US3798505A

US3798505A - Low voltage surge arrester

Info

Publication number: US3798505A
Application number: US00292079A
Authority: US
Inventors: R Reckard; R Morse
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1972-09-25
Filing date: 1972-09-25
Publication date: 1974-03-19
Anticipated expiration: 1991-03-19

Abstract

A secondary surge voltage arrester having a high impact resistant molded housing that is provided with supporting struts for mounting a sparkgap assembly in a desired, predetermined spaced relationship with respect to the interior walls of the housing thereby to minimize the risk of flashover of the sparkgap assembly. The arrester is further characterized by incorporatng a special spring that is effective to maintain a precise sparkgap electrode spacing and at the same time to limit lateral movement of the spark-gap assembly within the housing.

Description

[ Mar. 19, 1974 UnitedStates Patent [191 Reckard et al. I 9

3,258,635 6/1966 Carothers.............................

[ LOW VOLTAGE SURGE ARRESTER.

[75] Inventors: Ronald M. Reckard; Raymond I.

Assistant Examiner-Harvey Fendelman Attorney, Agent, or Firm-Myles P. Vale; Volker R. Ulbrich; Francis X. Doyle [73] Assignee:

[22] Filed:

Appl. No.: 292,079

[57] ABSTRACT A secondary surge voltage arrester having a high impact resistant molded housing that is provided with supporting struts for mounting a sparkgap assembly in a desired, predetermined spaced relationship with re- 92 N 0 WEB 1 3 2 0 @6H /4. 72 1 3 8 M4 m UBW 3y m L h l C C S L U .m 2 1 5 5 spect to the interior walls of the housing thereby to minimize the risk of flashover of the sparkgap assem- 4 3 $7 3 l 3 e. 00 6D 1 9 66 l. 2 m3 4 n2 ml 3 e S f 0 d l e .I F 8 5 r1 bly. The arrester is further characterized by incorporatng a special spring that is effective to maintain a [56] References Cited UNITED STATES PATENTS precise sparkgap electrode spacing and at the same W m u H" mm ne 3 i BGOM 8337 5675 9999 1111 0722 6 60 762 8653 59 oo 2337.

time to limit lateral movement of the spark-gap assembly within the housing.

12 Claims, 6 Drawing Figures 666 333 555 lll 333 1 LOW VOLTAGE SURGE ARRESTER BACKGROUND OF THE INVENTION The invention relates to surge voltage arresters of a type commonly referred to as lightning arresters. More particularly, it relates to a novel housing and support means for a surge voltage arrester of a type often utilized to protect home appliances from damage due to lightning strikes or other induced voltage surges on secondary electric power distribution lines.

In the field of electrical power transmission and distribution, the use of sparkgaps, and combinations of sparkgaps with various types of non-linear resistance valves to form lightning arresters, is well known. In general, when a sparkgap is combined with a non-linear resistance valve to form such an arrester, the spacing of the sparkgap is used to determine the arrester sparkover protective characteristic while the non-linear resistance valve is used to reseal the arrester by limiting power-follow current from the protected power line after a surge voltage has been discharged to ground through the arrester. Numerous engineering and design refinements have been made in the structure of sparkgap electrode arrangements, as well as in the types of materials used to make non-linear resistance valves for these arresters. However, most such changes have occurred in the area of high voltage arresters, i.e. those used to protect electric distribution or transmission lines rated to carry power at several thousand volts. On

the other hand, the. designs for secondary surge voltage arresters has tended to remain quite simplified over the years. Specifically, for surge voltage arresters that are designed to protect equipments from voltage surges in the range of 150 to 600 volts, it has become common practice to use a simple sparkgap electrically connected in series with a body of pellets or granules of non-linear resistance valve material, which are confined by the inner walls of the arrester housing.

This conventional prior art structure of secondary arresters has been generally adequate in the past. However, as the use of electric power continues to grow, and particularly as longer secondary voltage power distribution lines are used to bring power to remotely located rural areas, the need for more sophisticated secondary arresters increases. Of course, the greater the length of secondary voltage distribution lines, the higher the associated risk is of either a direct lightning strike or an induced over-voltage surge on the line. Coupled with this heightened risk, the steadily larger number of relatively expensive electrical appliances that are being utilized in homes and businesses serves to multiply the risk of damage due to overvoltage surges on these lines. Thus, there are two major areas in which it is desirable to improve present day secondary voltage arresters.

The first of these areas of potential improvement is in the protective characteristics of the arresters. In this regard, it is desirable to assure an accurately controlled sparkover level of such arresters so that they can be used to provide a precisely known margin of safety above the basic insulation levels of the home applidue to moisture leakage around conventional arrester also be caused by formation of a low resistance tracking path along the interior surface of the arrester housing, adjacent which the arrester components are closely mounted. As mentioned above, in typical prior art secondary arresters, voltage. limiting valve pellets are simply stacked directly against the interior wall of the insulating housing of the arrester. This arrangement may result in some are tracking of these walls.

The second basic area of desirable design improvements is related to the prime cost of materials and labor needed to construct secondary arresters. The relatively low sales volume of such arresters, coupled with the relatively high expenses associated with the sale of one or two arresters to a given customer, serve to amplify the importance of prime cost reductions. At the same time, due to the nature of the application of secondary arresters, it is desirable that they be ruggedly constructed of high impact resistance materials that will not be easily damaged during the normal transportation and relatively rough handling to which the arresters are subjected prior to their installation. Both as a matter of aesthetic appearance and as a factor of cost reduction, it is desirable to design such arresters as compactly as possible.

SUMMARY OF THE INVENTlON In the preferred embodiment of the invention disclosed herein, a secondary voltage arrester is formed of a high-impact-resistant plastic material that is molded with integral supporting struts on its interior surface. The supporting struts are arranged to define supporting planes that are effective to hold a sparkgap assembly in spaced-apart relationship with respect to the interior walls of the arrester. The sparkgap assembly includes a pair of precision sparkgaps that are electrically connected in series with blocks of non-linear resistance valve material, to afford two discharge paths between a pair of line terminals and a ground terminal. A special spring is used to maintain accurate sparkgap spacing and to also hold the sparkgap assembly in a spacedapart relationship with respect to the interior walls of the arrester housing. A plurality of mechanically deformable supporting rods are used to cage the sparkgap assembly active components and hold them in a desired operation relationship. Finally, the arrester housing is hermetically sealed with a thermal-setting resin that encapsulates a plurality of line and ground conductors that are connected to the terminals of the sparkgap assembly within the arrester, and the final seal is accomplished by ultrasonically welding a cover to the opposite end of the housing.

A primary object of the invention is to provide a secondary surge voltage arrester that overcomes the shortcomings of prior art arresters that are discussed above.

Another object of the invention is to provide a secondary surge voltage arrester having a molded, high impact resistance insulating housing that is provided with integral support means for positioning a sparkgap assembly away from the interior walls of the housing.

A further object of the invention is to provide a surge voltage arrester with a special compression spring that is operable to maintain accurate sparkgap spacing of a sparkgap assembly while at the same time serving to hold the assembly in a predetermined relationship with respect to the arrester housing.

Still another object of the invention is to provide a surge voltage arrester having a sparkgap assembly that is characterized by incorporating a plurality of insulated support rods that form a cage around the active components of the assembly to hold these components in a predetermined operating relationship.

Still another object of the invention is to provide an hermetically sealed surge voltage arrester that is very compact in size and that minimizes the risk of moisture leakage into the arrester housing.

Additional objects and advantages of the invention will become apparent to those skilled in the art from the description of it that is presented herein, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 2 is an end view, taken along the plane 22 of FIG. 1, showing the interior of the arrester illustrated in FIG. 1, including the operating relationship between an arrester support means and a sparkgap assembly and compression spring that are important features of the present invention.

FIG. 3 is a side elevation view of the sparkgap assembly illustrated in FIGS. 1 and 2.

FIG. 4 is a perspective view, partly in cross section, of the housing of the arrester illustrated in FIGS. 1 and 2.

FIG. 5 is a perspective view of the special compression spring illustrated in FIG. 2.

FIG. 6 is a side elevation view of the compression spring illustrated in FIGS. 2 and 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1 and 2 of the drawing, it will be seen that there is shown a surge voltage arrester 1 comprising a molded insulating housing 2 that has an interior wall means 3 generally in the form ofa cylindrically walled cup. A high impact resistant, thermalsetting plastic material is used to form the housing 2. In this embodiment of the invention the well known, commercially available plastic Lexan, that is sold by General Electric Company, through its manufacturing plants in Pittsfield, Mass, is used to form the molded housing 2. Other equivalent materials may be used in modifications of the invention. As shown in FIGS. 1 and 2, the arrester housing 2 includes the cup-shaped portion 2a and a disc-shaped cover 2b. The cover 2b is hermetically sealed to the cup-shaped portion 2a by an ultrasonic welding operation. Accordingly, the juncture between these components is absolutely watertight and the only other possible access avenue for moisture to the interior of housing 2 is through a passageway 4 in the base of the cup-shaped portion 2a.

Mounted within the arrester housing 2 is a sparkgap assembly 5 and a special compression spring 6. Integrally molded with the interior wall means 3 of the housing 2 is a first set of supporting struts 7 and 7 located on one portion (designated by the bracket 8) of the wall means 3, to define a first supporting plane (designed by the line 7a). A second set of supporting

struts

9a, 9b, 9c and 9d is integrally molded on another portion (designated by the bracket 10) of the wall means 3, to define a second supporting plane (designated by the line numbered 9e). It should be understood that the first plane 7a and the second plane 9e are disposed in substantially parallel relationship to one another for purposes of the invention which will become apparent hereinafter. The sparkgap assembly 5 is mounted between the first support plane 711 and the second support plane 9e, in combination with the compression spring 6, which is mounted between the support plane 92 and one terminal of the sparkgap assembly 5.

Before describing the novel features of the sparkgap assembly 5, it should be understood that various types of precision sparkgap assemblies will be suitable for practicing the present invention. For example, the precision sparkgap electrodes disclosed in US. Pat. No. 3,435,290Lyman, which issued Mar. 15, 1969 and is assigned to the assignee of the present invention, are suitable for use in practicing this invention. More specifically, the preferred embodiment of the sparkgap assembly 5, as shown in detail in FIGS. 2 and 3, comprises a first sparkgap (not shown) defined between a first electrode 11 and a second, convoluted electrode 12 which is similar in construction to the sparkgap arrangement of the above-identified Lyman patent. A second sparkgap (not shown) is defined by the first electrode 11 and a third electrode 13. In order to limit power follow current across the first and second sparkgaps of the assembly 5, following the discharge of an overvoltage surge therethrough, a pair of disc-shaped, non-linear resistance valve blocks 14 and 15 are mounted respectively in electrically conducting relationship with the second electrode 12 and the third electrode 13 of the sparkgaps, and between a pair of flat metal line terminals 16 and 17, which are in electrically conducting relationship with the outer surfaces of the

valves

14 and 15, as shown in FIG. 3. As explained in the above-mentioned Lyman patent, the precision spacing of the first and second sparkgaps is set by a pair of pressed mica discs 18 and 1.9 that are mounted between the first electrode, or ground terminal 11 of sparkgap assembly 5 and the second and

third electrodes

12 and 13. Finally, four substantially parallel mounted supporting rods, two of which are designated in FIG. 3 by the identifying numbers 20 and 21 are positioned through apertures 16' and 17' in both of the line terminals 16 and 17 at spaced-apart points around the periphery of the

valve discs

14 and 15 thereby to form a cage around these valves and the sparkgap electrodes 11-13. It will be understood that two additional supporting rods are positioned on the opposite side of sparkgap assembly 5. One of these supporting rods is shown as the rod 31 in FIG. 2. Pursuant to the invention, the cage formed by the four support rods (20,21, etc.) is effective to prevent the electrodes and valves from moving from between the line terminals 16 and 17 even when the arrester 1 is subjected to severe mechanical shocks.

A novel feature of the invention resides in the construction and installation of the

support rods

20, 21 and 31. In the preferred embodiment of the invention, these rods are formed of a suitable plastic resin, such as the well-known, commercially available Nylon that is sold by Dupont Corporation through its Wilmington, Del. factory. As best seen in FIG. 3 both ends of all of the support rods 20, 21, (etc.) are crimped adjacent their respective outer ends to prevent these ends from being moved through the apertures 16' and 17 in the line terminals 16 and 17. Preferably, this crimping operation is-performed when the rods are at room temperature, so it is a purely mechanical operation; however, the ends of the rods may be thermally deformed, if desired. The enlarged portion formed by such crimping is designated in FIG. 3 by the numerals 21a and 21b on the rod 21 and by the numerals a and 20b on the rod 20. The other support rods, such as rod 31 are similarly crimped, as shown at 310 and 31b, in FIG. 1. In addition to serving as a clamping means for holding the line terminals 16 and 17 against the

valve discs

14 and 15, the respective outer ends of the support rods 20, 21, etc. perform an additional function in the present invention. Due to the fact that both ends, e.g. ends 20a20b, 21a- 21b and 31a-31b, etc. extend beyond the line terminals 16 and 17, they serve as limit stops to restrict the lateral movement of the sparkgap assembly 5 with respect to the first and second sets of support struts (7-7 and 9a-d). The ends 20a, 21a and 31a of

support rods

20, 21 and 31, respectively, extend through the first support plane 7a past the outer sides of the support struts 7 and 7, as best seen in FIG. 2. On the other hand, the lower ends 20b, 21b and 31b of the

support rods

20, 21 and 31 are positioned adjacent the outside edges of the compression spring 6 and are limited in lateral movement by engagement with the spring.

In order to better understand all of the functions of the special compression spring 6, reference will now be made to FIGS. 5 and 6 of the drawing. Preferably, spring 6 is fabricated from bronze plate stock. As shown, the compression spring 6 in this embodiment of the invention comprises a pair of generally

flat side members

6a and 6b, which are positioned in a common plane. A generally flat central member 60 is positioned between the

side members

6a and 6b in another plane. The central member 6c is joined adjacent its ends to the

side members

6a and 6b adjacent their ends by a pair of resilient connecting arms 6d and 6e, respectively. In order to firmly position the spring 6 against lateral movement when'it is mounted in its assembled position, as shown in FIG. 2, each of the

side members

6a and 6b has a pair of integral tabs 60' and 6a" and 6b and 6b projecting out of the common plane in which the

side members

6a and 6b lie. As clearly shown in FIG. 2, the projecting

tabs

6a and 6b extend past a portion of the second set of struts 9a-9d, toward the wall means 3 of the arrester housing 2. Thus, the

tabs

6a and 6b, as well as tabs 6a" and 6b", are operable to engage these predetermined areas of the second set of struts 9a-9b, thereby to prevent the

side members

6a and 6b of spring 6 from being moved laterally away from the second set of struts 9a and 9b.

Accordingly, because of the constraining operation of

tabs

6a, 6a", 6b and 6b with respect to the second set of support struts 90-4, and the limit stop operation of the projecting ends 20a, 21a and 31a of

support rods

20, 21 and 31 on sparkgap assembly 5, as described above, the sparkgap assembly 5 is held in spaced-apart relationship from the interior wall means 3 of housing 2. This arrangement protects the sparkgap assembly 5 from risk of flashover due to any contamination or arc tracking that might form on the interior wall means 3 of the housing 2. A further important function of the compression spring 6 is to bias the line terminal 17 toward line terminal 16, which is arrested in its movement by the first set of support struts 7-7'. This biasing force maintains the length of the first and second sparkgaps of sparkgap assembly 5 in their desired predetermined relationship.

In order to more fully explain the novel features of the first and second sets of support struts 7--7' and 9a-d, reference will now be made to FIG. 4 of the drawing. The housing 2 is shown in FIG. 4 as being broken away to clearly show the first set of support struts, which comprises the pair of struts 7-7. In addition, the second set of support struts, comprising the four

struts

9a, 9b, 9c and 9d, are clearly visible in this figure. It will be noted that each of the struts 9a-d, in the portions thereof, defining the second supporting plane 9e is substantially as long as the

respective side members

6a and 6b of the compression spring 6 (shown in FIG. 5 Thus, these support struts serve to firmly engage the

side members

6a and 6b over a major portion of their length. It will be apparent that other support strut arrangements may be used in alternative embodiments of the invention; however, it is important to provide at least a pair of spaced-apart struts in both the firt and second sets of supporting struts, in order to assure that the biasing force applied by compression spring 6 is uniformly distributed around the peripheries of the first and second sparkgaps of sparkgap assembly 5. Otherwise, the individual sparking points or teeth of the sparkgap assembly 5 (as explained in the abovementioned Lyman patent) may be burned back unevenly to thereby distort the sparkgap spacing.

Now, in order to complete the description of the novel surge voltage arrester of the invention, reference will again be made to FIGS. 1 and 3 to describe the preferred means by which the terminals of sparkgap assembly 5 are connected to suitable conductors. As shown in FIG. 3, line terminals 16 and 17 of sparkgap assembly 5 each contain deformable tongue portions 16a and 17a, respectively. These tongue portions are crimped onto exposed wires 22 and 23', respectively, of a pair of separate suitably

insulated conductors

22 and 23. In like manner, the first electrode or ground terminal 11 of sparkgap assembly 5 contains a deformable tongue portion 11a that is crimped onto an exposed wire 24, part of another insulated conductor 24. Thus, the surge voltage arrester 1 may be connected to protect either a one or two-wire power distribution system. When a two-wire system is to be protected, the

line conductors

22 and 23 are connected to the respective lines of the power system and the conductor 24 is securely connected to a solid electrical ground. On the other hand, if a single power line is to be protected, the two sparkgaps of sparkgap assembly 5 can be connected in parallel across the line by connecting

conductors

22 and 23 to the line and by connecting ground terminal 11, via conductor 24, to a suitable electrical ground terminal.

In order to provide a water-tight seal around the insulation of conductors 22-24, as well as around the wires 22'24, they are inserted through the passageway 4 in the bottom of the cup-shaped portion 2a of insulated housing 2, as shown in FIG. 1. A body of a suitable sealing compound 25 is positioned in the passageway 4 around the conductors 22-24 and, importantly to the present invention, around the inner ends of wires 2224, to thereby hermetically seal the sparkgapassembly-receiving chamber of the housing 2. The reason it is important to totally encapsulate the inner uninsulated ends of wires 2224' is to prevent moisture from being drawn by capillary action along the wires, past the sealant 25. It will be noted (in FIG. 1) that the inner surface 25a of body of compound 25 completely encapsulates each of the uninsulated portions of wires 22'24'. The body of sealing material 25 may be a conventional epoxy resin or other suitable water-resistant sealing material that has a coefficient of thermal expansion substantially identical to the coefficient of thermal expansion of the Lexan insulating housing 2, so that the sealant 25 is not cracked or broken loose from the inner walls of the passageway 4 when the arrester l is placed in service.

From the foregoing description of the invention, it will be apparent that various modifications and improvements may be made in it without departing from the true scope and spirit of the invention. Accordingly, it is our intention to define the scope of the invention in the following attached claims.

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

1. A surge voltage arrester comprising a molded insulating housing having interior wall means defining a chamber for receiving a sparkgap assembly, a first set of supporting struts mounted on one portion of said wall means to define a first supporting plane, a second set of supporting struts mounted on another portion of said wall means to define a second supporting plane, said first and second supporting planes being disposed in substantially parallel relationship, a sparkgap assembly mounted between said first and second planes, said sparkgap assembly comprising; first and second spaced-apart electrodes arranged to form a sparkgap therebetween, an insulating spacer disposed between said electrodes to hold them apart, a non-linear resistance valve, one side of said valve being positioned in electrically conducting relationship with said second electrode, and a generally flat metal terminal positioned in electrically conducting relationship with a second side of said valve, thereby to form a series circuit from said terminal, through said valve, across said sparkgap to the first electrode thereof; in combination with a compression spring mounted under compression between said first electrode and said second set of struts, said spring being effective to bias said first sparkgap electrode toward said terminal thereby to hold said first and second electrodes in spaced-apart relationship against opposite sides of said spacer, said terminal being positioned in fixed relationship with respect to said first supporting plane, said spring comprising a pair of generally flat side members positioned in a common plane, a generally flat central member positioned between said side members in another plane, and a pair of resilient connecting arms respectively joining said side members to said central member, each of said side members having a pair of integral tabs projecting out of said common plane, past a portion of said second set of struts, toward the wall means, said tabs being operable to engage predetermined areas of said second set of struts thereby to prevent the side members of said spring from being moved away from said predetermined areas.

2. An invention as defined in claim 1 wherein said connecting arms are, respectively, joined to opposite ends of said central member and to oppositely-disposed ends of said side members.

3. An invention as defined in claim 2 wherein said first and second sets of supporting struts each comprise at least a pair of spaced-apart struts, each of said struts in the portions thereof defining said supporting planes, being substantially as long as the side members of said spring.

4. An invention as defined in claim 2 wherein said spring is formed of a single piece of bronze plate stock.

5. A surge voltage arrester comprising a molded insulating housing having interior wall means defining a chamber for receiving a sparkgap assembly, a first set of supporting struts integrally molded on one portion of said wall means to define a first supporting plane, a second set of supporting struts integrally molded on another portion of said wall means to define a second supporting plane, said first and second supporting planes being disposed in substantially parallel relationship, a sparkgap assembly mounted between said first and second planes, said sparkgap assembly comprising; a plurality of electrodes arranged to define a first and a second sparkgap, a pair of non-linear resistance valves, a pair of line terminals, a ground terminal, and a plurality of support rods, said support rods being operable to maintain the line terminals in spaced apart relationship with the ground terminal disposed therebetween and with one sparkgap and one valve positioned in series circuit relationship, respectively, between each line terminal and the ground terminal; in combination with a compression spring mounted between one of said line terminals and one of said supporting planes thereby to force the other line terminal against the set of struts defining the other supporting plane.

6. An invention as defined in claim 5 wherein said support rods are formed of a deformable plastic resin, each of said support rods being positioned through apertures in both of the line terminals thereby to form a cage around said sparkgap electrodes and valves, said cage being effective to prevent the electrodes and valves from moving from between said line terminals and the ground terminal.

7. An invention as defined in claim 6 wherein at least one of each of said rods extends beyond one of said line terminals, on opposite sides of the set of supporting struts adjacent said terminal, thereby to form limit stops that are operable to engage the sides of said supporting struts to prevent the sparkgap assembly from being moved laterally away from said struts.

8. An invention as defined in claim 7 wherein said compression spring comprises a pair of generally flat side members positioned in a common plane, a generally flat central member positioned in another plane, and a pair of resilient connecting arms joining said side members to the central member, each of said side members having a pair of integral tabs projecting out of said common plane, past a portion of said second set of struts, toward the wall means, said tabs being operable to engage predetermined areas of said second set of struts thereby to prevent said side members from being moved away from said predetermined areas.

9. An invention as defined in claim 7 wherein each of said rods is crimped adjacent the respective ends thereof to prevent said ends from being moved through the apertures in said line terminals.

10. An invention as defined in claim 9 wherein said plurality of supporting rods comprises four substantially parallel-mounted rods arranged to define the re- 12. An invention as defined in claim 11 wherein each of said conductors includes an insulated wire at its inner end disposed in said passageway, and wherein said body of sealing compound completely encapsulates eachof said uninsulated wires thereby to prevent moisture from being drawn by capillary action along said wires past the encapsulating compound into the sparkgap-assembly-receiving chamber of said arrester.

Claims

10. An invention as defined in claim 9 wherein said plurality of supporting rods comprises four substantially parallel-mounted rods arranged to define the respective corners of a square within which said sparkgap assembly is caged.

11. An invention as defined in claim 5 including; means defining a passageway through the wall means of said housing, three insulated conductors extending into said passageway, said conductors being electrically connected, respectively, to said line terminals and the ground terminal, and a body of sealing compound positioned in said passageway around said conductors to hermetically seal said chamber.

12. An invention as defined in claim 11 wherein each of said conductors includes an insulated wire at its inner end disposed in said passageway, and wherein said body of sealing compound completely encapsulates each of said uninsulated wires thereby to prevent moisture from being drawn by capillary action along said wires past the encapsulating compound into the sparkgap-assembly-receiving chamber of said arrester.