US2412247A - Circuit breaker holding magnet and armature - Google Patents

Description

Dec. 10, 1946. D. I. BOHN 2,412,247

CIRCUIT BREAKER HOLDING MAGNET AND ARMATURE Filed July 28, 1942 '7 Sheets-Sheet l p; l k- F72 y INVENTOR. flan/A40 I Bow/v Dec. 10, 1946. D. BOHN 2,412,247

CIRCUIT BREAKER HOLDING MAGNET AND ARMAI'URE Filed July 28, 1942 '7 Sheets-Sheet 2 INVENTOR. flan A40 1. 505w Dec. 10, 1946. D. l. BOHN CIRCUIT BREAKER HOLDING MAGNET AND ARMATURE Filed July 28, 1942 '7 Sheets-Sheet I5 m w W Dec. 10, 1946. D. 1. BOHN 2,412,242

CZRCUIT BREAKER HOLDING MAGNET AND ARMATURE Filed July '28, 1942 7 sheets-sheet 4 cOA/DAEY BLOWOUT call.

M0 a TEm/NAL CONT/9C 7' L WACT TERMINAL INGED GOA/THC T f 16 J INVENTOR.

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Dec. 10, 1946. D. BOHN' 2,412,247

CIRCUI-T BREAKER HOLDING MAGNET AND ARMATURE Filed July 28, 1942 7 Shets-Sheet 5 mvmon' flaw/94.0 f 190/? BY a ATTORNEY.

Dec. 10, 1946.

D. 1. BOHN CIRCUIT BREAKER HOLDING MAGNET AND ARMATURE Filed July 28, 1942 '7 SheetsSheet 7 129/01? DEF/67V INVENTOR. flaw/240 j. Box/1v Patented Dec. 10,1946

CIRCUIT BREAKER HOLDING MAGNET AND ARMATURE Donald I. Bohn, Pittsburgh, Pa., assignor to I. T. E. Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Application July 28, 1942, Serial No. 452,613 7 Claims. (Cl. 175-336) My invention. relates to circuit breaker apparatus and more particularly relates to a novel magnetic structure controlling the closing and opening operation or" a circuit breaker.

In recent years, the rapid expansion of mercury arc rectifier installations at 600 volts, D. 0., both as to the total kw. installed and the relatively large number of units operated in parallel, has emphasized the importance of switchgear in providing suitable rectifier operation In the event of a backfire, the rates of current rise through a rectifier and its transformer windings lie, in general, between three million and six million amperes per second. With large installations, where 60 units of 5000 amperes each are operated in parallel, the ceiling value of these currents is far above a figure which could be tolerated both from the standpoint of continuity of operation and safety to equipment.

High speed breakers having a time of approxi mately .5 cycle from backfire initiation to current limitation may permit, in some installations, peak currents in the neighborhood of 60,000 amperes. While such a value is appreciably below that which would cause equipment damage, it is nevertheless undesirably high, in that surges and sympathetic backfires on other units often result. Breaker duty and maintenance are higher than would be the case with lower values of backfire current and the factor of safety is not as great as is desirable.

Application Serial No. 371,092, filed December 21, 1940, now Patent No. 2,390,966, issued December 11, 1945, shows in Figure 15 the current path during a backfire in a six phase rectifier. It will be noted that the current flowing through the cathode breaker is supplied by other rectifiers on the bus, and that the current flowing through the anode breaker is the same current plus the additional current from the other anodes of the faulted rectifier.

Under these circumstances high speed breakers are essential to insure effective interruptions.

The speed with which the armature of the trip or opening magnet functions is a material factor in the time of circuit breaker operation. Obviously, the lighter the mass of the armature, the less its inertia and the faster it can operate. On the other hand, the armature must have a sufficiently large effective area.

The breaker of the present invention employs a magnet and armature design. reducing the armature weight in a ratio of approximately 1:3, as contrasted with a conventional holding magnet.

As will be obvious, in order to secure the same eifective armature area for a smaller weight of armature, I may decrease the radius and correspondingly increase the length of the armature.

Quite obviously, however, an armature of such great length compared to its diameter would be entirely impractical from a mechanical and stiffness point of view.

In accordance with my invention, I carry out this principle of weight reduction which overcomes the mechanical defects noted above I have discovered that I may materially reduce the mass of the armature and thereby increase the acceleration thereof by so arranging the magnetic structure of the holding magnet that there are, in effect, a plurality of individual magnets, each with its individual armature.

Inasmuch as the center of the armature which is mechanically connected to the movable contact of the circuit breaker assumes the greatest share of the carrying load in operating the movable contact and this load on the armature is gradually reduced. as the edges of the armature are approached, I provide maximum thickness of metal at the center of the armature with a tapering armature construction toward the ends to a substantially reduced thicknessat the ends.

This serves to prevent any deflection of the center of the armature which might tend to occur if the armature were of uniform cross-section; such deflection at the center should it occur would result in a reduction of the holding force on the armature and hence result in a rapid progressive release of the armature.

In order that the distribution of armature mass in this manner from maximum thickness at the center to minimum thickness at the ends may correspond to the flux distribution, th magnetic circuits are so arranged that a maximum number of'lines of force exist at the center and the number of lines of force is reduced towards the edges of the armature.

My novel circuit breaker provides for tripping of the breaker on de-energization of the holding magnet armature and permits the armature of the magnet to be operated into engagement with the pole face of the magnet while the circuit breaker is still in disengaged position, the actual closin operations of the circuit breaker being performed by a separate power supply.

Accordingly, an object of my invention is to provide a novel magnet having a plurality of magnetic paths, each for conducting individual fluxes flowing through individual portions of the armature.

aeiaarr A further object. of my invention is to provide a novel armature structure in which the portion. of the armature subject to the greatest load carries more lines of force than other portions of the armature which carry smaller portions of the load.

Still another object of my invention is to provide a novel armature, the mass of which has been reduced to a minimum for the load it carries.

Still another object of my invention is to provide a novel magnet having novel magnetic path structures.

Still a further object of my invention is to provide a novel construction of a holding magnet in which tripping is effected by de-energization oi the magnet armature.

Still a further object of my invention is to provide a novel circuit breaker structure in which a flexible connection extends from the armature to the movable circuit breaker contact.

There are other objects of my invention which together with th foregoing will appear in the detailed description which is to follow, in connection with the drawings, in which:

Figure 1 is a schematic view of my circuit breaker operating element showing the contacts closed.

Figure 2 illustrates the open position or" the circuit breaker in Figure 1.

Figure 3 is a view corresponding to that of Fi ure 1 showing the movement of the apparatus for normally opening the circuit breaker.

Figure 4 is a diagrammatic showing of a slightly modified form of circuit breakers wherein'a solenoid closing mechanism is utilized instead of a motor.

Figure 5 shows the circuit breaker of Figure 4 in closed position.

Figure 6 is a detailed showing of a portion of the apparatus of Figures 4 and 5.

Figure 7 is an exploded view in perspective of the operating magnet of my circuit breaker.

Figure 8 is a view in perspective of my operating magnet in assembled position.

Figure 9 is a cross-sectional view taken on line 9-4) of Figure 8.

Figures 10 and 11 are diagrammatic views 11- lustrating the operations of the magnet of Figures 7 and 8.

Figures 12, 13 and 14 are additional diagrammatic views further illustrating the operation of the magnet. v

Figure 15 is a diagram of a composite current oscillogram comparing cycle and cycl anode circuit breakers employed in my invention.

Figure 16 shows the arcing structure.

Referring now to Figures 1, 2 and 3, I have here shown in schematic form the construction and operation of a circuit breaker utilizing my invention. The circuit breaker here shown includes circuit connecting members it and 02, which form the terminals of the circuit breaker and are arranged to be connected into the external circuit.

An L-shaped stationary contact member 93 having a contact surface 5 3 and a securing bracket I5, is mounted by means of the bolt it on the connecting bar Ii. The stationary contact it may be engaged by the movable contact I'll which also is an L-shaped member having a contacting surface It and a mounting bracket it.

A bolt 20 passes through the mounting bracket I9 and secures the movable contact ill to the upper portion of the movable contact carrying lever 22.

Lever 22 is pivoted for rotational movement at 23. A flexible laminated conductor 26 is secured in any suitable manner, as for instance, by the bolt 25 to the lower end of the lever and at its opposite end is secured by the bolt 26 to the end of the connecting bar i2.

When, therefore, the circuit breaker contacts are closed a circuit is completed from conductor 6 5' through the stationary contact 83 to the movable contact it through the movable contact carryinglever 22 and the flexible lead 2 to the connecting bar i2. A tension spring 38 is connected at one end to the ear ti on the movable contact carrying lever 22, and at the other end. the spring so is connected to a lug 32 mounted on the frame of the mechanism. Tension spring therefore biases the movable contact carrying lever 22'into counterclockwise rotation and hence biases this member to open circuit position.

When the circuit breaker is open as seen in Figures 2 and 3, then the movable contact lever 22 rotates counterclockwise against the stop 36, which limits further rotational movement thereof. The said stop is, of course, a.-- position as to permit the move" I ctationary contact to ensure proper circuit interrupting capacity.

When closed, the contacts are normally maintained in engagement by means the flexible member 35, which may take any desired form, such as a chain. The chain 35 is connected at one end to an ear 36 mounted on the contact lever 22 preferably approximately midway between the pivot point 23 and the free end which carries the movable contact ii. This chain passes over the roller 37' which is mounted on the operating crank 38. The other end of the chain is at 39 secured to the armature ii) which is normally held in engagement with the operating magnet 52.

The armature it is plvotally mounted on the lever 36 which is rotatably mounted on the pivot G5, which in turn is carried by lugs do associated with the frame of the magnet 62.

The magnet 552 is normally energized by a constant potential direct current coil 11 which provides adequate flux to maintain the armature 5G in contact with the pole pieces against the pull of the spring 30 transmitted by the chain or flexible member 35.

Current flowing through the series conductor i2 afiects the flux between the magnet and the armature so that under certain conditions of direction and intensity of current flow, as hereinafter described, the flux through the armature is inadequate to counteract the efiect of the spring to, and the circuit breaker contact is pulled to open position.

The crank 38 may be operated for the purposes hereinafter described to close or to open the circuit breaker independently of the magnet 42 and the armature (it.

A motor 59 is used to operate a multi-pole unit, driving, through'an insulating shaft, the high speed shaft 5! of small speed reducers 52; one speed reducer being mounted on each pole. The low speed shaft 58 of each speed reducer carries the crank 38 and its roller 3?.

If the motor to is run suirlciently to drive crank 38 through 360 and the armature 6B is sealed against the pole face of magnet 42, the effects of the chain 35 riding on the crank roller 31 is to cause the breaker to go through an open-close cycle, as shown in Figures 1 and 3.

A limit switch may be utilized for controlling the motor which, with suitablebraking, ensures that the crank and roller will stop at the proper point in the operating cycle either for closing or opening.

In Figure 2, the circuit breaker contacts are shown in the open position, having opened automatically because the flux in the magnetic path of magnet 42 and the armature 4|! was reduced beyond the critical value necessary to counterbalance the opening force exerted by the spring 30.

Accordingly, the spring has'caused the lever 22 to rotate counterclockwise, thus pulling the chain over the roller 31 and lifting the armature away from its magnet 42.

Figure 3 shows the first necessary step for reclosing the circuit breaker after it has opened to the position shown in Figure 2. With the breaker contacts disengaged and armature oil in its uppermost position, the crank iitl is rotated by motor through 180 so that the armature is permitted to fall by gravity against the pole face of magnet and the flexible member 35 is shown completely slackened having no tension at this particular phase of the operation. The circuit breaker may now be reclosed by energizing the coil H to assure that there is adequate holding flux passing through the armature All. The shaft 53 is then rotated by means of the motor preferably in a clockwise direction to ro- 1 tate the crank 38 and the roller 37 so that flexible member 35 is drawn taut and then is effective to pull the contacts into engagement and maintain them in the position shown in Figure 1.

To open the circuit breaker without relying on the automatic circuit breaker opening means, the field coil 4i may be deenergized, which will result in the release of armature to and a consequent opening of the circuit breaker; or the motor may be rotated so that shaft 153 is rotated through 180", thus bringing the circuit breaker to the position shown in Figure 3. Ineach case, the circuit breaker may be opened.

In the foregoing, the principle of the formation of my circuit breaker has been set forth in its simplest form.

Either of the contacts l3 or ill may obviously be resiliently mounted upon their respective supports.

The type of holding magnet shown in Figures l, 2 and 3, is of a conventional bucking bar type well known in the art. The actuating mechanism of the circuit breaker may, of course, be efiective with any of the well-known releasable holding means. The type of holding magnet which I prefer, however, to use in the circuit breaker of the present type, and which also has many additional functions and operations, is that shown in Figures 4 to 14 inclusive.

However, in Figures 4, 5, and 6, I have shown a somewhat modified type of circuit breaker which may operate in the same general manner, and which may be described in its simplest terms before the exact operation of the magnet itself is set forth,

In Figure 4, the modified circuit breaker is shown having the holding magnet of m invention which is energized by the field coil 63, which may create suf icientiiu'z: to attract and hold the armature The field coil may be energized from any direct current source as 88, the circuit to the field coil being closed by, for instance, the switch 8 3.. The armature it is pivotally mounted on the lever 6i which, in turn, is pivoted at 38 on the member so, which is rigidly attached button 15 which is secured to the upper portion of the rod 12.

- The contact members in the present case are illustrated as bridging contact 18, which, in the open position of the circuit breaker, bridge the contact members l1, l1 and, in the closed position .of the circuit breaker, bridge the contact member l8, 18. The members 18, 18 are, of course, the main current conductors while the members l1, 11 may, when bridged, energize any appropriate relay or signalling apparatus, or any appropriate motor circuit or other apparatus necessary for effective operation or the circuit breaker when it is open.

In order to close the circuit breaker, that is, in order to move the armature 52 from the position shown in Figure a to the position shown in Figure 5 so that the bridging contact member it? may bridge the contacts it, 78, the field coil 6| is first energized by closing the circuit there tothrough the switch 84. Thereafter, the solenoid coil 8b is energized by closing the switch 82, thus connecting the current source 63 through the leads 3% and to the coil 80. The plunger it is attracted downwardly thus pulling the rod downwardly and engaging the button it with the upper surface of the lever iii, and pulling the lever Ei'i downwardly.

Thearmature s2 is normally urged into raised position by the tension spring at fixed at its upper end and engaged at its lower end to the upper portion of the rod 28 which, in turn, is

secured to the armature 52. The attraction oi the solenoid plunger l3 downwardly by the coil Bil pulls the lever ill and the armature 82 downwardly against the force oi the tension spring 8''! When the downward movement has been completed, and the armature 62 has been scaled against the pole faces of the magnet Bil, the circuit breaker will normally stay closed despite the fact that the switch 82 (which may be a spring operated switch biased toward open position) now opens. That is, as long as the mag netic flux of operating magnet 50 through the armature 82 is sufiicient to counteract the force of the spring 81, the circuit breaker will remain closed, and the contacts 18, 18 will be bridged.

Accordingly, the solenoid plunger 12 may be permitted to return again to the raised position under the bias of, for instance, a spring mounted directly beneath it.

In Figure 6, I have shown the position of the solenoid plunger and the rod 12 with respect to the lever Bl at the moment the closing operation has been completed and before the solenoid plunger has been permitted to rise again to the position shown in Figure 5.

ivhen, now, owing to current conditions, hereinaiter described, which cause a decrease in the holding iiui: exerted by the magnet through the armature G2, the holding force of the magnet decreases below the pull exerted by the spring 2?, the spring is free to pull the armature t2 upwardly and, consequently, remove the bridging member N3 from bridging engagement with the contact 78 and to bridge the contact member 1?. ill. The holding or operating magnet Eli and its garages? function is set forth in Figures 7 to 14 inclusive and constitutes a vital element of my invention.

Referring now to Figure 7, there is here shown in partially exploded form the holding magnet 69 which constitutes a primary element of my invention. The holding magnet, as may be seen in Figure 7, comprises a rectangular structure consisting of stacks of laminations which provide spaced and interleaved pole pieces or opposite polarity. This system provides a plurality of short flux paths (hereinafter described in connection with Figure 12) through the armature and results in an extremely quick acting release. The electrical and magnetic properties and the advantages in actual operation of my holding magnet will be more specifically set forth. after the following description of the specific physical arrangement thereof.

The stacks of laminations are held together by a pair of non-magnetic frame plains till and M32. Plate lei is provided with a plurality of tapped perforations 9%, N33 to receive the ends iitil, Mi l of a plurality of studs Hi5. Studs tilt are insulated from the metallic laminations hereinafter set forth by the insulating bushings M36, M36. These studs we pass through corresponding openings M38, ltd in each of themetallic laminations as hereinafter set forth, and also pass through openings in the lower plate idB-all of the openings in the plates and in the laminations being in registry with each other; The lower end of v the studs are also threaded, and the entire assembly is securely integrated as a. single unit by means of the nuts ill which are threaded onto the ends Mil oi the studs Hi5, and held in place by the lock washers ll la and Washers ll lb. The washer lllb is of insulating material to ensure that the nuts I i l are appropriately insulated from the plate ldii.

A central opening M is provided in each of the plates I08 and W2 and registers with coring plate is shown lifted from the entire stack in order better to illustrate the complete unit.

In the construction shown in Figure 7, the holding magnet is provided with five layers of laminations Hi to H5. Each of these layers of laminations is separated from the adjacent layer by insulating plates 826 to H29 respectively.

Referring now to layer IZI, this layer, as do each of the others, consists of two sets of laminations. One of the sets or stacks l32 comprises sheets which are L-shaped in formation with one limb I33 forming the sides of the structure and provided with openings not, 908 to receive the studs N35. The other limb i351 forms a magnetic pole in the manner hereinafter described.

Layer it! comprises, in the same plane with laminations I32, another stack or layer of laminations M6 which consists of a plurality of sheets of a simple rectangular form and which forms an element of the other side of the structure. The stack Mil is also provided with openings not, me to receive the insulated bolts. An air gap M2 is provided between the limbs M35, forming a pole piece, and the end of the rectangular stack of laminations Md. The insulating plate I26 is placed immediately beneath the layer' l2! and immediately above the layer I22 in surface to surface engagement on opposite sides with each of the layers.

While sheet l26 should preferably be an insulating non-metallic sheet, it is sumcient, however, for purposes of operation of the holding magnet that it merely be a non-magnetic memher. The insulating sheet Mill is U-shaped in formation and is provided with the central opening M51; which registers substantially with the central opening H5 in each of the outer plates Hi2 and till to permit the conducting bar iii to pass therethrough. Sheet l2i also has openings we, ifit to permit the insulating bushings to pass therethrough.

The next group of laminations immediately beneath, that is, layer 622 has the same form as the laminations in layer i211, but the members are reversed with respect to each other. Thus, the stack Mild in layer i2? extends immediately beneath the limb 833 of stack H32 in layer HM; and limb i331: of stacks Hilda in layer l22 extends immediately beneath the stack l lli in layer (122i.

In layer 523, the positions of the stacks are again reversed so that the L-shaped stack extends beneath the L-shaped stack of layer 62H, and the rectangular stack of layer 023 extends beneath the rectangular stack in layer M26.

In layer Hi l, the positions are again reversed so that the arrangement of the stack corresponds exactly to that of layer B22; and again in layer till, the positions are reversed so that the arrangement of the stacks in the layer corresponds .to the arrangement in stacks i233 and 526.

Thus, in each adjacent layer, an L-shaped stack is in alignment with a rectangular stack, and a rectangular stack on the opposite side is correspondingly in alignment with the adjacent L-shaped stack on either side of the layer.

Insulating spacing plates, i271, E28 and are, simi-' lar in every respect to spacing plate 826, are introduced between successive layers of laminated stacks so that each successive laminated layer l2 l-l25 is magnetically isolated from the others.

The laminated stacks, aswell understood, are formed of magnetic material so that appropriate magnetic fluxes may be created in accordance with the operating characteristics hereinafter set forth.

An air gap M2 is provided in each layer between the rectangular stacks and the adjacent limb I35 of the L-shaped stack in the same layer for purposes hereinafter described in connection with Figure 14.

The pole pieces are formed by the limbs i355, 585a, 885b, i350 and Wild in the stack. Adjacent poles in adjacent layers are of opposite polarity in accordance with the structures hereinafter described. Thus, should pole I35 be north, then pole lliiia will be south, 53% will be north, i350 south, and l35d north. The poles of opposite polarity are interleaved as shown in Figure 7 so, that they extend substantially between each.

other to provide proper terminals for the magnetic paths through the armature in the manner hereinafter described. The manner in which the poles become of opposite polarity should be obvious upon inspection of Figure 7. Thus pole face i215 extends from the right-hand end I32 of the structure, and current induced in the laminated stack will produce a magnetic flux of a specific direction therein.

In layer I22, the fluxes will be of the same direction, but, however, pole face l35a extends from the left-hand side of the stack, and hence this pole will be of a polarity opposite to that of pole I35. Similarly, pole I35b extends once more from the right-hand end of the stack and pole I350 from the left-hand end so that in each case the polarity will be opposite. The arrangement is followed throughout the stack so that adjacent interleaved poles are of opposite polarity.

In order to complete the magnetic circuit between the ends of the laminations remote from the pole pieces, a single stack of rectangular 1aminations I50 is provided. This stack of laminations is secured between the end frame members IOI and I02 in spaced relation to the ends of the other laminations so that an air gap I5I is provided between the ends of stacks I32 and I40 and the stacks I50. This is done in order to reduce the possibility of saturating the magnetic material during normal operation.

The stack I50 is maintained in position, as will be obvious in Figure '7, by the insulated studs I05 which pass through corresponding registering openings in the stacks and in the end frame members.

The specific manner in which the studs 1 05 and their insulating bushings pass through the stacks of laminations and the end frames is shown in the cross-sectional view of Figure 9 where the stud and bushing passing through the registering perforations of the stacks I35 and I40 are shown. From Figure 9, it may readily be seen that the studs )5 do not provide any conductive path between the stacks. Preferably, the stud I05, while they may be of metal, should be of nonmagnetic material so that undesirable flux paths will not be provided.

In the assembly operation, the studs I05 are threaded into the threaded openings 503 in the frame member Mill. The insulating bushing 105 is then placed thereover, and the successive stacks of laminations and their respective insulating spacers are then placed over the studs, and the entire assembly locked in place by the nuts H l and their associated members.

When the various laminations and their insulating spacers and insulating irames are united in a single unit, they then assume the form shown in Figure 8. l,

The series conductor or bus bar I2 is shown passing through the opening M5 in the entire magnetic structure. The armature 40 is shown resting against the pole faces; and the direct current energization for the magnetic structure is provided by the coil 5!, the action of which corresponds to the action of coil 6| in Figure 4 or the action of coil 41 in Figure 1.

This direct current energization of the magnetic structure is obtained by reason of a magnetic interconnection between the coils and the magnetic structure. For this purpose, solid iron pole pieces I50, ISI are providedthese members being secured against the sides of the magnetic laminations by bolts I63 which pass through openings in the pole pieces I60 and I6! and enter the tapped perforations I64, I84 in the sides of the frame members I0! and I02 (see Figure '7).

A bolt IIi'I passes through perforations in the opposite pole pieces I60 and I6I (Figure 8), and maintains the magnetic core in position between these two pole pieces. This magnetic core corresponds to the member I81 of Figures 4, 5, 10 and 11. Although the poles I30 and ISI are shown extending to the right of the laminations I35and I40 in Figure 10, they may be reversed in direction if desired as shown in Figure 11. The coil 10 BI with terminal connection I68 (Figures 4, 5, 10 and 11) provides proper energization.

The direction and intensity of the magnetic flux of the magnetic structure herein described is influenced by two factors:

The first factor is the direction of the current flowing in the bus bar I2 which passes through the central opening H5 in the magnetic structure. This flux, however, is not relied upon to generate any holding force.

The other component of the magnetic flux in the magnetic structure is created by the pole pieces I6I and- IE0 and their core I67, which is surrounded by the coil 5|.

The direct current energization of the coil 5I produces a magnetic flux in the core I67 and in the pole pieces I60 and IBI through the poles I35 and I40 in each layer of the stack.

These composite actions are shown more speciiically in Figure 10.

-Thus in Figure 10 when the coil 5i is energized by a direct current source in a desired direction, the magnetic fluxes in the structure are shown by the arrows. The direct. current coil 6| creates a magneto-motive force driving the flux through the poles luiJ and iGI to the edges of the stacks of laminations.

This flux in the schematic showing of Figures 10 and 11 will flow through pole I6I through one of the magnetic laminations I35 and then through the armature 40 to the adjacent opposite pole 335a, returning through pole piece I50. A parallel magnetic circuit is provided from pole piece it! through laminations ltiib, armature 20 to laminations i35a, returning through pole piece i663. The flux flowing in laminations i351) divides as shown in Figure 12, some flowing through the armature 4b to laminations I350 and pole piece 556i. The manner in which the flux flows from pole to pole through the armature in each case is shown in the schematic cross-sectional view of Figure 12.

Thus, the flux in the laminations is divided into a. plurality oi paraliel flux paths through the armature, each of the paths including only its individual portion of the armature as distinuished from prior magnet structures in which all of the flux in the magnetic structure must flow through the entire armature. Accordingly, for the same armature mass, my present structure will conduct a considerably larger number of flux lines by reason of the number or multiple magnetic paths than is the case of the standard magnet in which all the flux flows through the entire structure in a single series path.

In addition to the flux paths between I35, l35a-I35d as will now be apparent, flux paths are provided from lamination i35 through armature 40 to laminations M0, 835a to 0a, etc.-

These paths are provided by reason of the slight overlaps of the armature do as shown in Figure 10 which magnetically connects laminations I35 with I46 through armature 40 and similarly magnetically connects each of the other corresponding sets of laminations.

Consequently, the magnetic flux flows not only from pole I35 through the stack I40 in each layer, but also flows from pole I35 to pole I35 in successive layers-the armature 40 providing the magnetic path between successive poles in successive layers. The flux thus provided is sumcient to maintain the armature 40 against the polgnpieces, against the bias of the spring 81 or atlases When current is flowing in the normal direction in the bus bar it, as shown in Figure 10, it creates a flux through the magnetic structure, in the direction indicated by the arrows, which augments that created by the current in thecoil 6i, so that the armature is even more firmly secured in position.

As may now be seen in Figure 11, should the direction of the current in the bus bar it be reversed, a flux through the magnetic structure in the reverse direction will be created thus tend ing to counteract the effect of the flux created by the coil ti. These two fluxes opposing each other thus will reduce the flux passing through the armature to a point where the bias of the spring 30 or at will be sumcient to overcome the pull of the magnetic structure, and the armature will be released to permit the circuit breaker contact to separate.

While in Figures 8, l0, and 11, the magnetic bracing the bus bar it, it might be advisable unl2 in the center of the armature may be deflected. That is, the point 8d, at which the external force exerted by the flexible chain 35 is exerted, may be drawn away from the pole face owing to the relatively small cross section required for the armature. In such a case, the slight flexing of the armature, which permits the center area. thereof to be drawn away, may thus decrease the magnetic fiux'therethrough at the center. This decrease in magnetic flux at the center will thus decrease the net counteracting force exerted by the magnetic structure to the pull at the point der certain desired conditions to extend the pole pieces iBll and iti so that the magnetic flux in these members will also embrace the bus bar iii.

A reversed current in the bus bar l2 will then not merely create a reversal of the magnetic flux in the magnetic structure itself, but will also set up a magneto motive force in the pole pieces Mid and lfil in a direction opposite to'the magneto- 'motive force exerted by the coil iii, thus tendand its energizing coil 6i and the magnetic force exerted thereby is sumcient to hold the armature so in position, and that this holding force is accentuated when current is flog through the bus bar it in the forward direction.

When current flows in the bus bar id in a direction opposite due to a fault condition, this magneto motive force is counteracted, as shown in Figure 11, and is rapidly diminished to an extent where the armature so may be released. 1

By reason of a plurality of poles which are thus provided, I have found that a very small armature, weighing approximately of the order of .55 pound, is all that is needed to maintain closed contact position of. the circuit breaker. The weight of the armature may thus materially be reduced. I The inertia of the parts, whichmust be brought into motion upon the occurrence of a condition which makes it necessary that the circuit breaker open, is also greatly reduced and the opening time of the circuit breaker is correspondingly decreased. The armature need only be sufiicient to provide an appropriate path for the magnetic fluxes, asshown in Figure 12, and need only be physically strong enough to support the chain or fiexiblemember 35 which is secured at 38 to the armature.

In Figure 12, I have shown a cross-section through the magnetic pole'pieces and the armature along approximately the center line. Again, since the armature need only be of sufilcient thickness and strength to carry the flux between adiacent pole pieces, .and thus is, in eflect, a plurality of small armatures bridging separate air gaps, the cross section of the armature may become so small in respect to the physical force existing that in an armature of uniform cross section, an effect may very well be created where- 89, thus permitting the pull to be exerted more strongly, thus making it possible for the center of the armature to be deflected even more, and thereby permitting a greater portion of the armature to be drawn away. This successive action, which may occur very quickly, will, owing to the flexing of the armature, permit the armature to be released.

Accordingly, the armature 68 is thickened at its center portion to provide a better path for the passage of magnetic fluxes thereat, and the center stack of laminations is thickened so that the center pole face 8335b is much thicker than the other pole faces.

Similarly, the pole faces adjacent the center pole face, that is,'pole faces idea and tilde, while not as thick as pole face will), are much thicker than pole faces H36 and ldfid.

Since the stacks of laminations toward the center of them'agnetic structure have the greatest thickness, consequently, they also have' the greatest pole area and provide the largest amount of flux flowing into the armature. The armature itself, since it is thickened a the center, also provides an appropriate path 101' this increased amount offlux. This flux is progressively decreased toward the center of the armature.

It thus becomes possible to provide an armature of a minimum weight with greater physi= cal strength than in cases where an armature structure of uniform cross-section throughout is used. it

Thus, in Figure 12, the poles i585, lllhb and i350! and indicated as being north. Flux lines 2% flow from pole led into the intermediate pole ltfia. Also, flux lines 2M flow from pole ld into the intermediate pole l35c. Flux lines 2&2 and 203 flow from the central pole 83Gb into the intermediate poles 835a and l85c. In each case, the magnetic circuit is completed from pole to pole through the pole pieces I68 and it! through the core lBi'.

0n the occurrence of reverse current conditions in the bus bar if, as shown in the diagrammatic sketch of Figure 11, the flux tending to hold armature All in place against the force of the counteracting spring is reduced so that the armature is permitted to move away from the magnetic structure. As armature d0 moves a slight distance away from the magnetic structure, as shown in Figure 13, thus creating the air gap 2 i ll, then, under normal or steady current conditions, the introduction of such an air gap will cause the building up of the leakage between the adjacent poles so that the flux passing into the armature is so rapidly reduced that the pull exerted by the magnetic structure becomes substantially zero at a very small air gap 25c, and the armature may then be drawn away from the magnetic structure very quickly.

During practical operating conditions in some installations, a fault current may increase in value at an exceedingly high rate. There are installations in which the rate 01' rise in current may be increased at ten million amperes per second. Under such conditions, it is essential that the speed of movement of the armature and the rate of rise of the flux in the air gap be so arranged that there shall be no tendency for the armature to be drawn back against the pole piece and so prevent the opening of the circuit breaker.

While the condition shown in Figure 13 represents a leakage flux from one pole piece to an adjacent one, which will occur during normal operating conditions, high rate of rise may change this action. At a very high rate of current rise, the flux increases correspondingly. I have found that rapidly changing flux will flow normally parallel to the plane of the laminations, and that they are so guided by the outer laminations that the cross leakage is substantially zero. Any flow of this flux of rapidly changing value normal to the plane of the laminations would tend to create eddy currents which would tend to oppose the cross flow. As a result of this condition, the situation shown in Figure 13, would not exist during a fault involving a very high rate of rise in current, and for this reason, it is necessary to provide, as shown in Figure 14, a relatively narrow air gap between the ends of a pole I35 and the rectangular stack M0. This air gap will provide a leakage for the flux produced by a current changing any value of rate of rise so that the tendency to draw the armature back against the pole pieces is eliminated.

From the above, it will now be clear that the magnetic path for fluxes flowing through the pole piece M60 is distributed through the laminations iii to H5. Because of the variation in the number of laminations in section i2i as compared to the next section I22 and I23, less lines of force will flow in the laminations i2 i, a greater amount of flow in I22 and still a greater amount in I23. The lines of force flowing in laminations I35 of layer iZl will in turn divide themselves, a larger proportion of such fluxes flowing from the lamination i35.to lamination i35a through the portion of the armature bridging I35 and 93511 as shown at 200 in Figure 12.

A smaller proportion of such fluxes flows from lamination i35 through the armature which bridges the gap M2 to the layer Mil. This is due to the fact that the reluctance of the smaller path to the armature from layer H35 to H9 is greater than the reluctance of the much larger path provided by the armature from layer i35 to NM.

Moreover, the lines of force flowing in the magnetic structure are greater than the lines of force which could be carried by the armature crosssection at this point which further determines the distribution of lines of force.

In general, the distribution of magnetic lines of force is as illustrated in Figure 12. A relatively small number of lines flows from lamination I35 to i3 5a through the armature of re== duced cross-section. A much larger number of lines 202 flows through laminations i851; and i351) through the armature of greater cross-section at this point. Thus, the portion of the armature which is subjected to greatest load also In order to further reduce the mass of the armature, a V-shaped groove is cut therein as shown at I'H in Figure 8, since the magnetic paths are such that substantially no lines of force would be flowing through this portion of the metal.

This is better shown and more evident from an examination of Figure 12, which shows portions of the metal between the lines of force 202 and 203 which perform no usefulfunction in carrying magnetic lines of force.

This same principle may be carried out in other portions of the armature, if desired.

The blow-out structure which I have found operating satisfactorily with the present circuit breaker is shown in Figure 16.

With the previous breaker, the current reached a value under a certain set of test conditions of 30,000 or 35,000 amperes when arcing was initiated, whereas, with this higher speed breaker, arcing may be initiated at appreciably less than half this value. speed of arc travel during the early formation of the arc with the prior arc extinguisher was unsatisfactory, resulting in distress and delayed current limitation.

The structure of Figure 16 employs a strengthened primary blowout responsible for initial arc motion and the transfer to the secondary blowout is made much earlier.

While I have here described my invention in connection with preferred, successful embodiment thereof, many variations in the actual form of the interleaved pole pieces, and many variations in the form and construction of the armature and of the circuit breaker itself, as well as many variations in the bucking bar arrangement and in the exciting coil and other elements of my invention, will now be obvious to those skilled in the art. Accordingly, I prefer to be bound not by the specific disclosures herein but only by the appended claims.

I claim:

1. In a holding magnet, a plurality of magnetic conductors of one polarity a common magnetic path for all of said magnetic conductors; a plurality of magnetic conductors of an opposite polarity; said magnetic conductors being arranged in a stack parallel to each other, the magnetic conductors of one polarity being interleaved between the magnetic conductors of the opposite polarity and spaced from each other; and an armature having a face simultaneously engageable with each of said magnetic conductors and completing a plurality of magnetic paths between adjacent magnetic conductors, the adjacent magnetic conductors providing leakage paths between each other when said armature moves away from said conductors.

2. In a holding magnet, a plurality of magnetic conductors of one polarity a common magnetic path for all of said magnetic conductors; a plurality of magnetic conductors of an opposite polarity; said magnetic conductors being arranged in a stack parallel to each other, the magnetic conductors of one polarity being interleaved between the rnagnetic conductors of the opposite polarity and spaced from each other; and an armature having a face simultaneously engageable with each of said magnetic conductors and completing a plurality of magnetic paths between adjacent magnetic conductors; said magnetic conductors having a different cross-sectional area; the cross-sectional area of the armature opposite each magnetic conductor being correspondingly As a consequence, satisfactory.

istering with thicker magnetic conductors.

3. In an electromagnet, a magnetic structure comprising a pair of pole pieces, an armature operable to an energized and de-energized position-means for providing a closed magnetic path through said magnetic structure and said armature and for providing a magnetic path hy= passing said armature, the magnetic path through said armature when said armature is in its energized position providing a, lower reluctance magnetic path than said by-pass and said armatureas soon as said armature starts to move to its second position providing a greater reluctance magnetic path than said by-pass.

4. In an electromagnet, a magnetic structure comprising a pair of pole pieces, an armature, a plurality of magnetic conductors extending from each of said pole pieces, said armature being in physical contact with said conductors when said magnet is energized and completing a magnetic circuit from one of said magnetic conductors extending from one of said pole pieces to one of said 5. In an electromagnet, a magnetic structure comprising a pair of pole pieces, an armature, a magnetic conductor extending from each of said pole pieces and means for providing a magnetic path from one to the other of said pole pieces try-passing said armature, said armature engaging said conductors to provide a closed magnetic path to said pole pieces of less reluctance than said icy-pass and said armature introducing an air gap connection in the magnetic path including said armature having a greater reluctance than said by-pass as soon as said armature breaks the contact connection to said magnetic path.

t. In an electromagnet, a magnetic structure comprising a plurality of pole pieces, an armature, a magnetic path through said pole pieces and said armature, and a magnetic path through said pole pieces and by-passing said armature, said ature presenting a closed iron magnetic circuit of less reluctance than said by-pass when said electromagnet is energized and said armature presenting an air gap connection in its magnetic path having a greater reluctance than said bi pass as soon as said armature moves on deenergization of said electromagnet.

7. In an electromagnet, a, laminated magnetic structure, an armature having an energized and a de-energized position, means for providing a its first disengaging movement away from said conductors providing a greater reluctance magmagnetic path through said magnetic structure and said armature, and means for providing a netic path by-passing said armature, the magnetic path through said armature when said armature is in one of its positions providing a lower reluctance magnetic path than said by pass and said armature as soon as it starts to move to its second position providing a greater reluctance magnetic path than said by-passr DONALD 1. some

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