nonlinear resistance material, and typically each grading resistor is generally rectangular in cross section, as shown in FIG. 1. Of course, it should be understood that annular grading resistors may be used in other forms of lightning arresters that include the present invention. As is also clearly illustrated in FIG. 1, in the preferred embodiment being described, each of the grading resistors is formed to at least partially surround one of the

sparkgap assemblies

15 or 16. And the axial length of the self-supporting columns of grading resistors 17 and 18 is greater than the axial length of their associated

sparkgap assemblies

15 and 16 by at least a predetermined amount. Part of such differences in these lengths are normally due to variances in manufacturing tolerances that inevitably exist between multi-component molded assemblies such as the column of grading resistors 17 and 18 and the multiple insulating plates that are used to form the

sparkgap assemblies

15 and 16. However, since it is necessary to assure accurate spacing between the respective electrodes (not shown) of the

sparkgap assemblies

15 and 16, these electrodes and their associated insulating plates must be held firmly together when the arrester is mounted in operating position. Accordingly, as will be described hereafter, the spring plates 20 and 21 are formed to be compressed within the predetermined amount of variance between the axial lengths of the

sparkgap assemblies

15 and 16 and their associated columns of grading resistors 17 and 18. Before describing this feature of the invention further, reference will now be made to FIGS. 2 and 3 of the drawing.

FIGS. 2 and 3 of the drawing illustrate one of the spring plates 20. As clearly shown in these figures of the drawing, the spring plate 20 has a first generally flat portion 20a and at least one resilient finger portion 20b. In fact, in this preferred embodiment of the invention the plate 20, and also substantially identical plate 21, include a plurality of

resilient finger portions

20b, 20c and 20d. In the unloaded condition of the spring plate 20, each of the

finger portions

20b, 20c and 20d are resiliently biased at angles with respect to the flat portion 20a thereof, to space the

free ends

20b, 20c and 20d of each finger portion away from the plane of the flat portion 20a a distance that is greater than the above-referred-to predetermined amount that defines the variance in lengths between the contact plate 150 on sparkgap assembly and the upper end of the selfsupporting column of grading resistor 17 when the spring plate 20 is positioned on one end of the grading resistors, as shown in FIG. 1. In this operating position the

free ends

20b, 20c and 20d of the

resilient finger portions

20b, 20c and 20d are in biasing engagement with the contact plate 15a. At the same time, the other contact plate 15b (see FIG. 1) of spark-gap assembly 15 is positioned in a plane adjacent the other end of self-supporting column of grading resistor 17. Therefore, the

contact plates

15a and 15b of the sparkgap assembly 15 are biased toward one another by the biasing force of the

resilient finger portions

20b, 20c and 20d of spring plate 20 when it is mounted in operating position. Of course, the spring plate 21 operates in similar manner with respect to a contact plate 160 and 16b of sparkgap assembly 16.

Although three resilient fingers are shown in the preferred embodiment of the spring plates 20 and 21, it will be appreciated that a greater or lesser number of such contact fingers might be used in other embodiments of the invention. However, it should be noted that each of the

finger portions

20b, 20c and 20d are shaped to define a substantially line contact with their respective

free ends

20b, 20c and 20d as they engage the contact plate 15a. These three line contacts are arranged with respect to one another to form equal parts of the respective three sides of an equilateral triangle, because it has been found that this arrangement has been particularly advantageous in providing a desired force distribution in the assembled sparkgap assembly 15, while at the same time providing a good electrical discharge circuit through the arrester 1.

Now, a second important feature of the spring plates 20 and 21 will be described. It will be noted by referring to FIGS. 2 and 3 that spring plate 20, which is substantially identical in shape to spring plate 21, is generally cylindrical in form and includes a plurality of

integral tab portions

20e, 20f and 20 that project beyond the periphery of the generally circular form of the plate 20. Each of the

tab portions

20e, 20f and 20g is positioned at an angle with respect to the flat portion 20a of the spring plate 20 so as to enable the tab portions to'be easily slipped into the housing 2 (see FIG. 1) of the arrester 1. This angular configuration of

tab portions

20e, 20f and 203 also serves to resiliently cushion any impact between them and the inner wall of housing 20, if they are moved into engagement with it during vibration of the arrester, such as might occur during normal shipping and handling during installation. It has been found that the best angle for the tab portions relative to the flat portion 20a is in the range 15 to 60". With such an angular arrangement of the tab portions, it will be appreciated that in alternative'embodiments of the invention, these tab portions may be forced into continuous engagement with the walls of housing 2, thereby to dampen any tendency of the self-supporting column to be shifted by arrester vibration. In order to prevent corona, or electrical current sufficient to cause radio noise, from being discharged through the

tab portions

20e, 20f and 20g to the inner walls of insulating housing 2, insulating means are mounted on the ends of each of the tab portions. In the preferred embodiment of the invention these insulating means comprise a layer of self-adhering

plastic material

22, 23 and 24 that is bonded to the outer ends of the tab portions, as shown in FIG. 2. Any suitable insulating plastic material may be used, but in this embodiment of the invention, a thermal-setting epoxy resin containing at least 20 percent, and preferably at least 50 percent, by weight of hydrated alumina is used, because such a composition inhibits electrical tracking, as is generally known in the art. An alternative embodiment of the insulating means of the invention is shown in FIG. 3 where a slip-on plastic jacket 25 is mounted over the tab portion 20f. In this embodiment it will be understood that similar plastic jackets (not shown) may be used to cover the other tab portions on spring plate 20. Of course, other insulating means may be used in other modifications of the invention.

In order to more fully describe the operation of the novel features of the present invention, reference is now made to FIG. 4 of the drawing which depicts a fragmentary view of the top grading resistor 17a of the self-supporting column of'resistors 17, the spring plate 20 and a portion of sparkgap assembly 15. These components are shown in their assembled or operating position, as they are in FIG. 1 of the drawing. In addition, a portion of the insulating housing 2 of arrester l is shown with respect to this subassembly. Thus, as shown in FIG. 4, during their operating life, each of the

tab portions

20e, 20f and 20g are positioned so that the insulating layers on the outer ends thereof may be shifted with the plate 20 to engage the inner walls of insulating housing 2 intermediate its two opposite ends. Since the

resilient finger portions

20b, 20c and 20d are deflected downward into engagement with the contact plate on sparkgap assembly 15, they prevent relative movement of the spring plate 20 with respect to the grading resistor 17a more than a predetermined distance. Accordingly, the spring plate 20 is operable to restrain lateral movement of the self-supporting column of grading resistors 17, while at l the same time compressing the insulating plates of sparkgap assembly 15 into their desired operating relationship. Of course, the spring plate 20 also provides a portion of the discharge circuit between sparkgap assembly 15 and an associated nonlinear resistance valve 11, as described above with reference to FIG. 1.

While it is believed that the foregoing description adequately teaches those skilled in the art how to practice the invention, it is apparent that various modifications and alternativeforms of the invention, as described, may be made, therefore it is my intention to encompass within the-scope of the following claims all such modifications and alternative forms of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A lightning arrester comprising; an insulating housing, a pair of electric terminals mounted respectively on opposite ends of the housing, a multi-gap sparkgap assembly having a pair of contact plates mounted respectively on opposite ends thereof, and a non-linear resistance valve unit mounted within the housing and electrically connected in series relationship with said sparkgap assembly between the terminals on said housing, including the improvement comprising, a plurality of grading resistors, each of said grading resistors being formed to at least partially surround said sparkgap assembly and being arranged within said housing in a self-supporting column, the axial length of said self-supporting column being greater than the axial length of said sparkgap assembly by at least a predetermined amount, and a spring plate having a first generally flat portion and at least one resilient finger portion, said finger portion being resiliently biased in its unloaded condition at an angle with respect to the flat portion thereby to space the free end of the finger portion away from the plane-of said flat portion a distance greater than said predetermined amount, said flat portion of the spring plate being positioned on one end of the self-supporting column of grading resistors thereby to position said free end of the resilient finger portion in biasing engagement with one contact plate of the sparkgap assembly, the other contact plate of said sparkgap assembly being positioned in a plane adjacent the-other end of said self-supporting column of grading resistors, whereby the contact plates of said sparkgap assembly are biased'toward one another by the biasing force of said-resilient finger portion when the spring plate is mounted in operating position.

2. An invention as defined in claim 1 wherein said spring plate has a plurality of resilient finger portions and each of saidfinger portions has its free end positioned in biasing engagement with said one contact plate of the spark-gap assembly.

3. An invention as defined in claim 2 wherein said plurality of finger portions comprises three finger portions, and each of said finger portions is shaped to define a substantially line contact with said one contact plate, said three line contacts being arranged with respect to one another to form equal parts of the respective three sides of an equilateral triangle.

4. An invention as defined in claim 1 wherein said spring plate is generally circular in form and includes a plurality of integral tab portions that project beyond the periphery of said generally circular form to positions where they can be shifted into engagement with the inner walls of said insulating housing by vibration of the arrester housing, thereby to hold the flat portion of the spring plate in spaced-apart relationship to said housing.

5. An invention as defined in claim 4 wherein each of said tab portions is positioned at an angle with respect to the flat portion of said spring plate thereby to enable said tab portions to resiliently cushion the impact of said self-supporting column against the spring plate when said tab portions are shifted into engagement with the housing by vibration of the arrester.

6. An invention as defined in claim 4 including insulating means mounted on the ends of each of said tab portions, said insulating means being effective to prevent electric current from flowing through said tab portions to the housing.

7. An invention as defined in claim 6 wherein said in-,

sulating means comprise a layer of self-adhering plastic material bonded to the outer ends of said tab portions,

8. An invention as defined in claim 7 wherein said plastic material is an epoxy resin containing at least 20 percent by weight of hydrated alumina.

9. An invention as defined in claim 6 wherein said insulating means comprises a plurality of slip-on plastic jackets that'are mounted respectively over the ends of 'said tab portions.

10. An invention as defined in claim 4 wherein said insulating housing is in the form of a hollow cylinder and said non-linear resistance valve unit is generally disc shaped with a diameter substantially equal to the diameters of said grading resistors each of which are in the form of a segment of an annulus, and including a compression spring mounted in a single column with said valve unit and grading resistors, said tab portions on said spring plate member being positioned to engage the inner walls of said hollow cylinder intermediate the ends thereof to maintain said single column in spacedapart relationship to said inner walls.

Claims

1. A lightning arrester comprising; an insulating housing, a pair of electric terminals mounted respectively on opposite ends of the housing, a multi-gap sparkgap assembly having a pair of contact plates mounted respectively on opposite ends thereof, and a non-linear resistance valve unit mounted within the housing and electrically connected in series relationship with said sparkgap assembly between the terminals on said housing, including the improvement comprising, a plurality of grading resistors, each of said grading resistors being formed to at least partially surround said sparkgap assembly and being arranged within said housing in a self-supporting column, the axial length of said self-supporting column being greater than the axial length of said sparkgap assembly by at least a predetermined amount, and a spring plate having a first generally flat portion and at least one resilient finger portion, said finger portion being resiliently biased in its unloaded condition at an angle with respect to the flat portion thereby to space the free end of the finger portion away from the plane of said flat portion a distance greater than said predetermined amount, said flat portion of the spring plate being positioned on one end of the self-supporting column of grading resistors thereby to position said free end of the resilient finger portion in biasing engagement with one contact plate of the sparkgap assembly, the other contact plate of said sparkgap assembly being positioned in a plane adjacent the other end of said self-supporting column of grading resistors, whereby the contact plates of said sparkgap assembly are biased toward one another by the biasing force of said resilient finger portion when the spring plate is mounted in operating position.

2. An invention as defined in claim 1 wherein said spring plate has a plurality of resilient finger portions and each of said finger portions has its free end positioned in biasing engagement with said one contact plate of the spark-gap assembly.

7. An invention as defined in claim 6 wherein said insulating means comprise a layer of self-adhering plastic material bonded to the outer ends of said tab portions.

9. An invention as defined in claim 6 wherein said insulating means comprises a plurality of slip-on plastic jackets that are mounted respectively over the ends of said tab portions.