US2473849A - Lightning arrester - Google Patents

Description

June 21, 1949. E. F. w. BECK 2,473,849

I LIGHTNING ARRESTER Filed April 15, l948- Fig.1.

WITNESSES: lNVENTOR MJAW' ATTORN Y Patented June 21, 1949 LIGHTNING ARRESTER Edward F. W. Beck, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa, a corporation of Pennsylvania Application April 13, 1948, Serial No. 20,690

6 Claims. 1

The present invention relates to lightning arresters, and more particularly to a high-voltage lightning arrester unit of greatly reduced height, as compared to lightning arrester units of conventional design and equivalent voltage rating.

The lightning arrester unit of the present invention is especially adapted for use in high-voltage station-type lightning arresters of unit construction, although it is a complete lightning arrester in itself, and may be used alone. Highvoltage station-type lightning arresters are usually of unit construction, and are made up of a suitable number of lightning arrester units, of standard voltage ratings, each of the units consisting of a suitable number of spark gap devices and valve elements, or resistors, assembled in series relation in a single stack and enclosed in a porcelain housing with metal end caps. The necessary number of these arrester units is assembled in series relation, the units being placed end-to-end in a vertical column with the end caps of adjacent units bolted together for mechanical and electrical connection. This type of construction results in a vertical column of great height as compared to its diameter, and in the higher voltage ratings, the height of the column becomes so great that it is not self-supporting, but must be supported from a suitable fixed support, such as a part of a substation structure, either by bracing or by suspension mounting. In the case of very high-voltage arresters, the required supporting structure and bracing become quite large and elaborate, and are relatively expensive, thus adding considerably to the cost of the installation. The necessity of supporting arresters in this way is, therefore, undesirable, but cannot be avoided with conventional arrester designs.

Another problem in the design of high-voltage lightning arresters is that of obtaining sufiiciently uniform distribution of voltage across the tall column of arrester units. The arrester is connected between a transmission line conductor and ground, and is subjected to the line-to-ground voltage, but because of the great height of conventional lightning arresters, the voltage does not distribute itself uniformly between the individual arrester units. Satisfactory operation, however, requires reasonably uniform distribution of the voltage, and in conventional designs, this has been obtained by means of grading rings, which affect the electrostatic field surrounding the arroster, and control the capacitances between the individual arrester units and ground in such a way as to make the voltage distribution sufficiently uniform for satisfactory operation. As the height of the arrester is increased, however, it becomes increasingly difficult to obtain sufficiently uniform voltage distribution in this way, and in high-voltage arrester units, the grading rings become quite large, so that the required clearance distance between the arrester and other apparatus is undesirably increased. When it is attempted to extend conventional lightning arrester designs to vary high voltage ratings, substantially higher than those which have been used heretofore, it is found that it is extremely difficult to provide an arrangement of grading rings which will give sufliciently uniform voltage distribution, because of the great height of the arrester.

Thus, the height of high-voltage lightning arresters of conventional construction results in the two serious problems of supporting the arrest-er without undue complication and expense, and of obtaining sufiiciently uniform voltage distribution. When it is attempted to apply the conventional type of design to extremely high-voltage lightning arresters, these problems become very acute because of the excessive height of the arrester, and it is extremely difficult to design lightning arresters for substantially higher voltage ratings than those which have been used heretofore, if it is attempted to utilize the conventional type of construction.

The principal object of the present invention is to provide a lightning arrester unit, suitable for use in station-type lightning arresters of unit construction, which is of greatly reduced height as compared to the height of conventional lightning arrester units of equal voltage rating, so that a high-voltage lightning arrester consisting of a vertical column of the new units is relatively short, and the problems of supporting the arrester and of obtaining satisfactory voltage distribution are substantially eliminated, or at least greatly simplified.

Another object of the invention is to provide a high-voltage station-type lightning arrester of very greatly reduced height as compared to the height of a conventional lightning arrester of equivalent voltage rating.

A further object of the invention is to provide a lightning arrester unit which is of such reduced height that a vertical column of such units, even for extremely high voltage ratings, will be short enough to be self-supporting and to have satisfactory distribution of voltage between the individual arrester units without the use of grading rings.

A more specific object of the invention is to provide a high-voltage lightning arrester unit consisting of a spark gap assembly disposed centrally in a housing and surrounded by two substantially concentric stacks of annular valve elements or resistors, the gap assembly and valve elements being connected in series, so that the discharge current flows. in a circuitous path and the height of the arrester is kept to a minimum even for very high voltage ratings.

The invention will be more fully understood from the following detailed description taken in connection with the accompanying drawing, in which:

Figure 1 is a vertical, longitudinal'sectional view of a high-voltage lightning- -arrester unit embodying the invention; and

Fig. 2 is a transverse sectional view approximately on the line II--II of Fig. 1.

The lightning arresterjshown in the drawin is especially. adapted" iorcuse as :a unit of; a highvoltage-zsjtationetype :llghtning arrester of unit construction, although its usefulnessds not necessarily limited. to. this;particulanmse; since it 'is a complete lightningarrester in-itselfi and; may be used assuchap Thelightningarrestennnitis contained in a housing or weather casing I, which is preferably made vof:porcelainsand which is of large diameter relatlyexto its height, as compared to the proportionsof conventional" lightning arrester units. 1. Therlwusing .ltzisr clQSed at its upper end byra-nmetaltemplate-2;which restsonpthe top of the housing;-l;:a.zgasket Sawing-interposed--between the housing iandzthentop plate tosseal the ting or casting 4 extends over the top of the housing inxcontactzwith-thestop plate 12,-. :and is secured to: the housingzinx-any: suitable :manner, as by cementing asnindicatedcati. :fllhetopfittingA preferably :hasia zflat ,upperrsurface and is provided vwithperipheral:openings 8 forthe reception of mounting bolts: ;.;-An .annular,.- :flanged metal bottonrfitting oncasting:.Lisprovided at-zthe bottom of the housing-I and-ls. secured to it in any Suitable s vycementing as lndicated at 5 8. The bottomrnttingd has;-:ar1lat#=bottomsurface :and is provided with-:peripheral openings 8 for mountingrboltse Therbot-tomsof-thehouslng l is closed by:-a.metal-..bottqm-plate 10:..which may be secured to the bottom fitting I by means of bolts H. -A gasket this preferably. interposed-betweenthe plate l0.-.a-n'd-.the hou sing l..to-seal the housing.

The, arrester includesasparkggap assembly I 3,

which may be ,ofianyssiiitab1Ei yp .-and which is I shown as a porcelainvenclosed.t'multlpleegap assembly. .The. gap assembly-isrcontained in -.a porcelaintube ,-l lrclosedatpthezends-by metal. end caps l5, whicharesealed :tmthe porcelain tube by soldering ,tmametallicglaze onathe porcelain, or in any other suitable -manner: ;='Ihe-'-sparkgap assembly consists of a plurality of metal electrodes l6 spaced apart lay-insulating, or high-resistance, spacers I'I.;;The gap-elementsv-aresarranged in a vertical column;nestingonathe-lower end-cap l5 of therporcelain: tube latmndra-rspring l8 islpla'ced in the top of the tube toxhold themgap elements firmly in place :and .toprovi'degoodelectrlcal contactwith the upper endicap. IS.

The spark :gap: assembly 1 3"zistplaced:substantially in-the center :ofrt-herzhousingaLzand; rests in a generally cup-shapedzinsulating member-v l9, which may be made;- of any: suitable; insulating material having 1 :rsuflicient. mechanical rigidity and dielectric strength. A molded material of Gil suitable characteristics may be used, or the member 19 may be made of porcelain or other ceramic material. A metal contact plate 20 is provided in the bottom of the insulating member IS. The contact plate 20 may be a copper plate placed in the member l9, and preferably secured thereto in any suitable manner, or it may be a coating of copper or other metal applied to the surface of the member [9 by spraying, or other suitable method. The insulating member l9 preferably rests on a spacer block 2| of porcelain, or other insulating material, which in turn is supported on the bottom plate ID, the thickness of the spacer 21 being made. such that the top of the spark gap assembly 13 is held tightly against the top plate 2 when-the arrester is assembled. If desired, a spring, or spring plate, might be inserted between the top of the spark gap assembly 13 and the top plate 2 to insure good electrical contact.

.The-sparkgap assembly l3-is surrounded by a plurality of annular valve or resistor elements 22. The valve elements 22 may be made of any suitable resistance material having valve characteristics, that is, amaterial whichnormally has very high resistance, b-ut-whichisharply.decreases its resistancewhen subjected to a high voltage, so as to permit the discharge of high surge currents, and which rapidlyincreases its resistance when the voltage drops, so as to pass only a small leakage current, which canv easily be interrupted by the gap assembly 13. The valve elements 22 may be made of any material ofthis kind, such as granular silicon carbide molded to the desired size andshape with a suitable binder, such as sodium silicate, and'baked. A metal contact coating is preferably applied to the end surfaces of each valve element. The valve elements 22 are annular in shape,v and they are placed in a stack in the cup-shaped insulating member .I 9 substantially concentrically with the spark-gap assembly it. The lowermost valve element 22 rests on the metal contact plate 20, so that the bottom of the stack of valve. elements 22 is electrically connected to .the bottom of thespark gap assembly l 3', which also rests on the contact plate 20.

Thearrester also includes a second .stack of annular valve elements 23, which are similar to the valve elements. 22, except that they are of largerdiameter. The valve elements 23 are assembled in a second stack which is substantially concentricwith thespark gap assembly l3 and with the first stack of valve elements 22. The stack ofvalve elements 23 rests directly on the bottom plate I0, so as to be in electrical contact with it, and the stack of valve elements 23 contains a greater number of valve elements than the first stack of valve elements 22, so that the tops of the two stacks are substantially in the I same horizontal plane, as clearly shown in Fig. 1.

An annular insulating member 24, of generally U-shaped cross-section, is placed over the tops of the-two stacks of valve elements 22 and 23. The insulating member 24 may be made of the same V material as the cup-shaped insulating member the entire assembly, consisting of the spark gap assembly 13 and the two stacks of valve elements, is connected in series between the top plate 2 and the bottom plate H]. A tubular spacer 26, which may be made of insulating material, such as porcelain, or of conducting material is placed between the annular insulating member 24 and the top plate 2 to hold the assembly firmly in place.

The inside leg 2? of the annular insulating member 24 is made longer than the outer leg so as to extend down a substantial distance between the upper parts of the spark gap assembly 13 and the inner stack of valve elements 22. Similarly, the wall of the cup-shaped insulating member 19 extends up a substantial distance between the lower parts of the two stacks of valve elements. Thus, the insulating members [9 and 24 provide insulating barriers separating those parts of the assembly which may have large potontial diiierences between them during a discharge, so as to prevent any possibility of flashover between parts of the assembly. It will also be noted that the spacer 2| and insulating member l9 space the bottoms of the sparlr gap assembly l3 and the inner stack of valve elements 22 a substantial distance from the bottom plate ill, while the tops of the two stacks of valve elements are spaced a considerable distance from the top plate 2. over to either the top or bottom plate.

It will be apparent that the insulating memhers I!) and 24 provide a substantial amount of electrostatic capacitance across arrester elements, and by properly proportioning the insulating members, the capacitance across the arrester unit can be made relatively large, which materially simplifies the problem of obtaining satisfactory voltage distribution over a seriesconnected column of arrester units. If the spacer 26 is made of, or coated with, metal, the voltage distribution across the multiple gap assembly I3 will be somewhat better than if an insulating spacer is used, and if, in addition, a metal plate or coating is provided on the upper surface of the insulating member 24, the electrostatic capacitance across the arrester unit is increased, with resulting improvement in the voltage distribution across a column of these units.

As previously indicated, the new arrester unit may be used by itself as a lightning arrester, but it is especially adapted for use as a unit of high-voltage station-type lightning arresters. When used in this way, the necessary number of arrester units is placed end-to-end in a vertical column with the end fittings of adjacent units secured together by bolts for electrical and mechanical connection. Since the top fitting 4 of each unit is in electrical contact with the top plate 2, and the bottom fitting l is in electrical contact with the bottom plate Iii, the entire column of arrester units is thus connected in series.

The new arrester unit contains a relatively large number of spark gaps and valve elements, and it can, therefore, be given a relatively high voltage rating. Since the arrester elements are arranged side-by-side to provide a circuitous discharge path through the unit, however, the height of the unit is very greatly reduced as compared to that of a conventional arrester unit of equivalent voltage rating in which the same number of gaps and valve elements would be arranged in a single vertical stack. Because of this reduced height, a high-voltage lightning arrester built up Thus, there is no risk of fiashof a number of these arrester units will be relatively short, as compared with arresters of conventional design, and, in general, such an arrester will be short enough to be self-supporting, and will have reasonably uniform distribution of voltage between the different arrester units without the necessity of using grading rings or other means for obtaining uniform voltage distribution.

It will be apparent that a lightning arrester unit has been provided which can be made of minimum height, for a given voltage, because of the arrangement of the arrester elements to provide a circuitous discharge path. This arrangement results in a lightning arrester unit which is of such reduced height and increased diameter, as compared to conventional arrester units, that a vertical column of the new arrester units is short enough to be self-supporting and to have reasons. ly uniform voltage distribution. Thus, very high-voltage lightning arresters can readily be provided without the diii'iculties and problems resuiting from the excessive height of high-voltage lightning arresters of conventional construction.

A preferred embodiment of the invention has been shown and described for the purpose of illustration, but it will be apparent that the invention is not limited to the particular details of construction shown. It is to be understood, therefore, that the invention is not restricted to this particular embodiment, but, in its broadest aspects, it includes all equivalent embodiments and modifica tionswhich come within the scope of the appended claims.

I claim as my invention:

1. A lightning arrester comprising a generally cylindrical housing, a spark gap assembly centrally disposed in said housing, a plurality of annular valve elements in the housing disposed in a stack surrounding the spark gap assembly, a plurality of annular valve elements of larger diameter than the first-mentioned valve elements disposed in a stack in the housing surrounding the first stack. and means for electrically connccting said spark. gap assembly and said two stacks of valve elements in series.

2. A lightning arrester comprising a generally cylindrical housing, a spark gap assembly centrally disposed in said housing, a plurality of annular valve elements in the housing disposed in a stack surrounding the spark gap assembly, a plurality of annular valve elements of larger diameter than the first-mentioned valve elements disposed in a stack in the housing surrounding the first stack, means for electrically connecting said spark gap assembly and said two stacks of valve elements in series, and insulating barrier means between the spark gap assembly and the first stack of valve elements and between the two stacks of valve elements.

3. A lightning arrester comprising a generally cylindrical housing, a spark gap assembly centrally disposed in said housing, a plurality of annular valve elements in the housing disposed in a stack surrounding the spark gap assembly, a plurality of annular valve elements of larger diameter than the first-mentioned valve elements disposed in a stack in the housing surrounding the first stack, means for electrically connecting the bottom of the spark gap assembly to the bottom of the first stack of valve elements, and means for electrically connecting the top of the first stack of valve elements to the top of the second stack of valve elements.

a. A :lightning arre'ster' "comprising a generally cylindrical housing, 'a:spark gap assembly centrally disposed in said housing, a plurality of annular valve elements in the housing disposed in astack surrounding the-spark gap assembly, a plurality of "annular valve elements of larger diameter than the first-mentioned valve elements disposed ina stack in the housing surrounding the first stack, means for electrically connecting the bottomof thespark gap assembly to the bottom of the-first stack of valve elements, means for electrically connectingthe top of 'the first stack of valve elements tothe top of the second stack of 'valve' elementspand insulating barrier means between at least theupper portions of the spark gap assembly and the first stack of valve elements and between at-least the lower portions of the two stacks of valve elements.

5. A lightning arrester comprising a generally cylindrical-housing, a spark-gap assembly centrally. disposed in said housing, a plurality of annular valve elements in the housingdisposed in a stack surrounding the spark gap assembly, a plurality of annular valve elements of larger diameter than the first-mentioned valve elements disposed in astaclc inthe housing surrounding the first stack, means for electrically connecting thebottom of the spark gap assembly to the bottom of the first stack of valve elements, means for electrically connecting the top of the first stack of valve elernents to the top of the second stack of'valve elements, a generally cup-shaped insulating member 'in'thebottom of the housing, the spark'gap assembly andthe' first stack of the valve elements'being disposed within said cup-v shaped member, and the cup-shaped member ex tendingeupwabdibetween the two stacks of valve el'ementsgand anl annularinsulating member extending over the tops ofthe two stacks of valve elementarsaidhannular insulating member havingta portion extending downward between the first-stack 'of valve elements and the spark gap assembly.

' 6. A lightning am-estencomprising a generally cylindrical housing, a spark gap assembly cen- 'tra'llydisposed in said housing; a plurality of annular-valve elements in the housing disposed a stack surrounding-the spark gap assembly, a plurality of-annular valve elements of larger di-- ameter than the first-mentioned valve elements disposed ina stack in the housing surrounding the-first stack, a generally cup-shaped insulating member in thebottom 'ofthe housing, the sparl: gap-assembly-and the first stack-of valve elements being: disposedwwithinsaid cup-shaped member, and the cup-shaped member extending upward between the twolstacksof-valve elements, means on the cup shapedt-membe-r for effecting elect cal connectionbetween the bottom of the s gap assembly and the bottom of the first of valve elements, an annular insulating mcrrber extending overthetops of the two stacks cf valve elements, said annularinsulating m having a portion extending downward bet the first stack of valve elements and the spark gap assembly, and means on the annular insulating member for effecting electricalconnection between the-tops of the two stacks of valve ele-- ments.

1""EDWARD F. W. BECK.

'* Noreferencescitecl.

Images