US3214634A

US3214634A - Shatterproof valve type lightning arrester

Info

Publication number: US3214634A
Application number: US261134A
Authority: US
Inventors: Norman K Osmundsen; John P Cage
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1963-02-26
Filing date: 1963-02-26
Publication date: 1965-10-26
Anticipated expiration: 1982-10-26
Also published as: DE1463765A1; CH424949A; ES296193A1

Description

1965 N. K. OSMUNDSEN ETAL 3,214,634

SHATTERPROOF VALVE TYPE LIGHTNING ARRESTER Filed Feb. 26, 1963 Fig.2.

INVENTORS Norman K. Osmundsen WITNESSES 8\ John F? Cage BY 76 ATTORNEY United States Patent 3,214,634 SHATT-ERPROOF VALVE TYPELIGHTNING ARRESTER NormanK. Osmundsen, Bloomington, and JohmP. Cage,

Richland Township, Monroe County, Ind., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa}, a

corporation of Pennsylvania Filed-Feb. 26, 1963, Ser. No. 261,134- 3' Claiins; (Cli 315-36) tend to flow through the arresteruntilits:normal:voltage.

insulative character is recovered. Under: normal: conditions; the follow current. is thus interrupted without' However, occasionally.-

damage to the arrester: device. the. lightning or follow energy flowing into the arrester causes block or gap damage'such that:followscurrentcom tinues to flow through the low impedancezgapcr' gaps with nominally little impedance limitationfrom5the;block. it-' self. In this fault condition, heat from and? arcingof the follow current can have explosive. or shattering effects on the arrester device. The extent to which these. effects occur is dependent insome'measure upon1the. energy." capacity of the system in which'thearrestcn is connected and further upon the impedance limitations within' the" system itself against. ground. current-'flowthrough' the arrester under faulted arrester condition.

More particularly, shattering or explosion" of" the arrester device apparently, is caused by the build' up of gas pressure'due to the'faulty. block'or' faultysgap' structure or by arcing along or against the inside of the arrester housing or by a. combination. ofthese factors. Even if a drop-out assembly'or'mechanism is used in the arrester to provide follow current interruption after a block fault 0CCUIS,.thel possibility of a shatter: or explosion still exists. Thus, damage can occur in someinstances before drop-out occurs and in other instanceseven after drop-out occurs if drop-out, does? not release pressure:- or after currentinterruption ifsufficient pressure-is in the interim built up in the arrester andrthe'arrester is later:

jarredor impacted by a servicemanror-by other means In accordance with the broad principles of:the'presentl invention, a valve type lightning arrester having a'n outer' housing. of insulativev material such: as: porcelain comprises an electrically insulative and; heat resistant in-- organic flexible or molded liner memberdisposed between internally, positioned series gap andblock assembliesand: the housing. The liner can be, disposedbetween either." the gap assembly or the block assembly andthe housing. or between the entire series combination of assemblies and the. housing. In this'manner, the gap andblock assemblies or either of these can'be spaced fromthe housing'by the liner, and the arrester is substantiallyxpre vented from shattering, or exploding when a fault de-. velops in the arrester block assembly; plosion prevention is due tofactorsincluding gas-abs0rp tionand arc inhibiting action \bythe liner.

Accordingly, it is an object of the invention, to provide a novel and'efficient valve type arrester whichis' protected from shatter or explosion.following-thedevelopr ment of a fault in the arrester.

Another object of' the invention is to provide a novel and efficient valve type arrester in whichv lining struc-- ture provides shatter prevention actIQn-andfurther serves to space the current discharge andarresting elements from the inner surface of the arrester-housing.

A further object of the invention is to provide a novel Evidently, ex-- 3,214,634 Patented Oct. 26,1965

and efficient valve type arrester wherein an. electrically insulative and heat resistant .inorganicv flexible. or molded liner member is disposed between the inner: surface of the arrester housing and the current discharge andar-- resting element or elements was. to. provide shatter: and explosion protection.

An additionalobject of. the inventionis; to provide a novel and-efficient valve type lightningj arrester wherein. a-liner' member is formed fromasbestos paper. and lo. cated for efficient prevention of shatterv and: explosion.

These and other objects of the. inventionwillbeco'rne more apparent upon consideration-of the following. dew

.tailed description alongwith the attacheddrawing,..-in=

which:

FIGURE 1 is an: elevational view ofa valve-type lightning arrester constructed inaccordance with the principles of the inventionand having a portion thereof removed to provide a view of the arrester interior; and

FIG: 2 shows a perspective view-'of-a-liner: member partly broken away and used in the-arrester: of FIG. 11.

More particularly, there is-shown-in F-IG. l-a lightning: arrester 10 of a type to be described here to the. extents necessary in developing; an understandingof the: invention. For amore particular descriptionof structural and. functional details which are not fully coveredin'thi-e writing, reference is. made to a copending;application entitled Circuit Interrupter, Serial No.- 181, 687,. filed. by. C. H. Carothers-on March 22, 1962. now PatentNo. 3,153,128, issued October 13, 1964 andassigned-to-the: present assignee, and to another copending application entitled Terminal Connector, Serial: No. 181,686,. filed by; R. J.- Lawrence and-C.-H. Carothers.onsMarchy2'2, 1-962- and also assigned to the present assigned Generally, the lightning arrester 10. is classified as a. valve-type arrester and itcomprisesan elongated tubuw lar housingor casing 12 in which'. there-are disposed. as spark gap assembly 14 and. a non-linearresi-stance block assembly 16; In order to-provide a -dischargeepath-fon lightning current and to provide for arresting power follow current, the. assemblies 14an'd 16-are.c0nnected-in electrical series between line terminal 18? and. ground: terminal 20.- a

. An insulative or porcelaincap. 22 issupportedin-sealedrelation. to the upper end of the housing 10 and. thecap 22in turnprovides support for the line terminal 18,. Securance of the terminal 18-t0 the housing;;cap-22 canbe provided bysui-table means such-as athreadednut. 19. In order to connectthe terminal 18 to aline con-- ductor, aninsulative hand wheel24 is-provided-with a conductive insert member 26 slidably engageable with:- athreaded'portion (notshown) of-- the terminal.18. A conductor can thus be securedto the terminal Ill-betweenthe insert member. 26. and--the-terminal.18 as indicated by'the. reference character 28 simply by h and tightening. movement of the hand'wheel 24. A more complete dc scription of. this connector structure. and theadvantages: thereof is set forthin the previously: menti-oned.cop end-.- ing application, Serial No..181,686'of R. J. Lawrence. and C. H. Carothers.

Thelower end. of thearrester housing-10 is also closed. in sealing relation, and in this instance. the. closure. ar rangement is.provided in the form .ofa drop-out device. 30.. Thedrop-out device 30supports theground terminal. 20 in a suitable manner andfurther, in order to breakthe line. togroundLcircuit and. in.this example torelease internal pressure, issuitably arranged to. become. dc.- tached from the arresterhousingilzl if anexcessiveheati producing fault current develops in the lightning arrester 10. Further descriptionof the character. of. the drop-out: device 30 or devices similar thereto -canbeobtainedbyreference to thev aforementioned. copending patent applications. An insulative hand wheel 32 similar or identical to the hand wheel 24 is also provided for threaded engagement with the ground terminal 20. Securance of a ground conductor to the hand wheel 32 is accomplished in a manner similar to that described in connection with the line terminal 18.

The spark gap assembly 14 is disposed in this instance in a separate compartment 34 and is provided for the purpose of normally insulating the line terminal 18 and the line to which it is connected from ground. However, when a lightning surge appears at the line terminal 18, the spark gap assembly 14 undergoes electrical break down and a relatively low impedance arc discharge path is produced therethrough. The assembly 14 can thus include, in a manner similar to that described, for example, in the aforementioned application Serial No. 181,686, one or more spark gaps each of which comprises a pair of disc-shaped electrodes 36 spaced from each other by a centrally disposed insulative member or cylinder (not shown) which can be formed from rutile or other suitable insulative material. A hollow cylindrical arc barrier member 38 is disposed between each pair of electrodes 36 adjacent the outer periphery thereof.

An insulative elongated rod 40 is employed to hold the spark gap assembly 14 together. Thus, the electrodes 36, the previously noted central insulative spacers, and a contact plate 42 receive the insulative rod 40 through respective central openings therein. It is also to be noted that a partition member 44 can be employed to divide the spark gap assembly compartment 34 from compartment 46 in which the non-linear resistance block assembly 16 is disposed. The partition member 44 is formed from a resilient insulative material such as cork-neoprene and it also can receive the insulative rod 40 and otherwise be disposed against the contact plate 42 so as peripherally to engage the inner wall surface of the arrester housing 12.

Final securance of the spark gap assembly 14 in assembled form can be accomplished through attachment of respective U-shaped nuts 48 (only one shown) to each end of the insulative rod member 40. Outwardly projecting arm or arms 50 of each nut 48 provides circuit continuity, for example between the spark gap assembly 14 and the line terminal 18 or the securing nut 19 thereon.

The contact plate 42 is provided with a central projection (not shown) extending upwardlyfor engagement with the adjacent gap electrode 36 through the insulative partition member 44. Accordingly, good electrical contact between adjacent conductive members in the spark gap assembly 14, and tight resilient support for the entire assembly 14 is provided by means of conductive coil spring 52 which is' preferably conductively shunted (not shown) and further is disposed between the contact plate 42 and upper contact plate 54 of the non-linear resistance block assembly 16 in the compartment 46.

One or more non-linear resistance blocks 55 are disposed between the upper contact plate 54 and a lower resilient coil spring 56 which makes electrical contact with the ground terminal 20 through the drop-out device 30. The block 55 is characterized with non-linearly decreasing resistance as a function of increasing voltage and for this reason the block 55 provides relatively low impedance to high voltage lightning discharges but relatively considerable impedance to lower voltage power follow currents. Accordingly, the block 55 is ordinarily effective.

to reduce the flow of power follow current after a lightning discharge has occurred through the arrester 10. The electrical properties just described can be provided for the block 55 through the selection of a suitable material, for example suitably processed silicon carbide or such processed silicon carbide with a binder such as a vitrified fired'ceramic bond or sodium silicate.

However, the lightning arrester can become damaged in use by unusually heavy lightning discharges or unusually heavy power current flows and such damage can initially take the form of the development of a fault in 4 the material of the resistance block 55. When a material fault does occur, the impedance characteristics of the block 55 are substantially altered or reduced and considerable current produced heat is generated so that resulting temperature rise produces vaporization of the block material. Build up of gas pressure and gas ionization in the arrester compartment(s) thus occurs. Similarly, it is also possible for excessive heat production and vaporization in the gap structure 14 to lead to such gaseous changes in the arrester compartment(s).

Under these conditions, undesired current arcing can occur, especially between the block 55 and the wall of the housing 12 or along the block 55 in the space between it and the wall of the housing 12. The described pressure build up or the thermal shock associated with the development of current arcing or a combination of these factors can accordingly cause the housing 12 to shatter or explode.

This can be true even if the drop-out device 30 is designed for ejection from the arrester housing 12 upon the development of a fault in the block 55. Thus, the development of shatter or explosion forces can occur in a shorter period of time than that which it takes the dropout device 30 to respond to a developed fault. Furthermore, in numerous marketed lightning arresters, drop-out devices or drop-out arrangements are not elfeetive to provide for pressure release from the arrester housing interior upon ejection thereof. It is also noteworthy that in some cases pressure build up in the interior of an arrester housing, such as after the development of a fault in the resistance block or blocks, is ineffective of itself to cause the arrester housing to shatter or explode but does cause such an explosion if the arrester housing is impacted by a servicemans tool or the like. In such cases, there is considerable risk of personal injury to the serviceman.

In order to reduce or eliminate the risk of shatter or explosion under the described and other conditions, a tubular liner member 58 is disposed between the assembly 16 or the assembly 14 or both of these assemblies and the inner surface of the wall of the housing 12. In most applications, disposition of the liner member 58 between the block assembly 16 and the wall of the housing 12 will be sufiicient substantially to prevent shatter or explosion of the housing 12.

The liner member 58 is preferably flexible or molded so that it can fit the contour of the block assembly 16 and further is so sized in thickness as preferably to provide good central positioning of the block assembly 16 relative to the inner surface of the wall of the housing 12. The material of the liner member 58 is preferably inorganic and non-carbonizing so as to be non-arc tracking, and it is also heat resistant as well as fireproof. In this manner, the liner member 58 is effective against current arc formation which is one of the apparent causes of the development of shattering or explosive forces. The material also provides some or preferably considerable gas absorption so as to inhibit pressure build up within the arrester housing 12.

Although fiberglass and other materials can be employed to form the liner member 58, it has been determined that asbestos paper has good qualifications on the basis of the above considerations. If a continuous roll of insulative material or asbestos paper is employed, the liner member 58 can be formed in several layers 60 (FIG. 2) or it can be formed as a single layer with a small amount of overlap if desired. The required thickness of the liner member 58 will of course to some extent depend upon the rating of the arrester in which it is employed.

In tests conducted for distribution type arresters, it was 5 determined that, over a fault current range of 25 to 5000 tests, four wraps of asbestos paper having a thickness of .015 inch were employed and, in another series of tests, a single wrap of asbestos paper having a thickness of 4 inch was employed. The asbestos paper can be made from either short or long asbestos fibers and preferably has a minimum fiber content of 88%. Fiberglass cloth having a thickness of inch also proved successful but advantages of using fiberglass in many applications are oifset by manufacturing handling problems associated with it.

The foregoing description has been presented only to illustrate the principles of the invention. For example, it is clear that the invention has application in lightning arresters of considerably different structure from that shown for the arrester of FIG. 1 so long as a basic need exists for preventing shatter or explosion of such arrester structures. Accordingly, it is desired that the invention be not limited by the embodiment described, but, rather, that it be accorded in interpretation consistent with the scope and spirit of its broad principles.

What is claimed is:

1. A lightning arrester comprising a generally cylindrical housing of insulating material, a plurality of arrester elements disposed in series relation in said housing and including a spark gap assembly and a non-linear resistance block assembly, said resistance block assembly including one or more blocks of molded material having a diameter less than the internal diameter of the housing, said arrester elements being centrally disposed in the housing with an annular space between the arrester elements and the housing, and a separate liner member disposed in said annular space and encircling at least a part of the arrester elements, said liner member comprising a non-adherent continuous member of heat-resistant inorganic material of sufiicient porosity to absorb gas.

2. A lightning arrester comprising a generally cylindrical housing of insulating material, a plurality of arrester elements disposed in series relation in said housing and including a spark gap assembly and a non-linear resistance block assembly, said resistance block assembly including one or more blocks of molded material having a diameter less than the internal diameter of the housing, said arrester elements being centrally disposed in the housing with an annular space between the arrester elements and the housing, and a separate liner member disposed in said annular space encircling and substantially coextensive with the resistance block assembly, said liner member comprising a non-adherent continuous member of heat-resistant, non-tracking inorganic material of suflicient porosity to absorb gas.

3. A lightning arrester as defined in claim 1 in which the liner member is made of asbestos paper.

References Cited by the Examiner UNITED STATES PATENTS 1,775,544 9/30 Alexanderson 330-67 2,374,527 4/45 Earle 31767 2,504,438 4/50 McFarlin 3 15-36 2,802,175 8/57 Eldridge 313231 2,888,608 5/59 Kalb 3l536 2,891,194 6/59 McStrack et al. 3l536 3,018,407 1/62 Innis 3 1536 FOREIGN PATENTS 3 32,594 7/30 Great Britain.

JOHN W. HUCKERT, Primary Examiner.

DAVID J. GALVIN, Examiner.

Claims

1. A LIGHTNING ARRESTER COMPRISING A GENERALLY CYLINDRICAL HOUSING OF INSULATING MATERIAL, A PLURALITY OF ARRESTER ELEMENTS DISPOSED IN SERIES RELATION IN SAID HOUSING AND INCLUDING A SPARK GAP ASSEMBLY AND A NON-LINEAR RESISTANCE BLOCK ASSEMBLY, SAID RESISTANCE BLOCK ASSEMBLY INCLUDIN ONE OR MORE BLOCKS OF MOLDED MATERIAL HAVING A DIAMETER LESS THAN THE INTERNAL DIAMETER OF THE HOUSING, SAID ARRESTER ELEMENTS BEING CENTRALLY DISPOSED IN THE HOUSING WITH AN ANNULAR SPACE BETWEEN THE ARREST ELEMENTS AND THE HOUSING, AND A SEPARATE LINER MEMBER DISPOSED IN SAID ANNULAR SPACE AND ENCIRCLING AT LEAST A PART OF THE ARRESTER ELEMENTS, SAID LINER MEMBER COMPRISING A NON-ADHERENT CONTINUOUS MEMBER OF HEAT-RESISTANT INORGANIC MATERIAL OF SUFFICIENT POROSITY TO ABSORB GAS.