US2338479A - Expulsion-type excess-voltage protective device - Google Patents

Description

Jan. 4, 1944. o. ACKERMANN EXPULSION-TYPE EXCESS-VOLTAGE PROTECTIVE DEVICE Filed Jan. 7, 1942 mvENToR 0U@ oke/mann.

ATTOR N EY evolving tube of the protective device.

manna Jan. 4, 1944 UNITED STATES PATENT y"OFFICE EXP-ULSxION-TYPE EXCESS-VOLTAGE PROTECTIVE DEVICE Otto Ackermann, Irwin, Pa., assigner to Westinghouse Electric & Manufacturing Company,

East Pittsburgh, Pa., a corporation of Pennsylvania Application January 7, 1942', serial No. 425.902

3 claims. .(01. irs-aol evolving insulating material disposed in the arc-" ing-space within the protective tube in such manner that the iiller is free to move a certain amount axially, radially, and rotatively about its axis, within the bore oi' the insulating gas- Protective tubes have been made, heretofor with insulating fillers which are non-movably mounted within the insulating tube of the device, as shown` in the original Torok Patent No. 2,050,397 of August 11, 1936, which is the original patent on the type of protective device to which my invention generically relates, and as is shown also in my most recent Patent No. 2,247,352, granted -July 1', 1941, on this general type of tube. Experience has shown that consecutive discharges usually pick the same channel in such protective devices, that is, the arcs iollow the same line along the walls of both the tube and the plug or filler, eroding them badly along this one line, and making no use of the rest of the material which is offered for volatilization or gas-evolution. This is probably due to the tendency of the arc to move to the path of the least deionizing action, which naturally would' be the one which has already been enlarged and partly deprived of deionizing matter by a preceding discharge.

At the same time, the plugged type oi.' protective tube is highly desirable by reason of the very definite current-limiting characteristic which is obtained in the long, highly restricted or narrow annular slot between the gas-evolving tube and the gas-evolving iiller or plug, which produces a high arc-drop which has the property of increasing its resistance or voltage-drop as the gaseous pressure builds itself up within the device, so much so, that after a time which may be of the order oi 1000 micro-seconds, or considerably less than a half-wave of the 60-cyc1e line voltage. the'power-voltage crest can maintain an arc of only a few hundred amperes, or other limor more locations.

ited current-value which can readily be completely extinguished .by the protective device at the first current-zero. Such plug-nlled protective tubes are very desirable, therefore, in inherently producing at least a partial current-limiting property which limits the magnitude of the power-follow current which usually ilows through the arc for the rest of the half-cycle after a momentary lightning-discharge; and this currentlimiting function avoids the necessity for a series resistor, even on power-lines of very large shortcircuit capacity.

It is an object of my present invention to avoid the eroding dimculties which have been experienced with previous plugged protective tubes by building the plug or filler so that it is free to' resiliently rebound in an axial direction, after a dscharge,.and atthe same time to randomly rotate itself, as a result ofthe mechanical reaction from the discharge, so that, when the plug `or ller settles down again after a discharge, the

line in its surface along which the arc had travelled is no longer disposed opposite to the line marked by the same arc along the bore of the tube. This action greatly reduces the qualities (such as roughening traces oi carbonization, increased cross-section, etc.) which may render yany one path preferable to a subsequent arc. Moreover, if such arc-facilitating features should still exist at all, they are now present at two This feature tends to distribute the discharges, which any one protector encounters during its life, more or less uniformly along the periphery of its bore and iiller, and it actually produces a. quite uniform wear of both.

Further objects of my invention relate to constructional details of the protective tube, and the employment of a single insulator for both the expulsion-gap tube and the series gap which is invariably connected in series therewith.

With the foregoing and other objects in view, my invention consists in the structures, apparatus, parts, methods, and systems hereinafter described and claimed and illustrated in the accompanying drawing, wherein:

Figure 1 is a vertical longitudinal sectional View through a so`called heavy-duty tube embodying my invention for use on 6900-vo1t distribution circuits having unlimited, or very large, short-circuit currents; and

Fig. 2 is a similar view of a second form of embodiment for systems whose fault-current is limited.

The heavy-duty protective tube shown in Fig. 1 comprises a main insulating tube 3 of fiber or other insulating gas-evolving material which is capable of evolving deionizing gases or particles in the presence of an electric arc. This tube is preferably mounted in a vertical position, and is preferably cylindrical, both as to its outer surface 'and its inner bore. rod 4 extends part-way into the top end of the insulating tube I, to constitute the upper elec.

device and terminates in a clamp 'I for engaging the line-conductor 8 which is to be protected against excess-voltage surges.

'I'he bottom portion of the'main insulating` tube 3 is surrounded by a strong steel tube I0 into which the insulating tube I is pressed with a tight press-tit. The steel tube III preferably extends slightly below the lower end ot the main insulating tube '3, to constitute `the lower electrode of my protective tube; and the upper end of the steel tube I Il preferably extends higher than the lower end oi' theupper electrode #-5, so as to strongly reinforce that portion of the insulating tube 3 which surrounds the lower extremity of the upper electrode. f

In accordance withmy invention,- I provide a loose plug and nller II which is disposed underneath the upper electrode 5, with a Alimited l amount of free'movement within the lower portion of the main insulating tube I. This illlcr Il is preferably made up of an outer ilber tube i2 having a tight press-tit on an inner ber bar or rod I 3, the bottom end-oi which is threaded or breaking. The outer diameter of the ller il is slightly less than the bore-diameter of the main insulating tube 3, to provide a long narrow annular gap-space therebetween, having a lateral or radial depth of the order of al, of an inch, or

other dimension suitable for building up con- L siderable gaseous pressure and a considerable arcing-voltage during the power-follow part ot an arcing discharge of the protective device.

The bottom end oi' the plug or illler I I rests on a steel pin 4I5 which is carried by vthe steel tube I at the bottom end of the main insulating sleeve 3. The length or height of the ilber plug or nller Il is such as to be spaced by about 1% of an inch, or other suitable spacing. from the bottom end of the upper electrode-tip B, so that the plug or illler II is iree to have a certain amount of longitudinal movement or rebound, within the main insulating tube 3, and also so as to provide a free arcing chamber IB between the upper end of the plug II and the lower end of the upper electrode 3, which may have a beneficial function in distributing the arc around different portions of the periphery of the inner plug or ller I I.

As in my previous patent, hereinabove mentioned, it isnecessary, in the particular design shown, to properlsr insulate the upper end of the steel tube I0 so as to prevent the occurrence of external flashovers outside of the main insulating tube 3. For this purpose, a thin insulating tube IBis sleeved over the top of the steel tube I0, so as to extend on up as far as the top oi A cylindrical steel 30 overhead line conductor 8.

55 described.

the main insulating tube 3, and the annular space between these two insulating tubes Il and 3. above the top oi the steel tube I0. is filled with an insulating compound I9 which is of a 5 type that will adhere to, or wet, the surfaces oi' both of the insulating tubes I8 and 3, and also of such character that it will not harden and crack, producing voids at low temperature. The insulating compound which is commonly used '10 for standard condenser-bushing assemblies is suitable for this purpose.

In the particular form of embodiment of my invention which isl shown in Fig. 1,l I also provide an additional outer tubular insulatingmeans 2|, in the form of a porcelain insulator which surrounds the upper portion of the protective device. The porcelain insulator 2| has a closed top end 22 which is perforated at 23 to receive the top portion of the-steel rod or upper electrode 4. 4The open lower end of the porcelain insulator 2| is spaced-from the steel tube I0 by means oi' a washer 24 which is welded at 2l to the steel tube Ill.

'.My heavy-duty protective device which is 25 shown in Fig. 1 is supported by means oi a grounded conducting supporting bracket 2l which is in mechanical engagement with the outler porcelain insulator 2i, for supporting the protectivev tube in a vertical position beneath the The supportingbracket .26 is provided with an arc-gap electrodemeans 2`Iwhich is in electrical connection with said bracket and which extends into a spacedgap relation 2 8 with-respect to the slteeltube or .35 lowerA electrode I0, so as to provide a series gap 28 between the lower electrode I0 and the ground-connection of thebracket 26, which is indicated at 29.

In the operation of the device which is shown '40 in Fig. 1, when the line 8 is subjected to an exto receive a steel tip Il for protecting the bottom. end of the i'iber plug or ller from chipping oil' cess-voltage surge, an arc is produced between the bottom surface of the upper electrode-tip I 4.? the filler II, and then through the long narrow annular space Vbetween the iller II and the bore of the main insulating tube 3, thence passing below the insulating tube,3 `to the steel sleeve or bottom electrode I0, or possibly making contact with the steel cross-pin l5 which is in engagement with the bottom electrode I0. As explained in my above-mentioned patent,` the reinforcing metal sleeve I0 also serves as a shield, iacilitating the breakdown oi' the internal arclng-path Just At the same time, an external arc flashes across the external gap-space 28 to the bracket-electrode 21, thus completing the circuit to ground at 29.

The excess-voltage surge on the line-conductor 8 usually lasts a relatively short number oi' microseconds, during which time the discharge may be very heavy, depending Aupon the severity of the lightning-stroke or other disturbance causing the excess-voltage condition. When this excess-voltage surge is dissipated, the line-voltage re-appears across the arcs within and without the tube, usually resulting in what is known as a power-follow current-flow, dependent upon the ability of the line to deliver a short-circuit current, and also depending upon the resistance of the arc within the insulating' tube 3 The initial momentary surge-discharge, and the usually much longer power-follow discharge, both produce gas-evolution from the fiber surfaces which are subjected to the play of the arc within the protective device, and these evolved gases build up tremendous gas-pressures within the main insulating tube, tending strongly, not only to burst the tube, but also to blast out everything in the tube. including both the upper electrode 4-B--6, and theilller or plug il and the outer metal sleeve to which they are pinned. The insulating tube r3 is protected against bursting by the strong steel tube I0, and at the same time the gas-pressure within the insulating tube presses the outer walls of the insulating tube so strongly against the steel tube that axial displacement between the two is substantially an impossibility. Experience has shown that my design is adequate to withstand the tremendous mechanical forces of the gaseous pressures which are developed withinthe main insulating tube 3 during a discharging operation ofthe device.

'I'he deionizing properties of the evolved gases result in a cumulative increase inthe electrical resistance, or in the voltage-drop required by the arc within the tube, thus developing a currentlimiting action which limits the power-follow current which can be delivered by the line-voltage,iollowing a momentary lightning-discharge. The result of these actions, is that the arcs are While I have illustrated and described my inventionin two forms of embodiment which are at present preferred by me, I wish it to be understood that such'illustration and description are v only by way of example and not by way of limitation, as various changes may be made by those skilled in the art without departing from the essential features of -my invention. I desire,

`therefore,- that the appended claims shall be accorded the broadest construction consistent with extinguished at the iirst current-zero following an excess-voltage discharge, and the device is capable of handling the heaviest lightning discharges, andthe heaviestshort-circuit currents which any line of the proper voltage-rating is capable of delivering. l

During a discharge, as above noted, the ller li is pressed verystrongly against its retainingpin i5. After the internal gaseous pressure 'has been dissipated, the filler ii rebounds from the pin l5, and perhaps chatters around in its space a bit, sothat it becomes rotated away from its former position, and the next discharge does not find a,dischargechanne1 of such marked preference and reduced clearing-ability as would exist if the filler had remained in its original position.

The form of embodiment of my invention which is shown in Fig. 2 is designed for distributioncircuits having a limited short-circuit capacity of not over 500 amperes R. M. S. It s similar to their language.

. I claim as my inventionz. v

1. An expulsion-type excess-'voltage''protective4 device comprising4 an insulating tube"having a cylindrically bored surface of insulating gasevolving material capable of evolving deionizing gases o r particles in the presence oi.' an electric arc, a loose llerdisposed for a limited amount of free movement v within said insulating tube, said filler having an outer cylindrical surface of insulating gas-evolving material capable of evolving deionizing gases or particles in the pres-4 `ence of an electric arc, the outer diameter of the ller being slightly less than the bore-diam-l eter of the tube, abutment-means for limiting the axial movement of the illler in the tube to a small but appreciable amount, while otherwise -1 leaving the ller free to move axially, radially,

androtatively about its axis, within the bore of the tube, and free to come to rest in .any position, and two spaced electrodes so disposed that the arc-gap between'said two electrodes includes the space between said illler and said bore, at

4v5least oneof the electrodes extending partway the heavy-duty tube which is shownin Fig. 1,

except fordetailsgof the supports, the omission of the porcelain insulator 2i, and a shortening of, the axial length of the discharge-space within the main insulating tube 3' below the lower tip 5' of the upper electrode l'. In the form of embodiment of my invention as shownin Fig. 2, the upper electrode 4' takes the form of a steel bolt whose head 3l is engaged by a metal terminalcap 32 which is screwed down into engagement withl the bolt-head. The terminal-cap 32 also carries an arc-gap electrode-means or rod 33 which extends in a spaced-gap relation below the overhead line-conductor B' which is to be Drotected, thus providing an external gap 28 between said overhead line-conductor 8' and the arc-gap rod 33 at the top of the protective tube.

The supporting-means for the protective tube which is shown in Fig. 2 is in the form of a grounded supporting-bracket 35 which is grounded at 36, and which is bolted to the lower end of the steel tube i0'. v

The operation of the device shown in Fig. 2 is similar to the operation of the more elaborate device which is shown in Fig. 1, except that the series arc 28 is formed between the upper electrode 4' and the line-conductor 8', instead of at the grounded end of the device, as in Fig. l. Ihe shorter length of the iiber plug or illler rinto said bore.

' 2. An expulsion-type excess-voltagey protective device comprising an approximately vertically disposed insulatingl tube having a cylindrical bored surface of insulating gas-evolving material capable of evolving deionizing gases or particles in the presence oi?4 an electric arc, a rodlike upper electrode extending into the top end of the insulating tube withal tight t therein, a tubular lower electrode oi' strong metal construction tting over the lower portion of the insulating tube with atight press-tit therebetween, said tubular electrode extending below the lower end oiv the insulating tube and extending up past the portion of the insulating tube that surrounds the lower end of the upper electrode,

a loose ller disposed underneath said upperv electrode with a limited amount of free movement within said insulating tube, said illler having an outer cylindrical surface of insulating gas-evolving material capable of evolving deionizing gases or particles in the presence of an electric arc, the outer diameter of the illler being slightly less than the bore-diameter of the tube, and abutment-means at the bottom of the insulating tube for supporting the filler so that its top end is spaced below the bottom end of the upper electrode.

An expulsion-type excess-voltage protective device comprising an insulating tube having a cylindrical bored surface o! insulating gasevoiving material capable of evolving deionizing gases or particles in the presence of an electric arc, a rod-like electrode o! the insulating tube with a tight fit between the inner end of said rod-like electrode and the bore oi' said insulating tube, a tubular electrode of strong metal construction tting over a portion of the insulating tube at the opposite end thereof, with a' tight press-nt therebetween', said tubular electrode overlapping the portion of the insulating tube that surrounds the inner end of the rod-like electrode, a loose filler disposed within said opposite end of the insulating extending into one end IIO exceed BDledtel'mil'led Spaing.

OTTO ACKERMANN.

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