US1392255A - Motor-control system - Google Patents

Description

E.YS..LAMMERS, JR.

MOTOR CONTROL SYSTEM.

APPLICATION FILED JUNE 13, 1917 1 ,392,255 PatentedSept. 27, 1921.

3 SHEETS-SHEET I.

75 EXc/f'er WITNESSES: INVENTOR y BY I 2 ATTORNEY E. s. LAMMERS, JR. MOTOR CONTROL SYSTEM.

APPLICATION FILED JUNE 13, I917. 1,392,255. PatentedSept- 27, 1921,

' 3 SHEETS-SHEET 2.

WITNESSES: INVENTOR Edwin S. Lammers, Jr.

i madiowzi m E. S LAMMERS, JR. MOTOR-CONTROL SYSTEM.

APPLICATION FILED JUNE 13, 1911. I PatQIIitBdSGPt' 27, 1921.

3 SHEETS-SHEET 3- WITNESSES INVENTOR a. 4 [dw/n Slammers, J25

EDWIN S. LAMMERS, JR, OF-WILKINSBURG, YENNSYLVA'NIA, ASSIGNOR TO WEST- INGHOUSE ELECTRIC & MANUFACTURING COMYANY, A. CORPORATION OF PENN- SYLVANIA.

Moron-common SYSTEM.

Application filed June 13,

T 0 all whom it may concern:

Be it known that I, EDWIN S. LAMMERS, Jr., a citizens of the United States, and a resident of Wilkinsburg, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Motor-Control Systems, of which the following is a specification.

. My invention relates to motor-control systems and it has for its object to provide a simple and effective arrangement for insuring the operation of a series of electromagnetically operable switches in a predetermined sequence.

My invention comp-rises a series of roressively actuated switches, each of w ich 18 provided with a pair of coils of substantially equal ampere-turns. It is necessary that both coils of any switch shall be energized in order to effect the closing of the switch, Either of the coils, when energized, exerts a pull that is sufficient to retain the switch in its closed position.

A series of switches arranged in the manner described above may be employed in various ways. For example, they may be embodied in a s stem for controlling the field excitation o dynamo-electric machines employed in connection with reversing blooming mills for rolling steel. They may also be employed in connection with electric motors for operating mine hoists or other machines in which it is desirable that the controlling switches operate in a predetermined sequence either automatically or in accordance with the position ofa manually operable controller.

In the accompanying drawings, Figure 1 is a diagrammatic view of the main and field circuits of a generator and an electric motor such asare employed in connection with steel mill operations. Fig. 2 is a chart indicating the sequence of operation of the various switches of the system shown in Fig. 1. Fig. 3 is a diagrammatic .view of circuits and apparatus illustratin my invention applied to the circuits 0 an electric motor. Fig. 4 is a diagrammatic view of the circuits and apparatus for controlling the various switches shown in the system of Fig. 1. Fig. 5 is a diagrammatic View of a series of switches arranged in accordance with my invention for automatically controlllng the c rcuits of an electrlc motor.

Specification of Letters Patent.

Patented Sept. 27, 1921. 1917. Serial No. 174,439.

Fig. 6 is a schematic arrangement of the principal circults of the system shown in Fig. 5.

eferring particularly to Fig. 1, a generator G and a motor M connected in a closed circuit. The generator G is provided with a field-magnet winding 1. The circuit of the field-magnet 1, which comprises a resistor 2, is controlled by reversing switches 3, 4, 5 and 6 and by a series of progressively actuated switches 7, 8, 9 and 10. The motor M is provided with a field-magnet winding 12 which is in circuit with a resistor 13. The resistor 13 is controlled by a second series of progressively actuated switches 14, 15, 16 and 17.

Reference may now be had to Fig. 4, in which the circuits and apparatus forcontrolling the several switches embodied in the system of Fig. 1 are diagrammatically switch, when closed, may be retained in that.

position when either of the coils is energized. The coils 18 are arranged to be energized in order in accordance with the position of the manually operable master switch or conare permanently troller 20. The circuits of the respective coils 18 are arranged to be controlled by the preceding switch to close in order that the switches may close in the predetermined sequence regardless of the rate at which the controller 20 is actuated to its full running position. The coils 19, which are connected in parallel circuit relation to each other, are arranged to be energized simultaneously.

Current for the various control circuits and for supplying energy to the respective field-magnet win ings of the generator and of the motor is furnished b an exciter generator E. The circuits 0 switches 7, 8, 9 and 10 are controlled by a relay 22 having an actuating .coil 23 which is connected, by means of conductors 24 and 25, across the terminals of a resistor 26 that is in series-circuit relation with the generthe coils 19 of ator and the m to ametnrewindin s. The

relay 22 accordingly controls the circuits of the coils 19 in accordance with the value of the current traversing the main circuit.

The effect of the operation of the relay 22 is controlled by a relay 27 which normally occupies its illustrated osition. The relay 27 is controlled by a 0011 28 that is in series with the coils 18 of switches 7, 8, 9 and 10 and is energized in accordance with the number of coils 18 that are connected in circuit by the controller 20. The relay 27 is controlled also by a coil '29 which is connected by means of conductors 30 and 31 across the terminals of the generator G. The coil 29 opposes the force of the coil 28 with a force t at is proportional to the value of the voltage of the generator G.

A spring 32-tends to retain the relay 27 in its illustrated position. During the operation of the controlling switches, the position of the relay is dependent upon the value of the voltage of the generator corresponding to the portion of the resistor 2 which is in circuit, as determined by the position of the controller 20, relatively to the actual voltage of the generator as measured by the degree to which the coil 29 is energized. The coils 28 and 29 tend to actuate-the relay 27 in opposite directions.

A relay 34, which is similar to the relay 22, controls the circuits of the coils 19 of the switches 14, 15, 16 and 17. The relay 34 is provided with an actuating coil 35 that is connected across the terminals of the resistor 26. The efi'ect of the operation of the relay 34 is controlled by a relay 36 which normally occupies its illustrated position.

The relay 36 comprises actuating coils 37 and 38 which respectively tend to actuate the switch toward and from the position in which it is illustrated. The coil 37 is connected in series with the coils 18 of the switches 14, 15, 16 and 17. The coil 37 is accordingly energized to a degree depending upon the number of coils 18 that are incircuit.

The coil 38 is connected, by'means of constationary. When the various relays and switches occupy their respective illustrated positions, a control switch 44 is closed and the coils 19 or the switches 7, 8 and 9 are energized by a circuit which extends from the positive terminal of the exciter E through a port on of conductor 43, relays 27 and 22, coils 19, which are in parallel relation, and switch 44 to the negative terminal of the exciter. The coils 18 of these switches are denergized because their respective circuits are open at the master controller.

The corresponding coils 19 of the switches 14, 15, 16 and 17 are energized by a circuit which extends from the positive terminal of the exciter E through a portion of conductor 43, relays 36 and 34, coils 19, which are in parallel relation, to the negative terminal of the exciter. The switches 14, 15, 16 and 17 are closed when the controller is in its off position. When the switch 10 is open, a circuit for the coil 18 of switch 14 is completed which extends from the positive ter minal of the exciter E through an interlock connected to switch 10, coil 18 of switch 14 and coil 37 to thenegative terminal of the exciter.

Since both the coils 18 and 19 of switch 14 are energized, this switch closes to complete a shunt circuit for the corresponding section of the resistor 13. The coils 18 of switches 15, 16 and 17 are respectively controlled by interlocks connected to the preceding switch to close, and the closing of switch 14 accordingly effects the closing of switches 15, 16 and 17 in the order named. The major portion 'of the resistor 13 is shunted by these switches and the motor is provided with a strong magnetic field for starting.

An interlock connected to switch 17 completes a circuit for connecting the coil 38 across the terminals of that section of the resistor 13 that is not controlled by the switches 14, 15, 16 and 17. The coil 38 is energized to a maximum degree because the value of the field current is a maximum. The force of the coil 38 predominates over that of the coil 37 and the spring 41 and the relay is overbalanced. It assumes its other operative position in which the coils 19 of the switches 14, 15, 16 and 17 are deenergized so long as the relay 34 remains in its illustrated position.

To accelerate the motor in the forward direction, the controller 20 is actuated to the left. as viewed in Fig. 4. When the controller occu ies position a, a circuit is completed whic extends from the positive terminal of the exciter through conductor 43, controller 20, interlock 45 of switch 3, actuating coils of reversing switches 4 and 6 and coil 28 of rela 27 to the negative terminal of the exciter As best shown in Fi 1, the closing of the switches 4 and 6 estab ishes a circuit for the field-magnet winding 1 of the generator which extends from the positive terminal of the exciter, through switch 4, resistor 2, field-magnet windin 1 and switch 6 to the negative terminal 0 the exciter,

In position b of the controller 20, a circuit terminal of the exciter, through conductor 46, interlock connected to switch 6, coil '18 of switch 7 and coil 28, to the negative terminal of the exciter. The switch 7 is now closed since both of its operating coils 18 and 19 are energized.

The closing of switch partly completes a circuit for the actuating coil 18 of switch 8 and the latter switch closes when the controller is actuated to the succeeding position 0. The switches 8, 9 and 10 accordingly close in order as the controller is actuated to its successive positions 0, d and .2. Substantially the entire resistor 2 is shunted and the voltage out the generator has increased to a corresponding degree. Each of the switches 8, 9 and 10, upon closing, completes a holding circuit for the coil 18 of the preceding switch to close and the switch 7,

upon closing, completes a holding circuit for the coils of the reversing switches. The innction of these holding circuits is to control the sequential operation of the switches during deceleration.

Upon the closing of switch 10, an interlock 47, which is mechanically connected thereto, opens the circuit previously traced for the coil- 18 of switch 14.. The latter switch does not open, however, because an interlock connected to switch 15-controls the holding ci cuit for the coil 18. The actuation of the controller to position f efiects the.

opening of the holding circuit for coil 18 of switch it through the interlock connected to switch 15. there is one less coil 18 in circuit with the coil 37, the force of the coil 3?. is overhalanced by that of the coil 38, causing the relay 36 to open, thereby to open the circuits of the coils 19. The switch 14 opens to insert the corresponding section of the resistor 13 in series with the field-magnet winding 12 to further accelerate the motor. The actuation of the controller to its succeeding positions effects the opening of switches 15, 16 and 17 in order to further weaken the field of the motor and thereby eiiect its acceleration to its normal speed.

The operation of the system has been described upon the assumption that the controller 20 is actuated in astep-by-step manner from its oil position to its full running position. in actual practice, however, the controller 20 may be actuated from the one position to the other by a comparatively quiet: continuous movement. In such case, operation of the reversing switches 4- switches 7, 8, 9 andlO occurs in the order described v 27, which controls the cir- .1 e not operate to interrupt the circuit 1 ot the c i s 18 heean e coils 18 of the latter group of circuit is such that the coil 28 is energized" to maintain the relay in its illustrated position. The generator voltage does not increase simultaneously with the o eration of the switches for increasingthe eld excitation of the generator.

The switches 14, 15, 16 and 17 open in order upon the closing of switch 10 since the holding circuits for the coils 18 of these switches are opened at the controller 20, and these coils are accordingly deenergized in order upon the opening of the preceding switch. The opening of switch 17 opens the shunt circuit for a section of resistor 13 and the coil 38 is accordingly deenergized. The coil Shisdenergized also since none of the coils 18 of the'latter groupof switches are in circuit. The relay 36 accordingly as sumes its normal position to complete circuits for theceils 19 in preparation for the closing of the switches.

The operation of the switches described above occurs without interruption in case the current traversing the main circuit of the motor andthe generator does not exceed a predetermined value. In case, however, the voltage of the generator is increased at such rate that the current traversing the main circuit exceeds the predetermined-value, the coil 23 is energized-to open the relay 22 and thereby open the circuits of the coils 19 of switches '8, 8,9 and 10.

They switches that are closed remain in this position because the corresponding coils 18 exert a pull that is sufiicient to retain them in the closed positions. The relay 22 occupies its open position so long as the current traversing the main circuit excoeds the predetermined value, and the operation of the switches is accordingly interrupted for a corresponding period. When the current falls to the predetermined value. the relay 22 closes and the closing of the switches continues in order unless the current again exceeds the predetermined value. In the same manner, the operation of the switches 1 15, 16 and 17 is interrupted by the operation of relay 34 in casethe coil 35 is suiiiciently energized to actuate the relay to its upper position. When the relay 34; cccupies its upper position, the circuits of the coils 19 are completed through the relay 36, and the opening of the switches to insert the resistor 13 in se ies with the field-magnet winding 12 is interru ted until the current traversing the main circuit falls to the pre determined value.

lit will he readily understoodthat the controller he actuated to its lull runnin position by a continuous movement and that the operation of the system will occur automatically. operation of the controlling switches is, interrupted automatically upon the occurrence of abnormal current conditions, but the operation of the switches is resumed when normal conditions again obtain. The voltage of the generator is thus increased and the field excitation of the motor is decreased at such rates that the motor is accelerated at a maximum rate consistent with safety.

To decelerate the motor, the controller is actuated toward its oii position. When the controller occupies position It, thecoil 18 of switch 17 is again energized by means of a circuit which comprises the coil 37 of relay 36. The coils 19 of the motor controlling switches are energized when the relay occupies its illustrated position.

The switch 17 accordingly closes to complete a shunt circuit for the corresponding section of resistor 13. The closing of switch 17 completes the circuit of coil 38 and, when the current traversing the field circuit of the motor reaches a value corresponding to the adjustment of the controller, the coil 38 predominates and the relay 36 is actuated to open the circuit of the coils 19.

When the controller occupies position g, the coil 18 of switch 16 is energized and the coil 37 of relay 36 again predominates to actuate the relay to its illustrated position and thereby complete a circuit for the coils 19, whereupon the switch 16 closes. The operation of the relay 36 occurs between the closing of the successive switches in order to prevent the shunting of the resistor at a rate faster than that at which the field current increases.

When all of the motor controlling switches are closed, the motor operates with a field maximum strength and its speed is accordingly decreased. The closing of switch 14 opens the holding circuit of c011 18 of switch 10 and restores the control of the latter switch to the controller 20.

hen the controller occupies position d, the coil 18 of switch 10 is deenergized and the pull exerted by the coil 28 is decreased to a corresponding degree. The force exerted by the coil 29 is a maximum since the enerator voltage is at its normal value. The coil 29 predominates and the relay 27 is accordingly actuated to its other operative position to open the circuits of the coils 19 that are controlled by it. The switch 10 accordingly opens to insert the corresponding section of resistor in circuit with the generator field-magnet winding.

The coil 29, of relay 27 predominates so long as the generator voltage exceeds the value corresponding to that for which the controller is adjusted. If the generator controlling switches are opened at a relatively rapid rate, the generator voltage is reduced to a value below that of the motor and the latteroperates as a generator. If the curspeed of the motor is decreasing tends to maintain the current traversing the main circuit at a maximum value and the speed of the motor is accordingly decreased at a maximum rate.

The operation of the motor in the reverse direction is effected by actuating the controller to the right, as viewed in Fig.4.

eversing switches 3 and 5 operate to complete the circuit of generator field-magnet winding 1 with the connections of the latter reversed with respect to the terminals of the exciter E. The operation of the several switches and relays differs in no material respect from that described in connection with the operation of the motor in the forward direction.

It will be noted that, in the system illustrated in Figs. 1 and 4, I rovide a series of progressively actuated switches for controlling the respective field circuits of an electric generator and an electric motor. Each of the switches is provided with a pair of actuating coils both of which must be energized to effect the closing of the switch and either or which, when energized, retains the switch in its closed position.

()ne member of each pairof coils is controlled by a manually operable master switch and by the preceding and succeeding switches to operate. The other coils are controlled simultaneously by a relay that is actuated in accordance with the value of the current traversing the main circuit comprising the motor and the generator armatures.

The effect of the operation of this relay is controlled by a second relay having coils which tend to actuate it in opposite directions. One of the coils is energized in accordance with the number of operating coils connected in circuit by the master switch. In the case of the switches for controlling the field circuit of the generator, the second coil is connected across the terminals of the generator. The corresponding relay is accordingly controlled in accordance with the actual generator voltage relatively to the value of the voltage corresponding to the adjustment of the controller.

In the case of the relay which coacts with the switches for controlling the motor field circuit, one of the opposing coils is connected succeeding switches to close.

in series with the coils controlled by the master switch and the other coil is so connected as to be energized in achordance with the current traversing the field circuit of the motor. This relay operates, therefore, in accordance with the actual value oi the current traversing the motor field circuit relatively to the value of the current corresponding to the adjustment of the master switch.

Reference may now be had to Fig. 3, in which a modification of my invention is diagrammatically illustrated. Line conductors 51 and 52 supply current to an electric motor, the armature of which is indicated at 53 and which has a shunt field-magnet winding 54. A starting resistor 55 is controlled by a series of progressively actuated switches 56, 57 and 58."

Theswitches 56, 57 and 58 are respectively provided with actuating coils 59 and 60, both of which must be energized to eifect the closing of the switch, but either of which exerts a pull of sufficient strength tov maintain the switch in its closed position. The motor circuit is controlled by an electromagnetically operable line switch 61; An interlock 62 connected to the line switch 61controls the circuits of the coils 60. A relay 63, having a coil 64 in series with the motor armature, controls the circuits of the coils 59. A master switch 65 controls the operation of the several switches.

To start the motor, the controller is actuated to the left, as viewed in Fig. 3. In position a, the coil 66 of line switch 61 is energized and the latter closes to complete the armature circuit of the motor through resistor 55. The interlock 62 partially completes the circuits of the respective coils 60.

In position b of the master switch, the coils 59 and 50 of switch 56 are energized and the switch 56 accordingly closes. The closing of switches 57 and 58 is effected upon the actuation of the master switch 65 to its succeeding positions.

The closing of the switches in the order named is insured by the provision of interlocks connected to the switches 56 and 57 for controlling the circuits of the coils of the The master switch may accordingly be actuated from its illustrated position to its full running position by a rapid movement. The switches then close in order in case the current traversing the motor circuit does not exceed a predetermined value. In case the current traversing the motor circuit reaches a value at which the coil 64 is energized to operate the relay 63, the several coils 59, which are energized upon the actuation of the master switch 65 to its full running position, are deenergized. If, for

example, the switch 56 is closed, tne operation of the relay 63 does not efi'ect the openbe controlled either manually by the adjust- I ment of the master switch 65 to its running position in a step-hy-step manner or the operation may occur automatically upon the actuation of the master switch to its full running position. While the operation of the motor is arranged i'or one direction only,

it will he understood that my invention is applicable equally as well to systems in which reversing mechanism is embodied for the purpose of operating the motor in opposite directions.

Referring now to Fig. 5, a second modification of my invention embodies an arrangement which operates automatically to accelerate an electric motor when such action is initiated upon the operation of a manually operahle master switch. An electric motor 69 has aseries field-magnet winding 70 and a shunt field-magnet winding 71. The armature circuit of the motor is controlled hy reversing switches 72, 73, 74 and 75. A starting resistor 76 is controlled by switches 77 and 78, each of which is provided with a pair of operating coils similarin all material respects to the corresponding coils of the systems previously: described. The motor circuit is controlled by an electromagnetically operable line switch 79. The control circuit is controlled by a master switch 80 and a low-voltage relay 81 which is closed when the master switch occupies its 05 position-and a control switch 82 is closed.- To startthe motor, the master switch 8 may be actuated, for example, in a clockwise direction, as viewed in Fig. 5, for the operation of the motor in the forward direction. A circuit is completed which extends from the positive side of control switch 82,

through overload relay 83, low-voltage relay I 81, master switch 80, coils of reversing switches 75 and 73, actuating coil of line switch 7 9, and overload'relay 84, to the negative side of the control switch 82. The re- 'versing switches 7 3 and 75 close to complete the armature circuit of the motor, and line switch 77, and accelerating rela 87, to the negative terminal of the contro switch 82. A second circuit, which is completed by the interlock 85, extends through coils 88 and 89.

The switch 77 is closed since both coils 86 and 88 are energized. The closin of switch 77 completes a circuit for a 0011 90 I terrupted by the accelerating relay 87, the

actuating coil of which is in series with the armature of the motor. The accelerating relay 87 is adjusted to operate when the current traversin the motor circuit corresponds to the normal load value. 'The'closin of switch 78 shunts the actuating coil 0 the rela 87.

T e operation of overload relays 83 and 84, which are adjusted for abnormal current values, efi'ects the opening of the reversing switches, the line switch 79, low-voltage relay 81 and switches 77 and 78. It is then necessary to return the master switch 80 to its oli' position to again initiate the starting operation.

I claim as my invention: V a

1. In a motor-control system, the combination with a generator and a motor in series circuit relation, each of said dynamoelectric machines having a field-magnet winding, and a resistor in circuit with each of said field-magnet windings, of means for controlling said resistors, said means comprising a plurality of electro-magnetically operable switches each of which is provided with a pair of magnet coils .both of which must be energized to close the corresponding switch, and means for insuring theener 'zation of one member of each pair of coil; in a definite sequence. a

2. In a motor-control system, the combination with a plurality of progressively actuated switches, of a air of operating coils for each of said switches, both of which must be energized to effect the closing of the corresponding switch, either of said coils being effective to retain said switch in its closed position, means for collectively controlling corresponding coils of each pair and means for selectively controlling other coils of each pair. p

3. In a motor-control system, the combination with a plurality of progressively actuated switches, of a pair of operating coils for each of said switches both of which must be energized to e'fi'ect the closing of the corresponding switch, either of said: coils being effective to retain said switch in its closed position, said coils and said switches being so connected as to insure the opening and the closing of said switches in a predetermined sequence, and means for-initiating the operation of said switches.

42. In a motor-control'system, the combination with a plurality of progressively actuated switches, of a pair of o eratin coils for each of said switches both 0 which must be energized to effect theclosing of the corresponding switch, either of said coils being effective to retain Said switch in its closed position, one member of each pair of coils, except that for the first switch to operate, being controlled by the precedin switch to operate, a controller for the sai members of the pairs of coils, and automatic means for controlling the energization of the other coils. I

5. In a motor-control system, the combination with a dynamo-electric machine and a plurality of progressively actuated switches operatively associated therewith, of a air of operating coils for each of said switc es, the circuit of one member of each pair of coils beingv controlled by the receding switch to operate, manually opera le means for controlling said circuits, and means for controlling the circuits of the other coils in accordance with the value of the current with said master switch, each of said coils except that for the first of said switches to switch to operate, and each of said coils except that for the last of said switches to close being controlled by the succeeding switch to operate.

7. In a motor-control system, the combination-with a dynamo-electric machine and a plurality of progressively actuated switches operatively associated therewith, of a pair of operating coils for each of said switches, the circuit of one member of each pair of coils 'being controlled by the preceding switch to operate,imanually operable means for controlling said circuits, automatic means for controllin the other'members of said pairs of coi s in accordance with the value of the current traversing said dynamo-electric machine, and means for controlling the effect of the operation of said automatic means.-

8. In a motor-control system, the combination with a dyanmo-electric machine and a plurality of progressively actuated traversing the circuit of said dynamo-electric I a master switch, an actu- .close being controlled by the preceding switches operatlvely associated therewith, of

cuit and a plurality of progressively actuated switches for controlling the same, of a pair of operating coils for each of said switches, manuall operable means for controlling one member or each pair of coils, a relay for automatically controlling the other coils in accordance with the value of the current traversing said circuit, and a second relay for controlling the efiect of the operation of the ether relay in accordance with the actual circuit conditions produced by said manually operable means relatively to the circuit conditions corresponding to the adjustment of said manually operable means.-

10. In a motor-control system, the combination with a dynamo-electric machine and a plurality of progressively actuated switches operatively associated therewith, of a pair of operating coils for each of said switches, manually operable means for controlling one member of each pair of coils, and means for controlling the circuits of the other coils in accordance with the value of the:v current traversing the circuit of said dynamo-electric machine and in accordance with the actual voltage conditions obtaining in the circuit of said dynamo-electric machine relatively to the voltage conditions corresponding to the adjustment of the manually'operated means.

11. In a motor-control system, the com bination with an electric circuit and a plurality of progressively actuated switches for controlling the same, of a pair of operating coils for each of said switches, manuallyoperable means for controlling one member of each pair of coils, and means comprising a relay for controlling the other coils, said relay having opposing coils one of which is in series with the coils controlled by the manually operable means and the other of which is energized in accordance with the value of the current traversing said circuit.

12. The combination with an electromagnetic switch having a pair of actuating coils, of a switch in circuit with one of said coils and having an actuating coil in circuit with said other coil.

13. The combination. with a dynamo-electric machine and a plurality of switches for controlling said machine and having actuating coils in parallel relation to each other, of a switch for controlling the operation or said switches and having an actuating coil in series with said first=named coils.

14. The combination with a dynamo-elec trio machine having a resistor associated therewith, of a switch for controlling said resistor and having two actuatingcoils, a pair of double-throw switches adapted to close the circuit of one of said coils normally and when both of said switches occupy their abnormal positions, an actuating coil for one of said pair of switches responsive to the current of "said machine and a pair of opposing actuating coils for the other of said pair of switches respectively responsive to the voltage of said 'niachine and in circuit with the other of said two actuating coils.

15. The combination with a dynamdelectric machine having a resistor associated therewith and a plurality of switches "for controlling a portion or saidresistor, each having an actuating coil, or a relay for controlling said plurality of switches and having opposing actuating coils that are respectively energizedin accordance with the number of switch-actuatingcoils that are energized and the value of the voltage across a portion of said resistor 16. The combination with adynamo-electric machine having a resistor associated therewith, of a switch for controlling portion of said resistor and having two actuating coils, and aswitch for controlling the circuit of one of said coils and having a pair of actuating coils respectively in circuit with the other lof said two coils and connected across a portion of said resistor.

17. The combination with a pair as dynamo-electric machines each having a res1stor associated therew1th, of a switch for controlling each of said resistors and each .having a pair of actuating coils, both oi.

which, coils must be energized to efiect the operation of the corresponding switch, means for closing the circuits of one coil of each oi said switches, and means controlled by' one of said switches for closing the other coil of said other switch.

18. The combination with a dynamo-sled n said pairof switches and having opposing actuating coils. each in circuit with one cl" said pair of switches.-

20. The combination with a pair ct dynamo-electric machines each having a resistor associated therewith, of a switch for controlling each of said resistors, and interlocking means controlled by each of said switches for insuring their successive operation.

21. The combination with a pair of dynamo electric machines each having a re s'istor associated therewith, of a switch for controlling each of said resistors and each having an actuating coil, means controlled by one of said switches for closing the circuit of the coil of said other switch when said one switch occupies an inoperative position, a switch for controlling the flow of current through the resistor which is controlled by said one switch, and means controlled by said controlling switch for clos ing the circuit of the coil of said one switch.

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

EDWIN S. LAMMERS, JR.

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