US1392056A - Control system - Google Patents

Description

H. D. JAMES;

CONTROL SYSTEM.

APPLICATION FILED MAYZ7,1918- Patented Sept; 27,1921.

2 SHEETS-SHEET L an M 62 WITNESSES:

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ATTORNEY 2 SHEETS-SHEET 2.

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CONTROL SYSTEM..

APPLICATION FILED MAY 27. 1918. 1,392,056, PatentedSept. 27, 1921.

1 INVENTOR Hemyfldk mm ATT( )RNEY jvlfNEssEs I HENRY D. JAMES, 013 EDGEWOOD PARK,

HOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION VANIA.

PENNSYLVANIA, ASSIGN OR TO WESTING- F PEN N SYL- CONTROL SYSTEM.

Application filed May 27,

To all whom it may concern Be it known that I, HENRY D. JAMEs, a citizen of the United States, and a resident of Edgewood Park, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Control Systems, of which the following is a specification.

My invention relates to systems of control of general application, but more particularly to systems of control for electric motors, such, for example, as motor-accelerating systems involving main switches or contactors designed to close in succession to shunt a resistor. In systems of the character above designated. each contactor is customarily provided with an auxiliary switch or a relay for governing the closing of the contactor, and, in order to avoid injuring the motor by excessive current, each contactor is adapted to close before the relay for controlling the next succeeding contactor can operate.

()ne object of my invention is to provide an improved motor-accelerating system of the type indicated.

Another object of my invention is to pr ovide a system, the parts of which may be standardized, thus effecting a saving in manufacture and maintenance.

A further object of my invention is to provide a novel accelerating system in which the motor may be disconnected from the line, and then reconnected, at reduced speed, without fear that the motor will be connected directly across the line with all starting resistance out of circuit, and the motor windings thereby injured.

According to my system, I arrange a relay or a plurality of relays in parallel circuit with the accelerating resistor of an electric motor, these relays being adapted to be successively actuated, due to a decreasing magnetism caused by the acceleration of the motor and the short-circuiting of portions of the resistor, to closed position to cause the closing of contactors which control the short-circuiting of the resistor. The relays and contactors are interlocked mechanically or electrically for a purpose to be described below.

Other objects of my invention will be apparent from the following description, when taken in connection with the accompanying drawings, in which Figure 1 is a diagrammatic View of a system, arranged according Specification of Letters Patent.

Patented Sept. 27, 1921.

1918. Serial No. 236,937.

to my invention, for accelerating a motor; g. 2 1s a similar View of a modification; Figs. 3, 4 and 5 are, respectively, a side and an end elevation and a plan view of a preferred switch employed in connection with the systems of Figs. 1 and 2; Fig. 6 is a diagrammatic view of still another modification; and Fig. 7 is a diagrammatic view illustrating my invention as applied to an alternating-current system.

Referring to Fig. 1, a motor, the armature of which is shown at 1 and the shunt field-magnet winding at 2, is connected be tween line conductors 3 and 4, separated by a line contactor 5, with a regulating resistor 6 normally in series with the armature 1. A master controller 7 controls the closing of the switch 5, through an energizing coil 8, by closing the contact 9. One or more contactors 10, 11 and 12 (three are illustrated), control the shunting of successive portions 13, 1-1 and '15 of. the regulating resistor 6, through the medium of energizing coils 19, 20 and 21, which energization is effected by the master controller 7 closing the contact members 16, 17 and 18. A coil 22 is connected in parallel circuit With the resistor 6. and a second coil 23 is connected across the terminals of the armature 1, the coil 23 being in circuit with a high external resistance 24. which may be embodied in the coil itself if desired. The energizing of the coil 22, as explained below, causes the successive closing of relays 25, 26 and 27 in accordance with the strength of the current passing through the coil 22. The coil 19 and the relay 25 are series connected in a circuit extending from the line conductor 3, through the contactor 5, the conductor 28 and the contact member 16, to the line conductor 4. The coil 20 and the relay 26. as well as the coil 21 and the relay 27, are in parallel relation with the coil 19 and the relay 25.

A preferred form of device for use in the system of Fig. 1, illustrated in Figs. 3, 1 and 5, forms the subject matter of a copending application, Serial No. 241,259, filed June 31, 1918. De Camp, relay, and assigned to the Vestinghouse Electric a. Manufacturing Company. Briefly. it comprises a coil, the current flowing through which creates a magnetic field which causes an armature to close. thereby releasing a. plurality of armatures. each bearing a relay contact member. These latter armatures tions, but, owing to the magnetic field above mentioned, the power of the springs is ternporarily overcome until the magnetic flux,

produced by the electric current, sinks to predetermined values. The armatures are thus operated in'succession, depending for their operation on the period of acceleration of the motor.

An insulating panel 29 carries two brackets 30 and 31 supporting the coils 22 and 23 which, when energized by current flowing through them, create magnetic fields for attracting an armature 32 and any desired number of additional armatures 33, 34 and 35. A compression spring 36 is adjustably mounted upon a non-magnetizable rod 37 slidably mounted in projections 38 and 39 which are rigidly connected to or are integral parts of the bracket 31. The

projections 38 and 39 serve also as pole pieces for the armatures 32 and 33, 34 and 35,

respectively. A bar 40 is rigidly connected to the rod 37, and normally engages the armatures 33, 34 and 35. The spring 36 thus normally maintains the armatures 33, 34 and in open position, with the members 41, which are carried by these armatures, in contact with the pole piece 39. The members 41 are preferably of non-magnetizable material to prevent freezing.

The armature 32 is provided with brackets 42, which are pivotally mounted upon the bracket 30, and is normally retained in the broken-line position, (Fig. 3), by a weak spring 43. The bracket 30 supports a non-magnetizable, U-shaped member 44, between the arms of which are pivotally mounted the armatures 33, 34 and 35, which carry, respectively, the movable contact members 45, 46 and 47 of the relays 25, 26 and 27, shown in Figs. 3, 4 and 5 as closed.

The stationary contact members 48, 49 and 50 of the relays 25, 26 and 27 are mounted upon the insulating ,panel 29. Springs 51 are attached to longitudinally adjustable members 52 and to the other ends of the members 41. The pole piece 39 is provided with longitudinally adjustable members 53 to regulate air gaps 54 between these members and the corresponding armatures. By means of this adjustment, or by means of the members 52, the action of the magnetic flux produced by the coils 22 and 23 maybe so regulated that the armatures 33, 34 and 35 will be operated in proper sequence.

The operation is as follows: Upon the actuation of the master controller 7 to. the position a, the coil 8 is energized to close the line contactor 5, which. completes the 22 creates a magnetic field which attracts the armature 32 to the pole piece 38. The rod '37 is thereupon pressed inwardly, in opposition to the force of the spring 36, forcing thebar 40 away from the armatures 33, 34 and 35. The motion of the armature 32 is from the broken-line to the full line position of Fig. 3. If the current is above a previously selected safe value, the flux of the magnetic field will overcome the forces of the springs 51 and the armatures will remain with the stops 41 in engagement with the pole piece 39. As the motor accelerates and the current begins to die down, the magnetic flux set up by the coil 22 becomes weakened. After a time, when the flux has decreased to a predetermined value, the spring 51 attached to one of the armatures, say the armature 33, will overcome the flux of this field, so that the relay 25 will be closed. The time when this operation occurs depends upon the air gap 54 and the tension of the spring 51. The relays 26 and 27 however, remain open.

If the master controller 7 has been actuated to the position b, acircuit maybetraced from the line conductor 3 through the contactor 5, the conductor 28, the relay 25, the coil 19 and the contact 16, to the line conductor 4. The closing of this circuit ener- "gi z'es the coil 19, which causes the closing on the contactor 10, and this, in turn, creates a shunt circuit for the portion 13 of the resistor 6. The motor then further accelerates to decrease the-voltage across the terminals of the coil 22 and thus weaken the magnetic field in the neighborhood of this coil, which permits the closing of the relay 26. A circuit is then made, assuming that the master controller occupies the position 0, from the line conductor 3, through the contactor 5, the conductor 28, the relay 26, the coil 20 and the contact 17 to the line conductor 4. The coil 20, thus becoming energized, causes the closing. of the contactor 11, and the consequent shunting of the resistor 14. After the motor has further accelerated, the magnetic field surrounding the coil 22 is again weakened and the relay 27 is closed, creating a circuit, if the master controller occupies the position (2, from the line conductor 3, through the conductor 28, the relay 27 the coil 21 and the contact 18 to the line conductor 4, thereby causing the energization 'of the coil 21 and the closing of the contactor 12. The resistor 6 is then entirely shunted from the armature circuit and the armature 1 .is connected directly across the line. i i

The shunting of the entire resistor- 6 deenergizesthe coil 22- and tends to release the armature 32 and open the relays 25, 26 and 27. This is prevented by the coil 23, which is ener zed by the 'counter-electromotive force o the armature 1.

The master controller 7 may obviously be actuated step-by-step or to the position (I in a single step. In the latter event, the above-described operations will take place automatically and in sequence.

It, now, the motor remaining at high speed, the master controller 7 be actuated to the off position, as illustrated, denergizing the coils 8, 19, 20 and 21, the con ta'ctors 5, 10, 11 and 12 open. On account of the coi'inter-electromotive force in the coil 23, however, the relays 25, 26 and 27 will remain closed for a limited time, whereby, upon again actuating the controller 7 during this time, the coils 8, 19, 20 and 21 becoming reenergized, the contactor 5 will close to reestablish the motor circuit, and the contactors 10, 11 and 12 will immediately close to again shunt the resistor 6. This tends to have the effect of suddenly throwing the armature 1 into the line circuit without any resistance in series with it. To prevent this happening, therefore, the contactor 10 and the relay 26 should be mechanically interlocked, as at 55, in such fashion that, when the contactor 10 is open, the relay 26 will also be open, thereby keeping open the circuit of the coil 20 to preventthe closing of the contactor 11. Similarly, the contactor 11 and the relay 27 should be interlocked so that, when the contactor 11 is open, the relay 27 will be kept open. The contactors 10 and 11, however, are free to close, leaving the relays 26 and 27 open.

Thus in the contingency referred to, upon the actuation of the master controller 7 to the off position, although the relay 25 will remain closed because of the counterelectromotive force in the coil 23, the relays 26 and 27 will be open because the contactors 10 and 11 are open. If the circuit be now reestablished by the closing of the master switch 7, the relay 25 being closed, the coil 19 will be energized to cause the closing of the contactor 10. Not until the contactor 10 closes, however, can the relay 26 close. The closing of the relay 26 will cause the closing of the contactor 11 through the energization of the coil 20. Not until the contactor 11 closes can the relay 27 close to cause the closing of the contactor 12. The closing of the contactors 11 and 12 will de pend upon the speed of the motor, as previously described, for the magnetic field created by current in the coil 23, thougn strong enough to maintain the relays 25. 26 and 27 in closed position, is not strong enough to effect their closing in the first instance.

The interlock may be electrical instead of mechanical. In Fig. 2 I have shown one arrangement for electrically controlling the operation of the contactors 10 and 11 and the relays 26 and 27. The contacts 16, 17 and 18 have been omitted from this drawing, but may be inserted in thesystem if desired.

The coil 19 is connected in circuit as before described. The circuit of the coil 20, however, is made from the line conductor 3. through the conductor 28 and the relay 2G to the'connecting point 57 of the resistors 13 and 14:. hen the resistor 13 is included in the circuit, the voltage is not sufficient to energize the coil 20, and the contactor 11, therefore, remains open.- hen the contactor 10 is closed, the circuit is completed to the line conductor 4 through this contactor, and the coil 20 becomes sufficiently energized to close the contactor 11. Similarly, the coil 21 is connected, at 58, in a circuit which includes the resistors 13 and 14, except when the contactor 11 is closed, thereby delaying the closing of the contactor 12 until the contactor 11 is closed.

In other unit-switch systems now in use, no positive means is provided for always operating the relays, and, therefore, the contactors, at just the proper time. In'systems employing mechanically interlocked contactors and relays, for example, the current does not always rise with sufiicient rapidity to hold the relays from closing, and there is, consequently, at such times, nothing to limit. the closing but the inherent time element of the relays themselves. Systems employing the ordinary series-lockout switch ave proved unsatisfactory for the reason that such a switch operates between fixed current limits only, and the current sometimes drops so rapidly through these limits that the switch has not time to act, and, accordingly, fails to close. It will be seen that, in my system, the value of the current determines the proper time of closing. All that is necessary is that this time be previously selected by proper design. I

It is further to be noted that my system does not depend on the operation of a current which is successively brought back to the same peak and then allowed to fall. In the ordinary series relay, each successive peak is relied upon to build up the magnetism for actuating the next following relay. In my system, the magnetism is continually falling according to a substantially straightline law. The closing of successive contactors causes no measurable rise in the magnetism. The advantage of a system which depends, for its operation, upon a continually falling voltage is that. at no time during the operation, is it necessary to depend upon magnetism building up.

This advantage follows directly from connecting the coil-22 across the terminalsof the resistor 6. It is possible. of course, to employ a system in which the coil 22 shall be connected in series with'the resistor. hether the arrangement be parallel or series, the motor ciu'rent decreases from a high peak to a low peak every time that a portion of the resistor is shunted. If the coil 22 be connected in series with the resistor, and the current peaks have the same value, the relays 25, 26 and 27 will close simultaneously. To avoid this simultaneous closing, the current may be arranged to drop to successively lower values, but, it is found that these values are so nearly alike that the relays 25, 26 and 27 must be set to operate at values so close to each other, that there is no danger of improper operation. Otherdifi'iculties in practical operation also pertain to the series arrangement. The arrangement of the shunt coil, as shown, permits widely different values of magnetism corresponding to the same motor current.

Another advantage of the shunt-coil arrangement is that, with shunt coils, standardization is possible, for the same coil may be employed for all applications and is independent of the size of the motor. If a series coil be employed, different motors and applications require the use of separately designed coils. 7

It should be emphasized that the operation of my system is, in no way, dependent upon the particular switch illustrated in Figs. 3, 4c and 5. Separate relays, like those illus trated in Fig. 1 of the De Camp application for relay, above referred to, may, of course, be employed; but it is possible to so design my system as to make it operative with any relay. ll have illustrated such a system in Fig. 6.

In this system, the individual relays 25, 26 and 27, of any ordinary type, are normally closed instead of, as in the De Camp relay, normally open. If desired, a single relay having three armatures may be-used. The coils 22, 22 and 22 for controlling the operation of these relays are connected in series (as shown) orparallel, in series with a resistor 59 (which may be omitted), across the terminals of the resistor 6. If a single relay having three armatures is used, the three coils 22*, 22 and 22 will be replaced by a single coil, as in Figs. 1 and 2. The relay 25 is provided with an additional pair of stationary contacts 60, adapted to be bridged in the upper position of the relay to close a circuit for the coil 8 across the line conductors 3 and 4. A switch 61 is mechanically interlocked with the line contactor 5 to short-circuit the contacts 60. The master controller 7 may correspond to either of the types illustrated in Figs. 1 and 2.

The closing of the controller 7 creates a circuit for the coils 22, 22 and 22 which extends from the line conductor 3, through the armature 1, the resistor 59 and the controller 7, to the line conductor 4. The relays 25, 26 and 27 are immediately opened. The opening of the relay 25 causes the closing of 65 a circuit which extends from the line conaaeacae ductor 3, through the coil 8, the contacts 60 and the controller 7, to the line conductor The consequent energization of the coil 8 causes the closing of the line contactor 5 and the switch 61. The former establishes the motor circuit, and the latter short-circuits the contacts 60 as follows: from the line conductor 3, through the coil 8, the switch 61 and the controller 7, to the line conductor 4. The coil 8 will thus remain energized to maintain the contactor 5 and. the switch 61 closed, even though contact be broken at 60.

The coils 22, 22 and 22 of the relays 25,26 and 27 are, as before, so designed as to cause the relays to close successively, according to a decreasing magnetism; or, if a smgle coil is employed, the relays may be of different weights, or may be actuated by springs of different strength. The relay 25 closlng first, a circuit is established from the line conductor 3, through the coil 19, the relay 25, and the contactor 5, to the line conductor a. The consequent energization of the coil 19 causes the contactor 10 to close and the resistor 13 to be shunted from the armature circuit. In similar fashion, when relays 26 and 27 close later, as previously described in connection with Figs. 1 and 2, the remaining portions of the resistor 6 will be short-circuited and the armature will be connected directly across the line. The necessity for a holding coil 23 is thus obviated.

It should be noted that the system of Fig. 6, like the systems of Figs. 1 and 2, insures that the motor shall not be connected across the line without starting resistance. The line contactor 5 cannot be closed until after the relay 25 has been raised to break the circuit of the coil 19; and the circuit of the coil 19 cannot be made, even though the relay 25 is in its lower position, until after the line contactor 5 has been closed.

' A study of the system of Fig. 6 will make evident another advantage of: the shunt-coil arrangement. For successful operation, it is necessary that the relays 25, 26 and 27 be open before the motor commences accelerating. This may be effected mechanically, as by the spring 36, or'(assum1ng that the coils 22", 22? and 22 of Fig. 6 are re laced by a single coil) electrically by line vo tage. If the coil were arranged in series with the resistor, itl would not be possible to open the relays by line voltage without,

at the same time, starting the motor.

My invention is by no means limited to direct current, as will be made evident by reference to Fig. 7, showing an accelerating system for a wound induction motor, the primary windings, connected in circuit with the line conductors 3 3 and 3 of a threephase transmission line, being illustrated at 62, and the secondary winding at 63. The.

. ed in the circuit of one of the secondary leads 4*, this switch 64 being adapted to close a circuit between two of the primary leads 3 and 3", which includes, in parallel relation, the relays 25, 26 and 27 and the corresponding actuating coils 19, 20 and 21 of the contactors 10, 11 and 12. The line contactor 5 may be closed in any desired way, as by means of the master controller 7 closing a circuit for the coil 8 between two primary leads 3 and 3".

Upon the actuation of the controller 7 to energize the coil 8, the line contactor 5 is closed to connect the primary windings 62 in circuit with the three-phase transmission line. Current then flows between the leads 4*, 4 and 4 of the secondary winding 63, through the resistor 6. Current flows also through the coils 64 and 22, which are connected in the circuit extending from one terminal of the lead 4', through the coil 64, and the coil 22, to the other terminal. The switch 65 therefore closes. With the fall of current in the resistor 6, and, therefore, also in the coil 22, the relay 25 first closes, establishing a circuit from the line conductor 3 through the switch 65, the coil 19 and the relay 25 to the line conductor 3*. The coil 19 is therefore energized to close the contactor 10 and short-circuit the portion 13 of the resistor 6. Similarly, the relays 26 and 27 are later .closed to energize the coils 20 and 21 to cause the short-circuiting of the remainder of the resistor. The closing of the relay 27 establishes also a circuit for the holding coil 23 extending from the line conductor 3 and, through the coil 23 and the relay 27, to the line conductor 3*.

Although I have illustrated my invention as applied to a motor-accelerating system, it will be understood that it may be equally well applied to other systems including resistors. In some systems, such, for example, as those for heating With eIectric furnaces, the resistor forms substantially the whole circuit, in which case the energization of the coil depends upon the drop in voltage of the whole circuit.

'VVhile the motor has been illustrated as arranged for operation in one direction only, it will be understood that my invention is equally applicable to systems in which reversing mechanism is employed for the purpose of operating the motor in opposite directions, and to other systems, such assys;

tems that involve dynamic-braking, field control, etc.

It will be understood that I do not limit my system to the specific forms shown, or to the specific switch devices illustrated in the figures,-but that any equivalent system and any equivalent switch devices maybe employed without departing from the spirit of my invention as claimed.

I claim as my invention:

1. In a control system, the combination with a resistor, and means for successively shunting a plurality of portions of said resistor, of means comprising a single coil dependent upon the voltage across said resistor for controlling said shunting means.

2. In a control system, the combination with a resistor, and means for successively shunting portions of said resistor, of means comprising a single coil dependent upon the voltage across said resistor and switch members controlled thereby for controlling said shunting means.

3. In a control system, the combination with an electric circuit including an electric motor, a resistor, and a plurality of switches for successively shunting portions of said resistor, of means comprising a single coil dependent upon the electrical conditions of said resistor for controlling the closing of said switches during the operation of the motor.

4. In a control system, the combination with an electric circuit including a resistor, and a plurality of electromagnetic switches for shunting portions of said resistor, of means dependent upon the portion of said resistor remaining in said circuit for successively effecting the operation of said switches.

5. In a control system, the combination with an electric circuit including a resistor, a switch for shunting a portion of said resistor, and means for closing said switch, of means dependent upon the voltage of said resistor for temporarily rendering said first means inoperative.

6. In a control system, the combination with an electric circuit including a resistor,

ing actuating coils, of means dependent.

upon the voltage across said resistor for delaying the closing of a switch by preventing the energization of its actuating coil for an interval of time after the previous switch has closed.

50 1 the coil is energized, means for rendering of said resistor, said switches havin 'actuating coils, and of means for contro ling the energization of sald coils, said means comprlsinga coil energized in accordance with the voltage across said resistor, and relay members operable at different degrees of energization of said coil for controlling the circuits of said actuating coils.

9. In a control system, the combination with anelectric circuit includin a resistor, a plurality of switches for shunting portions of said resistor, and controlling means having different power values for effecting the closing of each of said switches, of means for temporarily rendering said controlling means inoperative, and for renderin said controlling, means successively operat1ve..

I 10. In a control system, the combination with an electric circuit including a resistor, a plurality of switches for shunting portions of said resistor, and means for normally maintaining said switches in open position, of means for successively closing said switches upon said first means becoming successively weakened.

11. In a control system, the combination with an electric circuit including a resistor,

' and a plurality of electromagnetic switches for shunting said resistor, of means comprising a single coil in parallel with said resistor for creating a magnetic field,:a'nd means controlled by said .field and operable at difi'e'rent degrees of strength thereof for eflecting the operation of said switches.

12. In a' control system, the combination with an electric circuit including a resistor, and a plurality of switches for successively shunting portions of said resistor, of a coil in parallel circuit with said resistor, and means dependent upon the strength ofthe current in said coil for effecting the successive operation of said switches.

13; In a control system, an electric circuit including a coil, a lurality of switches, means for normally eeping said switches open, means for closing said switches, means rendering said,first means inoperative when said second means inoperative when the co is energized, "and means for rendering said said switches w en'said coil is energized be- 14. In a control system, the combination .witha resistor, and a plurality .of'switches for successively shunting portions 'of said resistor, of a coil connected across the ter I minals'of said resistor, and means dependent upon the strength of the current in said coil and operable at progressively decreasing values thereof to control the operation of said sively operating said relays when the said current falls progressively below predetermined values.

16. In a control system, the combination with a resistor, a plurality of switches for shunting portions of said resistor, and a series of relays for controlling the successive operation'of said switches, of a means comprising a single coil connected across the terminals of said resistor for controlling the operation of said relays.

17. In a motor-control system, the combination with. a motor armature, a resistor in circuit therewith, and a pluralityof switches having actuating coils for successively shunting portions of said resistor, of a plurality, of relays adapted to be closed to energize said coils, 'and means for preventing suflicient energization of one of said coils to close the corresponding switch when a prior switch is open.

18. The combination with a motor having a resistor, and a plurality of switches having actuatingcoils for short-circuiting portions of said resistor, of a relay' for controlling one of said actuating. coils, said relay an said one coil being connected in a circuit including a portion of said resistor controlled by another of said switches, and means for short-circuiting said portion of said resistor controlling the energization of each of said coils, each of several of said relays and the coil which it controls being connected in a circuit including ,a' portion of said resistor -when one of said switches'is open, said circuit including said switch and excluding said portion of said resistor when said switch is closed,said circuits being arranged so as to prevent the closing of said swltches when said portions of said resistorsare included in said relay circuits. j In a motor-control system, the combination with a circuit including a resistor, and a plurality of switches for successively shunting portions of said resistor, of means "dependent upon thevoltage across said resistor for keeping said switches open, means for successively closing said switches when ,the said voltage falls below predetermined values, and means for keeping said switches v closed when said resistor has been completely shunted; i

I has beenbro en.

21. In a control system, the combination with an armature, a resistor in circuit therewith, and a plurality of switches for successively shunting portions of said resistor, of a coil in parallel with said resistor, a second coil connected across the terminals of the armature, means dependent upon the current in said first coil for successively closing said switches, and means dependent upon the current in said second coil for retaining said switches in closed positions.

22. In a motor-control system, the combination with a motor armature and a resistor in circuit therewith, of: means for shunting said resistor, for maintaining said resistor shunted from said circuit, and for gradually reestablishin said shunt after said shunt 23. In a motor-control system, the combination with a inotor having an armature and a resistor in circuit therewith, of means for shunting said resistor; means controlled by the counter-electromotive force of said armature for keeping said-resistor shunted from said circuit, means for breaking said shunt when said circuit is broken, and means for gradually reestabhshing said shunt upon the closing of said circuit.

24. In a motor-control system, the combination with an electric circuit including a resistor, and a plurality of switches for successively shunting portions of said resistor, of a plurality of relays, means dependent upon the speed of said motor for successively closing said relays to cause the closing of said switches, means dependent upon the s eed of said motor for keeping said relays c osed, meansfor opening said switches when said motor circuit is opened, and means for thereupon opening some only of said relays, whereby, when the motor. circuit is again established, the resistor can not be immedi-' ately entirely shunted from the circuit.

25. In a motor-control system, the combination with a motor armature, a resistor in circuit therewith, and a plurality of switches for successively shunt ng portlons' of said resistor, of a plurality of relays for closing said switches, means actuated by the counter;

electromotive force of said armature for keeping saidswitches and relays closed when.

said resistor is shunted, and an interlock between certain of said switches and the corresponding preceding relays for opening said last named relays when said last named switches are open, whereby, when said circuit is broken and remade, the whole resistor will not be immediately reinserted into said circuit. v

26. In a motor-control system, the combination with a motor armature, a resistor in circuit therewith, and a plurality of switches for successively shuntingportions of said resistor, of means in parallel circuit with said resistor for controlling the closing of means for disconnecting said armature from said source, and means for thereupon preventing the operation of said second means until after the operation of said first means.

28. In a control system, the combination with an electric circuit including a resistor, and a switch for shunting said resistor, of means in parallel circuit with said resistor for effecting the maintaining of said switch in its open position during a predetermined period, and means for closing said switch at the end of such period.

29. In a control system, the combination with an electric circuit including a resistor, and a plurality of rela s for effecting the shunting of portions oi: said resistor, of a coilin parallel circuit with said resistor, said coil when energized to a predetermined value actuating said relaysto open position,

across said resistor and to the potential across the terminals of said machine for controlling the position of said switch.

31. The combination with a dynamo-electric machine, a resistor in circuit therewith,

and a plurality of switches for controlling said resistor, of means responsive to the drop in potential across said resistor and to the potential across the terminals of said machine for controlling the position of said switches.

32. The combination with a dynamo-electric machine and a resistor in circuit therewith, of means responsive to the drop in potential across said resistor and to the counter-electromotive force of said machine for effecting the shunting of said resistor and for maintaining the shunting of said resistor during normal operation of said machine.

33. The "combination with a dynamo-electric machine and a resistor in circuit therewith, of means responsive to the drop in potential across said resistor for effecting the shunting of said-resistor and responsive tothe counter-electromotive force of said motor for maintaining the shunting of said resistor. a r

In testimony whereof, I have hereunto subscribed my name this 29th day of April,

HENRY D. JAMES.

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