US1734235A - Lightning arrester - Google Patents

Description

N 1929 J. SLEPIAN v 1,734,235

' LIGHTNING ARRESTEH Filed April 2;, 1924 INVENTOR Joseph Slepian.

WITNESSEIS:

-ATTORNEY Patented Nov. 5, 1929 UNITED STATES PATENT OFFICE JOSEPH SLEPIAN, F SWISSVALE, PENNSYLVANIA, ASSIGNOR T0 WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA LIGHTNING ARRESTER Application filed April 21,

My invention relates to lightning arrestersand it has particular relation to spark gap devices used in such arresters.

One object of my invention is to provide a lightning. arrester which shall have a hlgh discharge capacity for lightning and surges and Whichshall produce thesmallest possible disturbance on the circuit which is to be protected.

Another object of my invention is to provide a lightning arrester having a relatively large discharge capacity for surges and overvoltages and a very low discharge capac ty for voltages of the order of the normal line voltage.

Another object of my invention isto provide an improved resistance material having directional conductivity for making my improved light-Bin arrester.

A still further 0 ject of my invention is to provide a new method of makin resistor materials of the above described c iaracter.

In making my improved arrester, I employ a gap electrode having directional conductivity, that is, being capable oi: conducting electricity in the direction of the discharge path between the gap electrodes but being almost an insulator in a direction transverse thereto. As a result, current passing through the gap is subdivided into a large number of minute currents, each traversing the relatively high resistance of the individual paths and requiring a relatively high voltage across the gap electrodes for maintaining the same.

"By properly proportioning the voltage necessary to maintain such current through the gaps of the arrester and the operating voltage of the line, I am able to prevent the passa e of material amounts of currents at line voltage while presenting a discharge path of relatively low resistance for voltages substantially above. the line voltage.

With the foregoing and other objects in view, my invention comprises the arrange-.

] ments, details of construction and processes described and claimed hereinafter and illus- 1924. Serial No. 707,843.

Fig. 2 is a similar view of a, modification of my invention,

Fig. 3 is a View in section of another modification of my invention, and

Fig. 4C is a view in perspective illustrating the principle of the pencil-like structure of the resistance plates employed in my invention.

Referring to Fig. 1, the iightning arrester comprises a cylindrical porcelain casing I having mounted therein a plurality of'parallel resistance plates 2 which are spaced from each other by mica spacers or rings 16 of about three mils thickness, as subsequent iy described, providing minute gaps 3 which are shown exaggerated in size, for the sake of illustration. The stack of plates 2 is held between two terminal plates 4 and 5 of conducting material such as copper. The upper terminal plate 5 constitutes one electrode of an auxiliary gap device 6 connected in series With the stack of resistance plates 2, the other terminal 7 of the auxiliary gap device leading to a terminal lead 8. The lower terminal plate 4 is connected to another terminal lead 9 which passes through an opening 10 in the lower portion of the casing. The two electrodes 5 and 7 of the series gap device 6 are held in spaced relation by a porcelain ring 12. The auxiliary gap device and the stack of plates are held in place bymeans of a clamping spring 13 and a cap 14 inelosing the upper side of the porcelain casing 1 and secured theretoby pitch or asimilar bonding material which fills the space 15 between the cap 14 and the casing.

- The principal novel feature of my invention is the particular construct-ion of the plates 2 and the mode in which the same are more. In the latter case the voltage requiredto maintain' a currentbetweeiithe' two cle t- 0 trodes is low and an increa sejof thecu the electrons and ions necessary to carry the] current through the space between the electrodes. Thus, an increase in the current increases the ionization of the space between the gap electrodes and consequently a lower voltage is suliicientv to pass larger currents;

However, when the current between the electrodes is sufiiciently low to avoid the heating of the terminals of the discharge upon the surface of the electrodes, there is not present a suflicient supply of electrons and ions to maintain the discharge at the low voltages of an ordinary arc and the discharge between the electrodes takes the form of a glow discharge, the minimum voltage necessary for maintaining a discharge of such character being the voltage corresponding to the socalled cathode drop? in the glow discharge.

According to my invention, the arrester has one or more gap devices, the individual gap devices being so designed as to practically force'the current between the gap electrodes to take the form of a glow discharge, requiring a high potential for maintaining the same and making actually impossible the formation of low-voltage arcs between the gap electrodes;

The plates 2, constituting the electrodes of my improved lightning arrester, are made of a directionally conductive resistance material which will be described in detail hereinafter, said material having suflicient conductivity in the direction of thedischarge between the electrode surfaces, but having a resistance of the order of an insulating resistance in a direction transverse thereto. The individual electrode plates are preferably spaced from each other by spacers of insulating material such as mica rings 16.

A good physical conception of the opera- 'tion of a lightning arrester made according to the foregoing description may be had by considering a gap device having an electrode plate, as shown diagrammatically in Fig. 4, formed by a multitude of pencil or filamentlik e resistance elements disposed in side'by side relation and bonded by a suitable insulating material. Suppose that the resistance of each pencil is 10,000 ohms and the breakdown voltage of thefgap is 500 volts.- When the voltage across the gap isgradually raised, a s ark will pass to one pencil and because of t e high resistance of the same, the current therethrough will be limited'to a small value, less than 50 milliamperes, in the case assumed.

The voltage necessary to maintain-such a current is relatively high and a reduction of the voltage considerably below the 'value of 500 volts will cause the discharge to become unstable and eventually interrupted. If the applied voltage is .raised to a value higher than 500 volts, enormous currents will flow, since the multiutde of individual gaps constituted by the terminals of the pencils and the opposite electrode surface will successively break down, each of the pencils carrying only a small current but requiring a definite minimum voltage in order to maintain the discharge. Taking, for instance, 50 milliamperes as the .current in each pencil and 1,000 pencils per square inch, we get 50 amperes per square inch, and for a plate having a surface of6 square inches a current of 300 amperes will discharge through the gap before the voltage is permitted to rise above approximately 500 volts.

In the practical construction of lightning arresters, certain additional refinements may be resorted to in order to make anarrester having good performance characteristics. Thus it is found that the extinction voltage,

that is, the voltage at which the minute current between the two electrodes will stop, is approximately equal to'the voltage of the cathode drop in a glow discharge. Thegaps' are accordingly so constructed that the breakdown voltage thereof corresponds to the voltage of the cathode drop in a glow'discharge. In practical applications of such construction, I may place an arrester, comprising a gap or a plurality of series connected gaps, across a line having an operating voltage somewhat lower than the voltage of the cathode drop times the number of serially disposed gaps. With suchconstruction, no discharge through the arrester will take place when the line is at the normal operating voltage, since such voltage is not suflicientto I maintain a discharge throughthe gaps. Any increase of the line potential causes a very free discharge through the arrester through the multiutde of parallel paths until the potential across the line is lowered to the point at which the discharge stops, and which corresponds, in the above cited case, approximately to the line voltage.

In the practical operation of arresters, the relief voltage, or the voltage at which the arrester discharges freely, -1S ordinarily so chosen as-to bel to 2 times the normal line voltage, and an auxiliary or insulating ga arrester is disposed in series with the stack of disc-gaps in order to prevent the passage of small leakage currents through the arrester, which would produce unnecessary heating of the same under normal operating conditions. The small spacing of the gap elements makes it very diflicult to secure a high leakage resistance for the minute gaps of the arrester, and accordingly, if the stack of plates is directly connected to the line, a small leakage current will pass therethrough at voltages of the order of the normal operating voltages.

In the practical embodiment of an arr-ester employing a plurality ofparallel plates constituting minute gap arresters, I employ a construction wherein the individual plates are beveled at their edges 17. The mica rings lightning discharges, or in general any highpotential discharges, from flashing over'the insulating spacer outside of the plate andeventually bridging over several of the plates and actually short-circuiting the same.

The end plates of the stack of discs of resistor material which make contact with the terminal plates 4 or 5 are so made as to prevent any sparking, which may be harmful to the arrester. I have found that if the end plates are placed directlyin contact with the metallic terminal plates, the end-plates are, for some unknown reason, shattered v and broken after passing a large'number of, discharges. I

A very good construction for making an intimate contact between the end plates and the terminal. plates and avoiding the shattering of the end plates consists in coating the contacting surface of each end platewlth a-layer 19 of conducting material such as graphite or, preferably, spraying thereon a layer of metal by means of the Schoop proc ess, for instance. The metallic layer 191s thus firmly united with the resistance plate and makes intimate contact with the individual high-resistance paths extending therethrough.

In Fig. 2 is showna modification of my 111- vention wherein the individual gaps of the arrester are formed by alternate plates 21 of resistor material and plates 22 of conducting material such as iron or brass, for instance. The close'spacing of the individual gaps 23 is obtained by means of mica spacers 24 as in the case of the arrester illustrated in Fig. l. The diameter of the resistor plates 21 is somewhat larger than the diameter of the plates 22 of conducting material. Such construction is instrumental in reducing any possibilities at a flash-over between the individual metal plates22 on account of the large path separating the same and the relatively lcw voltage gradient along the path.

I regard the above-described construction as a distinct feature of my'invention. v

Another modification of my invention is shown in. Fig. 3 wherein each gandevice constitutes an individual cell 26. Each gap cell comprises a ring 27 of insulating material, such as porcelain, having. mounted in the inner portion thereof a resistance plate 28 havin directional conductivity as described herein efore. The lower side of the resistor plate 28 is coated with a layer of metal 29 and is in electrical contact with a sheet-metal cover 30 having its outer edge bent and secured over an extending flange 31 of the porcelain ring 27. The other side of the resist ance plate 28 constitutes the active gap surface cooperating with the surface of a metal cover 32 which is secured to the outer edge of the porcelain ring 27 in the same manner as the lower cover 30.

If desired, an arrester employing resistor plates having directional conductivity may be efiectively operated with gaps having a break-down voltage which is considerably above the voltage of the cathode drop in a glow discharge. If a lightning arrester made with a larger gap is placed across a, line, the,

operating voltage 0 which corresponds to approximately. twice the, line voltage but in which the minimum voltage re uired- [for maintaining a discharge through t e arrester is somewhat belbw the operating voltage of the line, ood'performance and good protection will e secured without serious disturbances on the line, sincethe excess of line current which will pass through the arrester will be relatively small and the voltage for maintainingthe same will be sufliciently high to cause the discharge to sto {when the current passes through zero at t a, next alterna' tion.

A distinct feature of my present invention is the process of making the directionally conducting resistance elements utilized in arresters of the above-described character. According to one method, I ma obtain directionally conducting materia very high resistance for the passage of current in the direction transverse to the direction in which it is intended tobe conducted by assemblin filamentary threads of resistor material of t e desired resistivity in side by side relation and bonding the same into a mechanically homogeneous mass. The body so obtained is then cut in a direction transverse to the direction of the threads to PI'Q? duce electrode elements of the desired thickness. .The threads may be bonded with any suitable binder such as water glass or powdered kaolin, the binder serving also to in ture, and wind the same in sidey-side' rela tion upon a reel or frame. The thread may be passed through a refractory bonding mate ria such as-clay' before winding the same or theTBbdy-of the wound threads may be im prdgnated with the binding matenalafter i j having a sulate the individual threads from each other.

Winding. The plastic body of threads which is so formed may be cut into slabs or elements the thread-like body is cut into the desired shape. The resulting blocks of the material consist of fine, parallel, carbonized conductors which are insulated from each other by the insulating clay bond.

If desired, the thread may be impregnated or filled with a substance, such as with india ink or a colloidal solution of graphite, tending to give the thread a higher conductivity when carbonized.

a My invention is not restricted to the details and modifications described hereinbefore but -may be carried out in many other ways without departing fromthe spirit thereof and desire that the appended claims be awarded the broadest construction consistent with the prior art.

I claiin as my invention: Y

1. A space-current device operating on the glow-discharge principle and comprising two electrodes, at least one electrode being made of material having a plurality of closely packed, parallel, directionally conducting filamentary resistor elements carrying the glow-discharge current and disposed in the direction of the discharge path between the two electrodes, said filamentary resistor elements extending the entire length ot the electrode.

2. A spacecurrent device comprising two closely spaced electrodes, at least one electrode being made of material having a relatively large conductivity in the direction of the discharge path between the two electrodes and having a relatively low conductivity in a direction transverse thereto, the spacing between the electrodes and the character of said electrode being such that a continuous, substantially evenly distributed discharge oi: the glow tube is produced and maintained over the -cross-section of the discharge space throughout the continuance of a discharge.

3. A space-current device compr sing two electrodes, at least one electrode being made of material having a plurality of parallel, di-

. rectionally conducting paths disposed in the direction of the discharge path between the two electrodes, the resistance of the individual conducting paths being of such magnitude as to require a voltage of the order of the cathode drop in a glow discharge or more to maintain,

a current of a fraction of an ampere per path gap, the resistivity of the individual paths bememes ing relatively high and the resistivity between the individual paths in a transverse direction being so large as to substantially prevent pas sage of currents between one path and another, the number of conducting paths in said value in the direction transverse to the disverse thereto, the discharge conditions being such that no portion of either oil said electrodes is heated to a temperature of copious ionization, throughout the occurrence of a discharge.

7. A lightning arrester having two parallel plate electrodes separated by a ap, at least one of said electrodes being or a resister material having a relatively large conductivity in the direction of the discharge path between the two gaps and having relatively high resistance in a direction trans verse thereto, the back side of said electrode having a layer of a highly conducting substance, united thereto.

8. A lightning arrester comprising two parallel plate'electrodes separated. by a gap, at least one of said electrodes being made of a resistor material comprising a plurality of high resistance paths separated from each other by a relatively insulating bondingm aterial.

9. A lightning arrester comprising two parallel plate electrodes se arated lay a gap, at least one of said electro' es being made oif a resistor material comprising a plurality ofhigh resistance paths separated from each other by a relatively insulating bonding material, the outer side of said electrode being homogeneously united with a conducting la er.

l0. A lightning arrester having a plurality of spaced electrodes comprising a plurality of bodies of non-vaporizing conducting ire-- sister material having a relatively high specific resistance in one direction and a still higher sp'ecifi.'resistance of the order of an insulating resistance in a direction trans verse thereto, the spacing between the electrodes and the materials of said bodies being such as to insure a discharge in the term of a lid glow throughout the operation of the arrester.

11. A lightning arrester comprising a plurality of odies constituting gap elements, said bodies having'a resistance of the order of 10 ohms per square inch of cross-sectional area for currents flowing in the direction of the discharge paths across the gaps, and a re sistance of the order of an insulating material in a direction transverse thereto, the gap spacings and the materials being such that no portion of the arrester reaches a temperature of copious electron'emission throughout the operation of the device. 7

12. A lightning arrester comprising aplurality of parallel plates constituting closely spaced, parallel gap elements, the individualv plates having relatively large conductivity in the direction of the discharge path and a relatively high resistance in' a direction transverse thereto, the spacing and other characteristics being such that the discharges are maintained in the form of glow discharges without the formation of an arc.

13. A lightning arrester comprising a plurality of parallel plates constituting closely spaced, parallel gap elements the individual plates being of a material havin an extremel large number of closely pac ed, parallel-directionally conducting filamentar resistor elements'substantially insulated rom each other.

- 14. A lightning arrester comprising a plurality of parallel plates constituting closely spaced, parallel gap elements the individual plates being of a' material having an extremely lar e number of closel packed, parallel, directionally conducting lamentar resistor elements substantially insulated om each other, the resistance of each individual filamentary resistor element being more than 100 ohms.

15. A lightnin arrester comprising a plurality of paralle plates constituting closely spaced parallel gap elements the individual plates being of a material havin an extremely large number of closel pac ed, parallel dlrectionally conducting lamentar resistor elements substantially insulated m each other, the resistivity of the plates in the direction ofthe discharge filamentary resistor element being more than 1 ohm per centimeter cube.

16. A lightnin arrester comprising a plurality of paralle plates constituting closely spaced, parallel gap elements the individual plates being of a material having an ex-' tremely large number of closel I packed, parallel, directionally conducting filamentar" resistor elements: substantially insulated from each other, the resistivity of the individual filamentary resistor elements bein so lar e as to require avoltage of the or er of t e cathode drop ina glow discharge to mainv tain' a current of a; small fraction of an innpere per path between theopposite electrodes.

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