US2648034A

US2648034A - Alternating current electromagnet

Info

Publication number: US2648034A
Application number: US18578A
Authority: US
Inventors: John F H Douglas; Clarence T Evans
Original assignee: Cutler Hammer Inc
Current assignee: Cutler Hammer Inc
Priority date: 1948-04-02
Filing date: 1948-04-02
Publication date: 1953-08-04
Anticipated expiration: 1970-08-04

Description

953 J. F. H. DOUGLAS ETAL 2,648,034

ALTERNATING CURRENT ELECTROMAGNET Filed April 2, 1948 A) awn/r5 RANGE BIEN i U 550 am C'O/L C u/vs r04 ma:

0 R K RANGE o e-u (16550 was E ZXMWML XMMX %\%M Patented Aug. 4, 1953 ALTERNATING CURRENT ELECTROMAGNET John F. H. Douglas, Milwaukee, and Clarence T. Evans, Wauwatosa, Wis., assignors to Cutler- Hammer, Inc., Milwaukee, Wis., a corporation of Delaware Application April 2, 1948, Serial No. 18,578

4 Claims.

This invention relates to alternating current operating magnets for devices such as contactors and relays, and more particularly to control cir-.

cuits therefor.

As is well known, it is usually desirable in electromagnetically operated devices of various types such as contactors and relays that the pull of the operating magnet at all points in its stroke be substantially equal or only slightly in excess of the load offered by the operated device. One reason for this requirement is that excessive pull by the operating magnet at any point in its stroke is likely to cause excessive acceleration of the moving parts of the device, which in turn results in noisy operation of the device and undue wear of the magnet parts. However, it is frequently diiiicult in A. C. magnet operated devices to obtain a pull characteristic in the operating magnet which suits the load characteristic of the operated device.

The present invention has among its objects to provide an improved control circuit for A. C. magnet operated devices which enables adjustment of the pull characteristic of the operating magnet to suit various load conditions encountered in the operated device.

Another object is to provide a control circuit for A. C. magnets which enables adjustment of the pull characteristic of the magnet by control of the terminal voltage of the magnet coil at more than two points in the magnet stroke with a. constant supply voltage.

Various other objects and advantages of the invention will hereinafter appear.

The accompanying drawing illustrates an embodiment of the invention which will now be described, it being understood that the embodiment illustrated is susceptible of modification. without departing from the spirit and scope of the appended claims.

In the drawing,

Figure 1 is a diagrammatic view of an A. C. magnet operated switch having a control circuit embodying the invention associated therewith; and

Figs. 2 and 3 are graphic representations of certain characteristics of the embodiment shown in Fig. 1.

Referring to Fig. l, a control circuit embodying the invention is shown in connection with an A. C. operating magnet 2 to be supplied with current from an A. C. supply circuit indicated by lines L L The operating magnet shown may be of any conventional type, and as shown the same is provided with an energizing coil 3 which is mounted within a laminated field member 4 of rectangular shape having an opening in the lower side thereof for receiving a laminated armature 5. Armature 5 is normally held by gravity in the open position illustrated in the drawing and is movable upwardly within coil 3 into a closed position wherein its upper end seals with field member 4. As illustrated, armature 5 carries a yielding contact 6 which engages a pair of cooperating stationary contacts ii during upward movement of said armature into closed position. Armature 5 also has normally open auxiliary contacts 1 associated therewith which are closed during final movement of said armature into its closed position.

The control means for magnet 2 includes a condenser 8, a resistance 9, a normally open push button switch I 0 and a normally closed push button switch ll. As shown one terminal of coil 3 is connected to line L in series with condenser 8 and resistance 9 and the other terminal thereof is connected to line L in series with push button switches l0 and H. Upon depression of push button switch I0, coil 3 is connected across lines L L in series with condenser 8 and resistance 9 for response of armature 5. Upon release of push button 10, coil 3 is maintained energized through the medium of push button switch II and auxiliary contacts 1, pending opening of push button switch I l.

Referring now to Fig. 2, curve A represents the load imposed on armatur 5 during movement thereof into closed position. It is assumed that the pull of armature 5 throughout its stroke varies as illustrated by curve B in Fig. 2 when a constant A. C. voltage is applied to the terminals of coil 3. It will be observed from curve B that the pull of armature 5 in its open position is greater than that required for operation of the load, whereas at point C in the armature stroke the pull is insufficient for operation of the load. In accordance with the present invention condenser 8 and resistance 9 are connected in series in the energizing circuit of coil 3 to decrease the pull of the armature when the same is in open position, and to increase the pull thereof at point C in its stroke to thereby provide a pull characteristic indicated by dotted curve D which is desired for proper operation of the load.

The effect of condenser 8 and resistance 9 in the energizing circuit of the magnet will now be more fully set forth in connection with Fig. 3. In this figure it is assumed that the desired pull characteristic of armature 5 represented by curve D in Fig. 2 is obtained when coil 3 is subjected to a voltage E in the open position of armature 5, a voltage F at point C in the armature stroke, and a voltage G corresponding to the line voltage when said armature is moved into closed position.

As is well known, the inductive reactance of coil 3 is a function of the position of armature 5 and is in general higher in the closed position of said armature than in the open position thereof. Also as is well known, the impedance of the energizing circuit of coil 3 is reduced at any point in the armature stroke where the capacitive reactance of condenser 8 is less than twice the inductive reactance of coil 3, and is increased at any point in the armature stroke where the capacitive reactance of said condenser exceeds twice the inductive reactance of said coil. The greatest reduction in impedance is obtained at any point in the armature stroke where the capacitive reactance of condenser 8 equals the inductive reactance of coil 3 and the magnet circuit is then said to be resonant.

The voltage across coil 3 is increased to increase the armature pu-ll at any point in the magnet stroke where the impedance of the magnet circuit is reduced, and conversely the voltage across said winding is reduced to decrease the armature pull at any point in the armature stroke where the impedance of the magnet circuit is increased. Thus if the magnet circuit is rendered resonant at an intermediate point in the armature stroke, coil 3 will be subjected to a high peak resonant voltage at such point and will also be subjected to voltages of lower value in the open and closed positions of the armature.

If resistance 9 is not included in the armature circuit it is possible, with a suitable number of turns on coil 3, to proportion the capacitive reactance of condenser ii relative to the inductive reactance of said coil to render the mag net circuit resonant at such a point in the armature stroke that the desired coil voltages E and G are obtained in the open and closed positions of armature 5. However, the voltage of coil 3 then varies throughout the magnet stroke as illustrated by curve H in Fig. 3 and assumes a value I at point C in the armature stroke which may be considerably higher than the desired voltage F. It is also possible with a suitable number of turns on coil 3 to proportion the capacitive reactance of condenser 8 relative to the inductive reactance to said coil to render the magnet circuit resonant at such a point in the armature stroke that the desired coil voltage F is obtained at point C in the armature stroke and the desired coil voltage G is obtained in the closed position of the armature. However, the voltage of coil 3 then varies throughout the magnet stroke, as illustrated by curve J in Fig. 3 and assumes a value K in the open position of armature 5 which may be considerably higher than the desired voltage E.

In practice it has been found that if resistance 9 is not included in the magnet circuit it is impossible to control the impedance of such circuit by means of condenser 8 so that the voltage values E, F and G are obtained in coil 3 at three points in the armature stroke to provide the desired pull characteristic of the magnet illustrated by curve D in Fig. 2. However, it has been found that when condenser 8 and resistance 9 are both included'in the magnet circuit it is possible to control the impedance of such circuit for desired voltage values of coil 3 at three points in the armature stroke. For example, it has been found that with a suitable number of turns on coil 3 it is possible to adjust resistance 9 and the capacitive reactance of condenser 8 to maintain the voltage of coil 3 at values E and G in the open and closed positions of armature 5 and to also maintain the voltage of said coil at value F at point C in the armature stroke. When this is done the voltage of coil 3 throughout the magnet stroke varies as illustrated by curve L in Fig. 3 to provide the desired pull characteristic of the magnet illustrated by curve D in Fig. 2.

From the foregoing, it will be observed that in practice of the invention it is possible to increase the magnetic pull exerted on the armature in an intermediate portion of its stroke and maintain the same or decrease the pull on the armature in open position, while maintaining the pull on the armature in closed position at the same value obtainable when the armature coil is connected directly across the voltage source. In the appended claims such increase in pull in an intermediate portion of the stroke, and decrease in pull in open position, is defined relative to such unchanged closed position pull. The term increased relative to is to be construed to mean that the pull on the armature in an intermediate portion of its stroke is greater than the pull over the corresponding portion of the armature stroke obtainable when the armature coil is connected directly across the voltage source. The term decreased relative to is to be construed to mean that the pull on the armature in open position is made less than the pull in the corresponding open position when the armature coil is connected directly across the voltage source.

What we claim as new and desire to secure by Letters Patent is:

l. The method of modifying the Dull characteristic of an electromagnet having an armature movable between an open position and a closed position, and a coil energized from a source of alternating voltage, which method may be practiced without modifying-the magnetic pull on the armature in closed position and which consists in including capacitance in series with the coil to increase relative to the magnetic pull on the armature in closed position the magnetic pullon the armature throughout an intermediate portion of its range of motion and in coordinating with the coil and the capacitance series resistance of such value that the magnetic pull on the armature in open position is not increased relative to the .magnetc pull thereon in closed position.

2. The method of modifying the pull characteristicof an electromagnet having an armature movable between an open position and a closed position, and a coil energized from a source of alternating voltage, which consists in including capacitance in series with the coil to increase relative to the magnetic pull on the armature in closed position the magnetic pull on the armature throughout an intermediate portion of its range ofmotionandin coordinating with the coil and the capacitance series resistance of such value that themagneticpull on the armature in open position is reduced relative to the magnetic pull thereon in closed position, assuming a magnetic pull on the armaturein closed position such as that obtainable with the same electromagnet relieved of the aforesaid modifying influences.

3. The combination with an electromagnet having an armature movable between open and closed positions and a coil, a source of alternating voltage ,to whichsaid coil is connected, a

capacitor series related to said coil. said coil and capacitor respectively having a number of turns and capacitance value such that the magnetic pull on said armature for an intermediate portion of its stroke is increased relative to the magnetic pull on said armature in its closed position, and a resistor in series with said coil and said capacitor, said resistor being of a resistance value such that the magnetic pull on said armature in open position is not increased relative to the magnetic pull thereon in closed position, the foregoing using for reference such magnetic pull on the armature in closed position as that obtainable With the electromagnet relieved of the aforesaid influence of said capacitor and resistor.

4. The combination with an electromagnet having an armature movable between open and closed positions and a coil, a source of alternating voltage to which said coil is connected, a capacitor series related to said coil, said coil and capacitor respectively having a number of turns and capacitance value such that the magnetic pull on said armature for an intermediate portion of its stroke is increased relative to the magnetic pull on said armature in its closed position, and

a resistor in series with said coil and said capacitor, said resistor being of a resistance value such that the magnetic pull on said armature in open position is decreased relative to the magnetic pull thereon in closed position, the foregoing using for reference such magnetic pull on the armature in closed position as that obtainable with the electromagnet relieved of the aforesaid influence of said capacitor and resistor.

JOHN F. H. DOUGLAS.

CLARENCE T. EVANS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,040,677 Suits May 12, 1936 2,131,424 Bechberger Sept. 27, 1938 2,402,573 Pell June 25, 1946 2,404,982 Owens July 30, 1946 FOREIGN PATENTS Number Country Date 379,711 Great Britain of 1931 602,989 Germany Sept. 20, 1934