US2247506A

US2247506A - Control system for electric translating devices

Info

Publication number: US2247506A
Application number: US252000A
Authority: US
Inventors: William J Kutcher; John D Leitch
Original assignee: Electric Controller and Manufacturing Co LLC
Current assignee: Electric Controller and Manufacturing Co LLC
Priority date: 1939-01-20
Filing date: 1939-01-20
Publication date: 1941-07-01
Anticipated expiration: 1958-07-01

Description

y 1941- w. J. KUTCHER 2.247.506

CONTROL SYSTEM FOR ELECTRIC 'I'RANSLATING DEVICES Filed Jan. 20, 1939 2 Sheets-Sheet 1 L|--7 M L2? u 4 m: c L3 T 1 1 M 28% INVENTORS f 2 WILLIAM J. KUTCHER &

JOHN D.LE|TCH THEIR ATTORNEY.

July 1, 1941. w. J. KUTCHER EIAL CONTROL SYSTEM FOR ELECTRIC TRANSLATING DEVICES Filed Jan. 20, 1939 2 Sheets-Sheet 2 REV 432! m ATTORNEY.

Patented Jul 1, 1941 CONTROL SYSTEM FOR EIEOTBIC TRANS- LATING DEVICES William J. Kutcher, East Cleveland, Ohio, and John D. Leitch, Manhalset, N. Y., asslgnorl to The Electric Controller & Manufacturing Company, Cleveland, Ohio. a corporation of Ohio Application January 20, 1939, Serial No. 252,060

18 Claims.

This invention relates to a control system for an electric translating device, the illustrative example hereinafter disclosed being an improved control system for automatically short circuiting the starting impedance in a motor circuit during acceleration of the motor and introducing a time delay between the closing of successive starting switches, the extent of the time delay intervals being influenced by the load on the motor during acceleration. Embodiments of the invention in connection with other electric translating devices are apparent from the illustrative example and will not be specifically described.

Heretofore, in the control of translating devices by timing circuits, timing circuits similar to that hereinafter described have been provided, but the prior circuits have been operatively connected to the translating device in a manner such that the timing intervals thereof were in indirect relation to the magnitude of that electrical condition of the translating device on which the timing circuit depended for its energization. Such a timing circuit, so related, is set forth and described in United States Letters Patent No. 2,024,019, issued on December 10, 1935, to David C. Wright. The timing circuit was employed in the Wright patent for a resistance welder and provided a time interval which was indirectly related to the magnitude of the current flowing through the welding electrodes. The timing circuit employed in the present invention, in many respects, is similar to that of the Wright patent, but is connected differently to the translating device so as to provide timin intervals which are directly related to the amount of current flowing to an electric translating device, or, in the illustrative example, which are in direct relation to the load on the motor.

Various well known means have heretofore been used for automatically and successively short circuiting portions of the starting resistance in a motor circuit so that the starting current of the motor would not exceed certain predetermined values. Those systems which provide a definite time delay between the successive closing of the resistance shunting switches have, among other disadvantages, the disadvantage that, if the time delay periods are adjusted for an intermediate load, the periods are too long for lighter loads and too short for heavier loads. As one example,

that often during cold weather the acceleration contactors close too quickly if the acceleration time is definitely predetermined. As another example, a motor may be used to drive a wide range of loads varying from twice full load to extremely light loads. If the acceleration time is set so that excessive current peaks are prevented from occurring under heavy loads, then, on light loads, the motor is accelerated at a much lower rate than is economically or otherwise desirable.

In order to overcome such disadvantages in the case of direct current motors, systems have been developed for automatically excluding starting resistance at a rate dependent upon the electrical condition of a motor circuit during the accelerating period. Two of the more common of such systems are known as counter electromotive force acceleration and current limit acceleration. One of the disadvantages common to both of these systems is that they cannot start or accelerate a stalled or too heavily loaded motor since, under such conditions, the counter electromotive force either does not exist or does not increase. In the case of current limit acceleration, the current does not decrease sufficiently to cause relay operation unless the motor rotates at an appreciable speed. Various means have been used to eliminate these defects, and such improved systems are known as combined time limit and current limit. All of such improved systems, however, are primarily adapted to determine only short time intervals, generally are not readily adjustable for difierent load conditions, and are not adaptable for use with alternating current motors.

Again, one or two minutes may be required to bring an alternating current or direct current motor driving a heavy inertia load up to full speed. This necessitates either the use of many acceleration steps, each having a relatively short time interval, or the use of fewer steps, each having a longer time interval. The use of fewer steps of longer duration is the more economical of the two, but heretofore has not been used to as great an extent as desired because of the difliculty of providing a satisfactory means to measure the long time intervals.

The present invention is an automatic motor control system which is capable of causing acceleration at a rate dependent upon the motor load during the accelerating period, and capable of causing the starting resistance to be shunted even though the motor is stalled or the amount of motor current is excessive. The present system also is operative in-a manner such that the duration of time which may be Obtained between the successive operations of the accelerating switches is practically unlimited and the time delay intervals may be readily adjusted over a wide range, whereby the system is adaptable for use with motors driving any type of load and with motors which inherently require a long acceleration period.

For purposes of illustration, the invention is disclosed in detail in the drawings and description hereof as applied to alternating current motors, but the invention is not to be limited to the exemplary embodiments.

The invention, in one illustrative embodiment, includes a. transformer which supplies alternating current to a rectifier, and the direct current output of the rectifier charges a condenser to a predetermined voltage. Upon the attainment of the predetermined voltage, the condenser discharges through a discharge device and operating winding of a relay which is thereupon operated to control an accelerating contactor. In order to modify the charging time of the condenser in accordance with the load on the motor, the primary of the transformer includes two windings. One of these windings is a potential winding connected across two of the supply conductors leading to the motor, and the other is a current winding connected in series with one of the supply conductors. The flux set up by the current winding is opposed to that set up by the potential winding so that the resulting flux, and consequently the secondary voltage of the transformer, are reduced in accordance with the electrical condition of the motor circuit, for example, in inverse relation to the amount of motor current. Since the charging time of the condenser is inversely dependent upon the resulting flux, any reduction in the resulting flux increases the condenser charging time and consequently provides a longer time interval before the relay operates.

Another illustrative embodiment of the invention is one which effects control of alternating current motors wherein a separate current transformer is utilized instead of the current winding of the single transformer. In such instance, the current transformer has its primary winding in series with a conductor leading to the motor, and the secondary voltage of the separate current transformer is rectified and the direct current output from the rectifier is connected in opposition to the rectified output from a potential transformer which is connected across the supply conductors. The reduced direct current voltage resulting from the opposition of the voltages charges a condenser to a predetermined potential, and necessarily the charging interval is greater than would be required were the potential transformer voltage or current transformer voltage used alone. Due to the opposed voltages, therefore, the time interval becomes directly related to the amount of current flowing in the primary winding of the current transformer. Thus, the condenser absorbs energy in an inverse relation to the motor current, and, consequently, the heavier the load on the motor, the greater the motor current, the less the condenser charging voltage, and the longer the acceleration time.

An object of the present invention is to provide a system for controlling the operation of an electric translating device in accordance with the differential between two similar, but relatively varying, electrical conditions of different circuits, one of which is associated with the device and in one of which the said condition is continuously predominant over the said similar condition of the other.

One of the principal objects of the present invention is to provide a system for controlling the operation of an electric translating device by an operative relation between a condenser and the current condition of the device such that the charging rate of the condenser is inversely related to the current condition of the device.

Another object is to provide a control system for an electric motor in which a means responsive to a predetermined potential is connected across an electric energy absorbing device so as to change the condition of motor operation in inverse relation to the load on the motor.

An important object of the invention is to provide a system of motor acceleration for a motor in which a time delay device is provided which may be adjusted to provide a suitable acceleration of the motor under normal working conditions and which, without change or adjustment, accelerates the motor properly under different or changing conditions or under abnormal working conditions.

A correlative object of the present invention is to provide a system of motor control which combines all of the advantages of the definite time delay systems and the current limit systems and which can be adjusted readily to provide a wide range of acceleration periods.

Another object is to provide a motor control system incorporating a single time delay device which controls a plurality of accelerating switches in response to variations in the value of current in a motor circuit, the time delay intervals betwen operation of the switches being longer when the current value is large and being shorter when the current value is small.

The long time intervals obtainable by this invention makes it especially suitable for the control of primary resistance or reactor type starters, and of reduced voltage starters for alternating current motors. Synchronous motors are generally brought up to speed as induction motors, and, as the speed approaches synchronism, full voltage is applied to the armature winding and direct current is applied to the field winding. Heretofore, it has been necessary to use a relay having a definite time delay in order to obtain the long time interval necessary for a synchronous motor to reach its synchronous speed. Relays responsive to the electrical condition of the direct current field winding have been used, but these relays are adjusted so that they will not respond unless the motor reaches a predetermined speed. If the motor is overloaded, it may still be desirable to force it to operate at synchronous speed by energizing the direct current field, although the induction motor torque may not be sufficient to increase the speed to a point where the pre-set frequency relay responds. By the use of the present invention, a long time delay interval may be obtained between the closing of the alternating current contactor and the direct current contactor, which time interval is dependent, not upon the attainment of a predetermined speed. but upon the amount of current flowing in the primary circuit during that interval regardless of motor speed.

It is, therefore, a further object of the present invention to provide a control system suitable for controlling the switching operation of a synchronous motor after a time interval dependent upon the amount of current flowing in a circuit of the motor regardless of whether or not the motor has reached a predetermined speed.

Another object is to provide a readily adjustable time delay means having no moving parts, other than the movable contacts of a small relay, for controlling the acceleration of a motor in accordance with the value of current flowing to the motor.

Other objects and advantages will become apparent from the following specification, wherein reference is made to the drawings, in which;

Fig. 1 is a simplified wiring diagram illustrating the time delay circuit and a connection between the circuit and an induction motor;

Fig. 2 is a simplified wiring diagram illustrating the time delay circuit and another connection between it and an induction motor; and

Fig. 3 is a complete wiring diagram of the control system of Fig. 1.

In the form of our invention illustrated in Fig. 1, three supply conductors, LI, L2 and L3, connect an electric translating device, shown as an induction motor M, to a source of polyphase power (not shown). The motor M, as illustrated, is a wound rotor induction motor having the terminals of its rotor winding connected to sliprlngs, which, in turn, may be connected to any type oi secondary impedance controller. The control circuit includes a transformer 3 having a primary potential winding 2 which is connected in series with a resistor 26 across any two of the conductors LI, L2 and L3, depending upon the positions of the

adjustable connectors

21 and 23. The transformer 3 has a primary current winding I which is arranged to be connected in series with one or the other of the conductors L2 or L3, depending upon the position of a knife switch 8. The transformer 3 supplies alternating current to a full wave rectifier 9 through a secondary winding 5. The rectifler 9 may be of any suitable type but preferably includes a rectifying device 4 and a filter condenser B. The direct current output of the rectiher 9 is supplied to a stabilizing resistor I. Connected across the resistor I is a time delay circuit 35.

The time delay circuit 35 depends for its operation upon the time required to charge a condenser through a resistor and includes an adjustable resistor H, the contacts 3Ia of a relay 3 I, and a timing condenser 30 connected in series between the two terminals of the time delay circult, and an operating winding 3Iw for the relay 3i connected in series with a discharge device 32, the winding 3Iw and device 32 being connected in parallel with the condenser 30. By adjustment of the resistor II, a wide range of selected charging times for the condenser 30 may be readily obtained.

The discharge device 32 may be of any suitable type, but preferably has cold electrodes arranged in an attenuated gaseous atmosphere of neon, helium, argon, or the like. The contacts 3Ib of the relay 3|, when closed, provide a discharge path for the condenser 30 through the operating winding 3Iw to completely discharge the condenser 30. An adjustable resistor 33 may be included in the discharge circuit to lengthen the discharge time and consequently the time during which the relay 3| is energized. Another pair of contacts Me of the relay II is provided to control the acceleration contactors for th motorM in a manner to be described.

Any transformer connected to a source of constant potential ordinarily resists any tendency toward flux diminution and tends to make the resultant flux substantially constant. Therefore, any increase in the opposition flux produced by winding I tends to produce more flux in the winding 2. Assuming no resistor 2! is included, the resultant increased flux of winding 2 is accompanied by an increase in current in the circuit which includes the winding 2. However, because the resistor 28 is included in the circuit of the winding 2, the increased current produced as above described results in a decrease in voltage across the winding 2, and consequently the flux produced by the winding 2 remains substantially constant. As a result, the differential between the fluxes produced by the two windings varies inversely to the increase of the flux produced by the winding I. If the windings I and 2 are wound so that the flux set up by the winding 2 is always greater than and opposed by the flux set, up by the winding I, the resulting flux will cause a voltage across the winding -5 which is directly related to the differential of the two fluxes, and consequently inversely related to the amount 01 flux produced by the winding I, to the amount of current flowing to the motor, and to the load on the motor. If the current is high, the opposition flux due to the winding I is greater and the voltage across the secondary winding 5 is correspondingly reduced. The lower the voltage across the winding 5, the lower the direct current voltage output of the rectifier 3, and the longer the charging time of the condenser 30.

Assuming that the windings I and 2 are so wound in relation to the currents flowing therein that the fluxes oppose each other, it is obvious that the currents in the two windings must be substantially in phase in order to obtain the desired voltage reduction in the rectifier output. The proper phase relationship may be obtained by means of the knife switch 8, which has a pair of blades 8a and separate blades 8b and 8c. The blades are preferably arranged to be operated simultaneously as shown in Fig. 3.

When the knife switch Ii is in one position, the blades 8a connect the primary winding I in series with the conductor L3 and the blade completes the circuit from the conductor L2 to the motor M. When the knife switch 8 is in the other position, the blades 8a connect the primary winding I in series with the conductor L2 and the blade 3b completes the circuit from the conductor L3 to the motor M.

By merely properly positioning the knife switch 8, it; is possible to select a motor current which is within at least 60 degrees of being in phase with the voltage across the conductors to which the potential winding is connected. Further phase adjustments can be made by altering the connections to the potential winding 2 by means oi. the adjustable connectors 21 and 2B.

The system, as illustrated in Fig. 2, eliminates the necessity of obtaining proper phase relationship by the use of two separate transformers.

In Fig. 2, a current transformer II) has a primary winding II connected in series with one of the conductors, shown as conductor L3, of the three supply conductors Ll, L2 and L3 leading from a source of polyphase power (not shown) to the induction motor M. The transformer II has a secondary winding I2 across which is connected a rectifier I3, including a full wave rectifying device H, the output terminals of the rectifier i! being connected to a stabilizing resistor i5. Across any two of the supply conductors, shown as conductors L2 and L3, is connected a primary winding 2| of a potential transformer 20 having a secondary winding 22. Across the secondary winding 22 is connected a full wave rectifier 23 including a rectifying device 2|, the output terminals of the rectifier 23 being connected to a stabilizing resistor 25. A filter condenser lil is connected in parallel with the resistor I and a filter condenser 25 is connected in parallel with the resistor 25 for smoothing out the output voltages of the rectifiers i3 and 23 respectively.

One terminal of each of the resistors i5 and 25 are connected together by means of a conductor IS. The other terminal of the resistor 25 is connected to one terminal of the time delay circuit 35, described in connection with Fig. 1. Since the time delay circuit is essentially the same in all the illustrative embodiments, like elements thereof are referred to by like numerals throughout all figures and descriptions of the present specification. The other terminal of the time delay circuit 35 is connected to a point on the resistor i5 through an adjustable connector l9.

It is apparent that any alternating voltage between the conductors L2 and L3 is transformed and rectified by means of the transformer 20 and the rectifier 23 and causes a direct current to flow through the resistor 25. This current causes a potential drop across the resistor 25 which charges the condenser 30 through the closed circuit including the resistor l'l, portion n of the resistor i5, and the conductor l6. After a definite time delay period, the potential across the condenser 30 will have reached a magnitude such that the discharge device 32 breaks down and permits current to fiow through the winding 38w of the relay 3|. The relay 3i, in response to energization of its winding 3Iw, closes its contacts Me to control the motor, closes its contacts Jib to completely discharge the condenser 30, and opens its contacts 3m to disconnect the coil Slw and the condenser 30 from the charging circuit.

The time delay interval obtainable by a circuit using the transformer 20 alone is, however, accurately and definitely predetermined in extent. In order to change the time delay interval so that it will be longer if the motor is heavily loaded and shorter if the motor is lightly loaded, the current transformer Ill and the rectifier i3 have been provided. If current fiows through the primary winding II, a voltage is present across the secondary winding l2 and becomes rectified by the full wave rectifier l3, causing a direct current to flow through the resistor i5. This current causes a potential drop across the resistor i5 in opposition to the potential drop across the resistor 25, that is, the voltage across the resistor 25 tends to make the right-hand plate of the condenser 3|) negative, whereas the voltage across the resistor l5 tends to make the left-hand plate of the condenser 30 negative. The difference in value between these two potential drops is the resultant voltage effective for charging the condenser 30. Since the resultant voltage is less than the voltage drop across the resistor 25 alone, a longer time is required to charge the condenser to any particular value, the additional time being directly dependent upon the amount of current flowing to the motor M or the particular translating device being controlled, and, in the case of a motor, therefore, being inversely related to the load.

A current transformer having its primary winding in series with a motor armature produces a voltage across its secondary winding which is proportional to the current in the armature circuit, provided that the current transformer is designed to maintain its transformation ratio constant over a necessary range. As is well known, the starting current taken by any particular electric motor varies to a great extent. From the characteristics of a current transformer, it is known that the secondary ampere turns are approximately equal to the primary ampere turns and that the voltage across the secondary is equal to the product of the secondary current and the resistance connected across its terminals.

The voltage drop across the resistor 25 must always be greater than the opposition voltage drop across the effective portion of the resistor i5 so that the resultant voltage charges the condenser at a rate which is in an inverse relation to the motor current, and eventually to a value such that the condenser will discharge through the device 32. If the potential drops across the two resistors were equal, the condenser would not charge, and if the voltage drop of the resistor l5 were greater than the voltage drop of the resistor 25, the condenser would charge at a rate directly related to the motor current, and the time of charging would be in an inverse relation instead of in a direct relation to the motor current. It is desired to always charge the condenser at a rate which is inversely related to the electrical condition of a motor circuit so that its time of charging is directly related to such electrical condition.

In case the motor M should be stalled and thus be taking a high current, it is possible that the voltage across the resistor i5 would be as great as or greater than the voltage across the resistor 25. To prevent such a condition from occurring, the current transformer i0 is preferably designed with an iron core of such a cross section that it can become saturated when a current of comparatively low value is flowing through the winding ii. Thus, by proper design of the current transformer ill, the motor M can be started and properly accelerated eventually even though it is stalled so as not to start on the first few steps of control, or for other reasons requires excessive starting currents.

Referring now to Fig. 3, the wound rotor induction motor M is arranged to be energized through the three conductors Ll, L2 and L3, leading from a source of power (not shown). interposed in the conductors LI and L2 is an electromagnetic contactor 40 having an operating winding 40w, interposed in the conductors L2 and L3 is an electromagnetic contactor ll having an operating winding liw and normally-open auxiliary contacts Ma, and interposed in the conductors L2 and L3 is an electromagnetic contactor 42 having an operating winding 42w and auxiliary contacts 420.. The contactor H is arranged to connect the conductors L2 and L3 to the motor M so that the motor operates in the forward direction, whereas the contactor 42 is arranged to connect the conductors L2 and L3 to the motor M so that the motor M rotates in the reverse direction.

The secondary winding of the motor M is connected to a suitable current limiting device, illustrated as a star-connected resistance bank having three branches, RI, R2 and R3. Each of the three resistance branches RI, R2 and R3 comprises four resistance sections, a, b, c and d, connected in series, electromagnetic contactors 5D to 53 inclusive are associated with the resistance bank. The electromagnetic contactor 5|) is operative, when closed, to short circuit the section a, the electromagnetic contactor 5| is operative, when closed, to short circuit the sections a and b, the electromagnetic contactor 52 is operative, when closed, to short circuit the sections a, b and c, and the electromagnetic contactor 53 is operafive, when closed, to short circuit the sections a, b, c and d. Operating windings 50w, 5lw, 52w and 53w are associated with the contactors 50 to 53 inclusive, respectively. The contactors 5| and 52 have normally-open auxiliary contacts 5 lb and 521) respectively and normally-closed auxiliary contacts 5|a and 52a respectively. The contactor 50 has a normally-open auxiliary contact 50a.

The resistance section a of the resistors RI R2 and R3 is the plugging section, and its associated short circuiting contactor 50 is under the control of a relay 8| having a winding Blw connected in series with a condenser 60 across the resistance section a. This type of plugging relay is more fully described in the co-pending application of John D. Leitch which resulted in Patent No. 2,165,491 on July 11, 1939.

Electromagnetic relays

54, 55 and 56 are provided to control the operation of the contactors 5|, 52 and 53 respectively and have operating windings 54w. 55w and 56w respectively. Each of the

relays

54, 55 and 56 has two normally-open contacts denoted by the corresponding numerals with subscripts a and b respectively and one normally-closed contact denoted by thacorresponding numerals with the subscript c.

The operation of the

relays

54, 55 and 56 is automatically controlled by the relay 3|, the winding 3|w of which is connected in parallel with the condenser 30 of the timing circuit 35, which is the same timing circuit as the timing circuit designated in Figs. 1 and 2 by the numeral 35.

In Fig. 3 the timing circuit 35 has been shown as connected to the conductors leading to the motor M in the manner disclosed in Fig. 1, it being understood that the connections of Fig. 2 could be used as well.

The primary winding I of the transformer 3 is arranged to be connected in series with either one of the conductors L2 or L3, depending upon the position of the knife switch 8. When in the lower closed position, the blades 8a of the knife switch 6 connect the winding l in series with the conductor L3 and the blade 80 completes the circuit for the conductor L2. When in the upper closed position the blades Ba connect the winding I in series with the conductor L2 and the circuit to conductor L3 is completed through the blade 81).

For clearness in illustration, the

connectors

21 and 28, shown in Fig. l, have been omitted from Fig. 3, since their use is not essential to the operation and, if desired, they could be interposed in the conductors 9|) and 93 in a manner which is disclosed in Fig. 1.

To control manually the direction of rotation h and speed of the motor M, a master switch 60 is provided. The master switch 60 includes segments G2 to 61 inclusive for controlling the acceleration in the forward direction, and segments 12 to 11 inclusive for controlling the acceleration in the reverse direction. A segment BI is arranged for selectively connecting the various segments 62 to 61 inclusive and 12 to 11 inclusive to the source of power. The circuit terminals 1| are relatively movable to any of the forward or reverse positions to complete various circuits from the source of power to the relays and contactors.

The operation of the controller diagrammatically shown in Fig. 3 is as follows:

Assume that power is supplied to the conductors Ll, L2, and L3, that the knife switch 8 is in a closed position, and that the master switch 6|] is moved quickly from the ofi position to any position in the forward direction. In such case, the circuits to the operating windings of the contactors 46 and 4| are completed without any time delay. The circuit to the winding 4010 is from the conductor L3 through a conductor 90, one oi! the circuit terminals H the segment 6| oi the master switch 60, the segment 62, another of the circuit terminals H, a conductor 9|, the winding 40w, and the

conductors

92 and 93 to the conductor L2. The circuit to the winding 4 lw is completed from the energized segment 6| to the segment 63, a conductor 94, the winding M11), and the

conductors

95 and 93 to the conductor L2.

The contactors 4|) and 4| close their main contacts in response to the energization of their operating windings to connect the primary winding of the motor M to the source of power. Immediately upon the closure of the contactor 4|, the contactor 50 closes to short circuit the plugging resistance section a of the resistor banks RI, R2 and R3. The circuit to the operating winding 50w of the contactor 50 is from the energized segment 6| to the segment 64, through a conductor 96, the now closed auxiliary contacts 4|a of the contactor 4|, a conductor 91, the normallyclosed contacts Bla of the plugging relay 8|, the winding 50w, and conductors 99 and 33 to the conductor L2. The contacts of the plugging relay Bl are not opened at this time because the resonant circuit including the winding 8|w and the condenser is adapted to cause energization of'the relay 8| only when a current of substantially twice line frequency flows in the secondary winding of the motor M.

The closure oi! the contactor 4| also completes a circuit to the primary potential winding 2 01 the transformer 3 which is from the energized conductor 91 through a conductor I01, the normally closed contacts 54c of the relay 54, a conductor llll, the primary winding 2, the resistor 26, and the conductor 93 to the conductor L2.

Assuming that the position to which the master switch was moved initially was to the fourth position in the forward direction, a parallel circuit is completed to the primary potential winding 2 of the transformer 3. This circuit is from the energized segment 6| to the segment 65, through conductors I00 and 44, the normallyclosed contacts 550 of the relay 55, the conductors I02 and IN, the primary winding 2, the resistor 26 and the conductor 33 to the conductor L2. In this fourth position of the master switch, a further parallel circuit is completed likewise to the primary winding 2 through the segment 66, a conductor III), the normally-closed contacts 560 of the relay 56 and the conductor 13 to the conductor |0| and thence through the winding 2, the resistor 26, and the conductor 93 to the conductor L2.

The primary series winding I of the transformer 3 is energized by virtue of its being connected in series with the conductor L3 or L2, de-

pending upon the position of the knife switch 3. with both the primary windings I and 2 energized, the timing circuit 33 is ready i'or operation. The circuit to the condenser 39 is completed through the now closed contacts 39:: of the plugging contactor III and the conductors 33. Consequently, the condenser 39 begins to charge, and continues to do so by virtue of a voltage created by the differential in the opposed fluxes set up by the currents in the winding I and 2, as more fully described in connection with Fig. 1. Therefore, the condenser charges in a time interval which depends upon the adjustment of the resistor I1 and which is directly related to the amount of current flowing in the conductors L2 or L3. The higher the motor current, the slower the charging rate, and the longer the charging time. The condenser is therefore charged at a rate inversely in accordance with the electrical condition of a motor circuit.

The condenser 39 continues to charge until it is charged to a predetermined potential, upon the attainment of which the condenser discharges through the winding 3Iw and the device 32. The relay 3| operates in response to the energization of its operating winding 3Iw and closes its contacts 3Ic. The closure of the contacts 3Ic sets up a circuit extending from the energized conductor 99. through a conductor I, the contacts 3Ic, a conductor I95, the normally-closed contacts Bio of the acceleration contactor II, a conductor I99, the winding 94w the relay 94, and the conductors 99 and 93 to the conductor L2. In response to the energization of its operating winding 53w, the relay 53 closes its contacts a and 59b and opens its contacts 540.

The movement of the relay 3I to the energized position also causes closure of contacts 3 lb which permits the complete discharge oi the condenser 30 through a circuit such as illustrated and which includes the resistor 33 and the winding 3Iw. The time of discharge. and consequently the time during which the relay 3| is energized, may be predetermined by adjustment of the resistor 33. As soon as the condenser 39 is completely discharged, the relay winding 3Iw is deenergized and the relay 3| returns to its normal position. The relay 54 remains energized to maintain the circuit to the winding Blw of the contactor 5|, however, since the contacts Ila, when closed, complete a holding circuit for the winding 54w, which circuit extends from the now energized conductor 91 through the conductor II", the contacts 53a, the winding w, and the conductors 99 and 93 to the conductor L2. The closure of the contacts 53b completes a circuit from the now energized conductor I 99, through the contacts 54b, a conductor I99, the operating winding 9lw of the contactor BI, and the conductors 99 and 93 to the conductor L2.

The contactor Si in response to energization of its operating winding Blw closes its main contacts to short circuit the resistance sections a and b causing an increase in torque of the motor M or a change in the operation of the particular translating device under control. If the motor M is free to rotate, the short circulting of the resistance sections a and b results in an increase in speed. Opening .of the normally-closed contacts 540 disconnects one circuit to the transformer winding 2 but the winding 2 remains energized through the normally-closed contacts 950 and Site. If the master switch 99 had been moved only to the first position, the circuits through the normally-closed contacts 550 and 580 would not be completed through the segments 93 and 99 of the master switch 99, and further shunting of the resistance sections would be arrested.

By adjustment of the resistor 33 or by proper selection of the resistance of the winding 3Iw. the contacts 3 le are caused to Open during the interval between the closing of the contacts 54a of the relay 54 and the contacts 3 lb of the contactor II. Upon deenergization of the relay 3 I, the contacts 3Ia close to start the second time interval, and its duration is determined by the potential applied to the condenser 39, this potential being derived from the opposed fluxes as in the preceding step above described. At the expiration of the second time interval, the relay 3I again operates and this time causes energization of the winding 3510 of the relay 93.

The circuit to the winding 55w is from the energized conductor I99, through the contacts Me, the conductor I99, the normally-closed contacts 92a 01 the contactor 52, the now closed contacts lb of the contactor il, a conductor I99, the winding 55w, and the conductors 99 and 93 to the conductor L2. The closure of the contacts "a in response to the energization of the winding 33w completes a holding circuit for the winding to so that its energization is not dependent upon the subsequent deenergization of the relay 3|. This holding circuit extends from the energized conductor I99 through the conductor II. the contacts 53a, the winding 55w, and the conductors 99 and 93 to the conductor L2. Closure of the contacts 551: completes a circuit from the energized segment 9|, through the segment 69, the conductor II9, the contacts 55b, a conductor III, the winding 5210 of the contactor 92. and the conductors 99 and 93 to the conductor L2. The contactor 52 in response to energization of its operating winding 92w closes its main contacts to short circuit the resistance sections a, b and c to permit a further increase in motor torque.

Opening of the normally closed contacts We of the relay 55 disconnects one of the remaining parallel circuits to the primary winding 2, but the primary winding 2 remains energized through the normally closed contacts 580. since the master switch 69 is in the fourth position. Shortly after the contacts 55a. close and shortly before the contacts 52b close, the relay 3| returns to its normal position and starts another timing interval.

At the expiration of this new timing interval, the relay 3| again closes the contacts 3lc, which this time complete a circuit from the conductor I99 to the conductor I95, the now closed contacts 52b of the contactor 52, a conductor "2, the winding 5910 of the relay 55, and the conductors 99 and 93 to the conductor L2. In response to energization of the operating winding 58w, the relay 53 closes its contacts 56a to complete a holding circuit for the winding 56w and also closes its contacts 96b to complete a circuit from the energized segment GI through the segment 91, a conductor I I3, the now closed contacts 5612, a conductor H4. the winding 53w of the contactor 53, and the conductors 99 and 93 to the conductor L2. The holding circuit for the winding 59w is from the energized conductor IIIl through the contacts 530, the winding 58w, and the conductors 99 and 93 to the conductor L2.

The contactor 53 in response to energization of its operating winding 53w closesits contacts to short circuit all of the resistance sections a, b, c and d to permit the motor M to operate at its normal speed or to exert its normal torque. The

primary winding 2 is now disconnected from the source because the contacts 54c. 55c and lie are opened, and consequently the timing circuit no longer operates. Thereafter, ii the current in the winding t should be enough to cause charging of the condenser 30 to its discharge value, no circuits would be changed upon operation of the relay 3|.

If it is now desired to stop or reverse the motor M, the master switch 60 may be moved from the fourth position in the forward direction to any position in the reverse direction. All of the contactors and relays become deenergized as the master switch 60 is moved through the off position, but the contactors l and 4! become energized to supply reverse power to the motor I! as soon as the master switch Bil is moved to one of the reverse positions. At the instant that reverse power is applied. the frequency of the current flowing in the resistance section a of the resistance branch RI becomes approximately equal to twice the frequency of the source oi. supply. As a result, the tuned circuit including the condenser 80 and the operating winding 8Iw of the plugging relay 8| becomes energized and causes opening of the contacts Mo to prevent the energization of the operating winding 50w of the contactor 50. The contactor 50 is thus held in open position to prevent the starting of the timing period for the acceleration contactors 5|, 52 and 53 and also to prevent the short circuitin of the resistance section a during the time that the motor is decelerating from a forward running condition to a stand-still condition. As the motor speed approaches zero, the frequency of the current in the resistance section 11 decreases to the frequency of the source of supply. At this time, the relay winding 8 I10 becomes deenergized and permits the reclosure of the contacts 8 la.

As soon as the contacts Ola are closed, the winding 50w becomes energized over a circuit previously described in connection with the forward direction of operation except that the contacts 42a instead of the contacts Ma complete the circuit. The contactor 50 consequently closes to short circuit the section a and also closes its auxiliary contacts 50a which starts the timing peirod for the contactor 5|. If the position to which the master switch 60 is moved is the fourth position in reverse, the resistance sections b, c and d are caused to become short circuited successively, each in delayed relation to its predecessor, by means of the contactors 5|, 52 and 53. the

relays

54, 55 and 5G, and the timing circuit 35, as previously described in connection with the forward direction of rotation.

It will be obvious to those skilled in the art that if the master switch is moved from the off position to the first, second or third positions in the forward or reverse directions, a similar sequence of operations will take place depending upon the position in which the master switch 60 is placed, except that certain of the accelerating contactors beyond said positions in the direction of movement of the switch 60 will not close. For instance, in the first position only contactor 50 will close, in the second position 50 and ii will close successively in delayed relation, and in the third position 50, 5| and 52 will close correspondingly, so that the delayed intervals are cumulative for any selected on position.

If at any time when the motor M is running, it is desired to control its speed, the master switch ill may be moved to any selected position and left there. If the speed is to be increased by such movement, the proper amount of secondary resistance will be short circuited after time delay intervals. It the speed is to be reduced by such movement, the proper amount of secondary resistance will be reinserted by operation of some or all of the contactors B0 to 53 inclusive. depending upon the extent of movement oi the master switch M. r

The system of interlocking contacts shown in Fig. 3 is applicable only when the relay lilre-, mains closed for but a short interval of time. This short interval may be obtained by so designing the coil liw that it has a very small ohmic resistance, since the discharge time of a condenser is directly dependent upon the ohmic resistance of its discharge path. The resistor 33 shown in Fig. 1 may be used to give an adjust ment of the discharge time. The relay 3| need only be energized long enough to cause closure of the proper one of the

relays

54, 55 or 56, and must become deenergized and open the contacts 3lc before either contactor 5| or 52 closes its respective auxiliary contacts Slb or 52b.

Although the relay system shown for purposes of illustration has certain advantages peculiar to itself, it will be obvious to those skilled in the art that relay systems other than the one disclosed and having some of the advantages thereof, or other advantages, can be devised readily after having the benefit of the applicants description. For instance, in controllers employing contactors which close very rapidly, additional relays can be used to prevent the operation of more than one contactor for a single operation of the timing relay 3 I. In such case, the contactor and relay operation can be made independent of the length of time that the relay 3| is energized.

The invention is not limited to the control of secondary resistance shunting switches, since the same fundamental circuit can be readily adapted to control the shunting of primary impedance, the operation of an electromagnetic compensator for controlling the voltage applied to the primary of an induction or synchronous motor, the application of the direct current field in the case of a synchronous motor, and switching operations of any other electrical translating device.

We claim:

1. In a control system for an electrical translating device including a circuit and employing the charging of a condenser for controlling the operations of the device, means for charging the condenser at a rate which is inverse to an electrical condition of the circuit of the device to be controlled and comprising a coil operatively connected to the circuit of the device for energization in a direct relation to the degree oi energization of said circuit, another coil connected to a different source of energy and operative to produce flux in opposition to and greater in intensity than the flux produced by the first coil, a coil connected to the condenser and oprative, when it is energized, to cause charging of the condenser, and all of said coils being concurrently inductively related to each other, whereby the condenser is energized by flux resulting from the difierential in the flux of the two first mentioned coils.

2. The combination with an electric translating device to be controlled, a control system operable when energized for controlling the device, a condenser operative when charged to a predetermined value to discharge automatically, means responsive to the discharge current of the condenser for effecting energization of the con- I prising accelerating means for the motor, means to arrest for temporary periods the accelerating action of the accelerating means in difierent stages thereof, the arresting means including a control circuit adapted to be electrically associated with a motor circuit for energization thereby, a condenser, charging means for the condenser and connected to the condenser and to said control circuit in a manner to cause said charging means to charge the condenser at a rate inversely related to the amount of current flowing to said motor when the control circuit is electrically associated with said motor circuit, and means responsive to a predetermined charge on said condenser for operating said acceleratlng means.

4. The combination with an electric translating device to be controlled and including a circuit having a variable electrical condition dependent upon the operating condition of the device, a control system operable when energized for controlling the device. a condenser operatively associated with the control system and operative when charged to a predetermined value to discharge automatically, and means operated by the discharge from the condenser for efiecting energization of the control system, of a condenser charging circuit electrically associating the condenser and the circuit of the device in a manner to cause the condenser to charge at a rate which is dependent upon and in inverse relation to the electrical condition of said circuit of the device.

5. A control system for controlling the control means of the known combination of an electric circuit and a control means for the electric circuit, said control means comprising a current responsive device adapted to be energized when connected to said circuit and when so connected and energized operative by current flowing in said circuit 'to produce an electrical condition directly related to said current, a device capable of producing a substantially constant electrical condition similar to and continuously predominant in magnitude with respect to and in substan-tial alignment vectorially with the electrical condition produced by the current responsive device, means operatively associated with the said devices to operatively associate said electrical conditions to render the arithmetical 'difi'erential in said conditions available for operation of the control means, and means associated with the control means and said last named means and, when so associated, responsive only to the magnitude of said differential in conditions to control said control means in accordance with the magnitude of said differential in said electrical conditions.

6. A control system for controlling the control means of the known combination of an electric translating device having a circuit and a control means for the electric translating device, said control system comprising a current responsive device adapted to be 'energized when connected to said circuit to produce a unidirectional voltage in direct relation to the current in said circuit, a device capable of producing a substantially constant unidirectional voltage continuously predominant with respect to the voltage produced by the current responsive device, and circuit means electrically connected to the control means and operatively associated with said devices and having impressed thereon the said two voltages for relating the said two voltages to create a diiferential in said voltages available i or controlling the control means.

'7. A control system for controlling a control means in response to the electrical condition of an electric circuit of an electrical translating device controlled by said control means, said system comprising means electrically associated with said circuit for creating an alternating flux directly related to the electrical condition of said circuit, and means for creating an alternating flux which is continuously greater than the alternating flux created by said first flux creating means, means associated with the said two flux creating means for relating the said two fluxes to create a differential alternating flux, and means responsive to said differential flux to control said control means in accordance with the amount of said diiferential flux.

8. A control system for controlling the control means or the known combination of an electric circuit and a control means for the circuit, said control system comprising means for creating an alternating current flux directly related to the amount of current flowing in said circuit, means for creating an alternating flux which is continuously greater than the alternating flux created by said first flux creating means, means associated with the said two flux creating means for relating the two fluxes to create a differential alternating flux, means responsive to said differential flux for creating a voltage directly related to said diiferential flux, and time delay means associated with said control means and responsive to said voltage for controlling said control means after an interval of time indirectly related to the amount of said diiierential flux.

9. A control system for controlling the control means of the known combination of an electric circuit and a control means for the electric circuit, said system comprising a current responsive device adapted for connection to said circuit and when so connected operative by the current flowing in said circuit to produce an electrical condition directly related in magnitude to said current, a device capable oi producing a substantially constant electrical condition similar to and continuously predominant with respect to the electrical condition provided by the current responsive device, means operatively associated with the said devices to associate said electrical conditions to create a differential in electrical conditions, an energy accumulator which is operatively associated with the first named means and is rendered operative by said diflerentlal in electrical conditions, and means operatively associated with the control means and operated by the accumulator for causing operation of said control means, whereby the circuit is controlled in an inverse relation to the current flowing therein.

10. A control system for controlling the control means of the known combination of an electric translating device which is adapted for connection to a main circuit and a control means therefor, said system comprising a current responsive device adapted for connection to said main circult and when so connected operative by current flowing in the main circuit to create an electrical condition in direct relation to said current, a device for creating an electrical condition in relation to the electrical condition of the first device sufllclent to provide a difierential electrical condition which is in inverse relation to the current flowing in the main circuit, a time delay means operatively associated with said devices and with said control means and including a condenser and means operated. thereby when said condenser is charged to a predetermined degree to operate said control means, and means operatively associating the condenser with the diflerential electrical conditlon to charge the condenser in accordance with said differential electrical condition.

11. A control system for controlling the operation of the control means of the known combination of an electric translating device which is adapted for connection to a main circuit and a control means therefor, said system. comprising a current responsive device adapted for connection to said main circuit and, when so connected, operative by current flowing in the main circuit to produce a variable voltage in direct relation to said current, means for supplying another voltage different from the variable voltage, and means to relate said voltages in a manner to produce a dlfierentlal voltage which is in inverse relation to the current flowing in the main circuit, and a condenser connected to said devices in a manner to be charged by said diiierential voltage and operatively associated with said control means and operative when charged to a predetermined degree to discharge and to effect operation of said control means.

12. The combination with an electric motor, an energy absorbing device capable of being charged to a predetermined potential, and means responsive to a predetermined potential across said device for changing the condition of motor operation, of means adapted to be connected to a circuit of the motor and when so connected capable of creating a voltage equal to the differential between a voltage proportional to the current in the said motor circuit and a substantially constant continuously predominant reference voltage, and means for subjecting said energy absorbing device to said differential voltage to produce said predetermined potential, whereby said motor operation is controlled in inverse relation to the current in the motor circuit.

13. The combination with a motor acceleration system wherein a charge absorbing device operates as an arresting means to arrest the action of an acceleration means until the accumulation of a predetermined charge on the device, of a charging means having an output voltage inversely related to the value of current flowing in said motor circuit and operative to charge said charge absorbing device.

14. The combination with an accelerating means for an electric motor, means to arrest for temporary periods the accelerating action of the accelerating means in different stages thereof, the arresting means including a control circuit adapted to be electrically associated with a motor circuit, an energy absorbing device in said control circuit, and means responsive to' a predetermined electrical cause operation oi tricai translating device adapted to be connected for operation to a source of power through a supply circuit and a control means for the electrical translating device, said control system comprising a control circuit electrically associated with said supply circuit for producing a voltage proportional to the current in said supply circuit when said device is connected for operation, a control circuit for producing a voltage similar to and continuously predominant over that produced by the flrst control circuit, means adapted to electrically associate said circuits to cause said voltages to be in opposed relation to each other, an electrical charge absorbing device, said charge absorbing device and said control circuits being electrically connected together in a manner to subject the charge absorbing device to the difl'erential in said opposed voltages for charging said charge absorbing device, and means adapted to control the control means in response to a predetermined charge on said charge absorbing device.

16. The combination with an electric translating device to be controlled, a control system operable when energized for controlling the device, a. condenser, means responsive to a predetermined electrical condition 01 the condenser for effecting energization of the control system, and means operable for electrically associating the condenser with a voltage dependent upon the amount of current flowing to said device for charging the condenser by said voltage, of means for rendering the last named means operative in inverse relation to the said amount of current.

1'1. The combination with an alternating current motor, adapted to be connected to a source of alternating current through supply conductors, a control system operable when energized for controlling the motor, a condenser, and means responsive to a predetermined electrical condition of the condenser for effecting energization of the control system, of means inductively related to said supply conductors for charging the condenser wlth a voltage inversely dependent upon the amount of current flowing to said motor through said conductors.

18. The combination recited in claim 13 characterized further in that the charging means comprises a transformer, a rectifier for producing a unidirectional voltage proportional to the secondary voltage of the transformer, a source of unidirectional voltage, and a circuit for opposing the two unidirectional Voltages to obtain said output voltage.

WILLIAM J. KUTCHER. JOHN D. LEITCH.

CERTIFICATE OF CORRECTION. Patent 'ue. 3,2!!!7506. July 1, 19m.

' WILLIAM J. KUTCHER, ET AL. It is hereby certified that error appears in the printed specification of the above numbered patent requiring a) rrection as follows: Page 7, first column, line ha, for "paired" read --period--; page 8, first column, iine 11.5, claim 5, for the word "means" read --syetem; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

si ned and sealed this 16th day or September, A. 1). 191m.

Henry Van Aredale,

(Seal) Acting Commissioner of Patents.