US1819207A - Circuit breaker - Google Patents

Description

Aug. 18, 1931. J. sLEPlAN CIRCUIT BREAKER Filed Sept. 8, 9 5

8 Sheets-Sheet l INVENTOR Joseph ,Sle nian. BY

ATTORDNEY Aug. 18, 1931. J, SLEP N 1,819,207

CIRCUIT BREAKER Filed Sept. 8, 1925 8 Sheets'-Sheet 2 Tie 3 a Generator LO d WITNESS; INVENTOR gose vh Sla om/7.

ATTORNEY Aug. 18, 1931. J. SLEPIAN CIRCUIT BREAKER Filed Sept. 8 1925 8 Sheets-Sheet 3 INVENTOR WITNESS.

ATTORNEY Aug. 18, 1931 J. SLEPIAN CIRCUIT BREAKER Fi led Sept. 8, 1925 8 Sheets-Sheet 4 Land INVENTOR Jos h 528 M77. BY 8P F III IIIIIIII @Generator WITNESS:

ATTORNEY Aug. 18, 1931. SLEPIAN CIRCUIT-BREAKER Filed Se t. 8, 25

8 Sheets-Sheet 5 INVENTOR J0 e h 518 an. BY [m WlTNESSf ATTORNEY Aug. 18, 1931. J. SLEPIAN 1,8 ,2

C IRCUIT BREAKER Filed Sept 8 1925 8 Sheets-Sheet 7 Fig.23. 7 7 .24.

' WIN! INVENTOR J 77516 22m, BYase v 4 P ATTORNEY Aug. 18, 1931. J, SLEPIAN 1,819,207

CIRCUIT BREAKER Filed Sept. 8, 1925 8 Sheets-Sheet 8 WITNESS? 05 77-516 fan. 4' P A'TTORNEY Patented Aug.'18, 1931 .UNITED STATES PATENT! OFFICE JOSEPH SLEPIAN, OF SWISSVALE, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELEC- TRIO & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA CIRCUIT BREAKER Application filed September will interrupt large currents at high voltages without arc re-ignition and with minimum line disturbance.

In oil circuit breakers which have heretofore been almost exclusively utilized for interrupting high-power circuits, the current interruption is effected by drawing an are under oil, in order to prevent arc re-ignition after the alternating current in the arc has passed through zero value.

Very serious disadvantages are presented by oil circuit breakers, which have been the only means heretofore found suitable for interrupting the circuits of modern alternating-current distribution systems, capable of energy concentrations of the order of :1. million 'kva. The are energy of a heavy shortcircuit, released under the oil when opening the arcing contacts of the circuit breaker, decomposes the oil and generates gases with explosive violence. mendous pressures developed by the enerated gases, oil circuit breakers must enclosed in enormous oil tanks of massive construction. Y

As a result of the difliculties just outlined, the design of circuit breakers for power installations has become of more concern than the design of the generating equipment that supplies the current and the cost of the interrupting equipment frequently approaches that of the generating equipment.

Another great disadvantage of oil circuit breakers is the fire hazard and danger to life involved in their operation. The gases developed in such circuit breakers form explosive mixtures, and, in many cases, the high-pressure tanks are burst by the resulting explosions, causing oil fires and endan gering the surrounding property and the lives of the personnel.

I have found that the arc resulting from the opening of a circuit breakerin air can be fully interrupted and that are re-ignition may be prevented even to a larger extent than To withstand the tre-' 8, 1925. Serial 170. 54,930. I

in the case of oil circuit breakers, by introducing, into the space between the arc electrodes special de-ionizing means in the form of conducting sheets or nuclei placed across the are which rapidly reduce the conductivity of the arc space after the arc current passes through zero. The de-ionizing means are preferably so arranged as to interfere as little as possible with the arc play as long as the arc lasts. By providing a sufficient number of such de-ionizing sheets, I am able to fully control the speed at which the space between the arc electrodes loses its conducting character and becomes an insulator without introducing special arc-quenching mediums, such as oil or similar substances.

My invention will best be understood by reference to the accompanying drawings,-

wherein Fi re 1 is a side elevational view of a circuit breaker embodying my invention, a part of the arc chamber being shown in section;

Fig. 2 is a sectional view on the line II+II of Fig. 1, showing the arc chamber of the circuit breaker;

Fig. 3 is a top plan view of the arc chamber and the arc blow-out magnet of the circuit breaker shown in Fig. 1;

Fig. 4&8 a diagram illustrating the as..-

tions of the circuit breaker shown in Fig.1;

Figs. 5 and 6 are diagrammatic views i1- lustrating the process of de-ionization of the are space between two arcing electrodes:

Figs. 7 and 8 are views similar to 5 and 6, illustrating the pro ess of de-ionization when (is are place in the space between the e ectrodes Fig. 9 is a curve diagram illustrating the phenomena taking place upon the opemng of a circuit. breaker embodying my'in vention;

Fig. 10 is a diagrammatic view of'ap ratus and circuits embodying my circuit breaker in a modified form;

Figs. 11 and 12 are horizontal sectional views of arcing chambers, embodying modifications of my invention;

Figs. 13 to 21, inclusive, Iare vertical sec Fig. 22 is a horizontal sectional view on the line XXII-XXII of Fig. 21;

Fig. 23 is a vertical sectional view, similar to Fig. 21, showing a still further modification of my invention;

Fig. 24 is a horizontal sectional view on the lines XXIVXXIV of Fig. 23,

Figs. 25 and 26 are vertical sectional views, similar to Fig. 21, showing other modifications of my invention;

Fig. 27 is a vertical sectional view of an arcing chamber illustrating a still further modi 'cation of my invention;

Figs. 28 and 29 are horizontal sectional views of arcing chambers embodying modifications of my invention; and

Fig. 30 is a verticalsectional view including all of the modifications of my invention.

Referring to Figs. 1 to 3, inclusive, a circuit breaker is shown comprising two main contact members 1 and 2 mounted upon insulating bushings 3 and 4 secured, one above the other, upon a structural-iron supporting frame 5. The contact members 1 and 2 comprise terminal rods 6 and 7 extending to the back side of the supporting frame, through perforations in the centers of the insulating bushings 3 and 4.

Supported jointlyby the lower insulating bushing 4 and an insulator 11, below the same, is the main bracket 12 of the circuit breaker, carrying a shaft or point 13 upon which are rotatably mounted a main contact arm 14 and an upwardly extending arcing-contact arm 15. The main contact arm holds a main contact brush 17, consisting of laminated copper punchings, against the main contact members 1, 2.

The upwardly extending arcing-contact arm 15 of the circuit breaker carries an arcuate movable contact shoe 19, engaging a stationary arcing contact member 20, for effecting the final interruption of the circuit. The stationary arcing contact member has a slight tilting motion, being pressed downwardly, against the contact shoe 19, by means of a spring 21. The stationary member 20 is connected, by means of a flexible conductor 22, to one terminal 23 of blow-out coils 24, the other terminal 25 of the coil being electrically connected to a metallic supportmg frame 26 which is in electrical engage ment with the upper main contact member 1. The movable arcing contact shoe 19 is electrically connected to the swinging arm 15, which is, in turn, connected to the lower main contact member 2 through a flexible shunt 27 adjacent to the pivot 13.

The switch arms 14 and 15 are operated by atoggle mechanism comprising a bell-crank lever 28 which is pivoted to the switch frame 12 at 29. The inner end of the bell-crank lever is pivoted to two links 30 and 31 which are connected to the two switch arms 14 and 15, respectively. The switch arm 15 is drawn towards its open position by a spring 32, and the toggle link 31, which is connected thereto, is disposed above the line of centers of the toggle, so as to lock the switch in closed position. The circuit breaker is tripped by moving the outer end of the bellcrank lever 28 upwardly, thus breaking the toggle.

When the switch is opened, the movable arcing shoe-19, being of arcuate shape, does not break contact with the stationary contact member 20 until after the main contact members 1 and 2 are disengaged by the main contact brush 17. A pair of auxiliary contact members 33 and 34 are usually also provided to relieve the main contact members of the arcing incident to the transfer of the current from the main contact members to the inductive shunt circuit comprising the final current interrupting contact members 19 and 20 and the blow-out coil 24. As shown in Fig. 1, the stationary auxiliary contact member 33 is mounted on the frame 26 which is in electrical contact with the upper main contact member 1, and the movable auxiliary contact member 34 is mounted on the top of the main contact brush 17, which is in electrical contact with the lower main contact member 2, through the switch arm 14. The movable auxiliary contact member 34 is pivoted at 35 and is pressed toward the stationary contact member by means of a spring 36, in order to secure arolling and wiping motion when engaging or disengaging the stationary auxiliary contact member 33.

The principal feature of my invention resides in the provision of new and improved means for extinguishing the arc drawn between the arcing contact members 19 and 20. To this end, an arc chute 40 is provided above the arcing contact members 19 and 20. The lower portion of the chute terminates in two horn- like arcing plates 41 and 42, the plate 41 being in electrical engagement with the stationary arcing contact member 20, and the plate 42 being provided with resilient fingers 43 which engage the movable arcing contact shoe 19 when the latter is in its final open position, so that the arc is transferred from the arcing contact members 19 and 20 t0 the horn- like plates 41 and 42 leading to the arc chute 40.

The arcing chute 40 consists of four spaced vertical conducting plates 44, 45, 46 and 47, dividing the space between the upper ends of the horn- like arcing plates 41 and 42 into three separate serially-connected arcing chambers 48, 49 and 50, the two end plates 44 and 47 being in electrical c ntact with the arcing plates 41 and 42, respectively. Each arcing member is sub-divided into a large number of small spaces by means of conducting sheets or grids 51, disposed parallel to the arcing terminal plates 4 to 47, incluably reticulated, as will be explained later.-

In the embodiment shown in Fig. 1, they are wire grids 51 of brass.

,The space between the horn-like arcing " plates 41 and 42 may be enclosed, at the sides, by large insulating shields 52 engaging the edgesof the plates. ing chute 40 may be enclosed by insulating plat tias 53 engaging the edges of-the plates to 4 The are is forced into the arcing chambers 48, 49 and of the chute,'by means of the aforementioned blow-out coils 24, which are shown as being provided with a horseshoeshaped laminated iron core 54 terminating in pole-shoeplates 55 and 56, the plates 56 being the larger, and being disposed in engagement withthe insu'lating walls 52 and 53, as

shown in Fig. 2. The function of the blowout coil 94 is to cause the arc stream to be displaced laterally into the space traversed by the grid sheets 51, within an interval of time whicli'is-short as compared to the half-period of the alternating-current circuit to which the breaker is connected, so that the arc tween the arcing electrodes and to interfere as little as possible with the arc play. However, when the arc current asses through zero value at the be inning 0% the nextalternation,the grids fillingthe'spaoe between the arcing electrodes exercise an enormous deionizing action, as hereafter described, rapidly restoring the airspace in one or more of the arcing chambers to its original insulating condition and preventing the re-striking of the are upon the rise of terminal voltage which follows the extinction of. the arc in such chambers.

The grid chamber or are chute 40 is of suflicient extent, as compared to the speed of arc motion therewithin, to insure that the final interruption of the arc -shall be accomplished within the chute. The are movement within the chute is made fast enough to prevent melting of the grids or destruction of the insulation near the are under ordinary conditions of discharge.

In order to understand the de-ionizing In like manner, the arc- 51 ar'e preferably sorn'ade as to permit a continous are be-' action of. the grids utilized in the arcing or de-iom'zing chambers of my improved circuit breaker, it will be helpful to briefly discuss the phenoinena taking place in an alternating-current are discharge.

Spark discharge.Under ordinary condi tions, air and'other gasesare. excellent insulators. However, when a sufiiciently high potential is applied to two electrodes spaced by'an air gap, the air suddenly changes from its normally insulating state to a conducting state. This change, known as a spark discharge, is explained as follows: Air normally has a minute de'gree of ionization due to the radiation of radio-active elements in the earth, Under the influence of small electric potential gradients, this ionization provides a sli ht conductivity which is detected only by tlie most sensitive instruments. 'Under the influence oflarge electric potential gradients, these few ions move ver rapidly, and

their collisions with neutral mo ecules may be so ener etic that they may actually disrupt some 0 theminto positively and negatively charged parts. Thus, new ions and electrons are formed.

1 For example, assume that there is a single free electron between two electrodes to which a voltage in excess of breakdown voltage is applied. This electron moves rapidly toward the anode, and of its large numberof collisions with neutral molecules, assume that 1000 are sufliciently energetic to produce dis- 'ruption. We then have 1000new positiveions and 1000 new negative ions. The 1000 positive ions. start moving toward the cathode. Positiveions, having a much greater mass, are much less effective than electrons in producing ionizationrby-collision. Assume, further, that these positive ions, in movlng to the cathode produce only two new electrons near the cathode. ,These two electrons moving to the anode will produce 2000 new pairs ofions. The 2000 positiveions moving to the cathode will produce 4 new electrons;

these four electrons'will produce 4000 positive, ions, 'and so on until great conductivity will be produced. 5 v 1 The number of pairs of positive and negative ionsproduced bycollision by an electron, per centimeter of advance in the direction of the electric Held, and the corresponding quantity for a positive ion, are rapidly increasing functions of the electric gradient;""""i;.-

Glow discharge-As soon as 'a discharge has been initiated by the process of ionization-by-collision, as just described, the electric field in the gap becomes distorted. .A steep voltage gradient is developed in a thin layer, known as thecathode dark space, adjacent to the cathode. The voltage drop in said thin layer, or the cathode drop, is of the order i broken down and the current density is not too high, the conduction across the gap takes the form of a glow discharge, in whichthe positive ions, and to a smaller extent the electrons and negative ions, moving through the high-gradient field of the cathode drop toward the cathode and the anode, respectively, continue to produce new electrons and ions by collision with the air molecules in the thin layers wherein the cathode drop occurs, thus supplying suflicient electrons and ions to produce a highly conducting state, or low voltage gradient, in the remainder of the gap.

Ara dz'sckarge.If, at some spot next the cathode, the energy input is sufficient to raise its temperature to such degree that it begins to emit electrons thermionically, or to heat a layer of gas very close to this spot to such a temperature that it is thermally ionized,'the current will concentrate at such spot. The cathode drop then becomes much smaller than in the glow discharge, since the necessary conduction is produced by thermionic electron emission, or by thermal ionization of gas very close to the cathode, rather than by ionization-by-collision. It is necessary, however, that the voltage drop in said thin cathode layer be sufiiciently high, in order that the available energy input may maintain the cathode or adjacent gas at a temperature producing the required thermionic emission or thermal ionization. It is, in general, also necessary that the voltage drop in said thin cathode layer be sufiiciently high to produce therein electrons by ionization for neutral-- izing the space charge of the electrons. For ordinary electrode materials, twenty volts is sufficient for the purposes just mentioned.

In addition to the voltage drop at the cathode, there is avolta e drop of about ten volts near the anode of the arc. Positive ions are produced in the field of the last-mentioned drop, by collisions of the swiftly moving electrons coming from the cathode. High temperature at the anode is not essential for the maintenance of the arc.'

The voltage gradient in the main body of the arc stream, between the regions immediately adjacent to the cathode and the anode, is very low. It is usually not sufiicient to produce any material ionization-by-collision. The positive ions necessary to neutralize the space charge of the electrons in the main body of the arc stream are probably the result of thermal ionization of the gas.

Thus, in an are, most of the current is carried by the rapidly moving electrons which move from the cathode and stream toward the anode. The space between the cathode and the anode is filled with positive ions neutralizing the space charge of the electrons and rendering the are highly conductive. The positive ions are produced by collision in the spaces near the cathode and the anode,

and in the remainder of the arc stream by thermal ionization,

AZtema'ting-currem area-In an alternatin -current are, the arc current passes period1cally through zero. The electrode which was a cathode in the previous alternation becomes an anode ;'the anode of the previous alternation becomes a cathode for the next following alternation.

At the exact moment when the current becomes zero, the space between the electrodes is still highly ionized. The voltage gradient is nearly zero throughout the arc space, so that there is no ionization-by-collision. .The electrode which is beginning to become a cathode is at a temperature too low to emit electrons thermionically. Thermal generation ofiions in the gas is being reduced ra idly by the cooling of the gas. Very shortly after the current is zero, generation of new ions has practically ceased.

At :the same time, the space between the electrodes is rapidly becomingdc-ionized. A certain proportion of the electrons will come sufiiciently close to positive ions to recombine with the same, thus neutralizing their charges. The rate of recombination is proportional to the density of the positive and negative ions in the space. If there is no fresh supply of ions, recombination will reduce the density of ionization inversely with the time. Thus, the space is losing its c0nductivity, and if the formation of new ions can be prevented, the are will not re-ignite.

Referring to Fig. 5, the and signs represent the ions in an arc discharge in air, between an electrode 79, which is becoming a cathode, and an electrode 80, which is becoming an anode, at the moment when the voltage and current are zero. Recombination is taking place, so that in Fig. 6, which represents the conditions a short time later, the density of ionization is reduced. During the time between the conditions illustrated in Figs. 5 and 6, the voltage has been rising, producing a gradient which moves electrons away from the cathode 79 and which moves positive ions toward the cathode 79.

There is thus formed a region 81 next to the cathode, which is nearly denuded of ions, only a few slowly moving positive ions being in said region, on their way to the cathode. The space 81 adjacent to the oathode thus has a much higher resistivity than the rest of the space and, consequently, most of the voltage applied to the electrodes will appear across said cathode space, producing an electric field of high gradient therein. As time goes on, the electrons will be repelled further from the cathode, and the high-resistance region will grow in thickness.

A similar de-ionized sheath 82 will also appear next to the anode. Y Owing to the relatively high mobility of the electrons, the gradient in this sheath will be very much less than that at the cathode, and it will not be furtherconsidered.

Thus, as a result of the action of the electric field, two regions of different characterlstics are produced. In the region 82 adjacent to the anodes, the electric gradient is very low, and the loss of ions is occurring principally by the process of recombination, in the manner previously described. The region 81 adjacent to the cathode is almost completely 'de-ionized by reason of the repulsion between the cathode and the electrons.

The boundary between the region 81 and the ionized arc spaces continues to. move out: wardly from the cathode as the de-ionization proceeds.

While the de-ionized region or sheath 81 near the cathode is thus growing in thickness, the applied voltage is also increasing. If the rate of voltage rise is so high that it imparts to the high-resistance sheath a voltage gradient suflicient to move the relatively few positive'ions remaining in said sheath at a velocity at which they will produce thermal ionization or ionization-by-collision, this region will lose its high resistance.

"he voltage which otherwise would be consumed by the cathode sheath is then transferred to the still highly ionized, highly conducting body of gas, a heavy current starts and the arc re-strikes.

However, if the de-ionization proceeds so fast that the thickness of the de-ionized cathode sheath increases at such rate that the voltage gradient in this region never reaches a value at which ionization-by-collision occurs, and the energy input is not suflicient to produce thermal ionization, the entire space between the electrodes gradually becomes insulating and the arc does not re-i ite. The circuit is accordingly interrupte Thus, if

the rate at which the voltage rises be maintained sufiiciently low compared to the rate of de-ionization, the voltage gradient in the cathode sheath will be too low for ionization; no new ions will be generated; only de-ionization will take place; the ions will be swept out of the arc path as the cathodesheath grows; and the arc will be permanently extin uished.

ppli'cdtio'n to circuit brewkera-Based upon the analysis of the phenomena taking tacts of an alternating-current circuit reaker, in the manner described hereinabove, I have determined the permissible rate of voltage rise at'which no 'arc-re-ignition would take place between such contacts as are ordinarily used. I have found that, with ordinary prior-art circuit breakers, operating in air, the permissible rate of voltage is so low that it is not feasible to make commercial,

large-current breakers for any voltages above relatively low values, on account of the physical limitations imposed by the material of COD- the contacts, the possible separation of the electrodes, and the constants of the circuit to be opened. Thus, for a pair of cop r electrodes separated one inch, the rate 0 -de-ionization is such that the rate of rise of voltage must be limited to less than 1 x 10 volts per second, if re-ignition is to be prevented.

If the alternating current to be interrupted is in phase with the voltage, i. e., of unity power factor, the rate of voltage rise is that of the alternating voltage wave, i. e., incommercial circuit breakers, that of a 60-cycle wave. However, the ordinary circuits and conditions under which practical circuit breakers must operate require the openin of currents having a power factor considera ly different from unity. In such case, the maximum rateof voltage rise across the terminals of-the circuit breakers is principally dependable size and cost, which would be required to carry a very large part of the interrupted current. Such constructions would be out of the question for commercial circuit breakers.

One of the principal features of my invention is an artificial increase of the rate of deionization of the space of the arc resulting upon opening a circuit breaker, immediately after the passage of the arc current thro zero. More particularly, I introduce into t e are space a large number of what may be termed artificial cathodes, multiplying the de-ionizing action of the main cathode and thus reducing the time of de-ionization to afraction of the' value it would otherwise require.

The shunting resistors, if they are used at all, are so proportioned with respect to the greatly increased permissible rate of voltage rise as to positively avoid" a voltage gradient In the circuit breaker shown in Figs. 1 to 4 the artificial cathodes are made in the form of ,wire grids 51 disposed across the arc path and assembled into a unitary structure. As the arcing contact arm 15 opens and draws the at which ionization-by-collision will occur.

through the perforations in the grids.

are, the same is blown upwardly into the grids by the field of the arc-blow magnets.

The ions which discharge to the grid wires are probably only few in number in comparison to the number of ions constituting the arc stream. But, at the moment when the arc current is passing through zero, ionizationby-collision'has ceased, and the gas is becoming too cool for thermal ionization; recombination is taking place, reducing the density of the ions; and at that moment, the discharging of ions to the grid wires radically reduces the conductivity of the space around the grids, Metallic parts of the grids thus, to a certain extent, act like cathodes forming centers of de-ionization, as will now be explained.

In Fig. 7, grid wires 51 are shown disposed in the space between the electrodes 44 and 45 of Fig. 1, at a moment which is soon after the former has become a cathode and the latter an anode, as in the case of Fig. 6. At a slightly earlier moment, when the ,current was passing through zero value, the space around the grids had been highly ionized throughout, filled with electrons and positive ions, as indicated in Fig. 5.

At the moment chosen. for Fig. 7, the lines of force of the increasing electric field, entering the grid wires on one side and leaving the same at the other side, are causing the sides of the wires facing the cathode to act as anodes and the sides facing the anode to act as cathodes. A sheath 83 is formed on the cathode side of each'wire, similar to the sheath 81 in Fig. 6. Under the influence of the increasing voltage, the sheaths 83 around all of the wires grow, taking the shape shown in Fig. 7 until the individual sheaths merge into a single sheath 84 over the entire surface of a grid 51, as shown in Fig. 8, similar, in every respect, to the sheath 81 near the cathode.

In the manner just described, the de-ionizat1on proceeds rapidly from a large number of sheaths or deionizing kernels 84, acting like so many cathode sheaths. The rising voltage is now distributed over a large number of hi hresistance, de-ionized regions, thus reduclng the voltage gradient sufiiciently to prevent lonization-by-collision in the gap space between the electrodes.

The rate at which the openings in the grids are de-ionized, so that the entire grid begins to act like a single de-ionizing surface similar to the cathode, depends upon the size of the openings. I have found that, if the openings in the grids are sufiiciently small, the rate of rise of voltage may be as high as 5 x 10 volts per second per grid, without danger of ionization and are re-ignition.

Thus, by interposing nine grids, of the character mentioned above, across the arc path in the space between electrodes spaced one inch apart, as in the case considered before, the permissible rate of voltage rise will be increased from less than 1 x 10 to 50 x 10 volts per second. With the 2200 volt,60 cycle circuit considered above, the shunting resiscircuit breaker operated in a resistance-less circuit, consisting of a source of alternating current and an inductance connected in series, and if the circuit were interrupted when the current was zero, the voltage at the interrupting terminals would instantaneously rise to the peak voltage of the source. That is, .the

rate of rise of voltage would be infinite.

However, in any practical circuit, on account of the inherent capacity and leakage, the rise of voltage is not instantaneous, but it is usually very rapid. When my improved breaker is utilized in any practical circuit carrying a sufliciently small current, the rate of rise of voltage, as limited by the circuit, will be less than that necessary to re-ignite the arc which is de-ionized by means of a grid structure, as described above. However, if the currents are very large, the -rate of voltage rise, as limited by the circuit, may be greater than that required for preventing restriking of the arc, as explained hereinbefore.

In order to secure reliable opening of the circuit breaker, independently of the magnitude of the current to be broken, and independently of the constants of the circuit, the improved circuit breaker shown in Figs. 1 and 4 is arranged to first reduce the current to be opened to a fraction of its maximum short-circuit value, before finally interrupting the circuit. To this end, the are drawn by the arcing contact of the circuit breaker is split into three sections, as explained above, each are playing in a separate chamber the first arcing chamber 48 being shunted by a resistor 85, as shown in the circuit diagram in Fig. 4, the second arcing chamber 49 being shunted by a much higher resistance 86, and the last arcing chamber 50 being without shunt.

In operation, when the arcing contact arm 15 is opened, the are which is drawn between the contact members 19, 20 is blown into the three chambers of the arc chute 40 of the circuit breaker, the three are sections being in series. The electrical conditions in the circuit are shown in Fig. 9, wherein the sinewave curve 87 represents the generator voltage plotted against time, the heavy dotted curve 88 represents the line current, the light 1 maining arcing chambers 49 and in series. ever, the second section 49 of the de-ionizing .The conditions illustrated in Fig. 9 correspond to those existing in an inductive circuit which imposes the heaviest duty on the 5 interrupting capacity of the. circuit breaker. The current is shown as being displaced from the voltage wave by almost 90. As the current passes through zero value at 91', the voltage across the terminals of. the'circuit breaker rises almost instantaneously to nearly the full value of the generator voltage and would cause re'ignition in all three sections of the arcing chamber but for the fact that the rise of voltage causes ,a flow of current through the relatively low value resistor 85, Fig. 4, shunting the first section 48of the arcing chamber. he rate of voltage rise across the terminals of this section of the arcing chamber is thus slowed down, as shown by the steep portion 89', of the light dotted curve 9 Y.

with heavy currents, the rates of voltage rise in the high-resistance shunt 86 of the second section 49 of the arcing chamber 40, and I in the unshunted section 50 of the arcing chamber, will be so high that the arc may reignite in these sections durin' the nextfollowing half-cycle,'as indicated y the last halfcycle of the current curve 88 in Fig. 9. However, the phase of the current with respect to the voltage will be greatly changed on account of the resistor 85, which is now in series with the circuit, so'that'the; current which now constitutes the arc in the twoarcing chambers 49 and 50 will be almost in phase with the voltage and will go through z'ero when thevoltage is zero. At the same time, the resistor 85 will reduce the current'through the circuit breaker to a fraction of its original .1 value. At the next reversalof the current,

.when the current goes through zero, the rate of voltage rise will be practically that of a -cycle wave and will not be sufiicient to cause restriking of the arc in the second and third sections of the arcing chamber.

When interrupting heavy currents, as in the case considered above, the first section 48 of the arcing chuteor de-ionizing chamber 40 is usually sufficient to reduce the interru'pted current to a fraction of its original value and to improve the power factor of the ("sameso that the unshunted section 50 of the circuit breaker is sufiicient then, to fully open the circuit. In such eases, the second section of the circuit breaker is not called upon to perform any duty.

However, when {the interrupted current is small and of low power-'factor, such as the magnetizing current of transformers connected to the line, the resistance shunting the first section 48 of the de-ionizing' chamber is usuall so low as compared to the react ance of t e circuit that it is ractically without infiuenceupon the magnltude and power factor of the hue current; in this case, howchamber 0 ens together with the first section 48 at the rst current zero. The relatively high value resistor ,86 shunting the second section of the circuit breaker is suflicient to materially reduce the small magnetizing current and to improve its power-factor so that the unshunted section 50 of the circuit breaker is capable of interrupting the residual current before the next alternation.

Thus, in case of relatively heavy, low power-factor currents, the first section of the de-ionizing chamber opens at the first current zero, the second and third sections opening together at the second current zero. In case of relatively small, low power-factor currents, the first and second sections both open at the first current, alternation, while the third, unshunted, section 0 ens at the second alternation. High-power Factor currents, of any magnitude, are usually opened by all three sections at the first current zero.

In a typical circuit breaker designed for 8600 volts, as shown in Fig. 1, I employ three de-ioniziug sections 48, 49 and 50, each section bein 4 between arc terminals, with 16 grids per inch. The grids 51 are of brass gauze having wires thick and perforations approximately 100 ft. per second.

Fig. 10 shows a modification of my invention wherein the three'arcing sections of the circuit breaker are combined into separate units, 91, 92, 93 each section having its own arcing terminals 94, 95 and 96 and separate auxiliary arc- transfer terminals 97, 98 and 99, with separate blow-out coils 100, 101 and .102 connected in series with the several arcing units. Thefirst arcing section 91 is shunte by an impedance in the form of a condenser 103, reducing the arcing current to a fraction of its value; the second section 92 is shunted by a condenser 104having a much higher impedance for still further decreasing the arcing current; and the last section 93 is without shunt. The blow-out coils to 102, cooperating with the individual arcing sections,

have a gradually increasing number of turns in order to give the requisite are blowing action, notwithstanding the reduced arcing currents in the sections.

The mechanical separation of the several auxiliary, or arc-transfer; contacts of the circuit breaker of Fig. 10 is preferably so timed that-the openings of the arc- transfer contacts 97,98 and 99, respectively, follow each other at intervals of one-half cycle or more, so that the arc is first interrupted only in the first section 91, reducing the line current through the series impedance 103. The section 92 then opens, further reducin the residual current by means of the impec ance 104. The last section 93 finally opens to completely interrupt the circuit- Instead of the condenser shunts 103, 104 shown in Fig. 10, I may use a resistor shunt, such as shown in Fig. 4, or a more complex shunt network.

Design of the (Zea-ionizing str'ucture.-Several features must be observed in the design of the de-ionizing structure utilized in my improved circuit breaker. First of all, it is considered desirable to make the grids with sufiiciently large interstices to permit the arc to play therethrough, as if there were no obstruction in the space between the opposing electrode surfaces of the are. It is desirable that the arc should play freely through the grid openings, without splitting up into many small serially connected'independent arcs. with their many separate cathode and anode terminals on different portions of the grids. With the arc velocities obtainable in a chute of moderate length and with currents of 10,000 amperes or more, there would, otherwise, be formed hot cathode spots on the grids, melting the metal of the grids, and the heated vapor slowing down the rate of deionization.

On the other hand, it is desirable to make the openings in the grids as small as possible, in order to increase the rate of de-ionization which is the greater, the more uniform the metal of the de-ionizing sheets is distributed across the arc space. Thus, the practical design of the grids is a compromise between the requirement for large openings in the path of the arc, in order to prevent the splitting of the are into many small arcs, and the requirementfor small grid openings in order to secure a large rate of rise of re-ignitiol} voltage.

I have found that the limiting rate of r1se of voltage which may be applied without are re-ignition is a function of the size of the grid openings, the thickness of the grid, the sp ing between the grids and the number of grids. In general, the limiting rate of rise of voltage per grid is increased by decreasing the grid spacing, decreasing the size of the grid openings, and increasing the thickness of the grids.

I For example, with grids of brass gauze, woven of wires .032 inches diameter and .03 inches between wires, the limiting rate of rise of voltage was found vto be 3.3 x 10 volts per second per grid when the grids were spaced .083 inches apart, and 5.1 x 10 volts per second per grid when they were spaced .030 inches apart, thus showing the advantage of close grid spacing.

Again, with grids consisting of copper plate thick with a circular hole of .08 inch diameter, and spaced apart, the limiting rate of rise of voltage was found to be 2 x 10 volts per second per grid.

With the same thickness of plate, and spacing between grids, but with .04 inch holes,

the limiting rate of rise of voltage was found to be 3.7 x 10 volts per second per grid, showing the great advantage of the smaller hole. \Vith similar grids inch thick, spaced inch apart, with a hole diameter of .081 inches, the limiting rate of rise of voltage was found to be 3.4 x 10 volts per second per grid, while for grids inch thick, spaced inch apart, with a .081 inch diameter round hole, the limiting rate of voltage rise was found to be 6 x 10 volts per second per'grid. This shows the advantages of thicker grids. The figures given above indicate that the grid spacing and the width of the grid openings should be made as small as is consistent with the mechanical requirements of the design, and the danger of melting by separate arcs.

I have obtained very good results with grids spaced of an inch from each other. A further decrease of the grid spacing introduces difficulties on account of the natural warping of the material of the grids, causing the same to contact with each other, and on account of the mechanical problem of providing a suitable insulating medium of the required thickness.

As stated before, 'a decrease in the size of the grid openings tends to split the are into separate short arcs. With a speed of arc motion such as is obtainable in an arc chute of moderate length, the arc terminals on the grids will melt the same and decrease the deionizing action. It has been found that this action of the grids takes place when the arcing voltage becomes greater than about 25 volts per grid. I have further found that it requires a much stronger magnetic field, or force, to move the are into the grids without melting when the size of the grid openings is reduced.

It is, of course, desirable, for the successful accomplishment of the de-ionizing action, that the rise in voltage across the arc terminals when the current becomes zero, shall beuniformly divided between the grids interposed between the arc terminals, in order to prevent an excessive voltage across any pair of grids. In high-voltage applications, where the number of grids in series is relatively large, it may happen that, on account of the capacity of the grids to the ground, and on account of the difference in the charges acquired during the arcing preceding the current zero, the voltage may not be uniformly divided among the grids, so that some of the same become overstressed and cause restriking of the are.

In order to positively secure uniform voltage distribution over all of the grids in the de-ionizing chamber, I may provide a highimpedance balancing resistor shunting the 109 is. connected in shunt to the several grids.

The impedance of the shunt resistor 109 is so-high that the current therethrough is substantially negligible, the principal function of the resistor being to maintain auniform voltage gradient between the grids. I

As stated before, the relation between the thicknessof the grid'and the size of the grid hole afiects the operation of the circuit breaker in two ways. In the first place, up to a certain point, for a given size of grid opening, the thicker the grid wire, the higher is the permissible rate of voltage rise without re-ignition. On the other hand, an increase in the thickness of the grids raises the arcing voltage per grid for the period before the arc extinction, causing-arc splitting and excessive heating of the grids, with a resulting decrease in the de-ionizing action.

The amount of current flowing directly to the metal of the grids in an arc is a function of the arc voltage per grid and is negligible for less than 20 volts per grid. However,

an increase in the arc voltage per grid above volts usually causes the grid current to become excessive and the functioni as are electrodes, causing me ting of the gri s. 7

As shown in Fi 12, I may combine the advantages of the t ick grids with respect'to the permissible high rate of voltage. rise,

.nectin thin wire with the advantages of thin grids with respect to low arc volt per grid, by contogether, in pairs, en the arc isplaying,

by reslstors 110.

there is no appreciable current in the resistors 110 between the grids of each pair, the grid openings being large enough to permit so P ay of the arc shunting said resistors. When the arcing current reaches zero, the grids making up a pair take on thesame potential, on account of the resistor connections between the same, and de-ionize the arc space like a thick grid.

The speed with which the de-ionizing action takes place in a given dB-ionizing structure depends upon the which the positive ions move thro the space of the are under the action 0 the electric field.

The speed which the ions acquire under the action of a field of unit strength is a measure of the mobility of the ions, and varies in ggsesinversely with the molecular weight.

, the positive ion in hydrogen will move' seven or eight times as fast as the-positive ion in air. Hence, if a de-ionizing chamber is enclosed in an atmosphere of hydrogen, theopening in the grids may -be made seven In Fig. 13 is shown a modification-of my invention, wherein a de-ioniiing structure 7 111 is enclosed in a chamber 112 which is I filled with hydrogen'supplied through openings 113 from a hydrogen generator or tank. 114. The de-ionizing structure comprises two arcing terminals 119 and a bank of grids 120 disposed therebetween. The are is started by the operation of a suitable operating mechanism 121 to interrupt the connection between the arcing terminals 119 o the circuit.

The rate of de-ionization of the arc space may also be increased by reducing the pressure of the gaseous medium in WhlCh the arc is drawn, as shown diagrammatically in F' 14, wherein a de-ionizing structure 122, suc as that shown in Fig. 13, is enclosed in a chamber 123 which is maintainedunder reduced pressure by means of avacuum pm 124. Since the velocity of the ions, acq under the action of a given electric field, increases with a decrease'in the pressure, the de-ionizing action is greatl improved when operating under such con 'tions. Thus, if the pressure is reduced to of the-atmospheric pressure, grids having openings 0.5 inches wide will 've the same rate of deionization as gri having openings 0.05 inches wide at atmospheric ressure. T

In order to obtain the de-ionizing effect. of the gridv structures, it is, of course, important that the are drawn between the arcing contacts, be moved into the grids be, fore the current passes through the next zero. It requires a relatively strong-tome to move the are into the grid structure. Accordingly, the magnetic blow-out mechanism, as shown in Figs. 1 to 3, inclusive, must produce a strong magnetic field across the space where the arc is drawn, in order to prevent the are from hanging at the entrance edges of the grids and m tingthesame. However, once the arc is in'thegrid structure, it is undesirable to move the arc ve fast, as it is diflicult to keep all parts of t e are at the same speed and the are tends to break up into separate arcs. The blow-out magnet shown in Figs. 1 to 3, inclusive, is so designed as to reduce the density of the magnetic field in the upper portion of the arc chute, the pole shoes 55 terminating about the middle of the are .chute, and the upper half of the pole-shoe plates 56 being of reducedthlckness to decrease the density-of the field.

In Fig. 15 is shown a sin 1e arc-chamber de-ionizing structure w groin the magnetic field in the interior of; thegridpstruc ture is still further reduced, by providin the pole-shoe plates 151 disposedon each s1 e of the grids with large perforations 152 greatly increasing the reluctance part of the magnetic circuit with a resulting decrease in the field strength.

Fig. 16 shows an arc chute similar to that in Fig. 15, wherein the magnetic field inside the grid structure is still further decreased by providing non-magnetic, highly conducting plates 161 on both sides of the grid structure adjacent to the pole shoe plates 162. Such construction secures a rapid falling off of the magnetic field as the arc enters the grid structure, since the eddy curents in the highly conducting, non-magnetic plates 161 exercise a shielding effect, preventing the flux induced by the pole shoes 162 from entering into the upper portion of the de-ionizing structure.

It may be desirable to positively prevent the arc from moving upwardly, outside of the grids. To this end, a blow-out magnet 163 may be mounted on both sides of the upper portion of the. grid structure 164' of the de-ionizing chamber. The blow-out magnet 163 is suitably excited to exercise a downwardly directed force upon the arc.

Fig. 17 shows another advantageous construction which secures the desired decrease of the magnetic field in the grid structure. The pole shoes 171 are staggered, and the field induced thereby has a tendency to drive the arc towards one side of thefree path 173 in the grids 'of the arc chute. Such are 1110- 7 tion promotes the continuityof the arc and opposes the splitting of the same. The highly conducting, non-magnetic plates 174 extend above the pole shoes 171 to prevent the flux induced by the pole shoes from entering the grid structure. The are moves in the arc chute principally by reason of the convection currents of the surrounding gas, as in the case of the well-known arc horn utilized in lightning arresters.

Referring again to Fig. 1, it is noted that when the arc is movin into the grid structure, a layer of hot iomzed gases usually adheres to the insulating walls 52 on both sides constituting miniature de-ionizing grids on both sides of the horn-like arcing chamber. Thus, in Fig. 17 the ends "of the individual grid sheets 177 abut against the insulating walls 178 on both sides of the horn-like arcing chamber 179. The individual grids are,

of course, insulated from each other by means.

of mica spacers 180.

Fig. 18 shows a de-ionizing chamber wherein the arc is moved into the arc chute 181 by means of an air blast. The arc is drawn between two horn-like electrodes 182 by means of an arcing contact arm 183. An air nozzle 184, whlch is supplied with air from a high-pressure source by means of a hose 185, directs a blast of air upon the arc which is drawn between the arcing electrodes 182. On account of the relatively narrow passage for the air at the lower portion of the arcing electrodes 182, the velocity of the air is very great causing a rapid movement of the are into the grid structure, as is required for satisfactory operation. The opening in the arc chute 181, however, is much larger than the opening at the lower portion of the arcing horn 182. The velocity of the air blast is, accordingly, greatly decreased and the motion of the arc is slowed down to a value required for the satisfactory operation of the circuit breaker.

In order to de-ionize the layer of gas near the insulating walls (not shown) on both sides of the horn-like arcing plates 182 the grids 186 of the de-ionizing chamber ave extensions 187 project-ing downwardly near the insulating walls leaving a free space in the middle for the motion of the arcing-contact arm 183.

The difiiculties resulting from .drawln the are between the electrodes outside the gri structure, and subsequently blowing the same into the grid structure, maybe avoided by drawing the are through the openings in the grid structure itself. Such construction is shown in Fig. 19, wherein the grids 191 in the arc chute 192 are provided with a longitudinal perforation 193 through which the arcing contact member 194 is moved by means of an arcing contact arm 195, similar to the arcing contact arm 15 in Fig. 1. The arcing contact member 194, which draws the arc, is preferably of rectangular cross-section, of narrow width and relatively great height so that'the perforation in the grids is of such width as to secure the de-ionization of the arc space in case that small-current arcs remain playing in the perforation 193 without moving into the grids.

Another construction for positively securing the drawing of the are within the grid structure is shown in Fig. 20, wherein the movable arcing electrode 201 makes a wiping contact with the grids 202 at the bottom of the de-ionizing chamber 203. One end of the arcing contact member 201 is covered with a block of insulating material 204 which is so alined with the surface of the arcing contact member 201 as to slide beneath the grids, behind the conducting surface of the contact member. The are is drawn by the moving contact member 201,

and is forced into the grid structure by the I insulating member 204.

In the foregoin explanation gridstructures made of wire gauze haire been described. It is, of course, clear that any other structure may be utilized which sub-divides the space between the arcing electrodes into a large number of small spaces, all of the spaces bein rovided with conducting centers or nuc e1 for exercising a de-ionizing action throughout the entire space between the arcing electrodes.

' In Figs. 21 and 22, the grids are shown in theform of metallic sheets 210 having per- -bronze. The spacing between theends o the comb teeth 214 is smaller than the width of the switch blade 213 so that,-when the same is in its closed position, shown in the drawings, the teeth of the de-ionizing combs are bent outwardly, ready to spring back and form a narrow slot immediately upon withdrawal of the switch blade. Such construction assures a positive de-ionizin action upon the opening of the circuit reak'er, since the are drawn by the switch blade 213 in the space between the teeth 214 of the grids 210 is enveloped, in every portion thereof, by a conducting de-ionizing member which will secure rapid restoration of the arcing space to its original non-conducting condition, without the necessity of further arc movement.

To operate the circuit breaker just described, the right-hand portion 215 of the comb-like grid structure may be withdrawn somewhat to the right so as to rovide a sufficiently large opening for inserting the switch-blade 213. The comb-structure is subsequently moved back into the normal operating position in vwhich the comb teeth of the grids are bent by the switch-blade, as shown in the drawings. The circuit breaker ma also be so constructed that the switch bla e is inserted into the comb-like structure from one side and removed therefrom through the other side, as indicated by the arrow 216 in Fig. 22. An additional grid structure 217 may be placed above the comb-like structure for receiving the arc between the comb-like grids, in Case flaiz'rc moves upwardly.

---=. Figs. 23 and is shown a de-ionizing chamber which secures the efiect of the comb like arrangement shown in Figs. 21 and 22, with a construction utilizing wire-gauze 'ds. The de-ionizing chamber is divided into a lower portion 231 and an upper portion 232 ressing on both sides of an arcing switch bhd; 233, the grids being of resilient material the switch-blade to s ring ba and the slots for the switch blade being somewhat narrower than the width of the switch, so as to cause the ends of the {ids facing c after the blade has been with rawn from the grid structure, in the direction shown by the arrow 234.

A very simple mechanism for avoiding the danger of re-ignition by reason of failure of the arc to move into the de-ionizin grid structure, is shown in Fig. 25. One of t e areingelectrodes is shown in the form of a conducting vessel 251 containing mercury 252,

its

the other electrode .being in the form of a metallic plate 253 which is downwardly movable until it contacts with the mercury. The metallic plate 253 carries an insulatin housing 254 in which is mounted a bank, 0 horizontally disposed located beneat the movable electrode 253 and are entirely immersed when the movable electrode is in contact with the mercury.

ids 255. The grids 255 are n When the electrode 253 is raised to its open osition, illustrated in the drawings, the arc is drawn between the electrode surface and the mercury and is confined to the space occupied by the grids 255, thus positively insuring a prompt de-ionizing action.

Another mechanism for drawing the are through the de-ionizing grids by means of mercu? is shown in Fig. 26, wherein a vessel 260, o insulatin material, is pivotally mounted to move rom the horizontal pos1-, tion shown in the drawings to a vertical position. The vessel 260 has two enlarged compartments 261 and 262, at the ends thereof, and the s ace between the two compartments is filled w th a bank of grids 263 of a construction similar to that described in connection with the other de-ionizin structures. Electrodes 264 and 265 extend into the compart ments 261 and 262, respectively, the two electrodes constituting arc terminals of the circuit breaker. The vessel 260 contains a body of mercury 266 which fills the lower portion thereof, providing a connection between the two electrodes 264 and 265. By turning the vessel 260 to the vertical positlon, the mercury breaks contact with the electrode 264 which is moved upwardly, and the receding mercury draws an are through the grids,

wherein the arc is subse 'uentl de-ionized.

In the design of the e-iomzing chamber,

care must be taken to avoid injury to the grid sheets by the are drawn between the main under circumstances, exercise a detrimentalefiect upon the grids.

The heating of the de-iom'zing grids in the arc chute takes place in two ways, first, byradiation and thermal conduction from the hot gases of the arc and second, by the direct evolution of heat at the surface of the grid material by the currents flowing into the grids. It has been found that, when a wire is placed in an are near an arc terminal and a potential is applied to it, considerable cur rent flows to the wire. further from the arc terminal, the current to the wire becomes negligible. Thus, in the case of a 50-ampere arc, a wire placed onesixteenth of an inch from either electrode and maintained volts negative with respect to the are carried a large current, while the same wire placed one-half inch from the arc terminal and maintained 140 volts negative with respect to thearc carried only a very small current.

I believe that the change in the amount of I current flowing to the wire, dependentupon the spacing of the same from the arc terminal, is due to the fact that the arc electrodes give off considerable quantities of metal vapor. Such vapor has a much lower ionizing potential than air and is, therefore, thermally ionized at a much lower temperature than air. Accordingly, when a wire is spaced close to one of the arc electrodes, it becomes surrounded by metal vapor and a relatively low potential will sulfice to produce a large current to the wire. However, when the wire is farther away from the electrode, it is surrounded by air and the current thereto will be negligible, even if the potential applied is relatively hi In Fig. 2 I have shown a de-ionizing chamber wherein the grid sheets 270 are protected from the effect of the vapor blast 271 emanating from the arc terminals 272, u on the electrodes, by bending the terminal plates 273, away from the grid structure and shaping them like horns. As the are 271 is moved upwardly in the grid structure, the arc terminals move outwardly upon the terminal plates 273 and the blast 271 is directed away from the grids instead of into the grids, as in the case where the terminal plates are parallel to the grid sheets. Many other constructions may be employed to 'protect the grid sheets from the direct action of the vapor blast emanating from the arc electrodes.

Thus, in Fig. 28, the arcing chamber 280, similar to that of Fig. 11, is provided with insulating barriers 281 breaking up the direct path between the terminal plates 282 and the de-ionizing grid sheets 283, the arcing between the two terminal plates 282 taking place through a somewhat tortuous path through staggered openings 284 in the insulating barriers.

In Fig. 29 is shown another modification of my invention wherein the grid sheets 290- are If the wire is moved.

held between insulating plates 291 which are provided, in the middle thereof, with openings 292 for the arc. The terminal plates 293, between which the are drawn by the interrupting terminals is blown, are placed outside of the insulating plates 291 and are so disposed that the arc blast 294C emanating from the arc terminals is directed away from the arc openings 292 in the insulating plates 291 on both sides of the grids.

Fig. 30 is a single view embodying adjunctive features of the figures heretofore described. In this figure the various reference numerals designate the same parts as in the preceding description so that the structure illustrated in Fig. 30 should be clear without separate enumeration of its component elements.

There has been described a variety of structures and has been set forth the principles 8.5

whereby it is possible to open circuits carrying very heavy currents at high voltages wit out the employment of oil for quenching the are drawn between the circuit-interrupting terminals. I have pointed out that, in alternating-current circuit breakers, are re-ignition maybe successfully prevented by artificially increasing the rate of de-ionization of the arc space, and so controlling the rate of voltage rise across the arc terminals that the I potential gradient in the de-ionized spaces never reaches a value at which re-ignition will occur.

My invention may be embodied in numerous other structures, and the features of the artificial increase of the rate of de-ionization may be embodied in other types of circuit breakers and in other devices wherein it is important to prevent arc lie-ignition. I desire, therefore, that the language of the appended claims the arc space into small spaces less than inch, said conducting elements being so su ported that the latter conduct substantia y no arc current.

2. The combination with an alternatingcurrent circuit, of acircuit breaker having 0.

de-ionizing chamber comprising parallel are terminal members and conducting nuclei subdividing the arc space between said terminal members into small spaces associated with said nuclei, means fordrawing an arc and transferring the ends of said arcto said parallel arc-terminal members, and means for limiting the rate of voltage rise between said terminal members.

.3. The combination with a circuit breaker,

a pair of,

Images