US1784760A - Circuit breaker - Google Patents

Description

Dec, 9, 1930.

- J. SLEPIAN CIRCUIT BREAKER Filed April 6. 1927' 3 Sheets-Sheetl INVENTOR Jaseph 549 0100.

WITNESSES: 62: Q

ATTORNEY J. SLEPIAN CIRCUIT BREAKER Dec. 9, 1930.

Filed Apr i1 6. 1927 s Sheets-Sheet 2 INVENTORI J55ep/7 5/ep/ or).

ATTORNEY WITNESSES:

Dec. 9, 1930. l "J. }'./EPIAN 1,784,755,

C IRCUI T BREAKER Filed April 6, 1927 3 Sheets$heet 3 Fig. 6.

WITNESSES:

@- 4 I v Jseph S/ep/afi BY k7, I W

Y INVENTOR I Patented Dec. 9, 1930 ONITED STATES PATENT OFFICE JOSEPH SLEPIAN,

OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR T0 WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA CIRCUIT BREAKER Application filed April 6, 1927. Serial No. 181,289.

My invention relates to circuitbreakers and particularly to arc-extinguishing devices thereof.

One object of my invention is to provide means for interrupting the flow of electricity through gaseous media.

Another object of my invention is the provision of a circuit breaker provided with an arc-interrupting device capable of opening high-voltage, large-current arcs in air or gas without recourse to oil or other arc-quenching media. Some of the aspects of my invention, are, however, applicable in connection 'with low-power, clrcult-opening devices, and

to a'variety of otheruses.

The principal field for immediate application of my invention is in connection. with alternating-current circuit breakers, and I shall hereinafter describe an embodiment of my invention as applied to such circuit breakers, without in any way intending to restrict-the scope of my invention, except as indicated in the appended claims.

According to the invention, the arc incident to the opening of a circuit is driven into an endless arc track and maintamed 1n continuous movement on said track until the arc:

has been extinguished. In order to extinguish the arc, the track is made in the form' of a chamber having deionizing surfaces. in close proximity to the arc, sub-dividing the latter into serially related arc sections. By continuously driving the are along said surfaces, they are maintained Fig. 1 is a diagrammatic view of a circuit and preferably the arc.

breaker embodying the principal elements of my invention; I

Fig. 2 is a detail view of an end plate embodie'd'in the deionizing structure.

Fig. 3 is a detail view of one of the intermediate plates in the deionizing structure;

Fig. 4 is a detail view of a different intermediate plate in the deionizing structure;

Fig. 5 is a sectional view along the line v-v of Fig. 7;

Fig. 6 is a sectional View along the line- VIVI of Fig. 7 and Fig. 7 is a side view, partly in elevation and partly in section, of the deionizing structure. The present invention is,-in some aspects, a further development of the circuit breaker described in my copending application Serial No. 54,930, filed'Sept. 8, 1925, and assigned to the assigneeiof the present application.

In the foregoing application, I have shown that large-power, high-voltage, alternatingcurrent circuits may be opened without recourse to oil or other arc-quenching media, by introducing into the are, conducting sheets or nucleiso distributed in the arc space as to quickly deionize' the same during the short interval inwhich the arc current is nearly zero. If the'rate of (leionization of the arc space is suificientlylarge, as comparedwith the rate of rise of voltage across the arc ter-- minals after the current zero, a deioniz ing structure of the foregoing character will safely prevent arc reignition after the current zero.

The deionizing structure described in the,

above-mentioned application had the form of a chamber in which a plurality of reticulated sheets of conducting material, such as brass, were closely spaced, transversely to The are was thus, everywhere and in all parts, close to portions of these conducting sheets.

. Practical tests, and theoretical considerations set forth in the above mentioned application, indicate that the rate at which the arc space is deionized depends directly on the" number of sheets disposed in a given arc'space and the intimacy with which said sheets embrace said space, inasmuch as the 'deionization proceeds from the cathode terminal surface of the are chamber and from the surfaces of the sheets facing in the same direction as the cathode terminal surface of the chamber.

On the cathode side of each sheet, a region that is nearly denuded of ions is formed, this region growing in thickness toward the next adjacent sheet until the entire spaces between the sheets are deionized. It is because of this deionizing action of the metallic portions of the individual sheets, which is similar to the deionizing action taking place near the cathode proper, that I often term the deionizing sheets or grids artificial cathodes.

In the above identified application, it was also pointed out that therate of the deionization of the space between the individual sheets of thedeionizing chamber is the greater, the

more uniformly the arcspace is filled with the deionizing sheets. That is, for most rapid deionization, it is desirable that the in-.

dividua-l sheets which extend across the arc shall be solid and that the arc shall-be broken up into short arcs which are individually confined between such solid metal sheets.

- Although the desirability of having solid sheets was fully recognized in said prior application, practical tests showed that, with the magnetic blow out structures then available, no successful arc de-ionizing structure for commercial circuit breakers could be developed with solid sheets, inasmuch as the serially disposed short are sections into which the arc would be divided by the sheets would form hot-cathode spots on the closely spaced deionlzing sheets, melting the metal and producing metal vapor which is less easily dethat can take over the duties ionized than air.

In addition, the melting of'the metal would very soon weld the sheets together and render the entire structure inoperative. On the other hand, the close spacing between the deionizing sheets is very essential to a satisfactory operation on high-current, high-voltage circuits if the rate of deionization of the are space is to be made sufiiciently large to permit the construction'of a circuitbreaker now performed -As an additional limitation, the speed of the movement of the are within the deionizing structure had to be relatively low on account of the limited length of the arc chute possible in commercial breakers; with too great arc speed, the arc would be blown from the deionizing structure and would hang at the ends thereof, with entire loss of the deionizing efiect of the structure.

As a result, the deionizingstructure described in the foregoing application was, to a certain extent, a compromise between the requirement for solid deionizing sheets to increase the rate of deionization of the are a into the arc space in order to ficial cathodes at the time the arc current was passing through zero, but, at other times,

as far as the arc was concerned, it aimed to leave the arc undisturbed 1n 1ts movement, so far as possible, and permltted 1t to play between the main are terminals of the chute,

as if no such sheets were there.

The choice of perforated sheets with a view to avoiding development of hot-arc terminals on the individual sheets seemed also to be required from the generally known theories of arc operation, as understood until recently. It did not seem possible that hotcathode spots on the grid sheets could be avoided if there were tobe a splitting up of the are into separate arc-sections, with distinct cathode and anode terminals on the individual solid sheets/w- Heretofore, it has been generally accepted that, in order to maintain an arc, that is, a self-maintaining discharge having a voltage drop at the cathode which is very considerably less than the normal glow discharge enough to emit electrons. Such temperature is higher than the melting temperature of,

the materials available for structures here in question, and would, accordingly be destruc-,

tive to such structures.

- Thus, as late as in 1923, K. T. Compton presented, in the Physical Review, volume 21,

page 226, etc., the result of a very thorough investigation of the nature of arc discharges, reaching the conclusion that the greater part of the current carried at the cathode consists of thermionically emitted electrons.

However, as a result ofexperimentsand studies, I have been led to the belief that thermionically active cathodes are not absolutely necessary for the maintenance of an arc discharge, and that, while frequently, are discharges operate with hot cathodes, it is also possible tomaintain an arc discharge under conditions where thecathode is cold, or, 1n any case, wherethe cathode has a temperature much below the temperature of electron emission.

Theoretical considerations, which are set forth, 1n the Physical Review for April, 1926, pages 407-412, and theoretical analysis by thermal ionization in a gas layer next to.

the cathode, instead of by thermionic electron supply from the cathode.

An arc witha cold cathode, such as I have described above, may be obtained by causing the arc to move so rapidly over an extended cathode surface, that no point of the cathode surface is subjected to the heat of the are for a time long enough to acquire a high temperature. When such an arc is obtained experimentally with copper electrodes, examination of the trace on the electrode surfaces shows that the current density there is very much greater than for an arc with a hot cathode.

Thus, I have found the current density with cold-cathode arcs to be about 30,000

a mperes per cm whereas, for example, the

usual carbon arc has a current density of only a few hundred amperes per cm This very high current density seems to required by theory also, because, to maintain a layer of air immediately adjacent to the cold cathode at a temperature high enough for thermal ionization, that is, at a temperature of several thousand degrees centigrade, requires a very large input of power there, and this may be obtained by a very high current density.

According to the present invention, the fact that an arc may be maintained without producing hot-cathode spots on the arc electrodes ismade use of in orderto provide a deionizing structure in which the arc incident to the opening of a circuit is driven between solid metallic .sheetsand is split up into small arc sections with distinct cathode and anode terminals, the arcs between the individual sheets being maintained in the form which I designated before as coldcathode arc 'discharges.-- I

Thus, the effectiveness of the deionizing structure used-in circuit breakersof the type described inmy foregoing application is greatly increased by making full use of the very large deionizing effect obtained with solid plates closely spaced transversely to the arc and maintaining the short arc discharges between said sheets in the form of cold arc discharges, as explained above. That is to say, irrespectively of whether my present understanding and explanation of the cold arc discharges is correct, I, provide a structure in which I sub-divide the arc incident to the opening of the circuit into a large number of small serially-connected arcsections playing in thin spaces between solid metal or conducting sheets without any considerable heating of said sheets and positively prevent ing melting orother injury to the sheets by reason of hot-cathode spots, or the like.

I have found that, if the arcs between the individual sheets are moved over the sheets with suflicient rapidity, there is no melting at the arc terminals and, presumably, the arccurrent carriers are supplied entirely by ther-,

mal ionization of the air next to the cathode and between the sheetslVith arc-blow-out structures heretofore employed, the speed with which the arc could be moved between the arc electrodes was limited by the fact that, within the time available for the arc' movement, that is, 1/ 120' of asecond, in case of (SO-cycle alternating current, the arc must remain confined between the de-ionizing sheets. If the arc was to be given a speed at which it could be maintained without heating the cathode, the prior arc-blow-out structure Would require a length considerably beyond what was practically possible. i x

In an effort to obtain an arc-blow-out structure in which the speed of the arc movement would be free from limitation with regard.

.to the length of the arc chute, and thus'to make possible are speeds at which the formation of hot-cathode spots on the electrodes should be avoided, I have devised a new type of arc-driving, or arc-blowing, arrangement which causes the arc to move over a limited area at such high speeds as are required to give the arc the necessary characteristics.

The new arc-driving arrangement is based -on the idea of producing a peculiarly shaped magnetic field which causes the arc to keep on moving at Very high Velocity repeatedly over the same path in a limited space to which the arc is intended to be confined, the high are velocity preventing excessive heating of the arc-terminal surfaces and the adjacent bodies so that the arc takes the form which I havetermed cold-cathode arc.

The novel arc-driving arrangement is not limited in lts utility to deionizing structures ofthe type using closely-spaced deionizing sheets disposed transversely to the arc, but it has opened a large number of possibilities in improving other types of electrical apparatus, and particularly switching apparatus utilizing other kinds of are or currentinterrupting structures. Some ,of the claims appended hereto are, accordingly, directed to the features of the new arc-drive structure,

irrespective of the type of apparatus in which.

it is utilized.

The diagrammatic illustration of the principal elements of a circuit breaker embodying my invention, as shown in Figs. 1 to 7, will make the novel featuresexplained hereinabove readily understood.

The circuit breaker shown in the drawing has the usual main contact members 1 and 2 arranged to be bridged by a main contact brush 3 that is held on a main contact arm 4. The arm 4 is pivoted to swing the brush 3 between the position in which it closes the 8 members in which the circuit breaker is open.

The circuit breaker is further provided with an arc-interrupting structure 5 comprising an arcing contact arm (5 having, at its upper end, an arcing contact shoe 7 adapted to engage a tionary arcing contact member 8 for finally interrupting the circuit, the arcing shoe 7 and the stationary arcing contact member 8 being suitably connected, as by means of conductors 9 and 10 that'inelude main blow-out windings 11, in parallel to the main contact members 1 and 2.

To open the circuit, the main contact arm 4 and the arcing contact arm 6 are swung to the right by means of a suitable toggle mechanism comprising a bell-crank lever, that is pivoted at 12, and links 13 so arranged that, in opening th circuit breaker, the brush 3 is first lifted from the contact members 1 and 2, diverting the current from the brush into the shunting circuit through the arcing contact arm 6', arcing contact shoe 7, stationary contact member 8, conductors 9 and 10, and blow-out winding 11. Further movement of the bell-crank lever fully opens the circuit by swinging arm 6 to the right, thus bringing about disengagement of the arcing contact shoe 7 and the stationary arcing contact member 8 at their arcing tips 14.

A pair of auxiliary contact members 15,

that are arranged to be opened somewhat later than the main contact members 1, 2 and 3, but somewhat earlier than the arcing-contact tips 14, are usually also provided to relie've the main contact members of arcing incident to the transfer of the current from the main brush 3 to the inductive shunt circuit including the blow-out coil 11 and the arcing contact members 7 and 8. Contact arm 4 is connected, near its hinge, to contact member 2 through the previously mentioned ;-my invention is'prin'cipally directed, comflexible connector 9 to complete a path through contacts 14 from contact member 1 to contact member 2.

The arc-extinguishing structure, to which prises an arc-chute 21 which extends above the space where the are between tips 14 of plates 26 and 27 thus define a straight rectangular chamber 28 having, at its lower end, a downwardly tapered arc-entrance chamber 29 extending between the inclined arc- horn plates 22 and 23 and the lower portions of the pole shoes 25. The magnetic flux induced between the pole shoes 25 has a direction transverse to the plane of the drawing so that, when the circuit breaker is opened and an arc is drawn between the arcing tips 14, the are is blown toward the inclined arcing horn plates 22, 23, and then upwardly along the latter through the entrance chamber until it reaches the straight portion of the arcing chamber 28.

The straight portion of the arcing chamber between the arcing plates 26 and 27 is filled with a plurality of solid metallic sheets or plates 31 which I have before designated as the deionizing sheets or grids of the arcinterrupting structure. The individual sheets are insulated from each other, as by means of paper strips at the edges of the sheets; I have, however, omitted these from Fig. 1 of the drawing which indicates only the air spaces between the sheets.

The circuit-breaker elements, described so far, resemble, in every respect, the elements of the circuit breaker described in the aboveidentified prior application, except that, in the present case, the deionizing sheets filling the arc-chamber between the vertical terminal plates 26 and 27 are solid instead of perforated. Other very important distinctions in respect to the differences of the design of the two types of deionizing strueture will be discussed later on.

Extending directly above the straight portion 28 of the deionizing structure, and as a direct continuation thereof, a circular extension 32 is provided into which the are from the straight portion 28 of the deionizing structure is driven and whereiii it is vcaused to travel along a closed path 33 around the center of the circular extension. When viewed from the side of Fig. 1, the deionizing sheets are as shown in Fig. 3.

In the practical construction of this type of circuit breaker, I make the vertical end plates 26 and 27 of the aro'chamber in the I the arclng contact members 7 and 8 is drawna/form shown in Fig. 2 of the drawing, with -horn plates .22 and 23. The upper ends, of

the inclined arcing horn plates 22 and 23 merge into vertical arcing plates 26 and 27, shown in detail in Fig. 2.

The pole shoe 25 and the vert cal arcing a lower straight portion 34 merging into a circular portion 35 at the top thereof. The individual deionizing sheets 31, which are disposed within the space between the end plates 26 and 27 have also a lower straight portion and an upper circular extension, as shown in Fig. 3.

While the straight portion of each of the end plates 26 and 27 is solid throughout its entire breldth, the straight portions of the intermediate deionizing sheets 31 have tapere'd slots 36 which are wide at the bottom and narrow down toward the top, each slot termmatmgat a point. I shall later explain the reasons for providing the tapered slots in the individual deionizing sheets. The circular portions of the end plates 26 and 27 -and of the individual sheets 31 of the deionizing chamber have central holes or openings 37. The sheets 31 have narrow radial slots- 38 in their circular portions, for reasons which will be explained later.

Assuming that the arc current, in the structure of Fig. 1 of the drawing, flows in the dlirection'from the left'to the right. as indicated by the circle having a cross in Fig. 3, the field in the lower straight portion of the deionizing chamber must have a direction as indicated by arrows 39 in Fig. 3, in

order to drive the arc upwardly along the straight, portion 41 of the arc path.

' After the are reaches the circular part of the deionizing structure, I cause it to travel along the closed circular path 33 by provide ing a radial magnetic field, indicated by the arrows 42.

Since a magnetic field transverse to an electriearc always moves the arc in a path normal to the lines of force composing that field, this radial field causes the arcs between the plates of the deionizing structure to trave1 around it continuouslyin a circular path as long as such arcs remain in existence. The radial field 42 is'obtained by means of suitable exciting coils arranged at intervals between the sheets to give a field of the required shape and strength, in a manner now to be explained.

In the arrangement shown in Fig. 1, there are two main groups of deionizing sheets 43 and 44, each group consisting of nine P-shape sheets. Between the left hand sheet of group 43 and the left-hand arc-terminal plate 27, is

provided a radial field coil 45 which is connected between the terminal plate 27 and the nearest deionizing sheet of the group 43. With the current in the coil 45 flowing in the direction indicated by the arrow. a radial magnetic field will be produced in the narrow spaces between the dcionizingsheets of the group 43, the dotted lines 46 indicating the direction and distribution in space of this fiux. In order to provide a radial field of relatively great strength without requiring an excessive number oii ampere turns in the exciting coils 45,-I provide a plurality of washers 47 ofmagnetic material along the return path of this radial magnetic flux.

In order to'provide the radial field between the five right-hapd sheets of the deionizing group 43, I connect, between the right-hand sheet of said group 3nd the left-hand sheet of the other deionizing group a pair of op-. positely wound coils 48 ant for inducing, in the spaces [between the'iespective sheets, the radial fiuxes. asindicated by the dotted fluxlines 51 and 52. Magnetic washers 53 between the coils 48 and 49 provide low-reluctance magnetic returnpaths for the fluxes.

induced by said coils.

A coil 54, disposed to the right of the deionizing group which is connected in the same manner as the left hand coil 45 and which is similarly associated with a set of magnetic washers 55, provides for the radial flux in the right-hand portion of the deionizing group 44.

As shown in Fig. 3, the plates 31 have radial slots 38 which prevent their annular portions from acting as short circuited turns to damp out the magnetic field due to the coils 45, 48, 49 and 54.

In the portions of the deioni'zing chamber where the circular portion of the structure is occupied by the exciting coils 45, 48, 49

and 54 and the associated magnetic washers I 47, 53 and 55, the deionizing sheets consist of only the straight lower extensions 61 shown in Fig. 4 of the drawings. Three sections 62, 63, and 64 of such short grids are provided in the structure below these three sets of cirin the resulting structure which may be roughly described. as of V-shape. The reason for providing this V-shape groove will now be explained;

The high current density existing in a cold-cathode arc must be considered when it is attempted to cause, as I do in my invention, a long are with low current density to be broken up into a series of short .coldcathode arcs. The following experiment illustrates the properties of an arc-which I use in accomplishing this. If a cold wire is plunged into an unconfined are which is playing out into the open, with only a low current density, and if the wire is given a negative electric potential with respect to the arc, only a small current of the order of a few milliamperes per cm will flow to the wire so long as it is cold, even though the wire is given a potential of several hundred volts relative to the arc. This is because the density of ionization in the arc is so low that the current carried to the cold wire is insuificient to raise the temperature of the air next to the wire to a ftemperature high enough for suficiently ihtense thermal ionization to make the wire function as a cold-cathode arc terminal.

If, however, the are into which the wire is thrust, isconfined to a restricted hole or slot, so that its current density is high, then the application of a negative potential of only 30 voltswill cause a very large current to flow to the wire while it is still cold. ,This is betion of cold-cathode arcs,

- the side walls of the groove.

mode of operation,

cause, with the high density of ionization, the more intense current which flows to the wire causes the air next to the wire to be ionized thermally with suflicient intensity for a cold-cathode arc to form there.

It has" already been stated that the producas the means of transferring the current path to the deion structure, requires that the arc current shall be concentrated in an extremely small crosssectional area. One object of the V-shape groove is to bring about this condition.

As the arc is driven upwards from the end strips 22 and 23 above-described by the field of magnet-24, its current flows through a relatively large cross section at comparatively low current density therein. The wide mouth at the base of the V- shapc groove permits this are to enter without difficulty. As the magnetic field forces the arc upward, the V-shape groove gradually contracts the cross-sectional area of the conductive path of the arc, this effect being due, probably, to the deionizing effect of the metal strips constituting As the crossthus gradually blown upward,

sectional area of the arcis constricted, while it is being the current density therein becomes greater and greater. The potential gradient of the arc rises at the same time. of this, by the time the arc has been forced to the apex of the V-shape groove, the current flow therein has been highly concentrated, and the voltage gradient has become sufiicient to force the arc to transfer to the narrow gaps between the deionizing plates.

I have found that, by properly proportion ingthe taper of the groove relative to the current to be interrupted, the arc may be made, to transfer readily to the plates of'the deionizing structure and there to operate as a series of cold-cathode arcs kept in motion by such means as the magnetic field herein described. a

This increase of current density and .of voltage gradient has obviously been gradual throughout the movement of the are up the tapering groove, and the arc is, therefore,

caused to break up into a series of short arcs,

running between the deionizing' plates, smoothly and without any abrupt transition in its electrical condition. Not only does this avoidance of an abrupt transition'facilitate the transfer "of the arc to the cold-cathode but it is of great value by virtue of the fact that it also minimizes electrical disturbances and the production of transients on' .the circuits on which current flowis being interrupted. I

Tracing, in detail, the steps in the process of are interruption in my circuit breaker, the

movement of the brush member 3 to the right interrupts the direct contact between members 1 and 2 and causes current to flow through winding 11 of the blowout magnet deionized structure 28, and

In consequence 24 to end plate'27, thence through arcing contacts 7 and 8 to contact arm 6 and conductor 9. As the contact arm 6 moves farther to the right, an arc is drawn between contacts 7 and 8. The arc is driven upward by the influence of the magnetic field between pole faces 25, the terminals of the arc transferring to the horns 22, 23, until it reaches the mouth of the V-shape groove in the deionizing structure 28. The are continues to rise under the application of this magnetic field, and the tapering groove gradually constricts the cross section of the arc, simultaneously increasing its voltage gradient, as has already been described.

By the time the arc has reached the apex of the V-shaped groove, the density of ionization has been raised by the resulting current concentration to such a degree that the currents which flow to the metal plates are great enough to cause thermal ionization of the gas adjacent to the cold metal plates. Underthese-conditions, the cold-cathode discharge, becomes possible between the plates 31 of the the are readily transfers, under the influence of the magnetic field, to the space between the plates above the apex of the V- shape groove.

While rising under the impulse of the magnet 24, along the straight portion of the chute, the arc sections in the plate groups 62, 63, 64, are shunted by the low-resistance coils 45,48, 49, 54, so that the current diverts from these arc'sectionsiinto the coils. By the time the arc has reached the top of the straight portion of the chute, the current in the arc sections 62, 63, 64'has reduced to zero, the coils 45, 48, 49, 54 carrying all the current and producing the radial magnetic field which drives the remaining are sections around and around the circular portion of the chute. v

During all the. time that the arc is in con-. tact with the metal plates of the deionizing structure, energy, being rapidly abstracted from it. Because of the rapidity with which the arc traverses the metal plates, no one spot on these over becomesheated'to a sufficiently high degree to emit an appreciable number of electrons or to melt.

It is readily seen from what has been said above that, in a deionizingstructure com rising merely a series ofmetal plates, wit iout the tapered slots wh-ich'I have provided.

which I have previously described,

in the form of heat, is

transition of the are from its initial continuinoperative for the purposes they are required to serve. The presence of the groove is, therefore, a material addition to my invention and the explanation of its function as given above, is believed to be correct, but, independentof its correctness, experience has proved beyond question the much greater eliectivendssin practice of deionizing structures provided with such grooves.

It will also be noted that the increase of are current density resulting from the constrictin effect of the walls of the V-shape groove has a further efiect in forcing the transition of the are from the single continuous form to the series of short arcs operating between the deionizing plates. ing force which a. given magnetic field exerts upon the air at any point is proportional to the current density at that point, so that constriction of the arc in the groove causes the force on the air in which the arc is playing to be greatly intensified and thus to carry the are between the metal plates.

The contour to be given to the tapering slots above described in the deionizing plates depends upon many factors, such as the amount of current to be interrupted, the strength ofthe blowout magnet and thedynamics of air flow in the structure. eral, we may say that the taper must be sufiiciently gradual. At each stage in the motion of the arc in the slot, the alternative is presented to it of standing still and being subj ected to the blast of air due to the action of the magnetic field, or of moving with the air and being subjected to the increased constriction ot' the slot. Either alternative causes its "voltage tobe raised and, evidently, it will follow that alternative which will give the least rise involtage. The slot should, therefore, be so designed that the rise in voltage in the are due to the increasing taper .is less than the rise in voltage which would be produced 1 1? the are stood still and was subjected to the air blast produced by the magnetic field. to interrupt.10,000 amperes at 2500 volts on a 60 cycle circuit, for example, a slot which doubles in width for every one half inch of length has been found to be etlective.

As to the proportioning of my deionizing structure, I have found that there should be such a number of gaps between the deionizing plates that not more than 300 volts should be impressed across each gap when the full linepotential appears across the terminals of the open breauer.

The reason for this limitation is that it has been found that, in the absence of any other intense source of ironization,-as the air gap between a pair of plate terminalsds decreased from a Value of, say, a centimeter, the voltage necessary to cause unlimited spontaneous ionization or breakdown of the intervening gap decreases until a certain mini- In gen- In a circuit breaker rated mum is reached. A further decrease of the gap is found to cause an increase of the voltage necessary to cause breakdown. This minimum voltage is in the neighborhood of 300 volts for air with copper electrodes, the gap at which this minimum 'oltage occurs being less than 1/1000 of an inch at atmospheric temperature and pressure.

After the alternating current in the arc in the deionizing chamber has fallen to zero. in the course'of the alternating current wave,

I thermal generation of ions ceases almost at once, due to the rapid cooling of the gas. The ions which are present at that time, however, disappear only slowly by recombination." The reversed electric field which springs up moves these ions into the solid deionizing plates, so that the deionization is thereby accelerated. This deionization does not become complete simultaneously throughout the space, but the layer next to the new cathode first becomes completely (le ionized, layers adjacent thereto still retaining a considerable degree of ionization.

For the very small currents necessary to initiate rupture of a spark gap,'the layers of air which are still ionized may be considered as part of the electrode plates, and the layer throughout which deionization has become complete becomes the real insulating medium under break-down stress. If this layer is thinner than that corresponding to the minimum breakdown voltage above-mentioned, the presence of that voltage across the adjacent electrode plates is naturally incapable of causing a new rupture in that deionizing layer, no matter how thin it may be. Un the other hand, if this layer has become thicker than the gap corresponding to minimum break-down voltage, the voltage on the electrode plates is likewise incapable of causing its rupture. would be that occurring at the instant of time when the completely deionized layer is of exactly the thickness corresponding to a minimum breakdown voltage in air. Therefore, under the worst conditions, rupture will not occur if thevoltage on each path of adjacent plates is less than the minimum value of 300 volts above-mentioned. In actual practice, cto allow a factor of safety and provide for possible efiects oi line surges, I provide one.

gapfor each 100 to 200 r. m. volts of line potential.

Another way of explaining this 300 volt limit, one which agrees with the above theory, is to use the well known experimental fact that, in the absence of a hot cathode, or (as I have now shown we must also say) a hot layer of gas next to the cathode, an electrical discharge takes the form of a glow, which requires at least 300 volts to be maintained for the case of copper electrodesin air.

With further regard to the design of the deionizing structure, it may be said that the The worst possible condition greater the number of plates.

deionizing eflect is, in general, greater the Economy of space, therefore, calls for as close a spacing of plates as possible. On the other hand, considerations of mechanical rigidity, difficulties of manufacture andthe danger of foreign substances finding lodgment between the plates and bridging the gaps, set a limitation on the closeness with which the plates may be spaced. One-sixteenth of an inch has been chosen as a compromise between these con-. flicting requirements.

As to the thickness of plates, it should be so chosen that the heat stored in the plates in an operation of the switch shall not raise their temperature unduly. Calculations show that it is only a thin skin of metal on the surface of each plate that can be effective in absorbing heat each time the arc passes a given point, so that thickness of plate has little influence on the speed which it is necessary to give the arc to prevent melting of the plates. Here again mechanical and manufacturing considerations are really the controlling factor in determining the selection of a thickness of one-sixteenth of an inch for the plates 31. Good heat conductivity and a high specific heat are important in fixing the permissible smallest speed of the arc, and so lead to the use of copper as a good material for the plates.

Immediately after the current in the arc reaches Zero, if the are does not reignite, the

voltage across the switch rises to the instantaneous value of the generated voltage in a very short time. This time is the natural period of oscillation of the supply circuit, and, for ordinary generators, transformers, etc. is'a few hundred-thousandths of a second. During this time, the voltage across successive pairs of deionizing plates must remain less than 300 if the arc is not to reignite there, as has been explained before. Hence, if the number of plates is such that the generated voltage divided by the number of plates is 100 to 200 volts r. m. s., a great degreeof uniformity is required in the distribution of the impressed voltage among the series of plates. It is evident that the series of deionizing plates constitutes a series of condensers, with the line. voltage impressed between its outside terminal members. An uneven distribution of this voltage among the various condensers may cause more than 300 volts to be impressed upon one pair of plates during the deionizing period, with. consequent reignition of the are there, thus throwing an increased gradient on the remaining members, so that, in this way, throughout the .whole series the arcs between plates may reignite under a voltage which would have been insuflicient to cause reignition if it had been distributed in a uniform manner. a

It can be shown that the electrostatic capacity bet-ween plates and from plates to ground, in a simple series of uniformly'sized and spaced plates, causes an uneven voltage distribution". To eliminate this effect and use the plates at their maximum voltage efiiciency, electrostatic shielding may be resorted to. Thus, 70,71, 72, 73, 74 and 75 in Fig. 1 show a shield of a type which makes the voltage distribution more uniform. The shield comprises conducting sheets enveloping the deionizing structure and insulated from it by its casing.

It will be seen that the conducting sheets intercept the lines of electric force which would otherwise extend from the grid plates to neighboring objects at ground potential. The component of charging current corresponding to an electric field extending to ground is thus replaced by one corresponding only to the electric field between the plates 31 and the conducting sheets just mentioned.

The potential of the latter is determined by 7 plates 31 which it covers are charged; plate 74 to have nearly the means of the potentials of plates 31 near-the middle of the deionizing structure; and sheets 7 5 to have nearly the mean of the potentials of plates 31 nearer end plate 26.

As a result of the small potential difference, the electric field between plates 31 and the sheets 73, 74 and75 is relatively small, and the component of charging current corresoonding thereto is likewise minimized. Since. as can be readily shown. it is this component. of charging current which causes nonuniform distribution of the line voltage among the plates after extinction of the arc, the use of such shielding means eliminates uneven voltage distribution and the undesirable consequences thereof described above.

This solution of the problem presented by uneven potential distribution between the plates is not limited to a series of three shielding members denoted by 7 3,' 74. and '75 but may be extended to comprise any desired number of elements vhere a hi her line volt ageor other conditions make it desirable to do so.

It will further be. evident that this device in Figs. 5, 6, and 7 t of the drawings will be described. As previously stated, the deionizing plates 31 are assembled in units of 9 plates, each pair of plates being separated by annular washers of fishpaper, one washer separating the outer edges of the plates and the other washer separating the plates at their inner edges. At each side of each unit of' 9 plates are assembled the magnetizing coils 45, 48, 49 and 54, while outside of these are the iron plates 47, 53 and 55 already de scribed. As many sets of these units as are necessary, in consideration of the line voltage, are assembled on a cylindrical core 7 6 of some suitable insulating material, and an insulating plate 77 is provided at the rear. This whole assembly of plates, coils and washers is pressed firmly together into a rigid unit by means of through bolt 78 and insulating collars 7 9 and 81. This construction is clearly shown in Fig. 7. An insulating shell 82, containing the conducting sheets of the static shield 7 O75, is arranged to enclose the sides of the entire unit and may extend beyond the end plate 26 for protective purposes.

The lower portion of the deionizing structure, comprising the deionizing plates 31 and 61 with their fish-paper separators and the end- plates 26, 27 and 77, are pressed firmly together by a pair of through bolts 83 acting thereon through spacing members 84, 85 and 86 of micarta. The sides of insulating shell are held firmly pressed against the edges of the fish-paper separators for the lowerparts of plates 31 and 61 by spacing member 84 just mentioned. Fig. 6 makes this construction clear.

The lower portions 87 of the insulating shell extend down and form the side-walls of the chute 0r chamber'in which the arc is drawn between arcing contacts 7 and 8, as previously described. To protect them from the heat of the arc, th e side walls are lined with plates 88 of soapstone. The are causes a slight vaporization of the metal of arc-shoe 7 and, to prevent the condensation of this metal from forming a continuous conducting coating across the face ofthe soapstone between arc horns 22 and 23, narrow deep grooves 89 are provided in the plates 88.

The are horns 22 and 23 are bolted to plates 88 to form a unitary structure therewith, fitting snugly between the sides of shell 87, and supported therein by insulating spacers 90, the upper face of this structure abutting against the lower endof end plates 26- and 27, as Fig. 7 shows. Flexible connectors 91 and 92 electrically connect arc horns 22 and 23 with end plates 26 and 27. The deionizing structure proper, thus constituted, is provided, on each side of the arcing chamber, with iron pole shoes 93 which fit tigthly against thepole faces 25 of the core 24 of the blowout magnet. The blowout magnet is energized by the windings 11 scription.

which are insulated from the core by micarta collars 94. Windings 11 may obviously be positioned anywhere along the core 24. For the sake of clearness, the diagrammatic Fig. 1 shows the windings near the rear of the breaker; in the practical embodiment shown in Figs. 5, nearer the front.

The entire deionizing structure thus constructed is supported, on the framework which supports'the gnain contacts 1, 2 and the operating levers, by an insulator 95; and the lower parts of side plates 87 are bolted to a shoulder 96 on the main contact 1. The

structure and details of the mechanism opcrating the main contacts may be in accordance with standard practice in circuitbreaker design and require no detailed de- While, utes, I have given the forgoing details of a practical embodiment of my invention, it is to be understood that many of these are merely illustrative and that variations of their precise form will be desirable in designing circuit breakers for other voltages and currents than those which I have specified above.

It will also be understood that many features which I have above described are adjunctive to each other, andj'wthat it is possible to provide circuit-interrupting means that shall be satisfactory for many purposes by the employment of only one of these various devices.

in accordance with the patent stat- Thus, while provide the above- 6, and 7 they are shown described V-shape groove in the deionizing structure .which facilitates the transfer of the arc to the annular portion of the upper path of the deionizing chamber, it will be clear that the use of such an annular portion to deionize the arc is not dependent. upon the of a V-shape groove. In-many inpresence stances, it will be possible to cause the arc: to transfer to operation between the deionizing plates, and to thus utilize the expedient of driving the are about an annular path, even although no such V-shape groove is part of the device. On the other hand, it will be clear that, for

many purposes, it will be unnecessary to 'p rovide the annular path for. the are since, a relatively short period of operation in the deionizing chamber may be sufiicient to cause its extinction. Therefore, a struc re in which the il-shape groove is present lit in which noprovision is made for an annular path for the arc would be within the purview of my invention. In fact, it is not essential that'the plates forming the sides of the V-shape groove be integral with those constituting the annular'path, and a structure embodying the V-shape groove but providing no path of operation for a sub-divided arc would still be within the scope of my invention.

- which co-operates with, but is The provision of electrostatic shielding for the deionizing structure-is in no ,way confined to the particular shaping of the grid plates or to the presence of the V-shape groove, but is individually applicable whereever a-series of deionizing plates is used, or wherever it is desirable that voltage stress be uniformized in a current interrupting device.

Also, the provision of the slots in the soapstone walls of the chute is a valuable feature not limited to, use in connection with the V-shape groove or the deionizing structure generally.

The principles which have been embodied in my circuit breaker are applicable to many other purposes than those of circuit.interruption. I desire, therefore, that the language of the accompanying claims shall be arc path accorded the broadest reasonable construction and that my invention be limited only by what is explicitly stated in' the claims and by the prior art.

I claim as my invention:

' 1. Circuit-interrupting means comprising a pair of members between which an arc maybe drawn and deionizing means adjacent the plates disposed to subdivide the are into a ach series of short arcs and of such configuration as to provide-a recurrentpath for said short arcs.

2. Circuit-interrupting means comprising a pair of members between which an arc may be drawn, deionizing'means adjacentthe arc path comprising; a series of metal plates arranged to subdivide the arc into a series of short arcs; having such configuration as to provide a recurrent path for said short arcs and means to cause said short arcs to traverse said recurrent path.

3. Circuit-interrupting means comprising a pair of members between which'an arc may be drawn, means to abstract energy from the sides of the arc, travel of said are to a recurrent path.

4. Circuit-interrupting means comprising a pair of members between which an arc may be drawn, means'adjacent to opposite sides of the arc path to absorb energy there-from, means to impel the are into the space between said energy-absorbing means and deionizing means adjacent tothe arc path comprising a plurality of metal plates disposed to subdivide the arc into a series ofshort arcs having such configuration as to provide a recurrent path for said short arcs.

. 5. Circuit-interrupting means comprising a pair of members between whichan arc may drawn, means adapted to deionize an are when brought into contact therewith and means to confine the travel of saidarc to a recurrent path adjacent said deionizing meansf- Q -6. Circuit-interrupting means compr sing comprising a plurality of metal.

bed

adapted to deionize a and means to confine .the'

a pair of members between which an arc may e drawn, means adapted to delomze an are .when brought into contact therewith, means toprovide a recurrent path distinct from said members for said are while in contact -with said deionizing means and means to provide a recurrent path for said are and means to cause said are to traverse said recurrent path. I

' 9. Circuit-interrupting means comprising a pair of members between which an arc may be drawn, a pluralitvof metal plates positioned in a portion of the arc path, means to deflect said are toward said metal plates, means to provide a recurrent path for said arc and means to-cause said are to traverse said recurrent path.

'10. Circuit-interrupting means comprising a pair of members between which an arc may rawn, a plurality of metal plates positioned in a portion of the arc path, means are when brought into contact therewith, m ans adapted to provide a recurrent path for said arc and means to cause said are to traverse said recurrent path.

11. Circuit-interrupting means comprising a pair of members between which an arc may be drawn, a plurality of metalplates positioned in a portion of the arc path and having notches tapering to an apex, means to deflect said are toward -said metal plates, means adapted to deionize an are when brought into are and means to cause said arc to contact therewith, means to provide a re current path for said are and means to cause said'arc to traverse said recurrent path.

.12. Circuit-interrupting means comprising a pair of members between which an arc may be drawn, means adjacent the sides of the arc ing a pair of members between which an arc may be drawn,

a structure comprising a ser1es of spaced metal plates positioned in a portion of the arc path and having notches which taperto an apex to form a substantially V-shape groove in said structure, means to deflect the are into said V-shape groove, said notches tapering to an apex to comprising a plurality of s notches and said plates being so formed and spaced that when the arc is running in the apex of said groove, the density of ionization is so reat as to make it ca able of readily trans erring to a cathode w ich is substantially not thermionically emissive, deionizing means ad'acent the apex of said groove comprising a flurality of spaced conducting plates disposed to subdivide the are into a series of short arcs, and of such configuration as to provide a recurrent path for said short arcs and means to cause said short arcs to traverse said recurrent path.

14. Circuit-interrupting means comprising a pair of: members between which an arc ma be drawn, a structure comprising a plurahty of spaced conducting plates positioned in a portion of the arc path and having notches taperingto an apex to form a substantially V-shape groove in said structure,

means to deflect the are into said V-shape' groove, one or more separate deionizing units adjacent the apex of said groove, each comprising a plurality of spaced conducting plates disposed to subdivide the are into a series of short arcs and of suchconfiguration as to provide recurrent paths for said short arcs, and windin s connected in series with said separate units and disposed to set up magnetic fields at right angles to said recurrent paths.

1,5. Circuit-interrupting means comprising a pair of members between which anarc may be drawn, a structure comprising a plurality of spaced conducting plates positioned in a portion of the-arc path and having form a substantially V- hape groove in said structure, means to deflect the are into said V-shape groove, one or more separate deionizing units adjacent the apex of :saidgroove, each unit comprising a pluralit of spaced conducting plates disposed to su divide the are into a series of short arcs and of such configuration as to provide recurrent paths for said short arcs, windings at each end of each de-ionizing. unit connectedv in series with said separate units and so disposed as to set up magnetic fields at right angles to said recurrent paths, and magnetic return paths for the flux of said fields between said deionizing units.

16. Circuit-interrupting means comprising a pair of members between which an arc may be drawn, a structure comprising a plurality. of spaced conducting plates positioned in a portion of the are path and having notches tapering to anapex to form a substantially V-shape groove in said structure, means to deflect the are into groove, one or more separate deionizing units adjacent the apex of said groove, each unit aced plates not over one-eighth of an inch t ick, and spacednot over one-eighth of an inchapart, dissaid V-shape.

posed to subdivide the are into a series of short arcs and of such configuration as to provide recurrent paths for said short arcs, windings at each end of each deionizing unit connected 1n serles with said separate units and so disposed as to set up magnetic fields along radii of said recurrent paths, and mag netic return paths for the flux of said fields between said deionizing means.

17. Circuit-interrupting means comprising a pair of members between which an arc may be drawn, a structure comprising a plurahty of spaced conducting plates positioned in a portion of the arc path and having notches tapering to an apex to form a substantially V-shape groove in said structure, means to deflect the arc to said V-shape groove, a deionizing structure comprising a plurality of substantially P-shape conducting plates, and means to cause said are to traverse an annular path through said P- shape plates.

18. Circuit-interrupting means comprising a pair of separable contact members between which an arc may be drawn, a structure comprising a plurality of conducting plates positioned in a portion of the arc path and having notches tapering to an apex to form a substantially V-shape groove in said structure, means to deflect the are into said V-shape groove, one or more separate deionizing units adjacent the apex of said groove,

each unit comprising a plurality of spaced substantiall P-shape conducting plates disposed to su -divide the are into a series of short arcs and of such configuration as to provide recurrent paths for said short arcs,

. and windings connected in series" with saidseparate umts to set up magnetic fields along radii of said recurrent paths.

19. Circuit-interrupting means comprising a pair of members between which an arc; may

current path for said are and means to cause said are to traverse said recurrent path. ZO Circuit-interrupting means comprising a pair of separable contact members between which an arc may be drawn, arcing horns positioned toreceive said are from said contact members, means'to progressively constrict said are as it lengthens between said horns, means to progressively increase the potential gradient of said arc as it recedes from said horns and deionizing means positioned to intercept said arc as it recedes comprising a plurality of spaced conducting plates transverse to the arc path, means to provide a recurrent path for said are and means to cause said are to traverse said recurrent path.

21. Circuit-interrupting means, comprising a pair of members between which an arc may be drawn, a structure comprising a plurality of spaced conducting plates adjacent the arc path and having notches ta ering to an apex to form a substantially V shape groove in said structure, a magnet to be energized when said are is drawn and positioned to deflect said are into said V-shape groove, one or a more separate deionizingunits alincd with 19 the apex of said groove, each unit comprising a. plurality of spaced conducting P-shape plates to sub-divide the are into a series of short arcs, and windings connected in series with said separate units to set up magnetic fields tending to drive said short arcs in a recurrent path about the loop of each P-shape member.

22'. Circuit-interrupting means comprising a pair of'separable contact members between which an arc may be drawn, a structure comprising a plurality of spaced conduct-ing plates adjacent to the arc path and having notches tapering to an apex to form a substantially V-shape groove in said structure,

drawn and serving to deflect said are into .said V-shape groove, one ormore separate deionizing units alined with the apex of said groove, eac unit comprising a series of conducting P-shape plates, spaced not over' oneeighth of an inch apart to subdivide the are into a series ofshort arcs, and windings connected in series with said separate units to set up magnetic fields tending to drive said short arcs in a recurrent path about the loop of each P-shape member.

23. Circuit-interrupting means comprising a pair of members between which an arc may be drawn, deionizing means comprising 5 a: plurality of spaced conducting lates positioned to intercept said are and means to cause a uniform distribution of potential differences among said plates when the arccurrent is substantially zero.

5 24. Circuit-interrupting means comprising a pair of members between which an arc may be drawn, deionizing means comprising a plurality of conducting plates spaced not over one-eighth of-an inch apart and positioned to intercept said are, and means-to cause a uniform distribution of potential difierences among said plates when the arc is extinct.

25. Circuit-interrupting means comprising a pair-of members between which an arc may be drawn, deionizing means comprising a series of spaced conducting plates positioned to intercept said are and of such configuration as to provide a recurrent path for said are, means to cause said are to traverse saidrecurrent path and means to cause a uniform distribution of potential difiere'nces among said plates when the are is extinct.

'26. In combination with a sourceof alternating electro'motive force, a circuit-intern ing means comprising a pair of members a magnet to be energized when saidarc is electrode at 'such velocity that substantially izing means adjacent the arc path comprising tween which an arc may be drawn, deionizing g means adjacent the arc path comprising a plurality of metal platesxto subdivide the are into a series of short arcs and of such configuration as to provide a recurrent path for said short arcs, and means to cause said short arcs to traverse said recurrent path, the arrangement of said plates being such that the potential difference between a pair of plates never exceeds three hundred volts.

27. Circuit-interrupting means comprising a pair of separable contact-members between which an arc may be drawn, a deionizing chamber having insulating side walls which is substantially enclosed and means for transferring the are to said chamber.

28. A method of extinguishing an electric are which comprises the steps of abstracting energy through the sides of the arc, subdividing the are into a series of shorter arcs S and causing said arcs to traverse a recurrent path.

29. A method of extinguishing an electric are which comprises the steps of subdividing the are into a series of shorterarcs and causing said arcs to traverse a recurrent path.

30. A, method of extinguishing an electric are which comprises the steps of increasing the density of ionization in said are, subdividing said are into a plurality of cold cathode arcs and causing said arcs to traverse a recurrent path. L

- 31. Electric discharge means comprising a plurality of spaced metallic plates and means to cause an are between said plates to traverse a recurrent path thereover.

32. An electric discha 'ge device comprising a metallic electrode nd means to cause an arc to traverse a recurrent path upon said 106 no vaporization of said electrode occurs.

33.' In combination with a source of alternating electromotive force, circuit-interrupting means comprising a pair of members between which an arc may be drawn, deionizing means adjacent the are path comprising a plurality of metal plates arranged to subdivide theare into a series of short arcs of such configuration as to provide a recurrent path for said short arcs, and means to cause said short arcs to traverse said recurrent path, the arrangement of said plates being such that the potential diflere'nce betweena pair of plates never exceeds that necessary to produce alow discharge.

34. In com ination with a source of alternati ng electromo tive force, circuit-interrupting means comprising a pair of members between which an arc may be drawn, deiona seriesof metal plates arranged to subdivide the arc into a series of short arcs of such configuration as to provide a. recurrent path for said short arcs, and means to cause said short arcs to traverse said recurrent [3o path, the number of said plates being approximately equal to the voltage of the source divided by the normal cathode drop of the material of which said plates are made.

35. Circuit-interrupting means comprising a pair of members between which an arc may be drawn, and means for causing a substantially uniform distribution of electric potential over the path of the are immediately after extinction of the arc.

36. Circuit-interrupting means comprising means for establishing an arc, a structure comprising spaced conducting plates positioned in a portion of the arc path and of such configuration as to provide a recurrent path for said are, windings disposed to set up magnetic fields perpendicular to said are path and means to impede the induction of currents in said plates by changes of current in said windings.

37. Circuit-interrupting means comprising means for establishing an arc, a plurality of conducting plates positioned in a portion of the arc path and having notches tapering to an apex, said notches halving in width in every longitudinal distance of from one-tenth to two inches, means adapted to deionizean arc when brought into contact therewith, means to provide a recurrent path for said are and means tocause said are to traverse said recurrent path.

38. Circuit-interrupting meanscomprising means for establishing an arc, a plurality of spaced conducting plates positioned in a path traversed by said are and means for causing a substantially uniform distribution of electric potential among said plates after interruption of the arc.

39. In combination with a source of alternating electromotive force,circuit-interrupt ing means comprising a pair of members between which an arc may be drawn, means adapted to deionize an are when brought into contact therewith and means to confine the travel of said are to a recurrent path adjacent said deionizing means.

40. The method of maintaining an electrical are which consists ill-moving said are over a recurrent path so rapidly that neither electrode emits a substantial number of electrons.

41. The method of interrupting the flow of current in an electric circuit which comprises opening a pair'of'separable contacts traversed v by said current, transferring the resulting arc to a recurrent path distinct from said contacts and moving the are so rapidly about said path that no electrons are emitted from said path.

In testimony whereof, I have hereunto subscribed my name this 28th day of March.

JOSEPH sLEPiAN.

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