US3324356A - Electro-magnet - Google Patents

Description

June 6, 1967 F. W. KUSSY 3,324,356

ELECTROH'MAGNET Filed June 30, 1966 5 SheeS-Sheet l @aux Il!" Il" IHI' /f JNVENTOR.

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5 .Sheets-Sheet 2 Filed June 30, 1966 F. W. KUSSY ELECTROMAGNET June 6, 1967 5 Sheets-Sheet 5 Filed June 30, 1966 IN VEN TOR. /l/A/ IV, /USS y 70 l//Vf United States Patent O 3,324,356 ELECTRO-MAGNET Frank W. Kussy, Birmingham, Mich., assigner to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Filed June 30, 1966, Ser. No. 561,909 6 Claims. (Cl. S17-155.5)

This application is a continuation-in-part of my copending .application Ser. No. 421,506 led Dec. 28, 1964 relating to electromagnets for actu-ating electrical switches and the like. In particular, the instant invention to an A C. excited electromagnetic contactor having a short operating stroke.

The Cataldo et al. copending U.S. application Ser. No. 189,915, filed Apr. 24, 1962, entitled, Electromagnetic Contacter, and assigned to the assignee of the instant invention, discloses a construction for a contactor which is closed upon actuation of an electromagnet. During the closing stroke for conta-eters of this type the magnet armature must initially overcome the force of return springs and at a point before the end of the closing stroke must overcome the combined forces of return springs and contact pressure springs. This point, hereinafter referred to as the critical position, is at the armature position corresponding to the point where the rnain contacts of the contactor make initial engagement. Thus, electromagnets for contactors should exert a high force at the moment the main contacts engage but in the fully open position of the manget the force exerted thereby should be relatively low.

In constructions of the prior art this characteristic was extremely difficult to obtain especially in view of the fact that contactor operation must also take place down to a predetermined voltage below rated voltage, and that for voltages below this predetermined voltage the contactor should not be stalled in the critical position. Adding to the problem was the fact that in the construction of electromagnetic contactors the yair gap between the armature and the stationary manget frame is relatively small and in cases of large size contactors the magnet pole faces are relatively large.

Large magnets of theprior art have a force-air gap characteristic which is fairly flat between the open and critical positions so that the desired force in the critical position can only be obtained by having a large mechanical load acting upon the armature in the open posi-tion" thereof. In order to overcome such a large mechanicall load a still larger magnet is required with this larger magnet having a relatively high power loss in the closedY position thereof.

Further, contactor magnets of the prior art have force characteristics which differ materially from the force characteristics of the load presented by the contactors. In particular, the prior art magnet exerted a much greater force in the portion of the stroke prior to Contact engagement than was necessary to overcome the force of the return springs. This excess force caused high acceleration of the main movable contacts before engagement with the main stationary contacts resulting in high impact on contact engage-ment with excessive contact wear. The prior art attempted to reduce excessive contact wear on impact by providing linkage constructions which were not only complicated but themselves were subjected to wear.

ICC

It is desirable to utilize a small control transformer for operation of large electromagnetic contactors. In most cases the size of this control transformer is not determined by the required volt-amperes of the closed magnet but by the permitted voltage drop to the open magnet since industry standards require that an electromagnetic contactor with a control transformer must pull in at a predetermined voltage below rated voltage. Typical electromagnet constructions have an in-rush current which is 8 to l() times as large as the holding current and in the open position of the magnet, have a high power factor There latter two conditions impose severe limitations upon the size of the required control transformer.

In order to overcome these disadvantages of the prior art the instant invention provides an electromagnet in which there is .a plurality of coil sections and a switching means to deactivate certain of these sections at predetermined positions of the magnet closing stroke. In a 4typical construction the magnet coil is provided with two sections which :are connected in series in the open posi-tion of the magnet, and just prior to reaching the critical position during the closing stroke one of these coil sections is deactivated by placing :a short circuit across this coil section. Since the coil is excited by alternating current of -constant voltage the ampere turns thereof for the same excitation voltage increases as 4the number of coil turns decreases. With the construction of the instant invention, during the ini-tial portion of the closing stroke, when only the force of the return springs must be overcome, the electromagnet exerts a relatively low force and during the remaining portion of the closing stroke the reduced number of coil turns enables the elec-v tromagnet to exert a much larger force to overcome the combined forces of the return springs and contact pressure springs. Further, since in the open position the required ampere-turns are small a relatively small control transformer can be used.

With this -type of coil switching arrangement the power factor in the open position of the magnet can be made relatively small by choosing wire of relatively low resistance -for the coil section which is shorted. If the power factor of the open magnet is low a still smaller control transformer can be used to control a large magnet.

In order to prevent overheating, .after a lcoil section is shorted its sh-orting circuit is opened. In so doing the coil section no longer vacts as a shorted transformer secondary winding. r

It will be shown that by extending the concepts of` the instant invention a coil having three or more sections with -associated shorting switches may be arranged to produce superior operation when the load imposed on the electromagnet has two or more abrupt increases during the course of the closing stroke. Such conditions arise when the contactor is provided with a plurality of auxiliary switches whose contacts engage at a point in the magnet closing stroke prior to engagement in the main contacts. Under such conditions one coil section would be shorted just prior to engagement of the auxiliary switchy contacts and a second setcion would be shorted just prior to engagement of the main contacts.

Accordingly, a primary object of the instant invention is to provide a novel construction for an electromagnet. Another object is to provide a novel construction for an electromagnetically operated contactor in which the force-air gap characteristic of the magnet is similar to the forcesencountered by the magnet during the force of the closing stroke.

Still another object is to provide an electromagnetically operated contactor in which -there is a novel means provided for achieving an abrupt increase in magnet force during the course of the closing stroke.

A further object is to provide a novel construction for the electromagnet of a contactor which enables the control transformer to be of reduced size.

A still further object is to provide a contactor having means to short sections of the magnet coil as mechanical load is increased and thereafter open the shorting circuit to prevent transformer action from causing overheating.

These as well as further objects of this invention shall become readily apparent after reading the following description of the accompanying drawings in which:

FIGURE 1 is a diagram which compares the forcestroke characteristic of a prior art electromagnet with the force encountered by the magnet during the closing stroke thereof when operating a contactor.

FIGURE 2 is a schematic of a magnet frame having two working gaps and a double section coil associated with each of the gaps.

FIGURE 2A is an electrical schematic showing the coil sections of FIGURE 2 connected in circuit with a s horting switch in accordance with the teachings of the instant invention.

FIGURE 3 is a schematic of a magnet frame having three working gaps and a single double section coil.

FIGURE 3A is an electrical schematic showing the coil sections of FIGURE 3 and a Shorting switch interconnected in accordance with the teachings of the instant invention.

FIGURE 3B is a schematic showing the double section coil of FIGURE 3 utilized with a magnet frame having two working gaps.

FIGURE 4 is a schematic showing a modification of the electromagnet illustrated in FIGURE 1.

FIGURE 5 is a schematic illustrating a contactor and auxiliary switches operated by an electromagnet having three section coils.

Now referring to the figures. FIGURE 2 illustrates a magnet frame consisting of U-shaped stationary portion or yoke 11 and inverted U-shaped armature 12 with working gaps 13, 14 between the confronting ends of the arms of yoke 11 and armature 12, and additional ixed gap 15 in arms of yoke 11. As is well known to the art, iixed Vgap 15 is provided in order to aid demagnetization when coils 17, 18 magnet 11, 12 is deactivated.

Coils 17, 18 are multi-turn units which surround the arms of frame portion 11 in a region of working gaps 13, 14, respectively. Coil 17 is provided with two multiturn sections 17a, 17b while coil 18 is provided with two multi-turn sections 18a, 18b.

The electrical connections between the coil sections is shown in FIGURE 2A. More particularly, the coil sections are arranged in a series circuit extending between terminals 21, 22 in the following order; section 17b, coil section 17a, coil section 18a, normally closed switch 120, and coil section 18b. Normally open Shorting switch 20 is connected from juncture 23 between -coil sections 17a, 17b, to juncture 24 between coil sections 18b and switch 120.

In a manner well known to the art, armature 12 is connected for operation of the main contacts of a contactor. Shorting switch 20 is arranged to be closed just before the armature reaches is critical position, the critical position being that position of the armature corresponding to the position of the contactor main contacts as they are initially brought into engagement. Operations of switches 20, 120 are coordinated so that switch 120 opens shortly after switch 20 closes so that shortly after closing of switch 20 coil sections 17a, 18a cease to act as a shorted transformer secondary. It should now be apparent to those skilled in the art that switch 120 may be of a delayed .4 opening type or may be mechanically connected to switch 20 to open a short time after closing of the latter.

The solid line A in the diagram of FIGURE 1 illustrates the force which an electromagnet must overcome in operating a typical contactor. That is, the portion a of line A shows that in the operation of the closing lstroke prior to engagement of the main contacts of the contactor the force to be overcome increases very gradually. Then, at the critical position there is an abrupt increase in the for-ce to be overcome as indicated by the vertical section b of line A. The gradual increase in force shown in portion a is due to the fact that the return spring for the electromagnet armature is being compressed. It is noted that this force would be constant with a gravity drop out contactor. The abrupt increase as shown in section b is brought about by the sudden encounter with the force exerted by the -contact pressure springs. These springs exert an increasing pressure during the contact overtrave] portion at the end of the closing stroke as indicated in section c of line A.

The dotted line B shows that prior art magnet coils produced a magnet force which increases gradually duringthe course of the closing stroke. The shaded area of FIGURE l, between curves A and B, shows that prior to contact engagement prior art magnet coil constructions produced a magnetforce much greater than required throughout the entire region between the fully open position and the critical position for the magnet armature.

The magnet construction shown schematically in FIG- URE 2A is such that with armature 12 in the fully open position all four coil sections are active. These coil sections may readily be designed to produce a force characteristic extending substantially parallel to section a1 of line A in FIGURE 1. At a position of armature 12 just prior to engagement of the contactor main contacts, switch 20 is closed thereby placing a short across coil sections 17a, 18a and thereby deactivating the latter sections. The reduced number of coil turns now appearing between terminals 21, 22 provides an increased value of ampereturns since the coils are provided with an A.C. excitation. Hence, the ux in Working gaps 13, 14 will increase abruptly and the force acting upon armature 12 will step to a point above section c of line A at the critical position and extend above section c to the fully closed position.

FIGURE 3 shows a magnet frame having an E-shaped stationary portion 30 providing three working gaps 31-33 between the legs of stationary portion 30 and armature 34. The center leg 35 of magnet frame portion 30 is surrounded by a coil having two sections 36a, 36b.

As shown in FIGURE 3A, coil sections 36a, 3617, with normally closed switch 139 therebetween, are connected in series between terminals 37, 38 with normally open Shorting switch 39 connected across coil section 36a and switch 139. The operation of the magnet embodiment illustrated in FIGURE 3 is the same as the mode of operation for the embodiment illustrated in FIGURE 2. That is, Shorting switch 39v is arranged to close just prior to engagement of the contactor main contacts, thereby increasing the number of ampere-turns, resulting in an abrupt increase in the force exerted in the magnet just prior to engagement of the main contacts of the contactor. Shortly after closing of switch 39, switch 139 opens to break the closed loop created by closing switch 39.

v FIGURE 3B illustrates coil sections 36a, 36h mounted to one leg of U-shaped stationary section 41 on a magnet frame having an inverted U-shaped armature 42 with the frame having two working gaps 43, 44, The electrical connections and operation for the embodiments of FIGURES 3 and 3B are identical.

The embodiment of FIGURE 4 is similar to that of FIGURE 2 except that the coil sections 51a, 52a which remai-n active during the entire closing stroke encompass a portion of the working gaps 53, 54. It is well known that leakage flux is reduced in a magnetic circuit by surrounding the air gap thereof by the magnet coil,

and that by reducing leakage the magnet force is increased. In prior art magnets of this type theforce air gap characteristic is even flatter than for a magnet in which no portion of the air gap is surrounded =by the coil. That is, magnet force in this type of magnet increases very little as the gap closes. Thus, with this type of magnet the force in the open position would have t-o be much greater than the force exerted by the return springs in order for the magnet to exert a suicient force at the critical position.

With the arrangement shown in FIGURE 4 this disadvantage of the prior art is overcome. More particularly, the coil sections 51h, 5211, which become shorted when the armature reaches the critical position, is located remote from the working gaps 53, 54. In the open position the arms of armature 55 are outside coil sections 51a, 52a and a relatively low force is produced in the fully open position. This force increases gradually as armature 55 moves toward the stationary portion 56 of the magnet frame. By the time armature 55 is in the critical position, the magnet pole faces are surrounded by coil sections 51a, 52a and leakage iiux is considerably smaller than for the fully open position of armature 55. This produces the desired steep characteristic at the critical position.

In the case of a contactor operated in conjunction with a plurality of auxiliary switches the magnet coil may be divided into three -or more sections as shown in FIG- URE 5. For example, as illustrated in FIGURE 5 the magnet coil is divided into three sections 61a, 61b, 61e with normally open switch 62 arranged for shorting section 61a and normally open switch 63 arranged for shorting sections 61a and 61b. The three sections 61a-61c are -connected in series circuit through normally open start control switch 64 and a normally closed stop control 65 to a single phase A.C. energizing source 66. This series circuit also includes normally cl- osed switches 91a, 91b. Holding contact 67 is connected in parallel with the start button 64. The magnet armature 68 is connected t-o contact carrier 69 which carries the bridging contacts and contact pressure springs for double break shorting switches 62, 63 as well las the bridging contacts of auxiliary switches 71, 72 and the bridging contacts for all three phases AC of contactor 73. One of the stationary contacts of switch 62 is connected to the junction between sections 61a, 61h while the other stationary contact of switch 62 is connected to the junction between normally closed switches 91a, 91b. One of the stationary contacts of switch 63 is connected to the junction between sections 6-1b, 61C while the other stationary contact of switch 63 is connected to the junction between switch 91h and source 66.

Closing of start control 64 brings about energization of -all three coil sections 61a-61c and armature 68 is caused to move downward against the force of return spring 74. At a point -just prior to the closing of -auxiliary switches 71, 72 shorting switch 62 closes thereby deactivating coil section 71a and increasing the current through coil sections 61b, 61C. This abruptly increases the closing force on armature 68. This abrupt increase is required because of added load imposed by contact pressure springs 71a, 72a as the contacts of auxiliary switches 71, 72 are brought into engagement. Thereafter, at a position just before the engagement of the main contacts of contactor 73, shorting switch 63 closes so that -both coil sections 61a and 6117 are deactivated and there is another abr-upt increase in the closing force acting on armature 68. This last abrupt increase in armature force is necessary in order to overcome the further load imposed by the contact pressure springs a', b, c of contactor 73 as the main cont-acts thereof lare brought liuto engagement. Switch 91a opens after switch -62 closes so that coil section 61a does not act as a shorted transformer secondary and for the same reason switch 91b opens after switch 63 closes. While the opening of switch 91 occurs subsequent to closing of switch 62 such opening need not take place prior to closing of switch 63 but may take place subsequent to such closing.

It should now be obvious that by choosing various r-atings between the number of turns of each of the coil sections it is possible to obtain a desirable force air gap characteristic for the magnet to avoid stalling in one or more critical positions. Further, by adjusting the position of the armature at which the shorting switch closes, an abrupt increase in magnet forces may be obtained at the desired armature position under all tolerance conditions. For more eflicient operation a normally closed auxiliary switch is opened a short time subsequent to closing of the shorting switch in order to lopen the shorting circuit for the inactive coil section and still maintain this coil section inactive. It is noted that a clapper type armature may also be operated in this same manner.

Accordingly, it is seen that this invention provides a novel A.C. energized electro-magnet whose force stroke characteristic may be matched more closely with load characteristics than is possible to achieve with any economical construction of the prior art.

Although there has been described a preferred embodi- -rnent of this novel invention, many variations and modications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specic disclosure herein, but only by the appending claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. In combination, an A.C. electromagnet including a magnetic frame and a current carrying coil which when energized generates magnetic iiux in said frame including a yoke and a relatively movable armature separable from said yoke to form a working gap, li-rst means biasing said armature to an open position wherein said gap is fully open, said armature being movable toward said yoke to a closed position by magnetic ux resulting from current tiow through said coil; second means producing -a force acting upon said armature in the direction of said first means after said armature reaches a critical position while moving toward said closed position, and additional means for causing an abrupt increase in ux generated by said coil when said armature is in a posiiton intermediate said open and said critical positions, said additional means including a normally open first switch which when closed places a short circuit across a first section of said coil and an increased current passes through a second section of said coil, said short circuit including a normally closed second switch operatively connected to said rst switch to open subsequent to closing of said first switch to open said short circuit while permitting said increased current to ow through said second section.

2. The combination as set forth in claim 1 in which the second section of said coil surrounds only a part of said gap, said part being adjacent to said yoke, said armature having a portion thereof extending into said second section when said armature is in said critical position.

3. The combi-nation as set forth in claim 2 in which said first section is disposed remote from said gap.

4. The combination as set forth in claim 1 in which there is a further means abruptly applying a further force to said armature acting in the direction of said additional force at predetermined position of said armature as the latter moves past said critical position toward said closed position, further means for causing another abrupt increase in iux generated by said coil when said armature is in a position intermediate said critical and said predetermined positions.

5. The combination as set forth in claim 4 in which the further means includes a normally open third switch which when closed places completes a shorting circuit across a lfirst part of said second section and a further increased current Ipasses through a secondu part of said second section, said shorting circuit including a normally closed four-th switch operatively connected to said third switch to open subsequent to closing of said third switch to open said s'hortin'g circuit while permitting said further increased current to ow through said second part.

6. The combination as set forth in claim 5 in which opening springs of a multi-phase contactor constitute the rst means biasing the armature to the open position, said contractor having a plurality of sets of main contacts and `a first set of contact pressure spring means for said mai-n' contacts, auxiliary switch means operated by said armature, said auxiliary switch means including separable contact means and a second set of contact pressure spring means for said separable contact means, said rst set of Contact spring means constituting said additional means, said second set of contact press-ure springs constituting said further means.

No references cited.

MILTON O. HIRSHFIELD, Primary Examiner.

J. A. SILVERMAN, Assistant Examiner.

Claims (1)

1. IN COMBINATION, AN A.C. ELECTROMAGNET INCLUDING A MAGNETIC FRAME AND A CURRENT CARRYING COIL WHICH WHEN ENERGIZED GENERATES MAGNETIC FLUX IN SAID FRAME INCLUDING A YOKE AND A RELATIVELY MOVABLE ARMATURE SEPARABLE FROM SAID YOKE TO FORM A WORKING GAP, FIRST MEANS BIASING SAID ARMATURE TO AN OPEN POSITION WHEREIN SAID GAP IS FULLY OPEN, SAID ARMATURE BEING MOVABLE TOWARD SAID YOKE TO A CLOSED POSITION BY MAGNETIC FLUX RESULTING FROM CURRENT FLOW THROUGH SAID COIL; SECOND MEANS PRODUCING A FORCE ACTING UPON SAID ARMATURE IN THE DIRECTION OF SAID FIRST MEANS AFTER SAID ARMATURE REACHES A CRITICAL POSITION WHILE MOVING TOWARD SAID CLOSED POSITION, AND ADDITIONAL MEANS FOR CAUSING AN ABRUPT INCREASE IN FLUX GEN-

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