US2275197A - Control system - Google Patents

Description

B. w. JONES CONTROL SYSTEM March 3, 1942.

Filed Nov; 30, .1939 2 Sheets-Sheet 1 Fig.2.

Inventor: Benjamin W. Jones, 9 His Attorney amZM March s, 1942. w. JONES CONTROL SYSTEM 2 Sheets-Sheet 2 Filed NOV 30, 1939' I M Pb 35 Inventor. 7 Benjamin WJones, b 7 6/] His Attorney the "plugging Patented Mar. 3, 1942 coN'raoL srsran Benjamin w lonea, Schenectady, N. 2., aaslgnor to General New York Electric Company, a corporation of Application November 30, 1939, Serial No. 306,933

cum-119') My invention relates to control systems, more particularly to systems for controlling the start- I) stopping and running of electric motors, and has for an object the provision of a simple, re-

liable, inexpensive and improved system 'of this character.

More specifically, my invention relates to systems for controlling the acceleration of an electric motor as a iunction of time. In addition, my invention relates to systems for controlling the counter current braking or plugging-of' an electric motor as well as the acceleration in the reverse direction after the motor has been slowed down by "plugging to a predetermined low speed, preferably substantially to zero speedor standstill.

Another object of my invention is the provision of electromagnetic means, preferably including a plurality of multilegged frames each having a pair of energizing windings, for controlling the connection of suitable current limiting means, such as a plurality of resistors, with the motor circuit controlled and for controlling the disconnection of said current limiting means from said motor circuit.

A further object of my invention is the provision of means for controlling the energization of the windings of at least one of the electromagnetic" devices so as to render the current limiting resistance used for plug8ing" inactive during normal starting and normal running operation of the motor substantially without time delay, while controlling the energizatlon 01 these windings during the counter current braking or plugging operation of the motor so as to prevent the electromagnetic device from rendering resistor inactive, until the speed of the motor is suificiently reduced for safe operation in the opposite direction, preferably this speed being substantially standstill.

A still further object of my invention is the provision of means for controlling the energization of the windings of the electromagnetic devices which control that portion of the current limiting means used for acceleration, such as a plurality of accelerating resistors, in a manner whereby each electromagnetic device is operated to render inactive the accelerating resistor controlled by it, only after a predetermined time interval has elapsed from the instant a preceding one of the resistors was rendered inactive.

In carrying my invention into eifect, I preferably employ an electromagnetic time interval device of the type disclosed and broadly claimed in the U. S, patent application of Fred H. Winter, Serial No. 187,753, filed Jan. 29, 1938. The Winter time delay device comprises a multi-legged magnetic structure having two energizing windings thereon and an armature carrying a switch contact, the armature being biased to a predetermined position. In the predetermined position, or what is termed the "normal unattracted" position, the armature is arranged to be magnetically restrained in this normal position when a certain one or both of the energizing windings are energized. The armature is moved to the attracted position from its normal position only when a certain one of the windings is energized and the other winding de-energized or when the windings are both energized in a direction to complement each other. Generally speaking, when both windings are energized in a manner to magnetically restrain the armature in its unattracted position, one of the windings may be short-circuited and then the other winding will cause a reversal of flux in a portion of the frame against the time delay effects of the other winding to effect time delayed operation of the armature to its attracted position. This type of time delay operation and certain modified forms of it are used in the sequential time delay control of the accelerating resistors to accelerate the motor.

A similar type of electromagnetic structure provided with an armature is used in the preferred embodiments of my invention to control the "plugging resistor. However, in this case one of the windings is connected to be energized-responsive to a suitable electrical condition of the motor circuit, such as the countervoltage of the motor. Under normal operating conditions of the motor, the last mentioned winding is energized in a direction to complement the magnetic forces generated by the other winding, thereby to operate the armature to its attracted position promptly without any substantial time delay. In this manner, if the motor is started from rest or is running in the proper forward direction, the "plug'ging resistor is promptly rendered inactive by short-circuiting and the control of the circuit is transferred entirely to the accelerating resistors. If, however, the motor is plugged,"

the countervoltage effect on one or both of the windings is such that the magnetic forces'in the electromagnetic structure magnetically restrain the armature from operation to the attracted position until the motor speed drops substantially to standstill. Thereafter, the armature moves to the attracted position to short-circuit the plugging resistor and transfer control to the accelerating resistors which, as more fully described hereinafter, are short-circuited sequentially with predetermined intervening time delays.

Further objects and advantages of my invention will become apparent from the following description and for a better understanding reference should now be had to the accompanying drawings in which Fig. 1 is a diagrammatic representation of a control system embodying my invention in one form; Fig. 2 is a side view of the Winter electromagnetic switch preferably employed in obtaining the desired plugging and time limit acceleration control of the current limiting resistors in the motor armature circuit; and Fig. 3 is a diagrammatic representation of a control system embodying my invention in another form.

Referring to the drawings, the motor to be controlled is indicated as having an armature II and a series field II, and this motor is arranged to be connected to a suitable direct current source of supply l2 including the supply lines LI and L2 for operation in either direction bymeans of pairs of reversing or directional contactors Fa and FD having the switches i3 and H for the forward direction of motor operation and the contactors Ra and Rb having the switches ii and I6 for the reverse direction of motor operation. The current limiting means or protective resistance included in the motor armature circuit has a plurality of sections, a resistance section I! being provided for controlling'the "plugging action and the resistance sections 13 and I3 being provided for accelerating purposes. Any number of resistance sections desired may be employed. The resistor I1 is controlled by means of a "plugging contactor 23 having a normally open shunting switch 2| and a normally closed auxiliary switch 22. and the resistor sections H and I9 are respectively controlled by the ac-- celerating conta ctors 23 and 2| provided with the normally open shunting switches 2| and 21 and the normally closed auxiliary switches 2| and 2|. A line contactor 23 having a normally open main switch 3| and a normally open auxiliary switch 3| is provided for disconnect ng the motor from the source of supply when a disconnecting switch 32 is open to de-energize the winding 33 of the contactor 29. In this manner, the source of supply |2 may be suitably energized and upon closure of the disconnect switch 32 the winding 33 is energized to close the main switch 3| of the motor circuit. Thereafter, the contactor 23 is sealed closed by closure of the auxiliary switch 3| until the supply I2 is de-energized.

Each of the contactors 2|, 23 and 2| is provided respectively with the auxiliary or restraining windings r and the main or closing windings c whose efiect on the operation of the contactors is more fully described here below. The restraining coil r of the contactor 2| is connected through the normally closed auxiliary switch 22 and across the terminals of the motor armature II and the reversing switches l3, II and H so as to be energized responsively to the countervoltage of the motor. The normally closed switch 22 is operated to the open position, when the contactor 2| moves its normally open shunting switch 2| to the closed position which shunts or short-circults the "plugging resistor il to render it inactive. The closing coils c of the contactors 2|, 23 and 2| are energized in a circuit which may be traced from line Ll through the disconnect switch 32 to a suitable manual controller, such as a drum controller 3|. The drum controller 3| suplies the closing coil 0 of contactor 2| from line Ll through a conductor 3|, the coil 0 and by the conductors 3| and 31 to line L2. The closing coils c of the contactors 23 and 2| .are similarly supplied from line Ll through the drum controller 3|, a conductor 33 and through the coils c. and the conductors 3| and 31 to line L2. As shown. the drum controller 3| must be moved to its second forward or second reverse position designated respectively as F2 and R2 to energize coil 0 of the contactor 20. Similarly, the drum controller operated by contactor Fa is must be moved to positions F3 and R3 to energize coils c of .the contactors 23 and 2|.

The restraining coils r of the accelerating contsctors 23 and 2| are respectively connected in parallel with the preceding resistance sections l1 and H through'the auxiliary contacts 25 and 2|. In this manner, coil 1' of the contactor 23 is energized by the voltage drop across the plugging" resistor II, when the switch 2| is open, and is shortcircuited by closure of the switch 2 I. Coil r of the contacior 2| is first connected across both of the resistance sections I1 and I3 so as to be energized by the voltage drop thereacross and is finally short-circuited upon closure of both of the switches 2| and 2|.

The principle of operation of the several contactors 2|, 23 and 2| will be best understood by referring to Fig. 2 wherein the preferred form of operating structure is illustrated. As shown, there is provided a pivoted armature 39 gravity biased clockwise to the normal position and carrying a suitable switching structure |0. This. armature cooperates with a multi-legged frame having a lower or closing leg C provided with the closing coil, 0 and a restraining leg R provided with the restraining coil r. The upper right hand end of the armature 3| normally resides adjacent an extending portion |2 of the frame H which in eiiect forms a third leg for the'frame. Thus two complete parallel flux paths are provided. The main ilux path includes the legs C and R, the connecting portion of the frame H and the lower left hand end of the armature 33. The secondary flux path by which the armature 33 may be magnetically restrained in the normal position includes the upper part of the armature, the leg R and the portion |2 of the frame Suitable shims of nonmagnetic material are provided at point |2 to adjust the reluctance of the secondary flux path.

With the foregoing understanding of the elements and their organization in this system the operation of the system itself will readily be understood from the following description:

Referring to Fig. l, the system including the source of supply i2 is shown normally de-energized. By suitable means (not shown) the source l2 including the lines Li and L2 may be energized. Thereafter closure of the disconnect switch 32 energizes the upper segment 0 of the master switch 3|, thereby connecting the winding 33 of the line contactor 23 in acircuit traceable from line LI and the segment |3 by conductor the coil 33, and the conductors 3| and 31 to line L2. Operation of the contactor 23 closes the line switch 3| of the motor circuit and also closes the auxiliary switch 3| to complete a holding circuit for the winding 33. The drum controller is then moved from the "off" position shown to its first forward position Fl, whereupon the forward control contactors Fa and Fb including the forward switches l3 and H are opershed and the motor armature Ill and field winding ll energized with all the resistance sections l1, l3 and II in the motor circuit. The windings of the forward oontactors Fa and Fb are energised from a segment of the drum controller 3| and through a conductor and these windings to the conductors 3| and 31 and line L2. Simultaneously, an auxiliary switch |I closed to energize the lower portion of the drum controller 3| in a circuit traceable from the segment through the conductor the switch |l', and a conductor |3 to a controller segment same direction in each leg. In this manner, the flux from the leg C is denied entrance into the leg "master switch 84 through the conductor ll, the

coil c and the conductors l and 31 to line LI.

It the motor is at standstill or is operating in its proper running direction, the contactor 2. quickly picks up to close the shunting switch 2i and short-circuits the "plugging resistor i1 substantially without time delay.

Referring to Fig. 2 for purposes of illustration,

in the "plugging" contactor 2| the winding r is so wound and connected as to aslist the flux generated by the winding c to cause the armature I! to pick up whenever the coil c is energized and the motor is at standstill or running in the normal direction. This is due to the fact that under these normal starting conditions coils r and c complement each other in causing flux to flow in the main flux path including the legs R and C of the frame I. As stated above, during normal starting very little current flows through coil 1. However, coil 1 does constitute a short-circuited winding that tends to give the contactor time delayed operation in moving the armature 33 to the attracted position by opposing the building up of flux in the leg R. Quick movement of the armature I9 to the attracted position during normal operating conditions of the motor is accomplished by increasing the reluctance of the secondary magnetic circuit by a suitable thickness of nonmagnetic shims at point 42 so that the plugging" contactor 20 is substantially quick closing in spite of having a shortcircuited winding r. Upon closing of the contactor 20, its auxiliary contacts 22 open to break the circuit of the coil r and thereby enable the contactor 20 to drop out or return to the normal position quickly upon a subsequent deenergization of its closing coil c when the drum controller is moved to the of! position or through the off position to a reverse position.

Before the closure of the shunting switch II by operation of the contactor 26, the restraining coils r of the accelerating contactors 23' and 28 are energized, coil r 01' contactor 23 as a function of the voltage drop across the plugging resistor i1 and coil r of the contactor 28 as a function of the voltag drop across the "plugging resistor l1 and accelerating resistor It. In each case the contactors 23 and 26 cannot pick up due to the fact that the holding force at point 42 of the secondary flux path of the contactors, shown in Fig. 2, aids the force of gravity in holding the armature 39 in the normal position. Thus it may be said that the contactors 23 and 28 are magnetically restrained or locked open in the normal position at this time. Also, the direction of energization or polarity of these restraining coils r R and through the main flux path and so is forced to pass across the gap 42 and Join with the flux in the secondary magnetic path in magnetically restraining the armature 38 in its normal position shown.

Upon closure of the shunting switch 2i, if the drum controller 34 was previously moved to its third forward position F3 to energize the coils c oi the contactors 23 and 26, restraining coil 1' of the contactor 23 is short-circuited by closure oi the switch 2| and the contactor a then operates to the attracted position after a substantial time delay. -Time delay operation of the contactor 23 results once the restraining coil 1' of the contactor is short-circuited since the closing coil 0 is then the only coil energized. The coil 0 finally brings the flux in the leg R. of the frame I to a zero value and then builds up flux in this leg in the reverse direction, all against the inductive delaying effects of the short-circuited coil 1'. Upon operation of the contactor 23 to the attracted position, shunting switch 24 closes to short-circuit the first accelerating resistance section II a predetermined time after the closure of the plugging" contactorswitch 2i. At the same time the auxiliary switch 25 of the contactor 23 is opened to break the shortcircuit on the restraining coil 1' of this contactor and prepare the contactor for fast drop out or return to the normal position when the closing coil 0 is subsequently deenergized by moving the master switch 34 to the "OH" or reverse positions.

After time delayed closure of the shunting switch 24 by the contactor 23, obviously the first accelerating resistor i8 is rendered inactive by short-circuiting and the current in the motor circuit increased to accelerate the motor. At the same time coil 1- of the accelerating contactor 25, which coil was first energized as a function of the voltage drop across the resistance sections i! and i8 and then by the voltage drop across the resistance section it alone when the resistance section I 1 was short-circuited, is itself short circuited by the closure of the shunting switch 24. Time delayed closure of the contactor 28 then occurs a predetermined time interval after the closure of the shunting switch 24. This closes the shunting switch 21 to short-circuit the resistance section I! and accelerate the motor to full speed.

The time delay operation of the contactor 26 is substantially identical to the time delay operation of the contactor 23 described above and is of the accelerating contactors 23 and 28 is such that they oppose rather than assist the closing magnetization of the closing coils c to maintain the contactors 23 and 28 in th normal open position even when the closing coils c are energized. This is due to flux' concentration at the holding gap 42, the flux in the legs R and C of the mag-.

netic frame Ii, shown in Fig. 2, moving in the due to a flux reversal and inductive retardation of flux change in the leg R. of the contactor 26 similar to that described in connection with the accelerating contactor 23. When the second accelerating resistance section it! is short-circuited by closure of the shunting switch 21, the motor is accelerated to full speed, all of the control resistance being rendered inactive. Simultaneously with the closure of shunting switch 21 the auxiliary switch 28 opens to break the shortcircuit on the coil r of the contactor 28, thereby enabling the contactor 26 to drop out or return to its normal position quickly without substantial motor has accelerated and increased its countervoltage, it is unnecessary to delay the shortcircuiting of the first accelerating resistor I! for the longer time delay interval because the countervoltage of the motor assists in preventing the current in the motor circuit from exceeding a safe value. Even though contactor 22 operates with a shorter time delay, the contactor 26 will operate with its usual time delay since itsoperation is dependent upon the closure of the shunting switch 24. In this case, since the coils c of both the contactor 22 and the contactor 28 are energized simultaneously by moving the master switch 24 to its position F3, coil c of the contactor 26 will always be energized prior' to the closure of shunting switch 24, and the time delay operation of contactor 22 will be due to a reversal of flux in leg R as previously described.

Assuming now that the motor is operating at full speed and that it is desired to "plug the motor quickly to rest and then accelerate it in the opposite or reverse direction, this operation is accomplished by operating the master switch 24 in the reverse direction to its reverse positions RI, R2, and R3. The operator usually accomplishes this operation in a single complete movement, quickly throwing the master switch from the full speed forward position F2 to the full speed reverse position R3. As the master switch is moved from forward position F3 to forward position F2, the energizing circuits of the accelerating contactors 22 and 26 are interrupted 1 and these contactors open their switches 26 and 21 to insert the resistance sections l8 and I9 into the motor circuit without any substantial time delay. As mentioned above, the contactors 20, 23, and 26 are all relatively fast on drop out because their auxiliary switches 22, 25, and 28 were opened with the operation of these contactors to the attracted position to break the short-circuits on the restraining coils r of each of the contactors. Movement of the master switch 34 from its position F2 to its position Fl causes the energizing circuit of the coil c of the plugging contactor 22 to be interrupted, as a result of which this'contactor opens its switch 2| and inserts the plugging" resistor I1 in the motor circuit. In a like manner, as the master switch 24 is moved to its central or "oil!" position, the energizing circuit for the forward contactors Fa and F17 is interrupted and these contactors open the forward switches. and I4 to disconnect the motor from the supply source. Also, the auxiliary switch 41 of the contactor Pa opens to de-energize the lower' portion of the master switch 24.

In the first reverse position RI ol the master switch 24 an energizing circuit is completed for the operating coils of the reverse contactors Ba and Rb. This energizing circuit is readily traced from line Ll through the disconnect switch 22,

p the segments 42 and, a conductor I2. the coils of the contactors Ba and Rb, and through the conductors 26 and 21 to line L2. The contactors Ru and Rb close their switches I! and II in response to energization and connect the motor to the line for rotation in the reverse direction. An auxiliary switch 52 of the contactor R8 is also closed to energize segment 42' of the controller 24. It should here be noted that even though the direction of the current supply to the motor armature II has been reversed by opening the forward switches l2 and I4, and closing the reverse switches I! and I, the restraining coil 1' of the plugging" contactor 20 is still connected across the terminals of the motor armature II from a point on line Ll to a point between the motor armature and its field winding Thus the countervoltage of the motor causes the coil r of the contactor 20 to be energized in a direction to oppose the magnetic flux generatedby the closing coil 0. That is, the flux in the legs R and C of the contactor 22 flows in the same direction in each leg to concentrate a flow of flux through the holding gap 42.

By properly designing the'reluctances of these magnetic circuits, the contactor 20 may be made to close when the motor reaches a predetermined low speed, preferably a speed approaching substantially standstill. At the predetermined low speed, due to the fall off of the counter-voltage of the motor, the closing coil energization is sumcient relative to the energization of the restraining coil to overcome the restraining flux at the gap 42 of the contactor and the force of gravity and the contactor closes to its attracted position. In this manner, by retaining the contactor 22 and its shunting switch 2| in the normal open position until the motor slows down to reduce its countervoltage sufliciently to permit operation of the contactor and the shunting switch 2| for short-circuiting the resistor ll, th motor i protected against the abnormal high currents that result during the plugging operation.

After closure of shunting switch 2|, acceleration of the motor in the reverse direction is then had as previously described in connection with forward acceleration. If the master switch has been moved to reverse posittion R3 before the switch 2| closed, a substantial and long time delay will occur in the operation of the contactor 22 to close its shunting switch 24. On the other hand, if shunting switch 2| closes before the master switch is moved to position R3, a substantial but shorter time delay in the operation of the contactor 22 will result, contactor 28 in any case operating with the long flux reversing time delay. Finally, with the closure of all the shunting switches 2|, 24, and 21, the motor is operated at full speed in the reverse direction.

,Referring now to Fig. 3, similar elements are numbered similarly to the numbering 1' Figs. 1, the forward and reverse contactors. the supply, the motor circuit and the master switch circuits being substantially the same as those shown in Fig. 1. Fig. 3 diilers from Fig. l in the manner in which the closing coils c and restraining coils r of the contactors 2|, 22 and 22 are connected and energized. In the present instance, the coil 1 of the "plugging contactor 22 is connected across the resistance section l1 and a portion of the reslstance section ll to a point X. This circuit may .ductors 62, 26, and 21 tbline conductor 21 which connects with resistor II. The coil of the contactor 22 is connected from line Li and the master switch 26 by a conductor 66 through the coil c, the midpoint between the coil 1' and the coil 0, the conductor 6|, and through the auxiliary switch 22 and the conductor 62 to the point x on resistor i2. Coil c is also connected, as stated above, in series with coil 2 and through it and the conductor 62; 26, and 21 to line L2. Thus coils r and c are connecting in series circuit from line Ll to L2 while a separate circuit including the auxiliary switch 22 extends from a midpoint between the coils r and c to point x On resistor IO. When switch 22 is closed, coil 0 is energized as a function of the voltage drop across the motor armature Ill, fleld winding II and resistances i2 and a portion of II; and coil 5 as a function of the voltage drop across the other portion of resistance l2 and the resistance ll.

The restraining coil 1' of the contactor 22 is connected across the resistance section II t be energized responsively to the voltage drop thereacross in a circuit which may be traced from the conductor 21 connected at one side of the resistance section I! through the conductors 26 and 62, the auxiliary switch 25, a conductor 66 to a midpoint between the series connected coils c and r, through the coil 1' to theother side of the resistance section ll. The restraining coil r of the contactor 26 is connected across both of the resistance sections l1 and II to be energized responsively to the voltage drop thereacross in a circuit which may be traced from the conductor 21 through the conductors 26 and 62, the auxiliary switch 28, a conductor 66 to a midpoint between the series connected coils r and c and through the coil r to a point between the resistance sections it and II. The closing coils c of the contactors 22 and 26 are energized from line LI and the lower portion of the master switch 26 through a conductor 61, the respective coils c, the respective conductors 66 and 66, the respective auxiliary switches 22 and 22, and by the con- The description of operation of the control system illustrated in Fig. 3 proceeds from the time when the motor is energized with all the resistance sections i1, i6 and I! inserted in the motor circuit. The initial steps to achieve this condition oi operation are the same as described in connection with Fig. 1, the source of direct current supply i2 being suitably energized, the disconnect switch 22 closed to operate the line contactor 23 and close its switches 22 and 2!, and the master switch 26 being moved from its oil position shown to its first forward position Fl to energize the forward contactors Fa and Pb to close the forward switches I2 and i6 and the auxiliary switch 61. I

At the time the motor the forward switches i2 contactor 22 is energized by closing and II, the coil 1' of the is also energized, its polarity or direction of energization being complementary to that of the closing coil 0 as energized later under normal operating conditions when the master switch is moved position F2. Coil r of the contactor ously stated, is connected across the resistance section I! and a portion of the resistancesection I! so as to be energized responsively to the voltage drop across this resistance. Briefly. this circuit may'bc traced from point! on the resistor l2 through the elements 66, 22, 6|, coil 1',

67, and 26 to the conductor 21 which Joins with 15' to its second forward 26, as previthe resistor ll. Even though coil 1' is energized, it cannot by itself close the contactor 22 due to the magnetic force on the armature 22 at point 22, the flux generated by coil 1' flowing in the secondary flux path of the contactor. Movement of the master switch, 36 to its position F2 energizes closing coil c of the contactor, and if the motor is atstandstill or running forward when coil 0 is energized, the contactor 22 closes quickly substantially without time delay. This prompt operation of the contactor 20 to the attracted position is due to the complementary fluxes from the coils c and 1' which assist each other in causing flux to flow in the main flux path so that flux ,flows in opposite directions in the legs R and C of the contactor. The coil c of the contactor 20 is connected to line Li through the auxiliary switch 22 to point X on resistori8 and in eflect is connected across the armature l2;'the fleld H, the resistance i2, and a portion of the resistance II to be energized by the voltage drop across the armature fleld, and this portion of the total resistance. Upon operation of the contactor 22, the auxiliary switch 22 opens to connect coil 0 solely in series with coil 1' and across the motor circuit from line Li to line L2. In this manner, after operation of the contactor 20, full line voltage is applied to the coils c and r to increase the holding force on the contactor in the attracted position and prepare the contactor for fast dropout.

The restraining coils r of the contactors 22 and 26 are connected through their respective normally closed auxiliary switches 26 and 22 for energization as a function of the respective voltage drops across the resistor and the resistors l1 and I2. Both of these coils are energized in a direction that opposes and prevents the closure of the contactors when their closing coils c are energized. When the master switch 26 is moved to position F2 before the closure of the plugging contactor 22 and its shunting switch 2|, the accelerating contactors 22 and 26 remain open since the restraining coils r of the contactors 22 generate fluxes that oppose the fluxes of the closing coils c to cause a concentration of flux at the point 22 of each contactor to magnetically restrain the armatures 22 of the contactors in the normal position. When shunting switch 2| is closed, the coil r of the contactor 22 is shortcircuited and tends to maintain the opposing flux of the leg R and then resist the building up of flux in this leg. The closing coil 0 of the contactor 22 after a predetermined time delay overcomes the effects oi the short-circuited coil r, reverses the polarity of *the flux in leg R and closes the contactor 22 to accelerate the motor.

The auxiliary contacts 26 of contactor 22 are opened withthe operation of the contactor to connect coil c and coil 1 of the contactor in series circuit across lines LI and L2. This circuit may be traced from line Ll through the master switch through the closed switches 2| and 26, and the conductor 21 to line L2. At this time both coil 1' and cello of the contactor 22 are energized in a direction to complement each other in increasing the total number of ampere turns closing and holding the contactor 22 in the attracted position. Thus a strong closing and holding force is obtained without the need for additional turns of energizing winding on the contactor other than those already resent in the coils r and c. At this time also. since the short-circuit previously on coil r has been interrupted by the being short circuited through the switch 2| which short circuits the resistance II. In this manner, closure of the contactor 22 is always in sequence after closure of the contactor 2|. Second, coil 1 of the contactor 2! acts as a timing means to always delay the operation of the contactor for a predetermined time after the coil 1' is short circuited. Third, the coil r acts as a closing means to increase the closing and hold ing power of the contactor 22.

Immediately upon closure of the shunting switch 24 which short-circuits the first accelerating resistor l8, the coil 1' of the contactor 2 is short-circuited. Thus the closing coil c is enabled to overcome, after a predetermined time delay, the inductive effects of the short-circuited coil 1' and reverse the polarity of the flux in the leg R. The contactor 26 and its shunting switch 21 closes to short-circuit the second accelerating resistor i9 and bring the motor up to full speed. During the closing of the contactor 20, its auxiliary contact 28 opens to connect the coil 1' in series with the coil 0 across the lines LI and L2. This series circuit may be traced from line Ll through the master switch 24 and the conductor 61, the coils c and r, the closed switches 24, 2i and 30 through the conductor 11 to line L2. In this manner the coils c and r are energized to complement each other and materially increase the magnetic forces closing and holding the contactor 28 in the closed position. Also, as in the case of'the contactor 22, the contactor 28 is ready for fast drop out or quick return to its normal position upon subsequent deenergization of the coils c and 1', since the auxiliary switch 28 has opened to interrupt the short-circuit on coil r.

If the contactor and its shunting switch 2i close before the master switch 24 is moved to its position F3, the coil 1' of the contactor 22 is simply short-circuited and serves to give a shorter time delay interval after the closing coil 0 is ener-.

gized before the contactor 23 closes. In this case, the closing coil c need only overcome the inductive eifects of the short-circuited 6011 r on the building up of flux in the leg R of the contactor 23. In any case, contactor 20 operates with the same predetermined time interval after the closure of the shunting switch 2, due to the fact that its closing coil c is always energized before the shunting switch 24 closes.

When the motor is plugged or reversed by quickly moving the master switch from its forward position F3 to its reverse position R2, the contactors 20, 23 and 26 drop out quickly. At the same time reverse contactors Ra and Rb operate to close the reverse switches II and I0 and auxiliary switch 52 for reversing the energization on the motor armature HI. Thereafter, due to the counter E. M. F. of the relatively backward running motor,'the voltage on the restraining coil 1' of the plugging" contactor 2! increases over the usual standstill or forward running voltage condition because of the increased current in the motor circuit due to the addition of the countervoltage and line voltage during the plugging" operation. Increased current in the motor circuit causes an increased voltage drop across the resistor I1 and that portion of resistor ll up to point X across which coil 1' is connected. The relatively higher energization of coil 1 increases the magnetic restraining force at point 42 of the contactor 22 so that the armature 29 is more strongly restrained in the normal position during-the plugging operation than is the case during normal starting or running conditions. If the point X on resistor i8 is correctly chosen, the voltage on the closing coil c of the contactor 20 will decrease over its voltage during standstill or forward running conditions of the motor or even reverse its polarity,-since the countervoltage of the motor comes into play. This will become apparent when it is understood that the closing coil c of the contactor 2| is connected across the motor from line Ll to point X or, stating it in another way, coil c is connected across the reversing switches l2, l4, l8, and II, the motor armature ll, the field winding H, the accelerating resistor II, and a portion of the accelerating resistor ll so as to be subjected both to'the voltage drop across the resistor II and a portion of the resistor I! as well as to the countervoltage of the armature II. In this manner, by relatively increasing the energization of the coil r during plugging" to increase the magnetic restraining force on the armature II at the point 42 and by relatively decreasing or reversing the energization of the closing coil c by the countervoltage applied to the coil 0, the contactor 2! is maintained open until the motor drops to a predetermined low speed from which the motor may be safely accelerated in the reverse direction. 7

Thereafter, the contactor 20 operates to its attracted position and closes the shunting switch 2| of the resistance section II. Operation takes place because as the motor speed decreases the countervoltage decreases and causes the energization of the closing coil c to increase and the energization of the coil r to decrease. With the closure of the shunting switch 2|, time delayed operation of the contactor 22 is initiated and, after a predetermined time interval, shunting switch 24 closes to short-circuit accelerating resistance section II and accelerate the motor. Again, a predetermined time after closure of the shunting switch 24, the contactor 22 operates to close its shunting switch 21 which short-circuits the accelerating resistance section II to bring the motor to full speed. The time delayed operation of the accelerating contactors 22 and 26 for motor operation in the reverse direction is similar for all purposes to the operation described for acceleration in the forward direction of motor operation.

Adjustment of the time interval operation of the various contactors may be made by adjusting the thickness of nonmagnetic shims at the point 42, shown in Fig. 2. Alternatively, time adjustment may be provided for by increasing or decreasing the resistance of the restraining coils r of the contactors 20, 23 and 20, and my invention contemplates such adjustment.

Although in the preferred forms of my invention shown I employ the Winter type of electromagnetic contactor, it will be obvious to those skilled in the art that other types of plural winding contactors or plural winding relays for controlling the usual single winding contactors may be employed without departing from this invenoperated including a 2,275,197 tion, and therefore, I do not wish to be limited to prising a plurality of resistor sections in the motor armature circuit, a plurality of switching means each including a shunting switch for shunting said resistor sections, electromagnetic time delay means for eiiecting operation of at least one of said shunting switches a predetermined time aiter another oi said switching means has operated including a magnetic structure provided with an armature normally biased to one position and arranged to be attracted and moved against said bias to an attracted position but also arranged to be magnetically restrained in said normal position, means for magnetically energizing said magnetic structure including a main winding and an auxiliary winding, means for energizing said main winding and said auxiliary winding, said windings when simultaneously energized serving magnetically to restrain said armature in said normal position, and means controlled by operation oi said other one of said switching means winding thereby enabling said main winding to overcome the magnetic eilects of said auxiliary winding on said armature after a substantial time interval has elapsed and effect operation of said armature to said attracted position after a substantial time delay, thereby to eflect substantial time delay operation of said one shunting switch by the interaction of magnetic effects of said energized main winding and said controlled auxiliary winding.

2. A time interval motor control system comprising a plurality oi resistor sections in the motor armature circuit, a plurality of magnetically operated switching means each including a shunting switch for shunting said resistor sections, electromagnetic time delay means for effecting operation of at least one of said shunting switches a predetermined time-after another of said magnetically operated switching means has magnetic structure provided with an armature normally biased to one position and arranged to be attracted and moved against said bias to anattracted position but also arranged to be magnetically restrained in said normal position, means for energizing said magnetic structure including a main winding and an auxiliary winding, means for energizing said main winding and said auxiliary winding, said windings when simultaneously energized serving magnetically to restrain said armature in said normal position, means controlled by operation of said other one of said switching means to control said auxiliary winding thereby enabling said main winding to overcome-the magnetic eilects of said auxiliary winding on said armature after a substantial time interval has elapsed and elect operation of said armature to said attracted position after a substantial time-delay, thereby to 'eflect substantial time delay, operation of said one shunting switch solely by the interaction of magnetic effects oi said energized main winding and said controlled auxiliary winding, and means including an auxiliary switch operated responsively to the operation of said armature to said ttracted position to control said auxiliary to control said auxiliary said armature to said normal position when said winding is de-energized.

3. A time interval motor control system comprising a plurality oi resistor sections in the motor armature circuit, a plurality of magnetically operated switching means each including a shunting switch for shunting said resistor sections, electromagnetic time delay means for efiecting operation of at least one of said shunting switches a predetermined time after another oi said magnetically operated switching means has operated including a magnetic structure provided with an armature normally biased to one, position and arranged to 'be attracted and, moved against said bias to an attracted position but also arranged to be magnetically restrained in said win ng for enabling i'ast return operation of normal position, said magnetic structure having a main winding and an auxiliary winding, means for energizing said main winding and said aux iliary winding, said wndings when simultaneously energized serving magnetically to restrain said armature in said normal position, means controlled by operation of said other one of said switching means to control said auxiliary winding thereby enabling said main winding to overcome the magnetic effects of said auxiliary winding on said armature after a substantial time in terval has elapsed and effect operation of said armature to said attracted position after a substantial time delay, thereby to eilfect substantial time delay operation of said one shunting switch solely by the interaction of magnetic effects of said energized main winding and said controlled auxiliary winding, and means including an auxiliary switch operable by movement of said armature to said attracted position to connect said main winding and said auxiliary winding in series circuit whereby said windings generate a complementary magnetic flux for substantially increasing the attracting force on said armature to said attracted position.

4. A time interval motor control system comprising a plurality oi resistor sections in the motor armature circuit, a plurality of magnetically operated switching means each including a shunting switch for shunting said resistor sections, electromagnetic time delay means for effecting operation of at least one of said shunting switches a predetermined time after another 01' said magnetically operated switching means has operated including a magnetic structure provided with an armature normally biased to one position and arranged to be attracted and moved against said bias to an attracted position but also arranged to be magnetically restrained in said normal position, said magnetic structure having a main winding and an auxiliary winding, means for energizing said main winding and said auxiliary winding, said windings when simultaneously energized serving magnetically to restrain said armature in said normal position, means controlled by operation of said other one of said switching means to control said auxiliary winding thereby enabling said main winding to overcome the magnetic effects 01- said auxiliary winding on said armature after a substantial time interval has elapsed and effect operation 01 said armature to said attracted position after a substantial time delay, thereby to effect substantial time delay operation oi said one shunting switch solely by the interaction of mag ing in series circuit whereby said windings generate a'complementary magnetic flux for substantially increasing the attracting force on said armature in said attracted position, said armature thereby quickly returning to said normal position without substantial time delay when said windings are de-energized.

5. A time interval motor control system comprising a plurality of resistor sections in the motor armature circuit, a plurality of shunting switches for shunting said resistor sections, electromagnetic time delay means for eiiecting operation of at least one of said shunting switches a predetermined time aiter another one oi said switches has operated including a magnetic structure provided with a multi-legged frame and an armature normally biased to one position and arranged to be attracted and moved against said bias to an.

attracted position but also arranged to be magnetically restrained in said normal position, said magnetic structure having a main winding on one leg and an auxiliary winding on another leg, means for energizing said main winding and said auxiliary winding, said windings when both energized magnetically restraining said armature in said normal position, said auxiliary winding being short circuited by closure of said other switch whereupon said main winding overcomes the magnetic eiiects oi said auxiliary winding in said other leg by gradually reducing the iiux therein to a zero value and then building up flux of reverse polarity therein against the inductive eiiects of said short circuited auxiliary winding to eiiect operation of said armature to said attracted position after a substantial time delay, thereby to eflect time delay operation of said one switch to shunt the respective one of said resistor sections after operation oi said other switch.

6. A time intervalmotor control system comprising a plurality oi resistor sections in the motor armature circuit, switches for shunting said resistor sections, electromagnetic time delay means for effecting operation of at least one of said switches a predetermined time after another of said switches has operated including a magnetic structure having a main winding and an auxiliary winding, means connecting said auxiliary winding for energization responsive to the voltage drop oi the resistor section controlled by said other switch, means for energizing said main winding, said windings when both energized generating flux in said magnetic structure ior preventing operation thereoi and of said one switch, said auxiliary winding being short circuited by closure oi said other switch whereupon said main winding is enabled to magnetize said magnetic structure to effect operation of said one switch for shunting the respective one of *said resistor sections a substantial time interval after the operation of said other switch and due substantially solely to the interaction 01' the magnetic eiiects in said magnetic structure by said windings.

7. A time interval motor control system comprising a plurality of resistor sections in the motor armature circuit, switches for shunting said resistor sections, electromagnetic time delay means for effecting operation of at least one oi said switches a predetermined time after another oi said switches has operated including a magnetic structure having a main winding and an auxiliary winding, means connecting said auxiliary winding for energization responsive to the voltage drop of the resistor section controlled by said other switch, means for energizing said main winding, said windings when both energized generating flux in said magnetic structure ior preventing operation thereoi and of said one switch, said auxiliary winding being short circuited by closure of said other switch whereupon said main winding is enabled to magnetize said magnetic structure to eiiect operation of said one switch ior shunting the respective one oi said resistor sections a substantial time interval alter the operation of said other switch, and means including an auxiliary switch operable by said electromagnetic means for interrupting said short circuit on said auxiliary winding substantially simultaneously with the operation of said one shunting switch thereby to enable iast return operation of said electromagnetic means when said main winding is de-energized.

8. A time interval motor control system comprising a plurality oi resistor sections in the motor armature circuit, switches ior shunting said resistor sections, electromagnetic time delay means ior eiiecting operation oi at least one oi said switches a predetermined time aiterv another oi said switches has operated including a magnetic structure having a main winding and an auxiliary winding, means connecting said auxiliary winding ior energization responsive to the voltage drop of the resistor section controlled by said other switch, means for energizing said main winding, said windings when both energized generating flux in said magnetic structure for preventing operation thereof and of said one switch, said auxiliary winding being short circuited by closure oi said other switch whereupon said main winding is enabled to magnetize said magnetic structure to eiiect operation oi said one switch for shunting the respective one of said resistor sections a substantial time interval aiter the operation oi said other switch, and means including an auxiliary switch operable by said electromagnetic means substantially simultaneously with the operation of said one shunting switch ior interrupting said short circuit on said auxiliary winding and thereby connecting said auxiliary winding for energization in series circuit with said main winding whereby said windings generate a complementary magnetic flux ior substantially increasing the holding iorce oi said magnetic structure.

9. A reversing motor control system comprising reversing switch mechanism for the motor,

a current limiting device in circuit with the motor, means including an electromagnetic structure having a multi-legged frame and an armsture for controlling said current limiting device, energizing means for said electromagnetic structure including a pair oi energizing windings on respective legs of said irame, means connecting one oi said windings acres the motor terminals so as to be energized responsive to the countervoltage of the motor for magnetically restraining said armature in a predetermined position during plugging" conditions oi said motor, and means ior energizing the other of said windings in a manner whereby during normal running operation oi the motor said energizing means when energized causes substantially prompt operation of said armature to another position to render said current limiting device inactive, said windings interacting during plu88in8" conditions oi the motor to generate flux in said electromagnetic structure for magnetically restraining said armature irom operating to said other position for rendering said current limiting device inactive until the motor speed is sufliciently reduced for safe forward operation in the opposite direction.

10. A reversing motor control system comprising reversing switch mechanism for the motor, a current limiting device including a plurality of resistance sections in circuit with said motor, means including an electromagnetic structure having a multi-Iegged frame and an armature and being provided with a pair of energizing windings for controlling at least a predetermined one of said resistance sections, means connecting one of said windings across the motor terminals and a portion of said current limiting device and in a manner so as to be energized responsive to the countervoltage of the motor, and means connecting the other of said windings across another portion of said current limiting device so as to be responsive to the voltage drop therein and in a manner whereby during normal running operation oi the motor said windings cooperate when energized to operate said armature to a predetermined position for rendering said predetermined one of said resistance sections promptly inactive, said windings interacting during plugging conditions of the motor to generate flux in said electromagnetic structure for magnetically restraining said armature from ren-, dering said last mentioned resistance section inactive due to a relative decrease or reversal of current flow in said one winding and a relative increase in current flow in said other winding during said plugging conditions until the motor speed is sufiiciently reduced for safe operation in the opposite direction, said armature thereupon operating to said predetermined position for rendering said predetermined one 01 said resistance sections inactive.

11. A reversing motor control system comprising reversing switch mechanism for the motor, a current limiting device including a plurality of resistance sections in circuit with said motor, means including an electromagnetic structure having a multi-legged frame and an armature provided with a pair of energizing windings for controlling at least a predetermined one of said resistance sections, means connecting one of said windings across the motor terminals and a portion ofsaid current limiting device and in a manner so as to be energized responsive to the countervoltage of the motor, means connecting the other of said windings across another portion of said current limiting device so as to be responsive to the voltage drop therein and in a manner whereby during normal running operation of the motor said windingscooperate when energized to operate said armature to a predetermined position for rendering said predetermined one of said resistance sections promptly inactive, said windings interacting during plugging" conditions of the motor to generate flux in said electromagnetic structure for magnetically restraining said armature from rendering said last mentioned resistance section inactive due to a relative decrease or reversal of current flow in said one winding and a relative increase in current flow in said other winding during said.

main winding and an auxiliary winding, means connecting each of said auxiliary windings across the preceding one of said resistors to be energized responsively to the voltage drop thereacross, means for energizing said main windings each in a direction to oppose the flux generated by said auxiliary windings in a portion of said frames, said windings when all energized generating fluxes in said frames that magnetically restrain said armatures in the normal position, said auxiliary windings being short circuited by the closure of the one of said switches controlling the preceding one of said resistors, and means for closing a first of said switches whereby the remaining switches operate in a definite succession each a substantial time interval after the operation of the preceding switch of the succession and due solely to a reversal of flux in said portions of said frames under the inductive effects of said short-circuited windings.

13. A reversing motor control system comprising a reversing switch mechanism, currentlimiting means in the motor circuit; said currentlimiting means having a plugging section and an accelerating section, means including a "plugging switch for rendering said plugging section inactive during normal running operation of said motor and formaintaining said plugging" section active during plugging conditions of the motor until the motor speed is sufiiciently reduced for safe operation in the opposite direction, means including a switch for controlling said accelerating section of said current limiting means, electromagnetic time delay means for ei-,

fecting operation of said switch a predetermined 'time after said plugging" switch has operated to render said plugging section inactive including 'a magnetic structure provided with an armature normally biased to one position and arranged to be attracted and moved against said plugging conditions until the motor speed is I sufliciently reduced for safe operation in the opposite direction, said armature thereupon operating to said predetermined position for rendering said predetermined one of said resistance sections inactive, and means including an auxiliary switch controlled by said armature for connectbias to an attracted position but also arranged to be magnetically restrained in the normal posi-- tion, means for magnetically energizing said magnetic structure including a main winding and an auxiliary winding, means for energizing said main winding and said auxiliary winding, said windings when simultaneously energized serving magnetically to restrain said armature in said normal position, and means controlled by operation of said plugging switch to controlsaid auxiliary winding, thereby enabling said main winding to overcome the magnetic effects of said auxiliary winding on said armature after a substantial time interval has elapsed and effect operation of said armature to said attracted position after a substantial time delay, thereby to effect substantial time delay operation of said accelerating switch by the interaction of magnetic eifects of said energized main winding and said controlled auxiliary winding.

BENJAMIN W. JONES.

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