US2473850A - Lightning arrester - Google Patents

Description

June 21, 1949. E. F. w. BECK ET AL 2,473,850

LIGHTNING ARRESTER Filed July 27, 1945 I l l I INVENTORS Edward/F'Mfiec/r and Jofin i/"eryzxsan.

ATTORNEY 0 d 1 v J 32 9 .5. Z 2 F 3 u r 9 1 Z 3 0 WITNESSES: 1 vf Patented June 21, 1949 UNITED STATES Zfiliditd PATENT OFFICE LIGHTNING ARRESTER,

Application July 27, 1945, Serial No. 607,430

7 Claims.

The present invention relates to lightning arresters and, more particularly, to a low-voltage lightning arrester which is capable of discharging very heavy surge currents without damage to itself.

The lightning arrester of the present invention is particularly intended for use on low-voltage circuits, such as railway signal circuits, or other exposed control or signal circuits, where the circuit must be reliably protected against lightning and against accidental grounding. The requirements for a lightning arrester for this service are rather exacting. The arrester must become conducting, and begin to discharge, at a relatively low voltage in order to prevent damage to the apparatus which it is to protect. It must be capable of discharging surge currents of considerable magnitude without producing a discharge voltage across the arrester which would be high enough to endanger the protected apparatus, and it should be able to handle high surge currents repeatedly without damage to itself. In addition, it should not be possible for an arrester for this service to become short-circuited, or perinanently conducting, under any conditions, since accidental grounds on such circuits as railway signal circuits cannot be tolerated. In the past, it has been found very difficult to provide a satisfactory lightning arrester to meet these somewhat conflicting requirements, and most types of arresters which have been available for this service have had either good protective characteristics, or good protection against short-circuiting, but not both.

The principal object of the present invention is to provide a low-voltage lightning arrester which is capable of discharging very heavy surge currents repeatedly without damage to itself, and with a relatively low discharge voltage across the arrester during a discharge.

A further object of the invention is to provide a low-voltage lightning arrester which is capable of discharging very heavy surge currents and which has good protective characteristics, but which cannot become short-circuited under any conditions, even in case of damage to, or failure of, a part of the arrester.

More specifically, the lightning arrester of the present invention includes a short spark gap, so as to have the low breakdown voltage required for protection of railway signal apparatus and similar equipment, with a valve element in series with the short gap to limit the power current after a discharge, so that the gap can interrupt it, since the short gap, by itself, would not be capable of interrupting the current. One electrode of the gap consists of a plurality of spaced points, so

that in case of failure of the valve element, or if for any other reason the current is not interrupted, the point or points involved will burn back until the arc is interrupted. Thus it is irnpossible for the electrodes to weld together and short-circuit the arrester.

Failure of the valve element would. usually be caused by the passage of very heavy currents, beyond the capacity of the valve element, such as might result from a direct lightning stroke, or from accidental contact of the low-voltage protected circuit with a higher-voltage power line. Such heavy surge currents thus might damage the arrester, making it necessary to replace it, and they might also cause an undesirably, or dangerously, high discharge voltage across the arrester. In order to avoid these effects, in the lightning arrester of the present invention, a sec-- and, longer spark gap is provided in parallel with the series-related short spark gap and valve element. In case of a heavy discharge through the arrester, the discharge transfers from the short gap and valve element to the long gap, thus relieving the sensitive short gap and valve element from the heavy discharge current, and pro testing them from damage, as well as keeping the voltage across the arrester low. The spacing of the longer gap is great enough so that it is capable, by itself, of interrupting the power current which follows a discharge, although such a gap would have too high a breakdown voltage to protect the circuit if used alone, and the electrodes of the longer gap are of rugged construction, so as not to be substantially damaged even by extremely heavy discharges. In this way, an arrester is provided which meets the exacting requirements outlined above for low-voltage signal-circuit lightning arresters, since the new arrester has a low breakdown voltage and is capable of discharging very heavy currents with a low discharge voltage but cannot become short-circuited under any conditions.

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 view, partly in side elevation and partly in section, of one form of lightning arrester embodying the invention;

Fig. 2 is a side elevation, with the cover partly in section, of a lightning arrester, showing another embodiment of the invention;

Fig. 3 is a plan view, partly in section on the line III-III of Fig. 2;

Fig. 4 is a longitudinal sectional view on the line IV-IV of Fig. 3; and

Fig. is a perspective view of an electrode element.

One embodiment of'the invention is shown in Fig. 1. The lightning arrester shown in this figure is mounted on a base I of insulating material, and includes a pair of spaced metal supports mounted on the base I by means of rivets 3, or in any other suitable manner. "The'supports 2 have extending ends which serve-asterminals for the device, andt'heirv'ertical' portions have sufiicient resilience to hold the -a'rrester elements between them under the necessary pressure. The arrester properincIudes-a pair of electrodes 4 and 5, and a cylindrical valve block or resistor element 6. The valve blo'clp G-may be made of any suitable resistance material having valve 'characteristlcs, that is-,-.a material which-has a-veryhigh-resistance,-or-is semiconducting, under normaleondit-ions, but which has a relatively-low resistancewhen a high voltage is applied to-it. Thus, the block. 6 may,

be made, for exampleot granular silicon carbide mixed with a suitable-binder, suchas: sodium silicate, and molded to'thedesired size and shape and baked. Such valve elementsare, of'course, well known inthe-art.

The electrode 5..is, a metal disk of substantially thesame diameter as the block 6, and isplaced in direct contact withsthe-block. -The other electrode 4 is generallycup-shapedand; as clearly shown in the drawing, points about its periphery,iormingthe arc terminals of the electrode. The electrodes 4 and 5 arespaced apart-by a ceramic zspacercmember l, which is placed "within thecup-shaped electrode 4 and bears.agalnstwtheiiplane electrode 5 to space .the'tips. of the points of the electrode 4 a predetermined 'distance"..frorrr the electrode 5, so as to form a shortspark gap which will have a sufficiently low breakdown voltage. The spacer 1 perferably hasa" central projection i2 which engages in an opening in the. electrode 5 to center the electrodein the assembly and hold it in position. .iIn the case of anarrester intended for use on railway signahcircuits; for example, the spacing of the electrodes 4: and 5 should be such that the breakdown voltage of the gap between them is less than3;000 volts.

A second pair of electrodesfl'and 9 is also provided. The electrodes 8 and!) arej'generally'cup shaped, as clearly shown in the drawing," and enclose the electrodes "4.and 5- and valve block 6. The electrode" 8 isplacedbetwe'en the electrode A and one of thesupports 2; the electrodes being secured to the-'supportfin any suitable manner, as by arivet I 0. electrode 9 is placedbetw'een"the'valve block 6 and the Othersupport'Z; and maybe secured to the support 2 by a rivet I l. "The' elements of the arrester are heldtogetherunder' pressure by the resilient supportsZfthe spacer spacing the electrodes 4 and 5 apartes stated above, and the spacer 1 and valve 'blo'ckfi'al'so spacing the electrodes 8 and 9 apart. *It will be' seenthat a spark gap is formed between the peripheral edges of the electrodes- 8 and" 9 which is considerably longerthanthe short' gap between the electrodes 4 and-5,"and -which-is in parallel to the series-related shdrt-spark-gap "and valve block 6.

In the operation'of this deviceywheldan overhas a plurality of spaced,

Theother cup-shaped.

thus restoring the king condition. If, however, the discharge current that the space between the electrodes 3' .ofthe Valve block 6 to such a small magnitude that it is readily interrupted by the short gap,

arrester to its normal insula through the arrester is relatively high, the longer gap between the electrodes 8 and 5 will spark oven-and the discharge is transferred to the longer gap. This efi'ect appears to occur bccause a'heavy discharge current produces such profuse ionization of the air in the short gap and 9 becomes sufficiently ionized to cause'breakdown inthe long gap at a much lower voltage than would otherwise be required. Thus; the heavy without substantial damage.

discharge is transferred to the longer gap, which has heavy, rugged electrodes which are capable of withstanding the heavy discharge current When the surge has passed, the power follow current is interrupted because of the relatively long "spacing of the longer gap.

Thus, a low-voltage arrester 'is'provid'edwhich has very 'good protective characteristics, since the short gap has a'low enough breakdown voltage to provide a good margin of protection, while the longer gap. is capable of discharging heavy surge currents without-damage, although such a gap would have too high a breakdown voltage to be used by itself for protection ofa low-voltage circuit. The discharge characteristics of this type of arrester are 'very good since the discharge voltage across the arrester is-relatively low, even for very heavy currents, so that 'the protected apparatus is not subjected to a high voltage during the discharge. In case the valve block 6 should fail,'or become punctured, so that a discharge across the short gap would not be interrupted, or if for any other reason the short gap continues to discharge, the point or points of the electrode 4, which ar involved in the discharge, will burn back until the gap is lengthened I the slots there-is provided suificiently to interrupt the discharge. Thus, there is no possibility of the 'arrester bridging, or becoming short-circuited, under any conditions, since the effect of a continued discharge is to lengthen thegap until-it. is interrupted. Even if this should'occuryhowever, the circuit is not left without protection: sincenormally only one or twopoints of the electrode 4 are involved in a particulardischarge, and after they have burned back and interrupted the discharge, the remaining points are still intact, and the arrester is'still operative to protect the circuit until it can be replaced. Thus, the new arrester fully meets'the exacting requirements outlined above for arresters' for railway signal circuits and similar applications.

" Another embodiment of the invention is shown in Figs. 2 through 5. Thearrester shown in these figures has a base l5, which is molded'of any suitable insulating material. The base !5 is generally rectangular in outline and has two slots iii and i 7 extending vertically through it. Between a transverse recess it. The arresterelements themselves include a metal electrode member it which extends upwardly through the slot it and is secured to the base l5 by means of a rivet Zil. The electrode 19 has an extending end '2! which serves as a terminal for the device. A valve block 22 and a metal electrode member 23 are placed in the recess The valve block 22 is made of a resistance material having valve characteristics, and may be similar to the block 5 described above in connection. with Fig. 3., except that it is preferably rectangular in shape. The electrode 23 is also rectangular and of the same size as the block 22, and it is placed. in direct contact with one side of the block 22, as shown. The electrode 23 has a portion E l bent at right angles to the electr do so as to extend into close spaced relation to the end oi the electrode l9, as clearly shown in Figs. 2 and 4, and the portion 24 of the electrode 23 terminates in a plurality of substantially parallel points which form the arc terminals of the electrode.

A third metal electrode member 25 extends through the slot ll of the base l5, and is secured to the base b a rivet 21. One end of the electrode 26 extends outwardly from the base to form a terminal 28. The other end of the electrode 26 extends up past the block 22 and electrode 23, and is bent over at right angles. The end portion 29 of the electrode 25 is bent down toward the upper end of the electrode Iii, so that a relatively long spark gap is formed between the electrode portion 29 and the end of the electrode The electrode 25 has oppositely extending spring elements 30 and 3! struck up from it, which bear against the block 22 to hold the block 22 and electrode 23 firmly in contact and in place in the recess l8, and also to effect electrical connection between the terminal 28 and the block 22. An angular insulating spacer 32 is placed between the block 22 and the upper part of the electrode lit to space the electrode from the block and to prevent accidental discharges between the upper part of the electrode 26 and the block 22 or electrode 23. The complete arrester is enclosed by a cover 33 of sheet metal, or other suitable ma terial, which fits over the upper part of the base I5 and is retained in position by indented portions M which engage in recesses 35 in the sides of the base l5.

It will be apparent that the operation of this embodiment of the invention is similar to the operation described above in connection with 1. Thus, when an over-voltage occurs, the short gap between the points 25 of the electrode 23 and the electrode if flashes over to discharge the surge. If th discharge current is relatively low, the surge is discharged through the short and the valve block 22, and, after passage or" the surge, the block 22 increases its resistance and limits current to such a low value that the short gap can interrupt it. In case of heavy d-charge current, the discharge transfers to the 1m r gap between the electrode portion 29 a the end of the electrode which are of r vely rugged construction so to be able dacharge heavy currents without substan 'al damage. The spacing of this longer gap is eno so that the follow current is interrul ed ter or the excess voltage. In case of ure of the block 22 under a low surge current, or if for any other reason the discharge continues across the short gap without being either interrupted or transferred to the longer the point or points 25 involved in the discharge burn back until the arc is lengthened and finally interrupted, thus preventing any possibility of bridging or shortcircuiting of the arrester.

It should now be apparent that a low-voltage lightning arrester has been provided which has very desirable characteristics for the protection of low-voltage circuits, such as railway signal circuits. Tests have shown that the new arrester is capable of discharging very heavy surge currents, of the order of 100,006 amperes or higher, such as might result from a direct lightning stroke. Such heav currents can safely be handled because of the provision of the relatively long spark in parallel with the series-related short spark gap valve element. Tests have indicated that in a typical construction ernbodying the invention, the long, parallel gap sparks over at discharge currents of the order of about 1500 amperes or higher, with a time delay of the order of only three microseconds. ihe discharge voltage across the arest during a discharge is very low, since for heavy-current discharges the valve element is 'by-r' seed by the parallel spark gap so that the discharge voltage is only the relatively low arc voltage. The long, parallel gap with its rugged electrodes protects the more sen sitive elements or" the arrester from damage due to heavy discharge C'dll s, and thus permits the arrester to discharge very heavy currents repeatedl without damage and without aiiecting the protective characteristics. The possibility of the arrester becoming damaged. or of the valve element failing or being punctured, is quite remote, but in case such failure should occur. or if for any other reason a discharge continues in the short gap without being either interrupted or transferred to the long gap, the points of the short gap burn back and interrupt the discharge without any possibility of the arrester becoming short-circuited, while the remaining points of the short gap are still available for subsequent discharges so that the circuit not left unpro ected until the damaged arrester can be replaced.

Thus, a low-voltage lightning arrester is provided which has very desirable characteristics, and

' which fully meets the exacting requirements of the type of service for which it is intended. Two specific embodiments of the invention have been shown and described for the purpose of illustration, but it will be apparent that various other embodiments are possible, and the invention is not restricted to the particular arrangements shown, but, in its broadest aspects, it includes all equivalent embodiments and modifications which come within the scope of the appended claims.

We claim as our invention:

1. A lightning arrester comprising a first pair of spaced electrodes, one of said electrodes having a substantially plane surface and the other of said electrodes having a plurality of points substantially equally spaced from the first-mentioned electrode to form a first spark gap therebetween, a block of resistance material having valve characteristics disposed in series relation with said first spark gap, and a second pair of spaced electrodes, said second electrodes enclosing the first pair of electrodes and the block of resistance material and forming a second spark gap of greater spacing than the first spark gap in parallel relation to the series-related first spark gap and block.

2. A lightning arrester comprising a first pair of spaced electrodes, one of said electrodes having a substantially plane surface and the other of said electrodes being generally cup-shaped and having a plurality of points about its periphery, spacing 2,473;eco

with said first spark gap, and a second pair of opposed, generally cup-shaped electrodes, said first spark gap and said block of resistance material being disposed Within said second pair'of electrodes and spacing them apart to form a second spark gap of greater spacing than the first spark gap and in parallel relation to the seriesrelated first spark gap and block.

3. A lightning arrester comprising a base of insulating material, a first electrode member supported on the base, a second electrode member supported on the base, said second electrode member having a portion extending into close spaced relation to the first electrode member to form a spark gap therewith, a block of resistance material having valve characteristics supported on the base in contact with said second electrode member, and a third electrode member supported in the base in contact with the other side of said block, said third electrode member having a portion extending toward the first electrode member to form a spark gap therewith of greater spacing than the first-mentioned spark gap. I

4. A lightning arrester comprisin a base of insulating material, a first electrode member supported on the base, a second electrode membersupported on the base, said second electrode memher having a portion extending into close spaced relation to the first-electrode member to form a 'spark'gap therewith, said extending portion of the second electrode member terminating in a plu- 1,

rality of substantially parallel spaced points, a block of resistance material having valve characteristics supported on the base in contact with said second electrode member, and a third electrode member supported on the base in contact with the other side of said block, said third electrode member having a portion which extends past the block and'the second electrode member to form a second spark'gap with the first electrode member in parallel relation to the series-related first-mentioned spark gap and block, the spacing of said secondspark gap. being greater thanthe spacing of the first spark gap.

5. A lightning arrester comprising a base of insulating material, said base having two slots extending therethrough and having arecess between the slots, a first electrode member extending throughone'oi said slots, a second electrode member and a block of resistance material having valve characteristics disposed in saidrecess,

said second electrodemember being in contact with one side of said block and having a portion extendin into close-spaced relation with said first electrode member to form a spark gap therewith, said extending portion of the second electrode member terminating in a plurality of substantially parallel, spaced points, and. a third electrodemember extending through the other slot inithe base, said third electrode member being in electrical contact with the other side of said block'and having aportion extendingtoward the first-electrode member to'iorm a second spark gap therewith, the spacing of said second spark gap being greater than the spacing of the first spark gap.

6.- A. lightning arrester for the protection of lov-x-volta.ge signal-or control 'circuits, said lightmal condition, of interrupting a'discharge after an excess voltage has passed, a valve-type resistor disposed adjacent said second electrode means and-having one side inv electrical Contact with the second electrode means so as to be in series relationwith the spark gap, and a'third electrode member disposed in electrical contact with the opposite'side of said resistor and extending past the resistor to form a second spark gap with the first electrode means, said second spark gap being relativelylong,as-compared to the first-mentioned spark -gap,--:and being long enough to be capable, by itselfgof interrupting a discharge after an excess voltagehas passed, both of said spark gaps having -open, unrestricted arc paths, and the second gap being disposed adjacent the first gap soas to be rapidly ionized by a discharge in the first gap.

'7. A lightning. arrester for the protection of low-voltage signal-.orvcontrol circuits, said lightning arrester oomprisingfirst and second elec trode means;'one' of saidnelectrode means having a substantially planexsparking surface and the other of said electrode means having a plurality of substantially parallel-points, means for supporting the-electrodemeans with said points spaced from saidplane sparking surfac to form short spark gap therebetween, said spark gap having a breakdown voltage less than 3,000 volts and being so short that it is incapable, by itself, in its normal condition, of interrupting a discharge afteranexcess voltage has passed, a valvetype resistor disposed adjacent said second electrode means andhaving one 'side in electrical contact with =thei-secondelectrode'means so as to be in series relation with the spark gap, and a third electrode .member disposed in electrical contact with the 'oppositeside of said resistor and extending past the resistor to form a second spark gapwith the first electrode means, said second spark gap being :relatively long, as compared to the first-mentioned spark gap, and being long enough to be capable, by itself, of interrupting a discharge after an excess voltage has passed, both of said spark gaps having open. un-

restricted arc paths,'and the second gap being disposed adjacent the first gap soas to be rapidly ionized by a discharge inthe'first gap.

EDWARD F. W. BECK. JOHN S. FERGUSON.

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

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