US2542805A - Lightning arrester - Google Patents

Description

Feb. 20, 1951 A. J. FlNK `2,542,805

LIGHTNING ARRESTER Filed June l, 1948 wlTNEssEs: 5 INVENTOR 72W@ W BY y @46 ATTOR N EY Patented Feb. 20, 1951 UNITED STATES PATENT G'FFICE 2,542,805 LIGHTNING MegniSTER4 Alison J. Fink', pittsburgh, Pa., assigner alweer"- inghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application'nme 1, 194s, serial No. 30,473

The present invellt'n krelates* to lightningk arresters, and more particularly, to a highvoltage ,lightning arresterunitt of -greatly reduced height, as compared togthejA heightpf lightning arrester. units f CQHVentOnal. @011- struction andequivalent voltage rating..

4 Thelightninguarrester unit of the present in- Ventio'rl is vest:eciallv adapted for` use in high.- Velta'ee, stati'eritype lightning arresters .of unit Construction; although it acomplete lighting arrester in litself and may berused as such. s ljlighvoltage, station-type lightning arrestare areusually .of unit, construtea and. are .merle .un of .a Suitable .number 0f lightning' erreslerlurlls, Of Standard voltage' ratings.; geen Qf the.V .units Cen- Sistirlg of.. a nlrrlberi el .spark ser. devisarld valve. elements. 0r Valve-,type resistors. assembled ,in Series relativa .ma Single, stack and ellcles'ed lne' D'Qrelan. housing.. with metal @nd tillgsl The individual arrester units are placed in .a Yertlal comme and the eed iilnerlf .asiljaoent units are bolted together for electrical and mechanical connection,' sp thaall the units are connected in series. This type. of Aconstrue` tion results" in a vertical column of greatheight" asy compared toy its diameter, and in th'e higher Voltage ratings', the height of the column is' so' great that it is nfot'self-supporting, but must' be supported' from somesyuitabi nxedi support; such as apart of a substation struoturaeither by' brae' ing or by suspension mounting". In the case of very high-voltage lightning arresters, the'arrester colurnnY is lso high that the required' supporting' structure and bracing become' quite' large and elaborate and are' relatively expfenSiw/"e,4 thus' add'-y ing considerably to the' cost' of theA installation'. Th'e necessity df supporting' the arrester this" way is, therefore, undesirable', but cannot be avoided with' highvolta'ge lightning arresters of conventional construction, because of the neces"-- sarily great height of the arrester column.

Another problem in the design of high-voltage lightning arresters of conventional construction' ist that of obtaining sufliciently uniform voltage distribution` across the tall .column of arrester units. The arrester column is connected between a transmission line conductor and1ground,'s'o that it is subjected to the line-to-gmundl Voltage, but because of the height, ofthe arrester, the voltage does not di-vide uniformly between the individual' arrester units. Satisfactory operation, however, requires a fairly uniform distribution of the voltage, and this has usually been obtained' by the use'of grading rings, which affect the electrostatic eld surrounding the arrester, and providev suinsolaires. (o1. 175-30) cient capacitance to make the voltage distribution sufficiently uniform forA satisfactory opera'- tion. `As .the heightof the, arrester column is increased, however, it becomes increasingly diiicultlto obtainI satisfactory voltageA distribution in this Way, and in `yery high-Voltagev lightning arresters, itis frequently necessary to employ two,

or even three, grading rings, which are of very large diameter and thus undesirably increase the space lrequired for the arrester and the necessary clearance distances to other nearby apparatus.

" A lightning arrester kcorristructon which sub,`

the valve elementsin theother two, the three columns being Vconnected together inseries with..

in Ythe housing. This construction permits a material reduction in the height of the arrester u nit, for a given voltage rating, so that a vertical column of these units is relatively short and cani be made self-supporting, even for very high volti age ratings. It has been found, however, that although this construction represents a material improvementin high-voltage lightning arresters, thearrangementof gap devices and valve e1ements in separate, seresconnected columns disposedside-by-side in the housing results in con'- siderable distortion of the electrostatic eld surrounding the arrester elements, which adversely affects the loreakdownvoltage of the arrester unit, both on surge voltages and on normal-frequency voltage. Y n

l The principal object of the present invention is to provide a lightningr arrester unit for use in high-voltage, station-type arresters which is of greatly reduced height, as compared to the height of lightning arrester units of conventional construction' and equivalent voltage rating, and in which substantiallyfuniform distribution of the voltage across the elements of the arrester unit is obtained. Y n

Another object of the invention is to provide a lightning arrester unit for high-voltage lightning arresters in whicha plurality of gap devices and a plurality of valve elements are arranged in a plurality of vertical columns in a housing,l with' the gap devices distributed throughout the assembly, and with all the gap devices and valve elements connected together in a series circuit which extends back and forth between the columns, the arrangement being such that substantially uniform voltage distribution is obtained.

A further object of the invention is to provide a lightning arrester unit for high-voltage lightning arresters in which a plurality of spark gap devices and a plurality of valve elements are arranged in a plurality of vertical columns in a housing and connected together in series, and in which the gap devices are shunted by substantial capacitances in order to improve the voltage distribution.

A more specic object of the invention is to provide a lightning arrester unit for high-voltage lightning arresters in which a plurality of spark gap devices and a plurality of valve elements are arranged in a plurality of vertical columns in a housing, with the gap devices distributed throughout the assembly, and with insulating members interposed in the columns which, in eect, divide the columns into sections and which include conducting means for connecting the sections of diiferent columns in series, the insulating members being so constructed and arranged that they provide substantial capacitances in shunt with the spark gap devices, so that good Voltage distribution is obtained.

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 sectional view of a lightning arrester unit embodying the invention, the arrester elements themselves being shown in elevation;

Fig. 2 is a top plan View of the arrester unit with the top tting and top plate removed;

Fig. 3 is a somewhat diagrammatic developed View showing the elements of the arrester in assembled relation; and

Fig. 4 is a schematic diagram showing the equivalent electrical circuit of the arrester unit.

The lightning arrester unit of the present invention is especialh7 adapted for use in high-voltage, station-type lightning arresters of unit construction, although it will be apparent that it is a complete lightning arrester in itself and may be used alone. As shown in the drawing, the arrester unit has a porcelain housing l, which is closed at the top by a metal top plate 2, a gasket 3 being interposed between the top of the housing I and the top plate 2. A ilanged metal top fitting or casting 4, which has a substantially ilat upper surface, is placed over the top of the housing I and secured to the housing by cementing, as indicated at 5, or by any other suitable means. The top tting 4 is provided with a plurality ol peripheral openings 6 for the reception of mounting bolts. An annular metal bottom fitting or casting l, which has a flat bottom surface and peripheral bolt holes, is provided at the bottom of the housing I and secured to the housing by cementing, as indicated at 8, or by any other suitable means. The bottom of the housing I is closed by a metal bottom plate 9, which is secured to the bottom tting l' by means oi bolts I0, a gasket I I being interposed between the bottom plate 9 and the bottom of the housing I to seal the interior of the housing.

The arrester includes a plurality of spark gap assemblies I2 and a plurality of valve blocks, or valve-type resistors, I3. The spark gap assemblies I2 may be of any suitable construction and are shown as enclosed multiple-gap assemblies. Thus, each of the spark gap assemblies I2 is contained in a tube I4 of porcelain, or other insulating material, which is closed at the ends by metal end caps I5 secured to the tube I4 by soldering to a metallic glaze on the porcelain, or in any other suitable manner. The spark gap assemblies themselves consist of a plurality of metal electrodes i5 disposed in the tube I4 and spaced apart by insulating, or high resistance, spacers II. A spring I8 is placed between the uppermost electrode I5 and the upper end cap I5 to retain the assembly of spark gaps firmly in position, and to obtain positive electrical Contact with the two end caps I5,

The valve blocks I3 may be made of any suitable resistance material having valve characteristics, that is, a material which is normally semiconducting, or of very high resistance, so that it will pass only a very small leakage current, but which sharply reduces its resistance under an excess-Voltage surge to permit the discharge of high surge currents, and which rapidly increases its resistance after passage of the surge to reduce the current to a small value which a series gap can easily interrupt. The valve blocks I3 may, for example, be made of granular silicon carbide molded to the desired size and shape with a suitable binder, such as sodium silicate, and baked. A metal contact coating is preferably provided on the end surfaces of the valve blocks.

The spark gap assemblies I2 and valve blocks I3 are disposed in three vertical columns, which are equally spaced from each other within the housing and supported on the bottom plate 9. As seen in the developed view of Fig. 3, the lefthand column and right-hand column include both spark gap devices I2 and valve blocks I3, alternating with each other, while the center column contains only valve blocks I3.

The arrester also includes a number of elongated, generally cup-shaped insulating members I9, 2U, 2I, 22, 23 and 24. These insulating members are all of similar construction and may be made of a ceramic material, such as porcelain, or of any other suitable insulating material, preferably of high dielectric constant. Each of the insulating members has a base 25 and vertically extending side walls 26, which extend a substantial distance above the base 25 so that the insulating members are generally cup-shaped. The insulating members are made long enough to extend between two of the columns of arrester elements, as clearly shown in Fig. 3, and they are made wide enough to accommodate the spark gap devices I2 and valve blocks I3, which are of about the same diameter. Each of the insulating members also has a metallic coating 21 on its inside horizontal surface and a similar coating 28 on its outside horizontal surface. The thickness of these coatings is somewhat exaggerated in the drawing, for the purpose of illustration. but they should be made thick` enough to be capable of carrying high discharge currents in the operation of the arrester.

The insulating members I'9 through 24 are interposed in the three columns of arrester elements so that, in effect, they divide the columns into insulated sections. Thus, in the particular embodiment shown, the outside columns, as seen in Fig. 3, are each divided into three sections, each of which includes a spark gap assembly I2 and a valve block I3, except the top section of the left-hand column, which consists only of a spark gap..y assemblyfand4 the .bottom ,sectionof the right-handy column, whichc. includes `.two valve blocksm 'Ihecenter column` is. dividedinto Vfive sections of..tvvovalv.e.4 blocks each.. The arrester elements of reach section rest inone end of. an insulating member andthe elements ofasection of anotl'iehv .column .are disposed in the opposite end Qitheinsulating member, sothat vthe insulating members-extend between. the columns, and their conducting coatingsll4 and.28 provide electrical connection .betweenthe sections.

-e-'l.`he.. conducting.coatings 21 and 28 connect all.

thesections in aseries circuit which extends back andi-forth between the columns. Referring to Fig. 3,-,the.series, circuitextends-i'rom .the top plate 2 thriough. the uppermost sparkgap assembly I2 of the. left-,hand column,'the.upper conductingcoating of the insulating member-28, theupper'most two.valve .blocks I3. of the center column, the lower conducting coatingk ofthewinsulating member I9, a valvelblock and a spark gap assembly ina the right-hand -olumniaconducting spacer 29,'theupper conducting coating of the insulating member 2 I twovalve blocks .in the center column, the lower conducting coating of the insulating member; 20, a valve block anda .spark gap assembly intheleft-hand column, aconducting spacer 29, the upper conducting coating of the insulating member 22, two valve blocks I3 ,in the center column-.and so on to the bottom plate 9. Thus the circuitextends. circuitously from column to column to connect all the spark gap assemblies and valve blocks in series between the top plate 2 and the bottom plate 9. The conducting spacers 29 may be short sections of steel pipe, or they may be any other suitable conducting members of proper length and having suicient rigidity and mechanical strength.

It will be noted that the insulating member I9 is inverted, with respect to the other insulating members, and that the metallic coating on its exterior surface is in electrical contact with the top plate 2. Similarly, the lowermost insulating member 24 is supported on conducting spacers 30, which may be similar to the spacers 29, but of greater length, and which support the lefthand and center columns and provide electrical connection between the lower metallic coating of insulating member 24 and the bottom plate 9. The thickness of the base 25 of the insulating members I9 to 24 is made great enough to space the adjacent arrester elements far enough apart to avoid any danger of puncture or ashover, since there may be a considerable difference of potential between the arrester elements on opposite sides of each insulating member. The side walls 25 of the insulating members extend vertically far enough to `provide insulating barriers between parts of adjacent columns which may have a considerable potential difference between them during a discharge, and thus all possibility of ilashover between different parts of the assembly is substantially eliminated.

Fig. 4 shows the equivalent electrical circuit of the arrester unit with all the elements of the arrester connected in series. 'Ihe insulating members I9 through 24, with their conducting coatings 21 and 28 on opposite sides, inherently have relatively high capacitance, and the arrangement of these insulating members in the assembly, as described in detail above, is such that the capacitance of one of the insulating members is connected across each of the spark gap assemblies, since the conducting coating on one Side of each CII of they insulating. members is connected .on one sidefof a spark gap assembly and the conducting coating on theother side is. connected inthe circuit on4 the opposite sideof the same spark gap assembly, Thus, the insulating members are represented as capacitors in Fig. 4, and it will be apparentfrom this Figure that each spark gap assembly I2 is-shunted bya substantialcapacitance. The 'arrangementI of thearrester elements, with the.. spark gap assemblies .distributed throughout the series circuit, and with theA capacitances providedby the insulating members acrossthe spark gap assemblies, results in a very uniform distribution ofvoltage across the elements of the arrester unit, so Vthathigh and consistent values of breakdown `voltage are.. obtained both on surge voltages andonthe normal-frequency voltage.

In .the useof the `arrester unit4 described above in a high-voltage, station-.type lightning arrester, a. suitable .number of these units are disposed end-.to-end in. a vertical column with their. adjacent .top `and .bottom ttings i .and 'l bolted togetherfor electrical vand mechanical connection, toconnect all the units in series. The .arrangement .of..the arrester elements in each unit results in a unit of greatly reduced height and somewhat increased diameter, .as compared to a conventional arrester unit ofequivalent voltage rating,..in which the samenumber of spark gap assemblies valve blocks would be disposed in a single `vertical stack..` A vertical column of the new arrester units, therefore, is materially shorter in height than a lightning arrester of the same voltage rating built up of conventional arrester units, and the reduction in height is suiiiciently great so that a vertical column of the new units, even for very high voltage ratings, is short enough to be self-supporting, eliminating the necessity for elaborate and expensive supporting and bracing structures. Such a co1- umn of arrester units is also short enough so that satisfactory voltage distribution across the arrester can usually be obtained without the use of grading rings, while the arrangement of the arrester elements within each unit described above results in uniform voltage distribution in each unit, so that high and consistent break- Y down voltages are obtained.

A particular embodiment of the invention has been shown and described for the purpose of illustration, but it will be apparent that various modifications and other embodiments are possible vvithin the scope of the invention. It is to be understood, therefore, that the invention is not restricted to the particular structural arrangement shown, but in its broader aspects, it includes all equivalent embodiments and modications which come within the scope of the appended claims.

I claim as my invention:

1. A lightning arrester comprising an insulating housing, a plurality of spark gap devices and a plurality of valve-type resistors disposed in a plurality of vertical columns in the housing, at

least some of said columns including both spark gap devices and resistors alternating with each other, a plurality of elongated, generally cupshaped insulating members interposed in said columns between the elements thereof, each of said insulating members extending from one column to another column and having continuous conducting coatings on both surfaces in electrical contact with the adjacent elements of both columns, successive insulating members extending between different pairs of columns in rotation to connect all the gap devices and resistors in a series circuit extending from column to column, and to connect the capacitance of each of the insulating members across one of the gap devices.

2. A lightning arrester comprising an insulat-v ing housing, a plurality of spark gap devices and a plurality of valve-type resistors disposed in three vertical columns in the housing, two of said columns including both spark gap devices and resistors alternating with each other and the third column including only resistors, a plurality of elongated, generally cup-shaped insulating members interposed in said columns between .the elements thereof, each of said insulating members extending from one column to another co1- umn and having continuous conducting coatings on both surfaces in electrical contact with the adjacent elements of both columns, successive insulating members extending between said third column and the other two columns alternately to connect all tne gap devices and resistors in a series circuit extending from column to column and to connect the capacitance of each of the insulating members across one of the gap devices.

3. A lightning arrester comprising an insulating housing, a plurality of spark gap devices and a plurality of valve-type resistors disposed in three vertical columns in the housing, two of said columns including both spark gap devices 0 Number and resistors alternating with each other and the third column including only resistors, a plurality of elongated, generally cup-shaped insulating members interposed in said columns between the elements thereof, each of said insulating members extending from one column to another column and having continuous conducting coatings on both surfaces in electrical contact with the adjacent elements of both columns, successive insulating members extending between said third column and the other two columns alternately to connect all the gap devices and resistors in a series circuit extending from column to column and to connect the capacitance of each of the insulating members across one of the gap devices, and the insulating members having substantially vertical side walls forming insulating barriers between the columns.

AUSTIN J. FINK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Steinmetz Feb. 7, 1928 FOREIGN PATENTS Country Date Great Britain Mar. 29, 1944 Number

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