US 3283196 A
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5 Sheets-Sheet 1 D. R. PARKER ETAL EXPULSION LIGHTNING ARRESTER Nov. 1, 1966 Filed Feb. 4, 1965 INVENTORS Delbert R. Parker Br Robert A. Kur BY 7 f} ATTORN WITNESSES Nov. 1, 1966 D. R. PARKER ET AL 3,283,196
EXPULSION LIGHTNING ARRESTER Filed Feb. 4, 1965 5 Sheets-Sheet 2 EXPULSION LIGHTNING ARRESTER Filed Feb. 4, 1965 5 Sheets-Sheet 5 LOAD-PSI O l I l I 1 IO 20 so 40 so so 70 so ANGLE 0F WIND FROM AXIS-DEGREES United States Patent 3,283,196 EXPULSIGN LIGHTNING ARRESTER Delbert R. llarker, Vienna, Ohio, and Robert A: Kurz,
Sharon, Pa, assiguors to Westinghouse Electric Corporation, Pittsburgh, Pa, a corporation of Pennsylvania Filed Feb. 4, 1965., Ser. No. 430,400 4 Claims. (Cl. 313231) The present invention relates to lightning arresters and, more particularly, to expulsion arresters having improved strength and increased surge current capacity.
In an expulsion arrester, arc extinguishment following a voltage surge is achieved by un-ionized gases evolved in the arc chamber and expelled with the arc gases through a vent. The arc path is thus deionized and the arc is extinguished to interrupt power follow current.
One of the primary determinants of surge current capacity in an expulsion arrester is the capacity of the arrester to withstand explosive-like pressure build-ups in the arc chamber. A proven approach to achieving pressure strength in the arrester is to rigidize the structure which encompasses the arc chamber. The strength properties of the chamber enclosure material or materials and the structural nature of the chamber enclosure thus is a direct determinant of the arrester pressure strength and surge current capacity. Additional information as to the general functioning of an expulsion arrester and as to specific known structure aimed at improved strength for such arrester can be obtained in a copending application entitled Lightning Arrester, Serial No. 237,671, filed by D. R. Parker on November 14, 1962, now Patent No. 3,209,194, issued September 28, 1965, and in US. Patent 3,040,203, entitled Expulsion Lightning Arrester, by G. Y. Hager, issued June 19, 1962, both of which are assigned to the present assignee.
The present invention encompasses structure organized to achieve improved strength and increased surge current capacity for an expulsion arrester. In accordance with its broad principles, an expulsion lightning arrester comprises a pair of spaced electrodes between which there is disposed an arc chamber surrounded by a tubular insulative member. Substantially continuous strands of glass are wrapped about the tubular member to a predetermined thickness and bonded together by means of or encased in a suitable resin to form a solid and strong casing for the arc chamber. The glass casing can be so disposed as to provide for retaining the electrodes against axial forces and accordingly characterize the arrester with improved axial strength as well as improved hoop strength and increased surge current capacity.
It is therefore an object of the invention to provide a novel expulsion arrester having increased surge current capacity.
Another object of the invention is to provide a novel expulsion arrester having increased hoop and axial strength.
An additional object of the invention is to provide a novel expulsion arrester in which reliable electrode placement is achieved with manufacturing economy.
A further object of the invention is to provide a novel expulsion arrester having improved strength while economy is achieved in reduced use of gas evolving fiber material about the arrester arc chamber.
These and other objects of the invention will become more apparent upon consideration of the following detailed description along with the attached drawings, in which:
FIGURE 1 shows an elevational View, partly in vertical section, of an expulsion lightning arrester constructed in accordance with the principles of the invention;
FIG. 2 shows a structural modification of the arrester shown in FIG. 1;
FIG. 3 shows a schematic view of the manner in which continuous glass strands are wound to form a part of the arrester of FIG. 1; and
FIG. 4 shows a graph representing the strength characteristics of a tube wound with continuous glass strands.
More specifically, there is shown in FIG. 1 an expulsion lightning arrester 10 comprising top and bottom end electrodes 12 and 14 between which there is provided an elongated insulative tubular member 16 enclosing an arc chamber 18. The tubular member 16 is formed from a material, such as vulcanized fiber, which emits a gas such as water vapor When subjected to arc heat so as to provide for deionization and are extinguis-hment in the chamber 18. The illustrated structure can be disposed in a conventional porcelain housing (not shown) or the like so as to adapt the arrester 10 for usual end uses.
In accordance with conventional practice, a filler member 20 having a helical groove 22 and preferably formed from the same material as the tube 16 is extended be tween the bottom electrode 14 and a stem 24 threadedly secured to the top electrode 12 and depending therefrom so as to provide increased surface area of the gas emitting material for are quenching purposes. A predetermined small spacing is provided between the outmost cylindrical periphery of the filler member 20 and the innermost cylindrical surface of the tube 16.
The tube 16 is seated on the bottom electrode 14 as indicated by the reference character 26, and the top electrode 12 is preferably threadedly secured to the tube 16 as indicated by the reference character 28. When a voltage surge causes an arc discharge between the electrode stem 24 and the bottom electrode 14, un-ionized gas is emitted from the filler member surfaces and the inner surface of the tube 16 as a result of the high are generated heat along such surfaces. The are gases and the emitted gases are vented from the chamber 18 through openings 30 in the bottom electrode 14 and on deionization within the chamber 18 the arc is extinguished.
To provide improved strength for the arrester 10 against arc chamber pressures associated with the arc generation and extinguishment process, there is provided an outer casing 32 comprising substantially continuous glass strands. A tubular metallic or steel casing 34 can be disposed directly over the fiber tube 16 and crimped thereagainst as indicated by the reference character 36 and against the bottom electrode 14 as indicated by the reference character 38. The steel casing 34 thus rigidly supports the bottom electrode 14 in the assembly, generally strengthens the arrester 10 and further provides an electrostatic shield for reducing sparkover voltage as explained in the previously noted Hager patent. The fact that the glass casing 32 is electrically insulative prevents external flashover from the top electrode 12 to the steel casing 34. The word glass in glass casing is used as a convenient descriptor and is not used in an exclusive sense as to the material make-up of the outer casing 32.
In the alternative, an electrostatic shield can be pro vided by a foil 40 (FIG. 2) conductively connected to electrode 14a and disposed at an interlayer location in glass casing 320 of arrester 1042 during the winding thereof. A substantially shortened metallic or steel casing 42 is disposed about the exterior of the glass casing 32a for mechanically securing the bottom electrode 14a in the assembly without current creepage from top electrode Securance of the shortened steel casing 42 to the glass casing 32a can be obtained by crimping the steel casing 42 as indicated by the reference character 44 into suitable grooves formed in the casing 32a.
Improved strength is achieved for the arrester or 10a in containment of internally generated pressures for reasons including the strength properties of the glass strands employed to form the glass casing 32 or 32a. In both arresters 10 and 10a, manufacturing economy is achieved since the tube 16 or 16a can have relatively less strength and thus can have a thinner tubular wall of expensive fiber material.
Since the glass strands are continuous (or substantially continuous, i.e. a small percentage of the strands may for some reason have discontinuities), excellent tensile strength results within the casing 32 or 32a and in turn leads to improved hoop and axial strength for the arrester 10 or 10a. In addition, axial assembly strength is conveniently and effectively achieved by inward taper of the top electrode 12 as indicated by the reference character 46 (FIG. 1) and associated inward taper of the glass casing 32 directly over the tapered surface of the electrode 12 Without a requirement for intermediate retaining rings or the like. Outward longitudinal displacement of the top electrode 12 is thus effectively prevented and it is rigidly supported in place. In the alternative, as shown in the arrester 10a of FIG. 2, threading 47 can be employed on the electrode 12a to achieve effective placement forces by the casing 32a on the electrode 1211.
As schematically illustrated in FIG. 3, the winding operation for the glass casing 32 can use a plurality of spools 49 from each of which a plurality or bunch of continuous glass strands 48 is drawn through a resin bath 50. A strand bunch of this type is commonly called roving. Preferably, the glass strands 48 are sized with a suitable material to be compatible for adherence with a preselected resin and such resin preferably is a suitable catalyzed epoxy resin.
To minimize surplus resin accumulation, the resin viscosity in the bath 50 can be maintained at about 500 centipoises or within a predetermined range thereof but not in excess of some upper limit such as 1000 cps. To this end, the bath temperature can be maintained between 40 C. and 45 C.
The glass strands 48 are drawn through the bath 50, suitably brushed by a wiper 52 or the like to remove excess resin and directed to a' winding head 54. The strands 48 are led from the winding head 54 to an arrester subassembly or, as shown a top-to-top pair of arrester subassemblies (including in this case the steel casing 34 of FIG. 1) mounted in a winding machine 56. The winding operation is then begun.
The angle a formed by the strands 48 with the longitudinal axis of the arrester 10 is termed the winding angle and is a determinant of strength properties in the finished product unit. As shown in FIG. 4, the load strength of a glass wound tube (and hence the glass wound arrester 10) varies with the winding angle a. More specifically, the hoop, compression and tensile strength of a glass wound tube vary according to differing curves 58, 60 and 62. Compression strength is nearly constant with winding angle, whereas tensile strength increases sharply as winding angle becomes less than 40 (i.e., the winding helix is widely spread and continuous strands become more aligned with the tube longitudinal axis) whereas hoop strength increases to very high values as the winding angle approaches 90 (i.e., the winding helix is very tight and the continuous strands become nearly circumferentially disposed about the tube). Preferably, the winding angle on is about 45 to obtain an optimum or nearly optimum balance in hoop and tensile strength for the arrester 10 or 10a. However, other tensile and hoop strength combinations suitable for arrester use can be obtained with other winding angles. Further, different winding angles can be used at different points in the winding operation on the same sub-assembly or topto-top pair of sub-assemblies. For example, a winding angle of could be used along a center portion of the top-t-o-top pair, so as to facilitate post-winding separation, while a winding angle of say 45 is used on the balance of the top-to-top pair.
As the glass strands 48 are layered on the arrester subassembly during winding (i.e. about the tube 16 and steel casing 34), some additional excess resin may be wiped off by hand or by other means. When the desired thickness is wound for the glass casing 32 the winding is terminated and the glass strands 48 are cut. The arrester 10 may then be placed in a gelling oven, for example, at C. for 15 to 25 minutes. Subsequently, the arrester 10 is placed in a cure oven for final cure, for example, for about 3 hours at 130 C.j:5 C.
The glass strands 48 are then encased in the resin in a solid mass providing high hoop, compression and tensile strength properties for the arrester 10. The same is true for the arrester 1011 when wound in a manner similar to that just described for the arrester 10. It is not necessary that the glass casing 32 or 32a be bonded to the fiber tube 16 or fiber tube 16a, although in practice it may be if desired, particularly since the glass casing 32 or 32a is disposed with mechanical tightness about the fiber tube 16 or 16a. To promote mechanical grip, threads 64 or 64a can be used on the other surface of the tube 16 or 16a. The threads 64 or 64a can also increase the length of a possible creepage path from the top electrode 12 or 12a to the steel casing 34 or the foil 40.
An alternate method of winding the glass casing 32 or 32a is to use a suitably formed mandrel and follow the steps previously described. When cured, the casing 32 of 32:: can then be fitted over the tube 16 or 16a. However, manufacturing expense and relatively poor casing fit are the major disadvantages of this alternate method as compared to the process in which the tube 16 or 16a is used as its own mandrel.
The foregoing description has been set forth only to illustrate the principles of the invention. Accordingly, it is desired that the invention be not limited by the embodiments described, but, rather, that it be accorded an interpretation consistent with the scope and spirit of its broad principles.
What is claimed is:
1. An expulsion lightning arrester comprising a tubular insulative member defining an arc chamber and effective to emit un-ionized gas when subjected to are heat, a pair of electrodes disposed adjacent opposite ends of said tubular member, one of said electrodes providing a vent for said chamber, an outer casing comprising continuous glass strands encased in a resin about said tubular member, and means for retaining said electrodes against axially directed pressure, said retaining means including at least one end portion of said outer casing tapered radially inwardly to provide longitudinal support for at least one of said electrodes.
2. An expulsion lightning arrester comprising a tubular insulative member defining an arc chamber and effective to emit un-ionized gas when subjected to arc heat, a pair of electrodes disposed adjacent opposite ends of said tubular member, one of said electrodes providing a vent for said chamber, an outer casing comprising continuous glass strands encased in a resin about said tubular member, an end portion of said outer casing tapered radially inwardly to provide longitudinal support for the other electrode, a tubular metallic member secured to said insulative tubular member and engaging said one electrode to provide placement support therefor, and electrostatic shield means disposed outwardly of said insulative tubular member and extending over a substantial portion of the inter-electrode space.
3. An expulsion lightning arrester as set forth in claim 2 wherein said continuous glass strands are disposed at an g e With the longitudinal axis of said tubular member.
4. An expulsion lightning arrester comprising a tubular insulative member defining an arc chamber and efiective to emit un-ionized gas when subjected to are heat, a pair of electrodes disposed adjacent opposite ends of said tubular member, one of said electrodes providing a vent for said chamber, an outer casing comprising continuous glass strands encased in a resin about said tubular member, said continuous glass strands disposed at an angle with the longitudinal axis of said tubular member, and means for retaining said electrodes against axially directed pressure, said retaining means including at least one end portion of said outer casing tapered radially inwardly to provide longitudinal support for at least one of said electrodes.
References Cited by the Examiner UNITED STATES PATENTS 10 JAMES W. LAWRENCE, Primary Examiner.
DAVID GALVIN, v. LAFRANCHI,
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