US1720624A - Motor-control system - Google Patents

Description

y 9, 1929- E. R. CARICHOFF ET AL- l.720,624

MOTOR CONTROL SYSTEM Original Filed May 4, 1925 lnVentor-s 2 Eugene R. Carichoff, Benjamin W Jones, y WWW Their Attprfiey.

Patented July 29,. 1929..

UNITED STATES EUGENE R. CABICHOFF BENJAMIN W. JONES, OF SCHENECTADY, NEW YORK, ASSIGNORS TO GENERAL ELECTRIC COMPANY, A. CORPORATION OF NEW YORK.

moron-common srs'rnn.

Application filed. May 4, 1925, Serial No. 27,698. Renewed January 24, 1929.

started and stopped and generally controlled in a safe, reliable and efli-cient manner.

T he invention has particular application to steel mill electric drives, although the inven-.

tion is not necessarily limited to such an application. One of the requirements of an auxiliary drive in a steel mill is that the driye shall in no way delay the operation of the null of which it is a part. When the operator moves the handle of his master switch of the motor control system to a running position, the motor must start or, failing to start after exertingthemaximumpossiblestartingtorque Within its capacity, it must be disconnected from the line. The motor must and will do its utmost, but it can do so without injury only when governed by the proper type of control equipment. The control must permit the .motor to go about its work with only normal effort, or in case of need, accelerate with. the

greatest power of which it is capable. The control must also provide'that the motor shall not be overtaxed, but having once done its utmost, shall be relieved of further effort which could only result in damage. Motor control systems operating on a function of the motor current have heretofore been used to a considerable extent, and such systems have met with success where the load condit-ions are practically constant. However, if

the loads are variable, thecurrent limit control must be adjusted to meet the worst condition, such as for example, the condition encountered when a steel mill is first put into operation and before the parts have limbered up. An adjustment for this value is fre quent] y too high for the normal running conditions so that the current limit control if set for the extreme conditions will be set for too high a value for the normal conditions and the time taken in accelerating the'motor is than is desirable.

Time limit control has been resorted to as a means for taking care of the above condition, but the previous time limit control arrangements with which we are familiar have left a great deal to be desired from the standpoint of simplicity of construction and arrangement and general reliability and efiectiveness of operation. Our invention is therefore dited particularly to improvements whereby a p ropcr timing action is obtained between the successive slicrt-circuiting of sections of an accelerating resistor in the motor armature circuit, whereby the timing action is obtained and the successive short-circuiting ofthe sections of the accelerating resistor is obtained by means of a simple, reliable and effective device incorporated in a control system which is itself simple and effective.

In carrying our invention into effect, we preferably employ a time interval. relay of the type disclosed and broadly claimed in an application of George B. .Starie, Serial No. 125,112, filed July 26, 1926, which is a divisional application of the application of George B. Starie, Serial No. 28,036, filed May 4:, 1925 (docket N 0. 33,328). The Starie time limit relay comprises a magnetic structure with a winding thereon and a magnetic movable element or armature carrying a switch contact, the armature being biased to the unattra-cted position and the switch contact carried by the armature being biased to a definite position in some cases the contact is biased to the closed position and in other cases the contact is biased to thevopen position as will be hereinafter explained). The armature of the electromagnetic device is biased tothe unattracted position by suitable means such as a spring, the tension of which may be adjusted so that when the armature is in the attracted position, it is magnetically held in that position against the action of the spring tending to move the armature tothe unattracted position. In accordance with our invention, the winding of the electromagnet is connected in multiple relation with a section of the resistor in the motor armature circuit so that when this resistor is short-circuited, the winding will also be short;circuited. By reason of the fact that the winding has a considerable inductive reflect, the short-circuiting of the winding will permit the induced current to maintain a magnetic flux in the magnetic structure of the electromagnet and thus maintain the armature in the attracted position for an appreciable interval of time. This time interval is employed for controlling the successive closings of a plurality of resistor switches for short-circuiting the sections of the motor armature resistance "in the desired succession.

As applied to a reversing control system in which the motor is plugged to eiiect a rapid reversal, the Starie electromagnetic switch or relay is employed to give a control of the motor in accordance with the value of the current in the motor armature circuit so that the plugging resistor will be short-circuited very promptly after the closing of the directional contactors for the motor when the motor is initially connected to the supply circuit, but when the connections of the motor armature to the supply circuit are reversed to the source of supply to obtain a quick reversal by the Well known plugging action, the electromagnetic device will delay the shortcircuiting of the plugging resistor until after the motor armature has substantially stopped rotating.

The invention of the present application is an improvement of the system and apparatus of our former application, Serial No. 527,520,

, filed January 6, 1922, a renewal of application, Serial No. 354,030 filed January 26, 1920, which discloses a system having broad features of similarity to the system of the present application and which broadly claims the system and apparatus of the present application.

For a better understanding ofthe invention, reference is had to the accompanying drawing, in which Fig. 1 is a very simplified diagram of a control system in accordance with the invention, Fig. 2 is a side view of the Starie electromagnetic switch employed by usin obtaining the desired time limit control and the sequential action of shunting the accelerating resistance step by step in the motor armature circuit, and Fig. 3 is a front View of the' switch. I

Referring to the drawing, the motor is indicated as having an armature 10 and a series field 11, and this motor is arranged to be connected to the direct current source of supply 12 for either direction of operation by means of the pairs of reversing or directional contactors 13 and 14 for the forward direction of motor operation and 15 and 16 for the reverse direction of motor operation. T he pro tective resistance included in the motor armaturecircuit has a plurality of sections, the section 17 being provided for controlling the plugging action and the sections 18 and 19 being provided for accelerating purposes. The resistor 17 is controlled by means of the plugging contactor 20 and the resistor sections 18 and 19 are respectively controlled by the contactors 21 and 22. The line contactor 23 is provided for completely disconnecting the motor from the source of supply when a disconnecting switch is open.

The electromagnetic switches or relays 25 and 26 are provided for controlling the pluggingresistor contactor 20 and the similar relays 27 and 28 are provided for controlling the accelerating resistor contactors 21 and 22 respectively. These contactors are under the control of the master'switch or controller 24, as will be hereinafter set forth. It will be observed that the winding of the relay 27 is connected in multiple relation with the plugging resistor 17 and that the winding of the with the plugging re istor 17 and the first accelerating resistor 18. This is for the purpose of obtaining a proper sequence in the 7 action of the relays as will be hereinafter fully explained.

The winding of the relay 25 is arranged to be connected across the motor armature 10 and the plugging resistor 17 for one'direction of motor operation and the winding of the relay 26 is similarly connected for the other direction of motor operation. It will be observed that these plugging relays 25 and 26 are normally open devices; that is, the switch contacts controlled by these relays are biased to their open positions. Relays 27 and 28, on the other hand, are normally closed devices, since their controlling contacts are normally in the closed position with the winding of the relay deenergized.

The relays 25 to 28 inclusive are preferably of identical construction with the exception that the contacts of the relays 25 and 26 are normally in their open positions, whereas the relays 27 and 28 have their contacts normally in the closed position. Each of these relays is preferably of the construction shown in more detail in Fig. 2, which as before stated, discloses the construction claimed specifically in the said Starie application.

means of the bolt 33. Cooperating with the magnetic structure is a magnetic movable element or armature 34 which is biased to the unattracted position by means of the spring 35, the force of which is adjusted by adjusting. the nut 36 on the bolt 37 on which the spring 35 is mounted. The bolt 37 is supported in position and the armature 34 is supported in position by means of the supporting member 38 whichis secured to the strap 29 of the magnetlc structure of the electromagnet, the armature having a knife edge bearing on the support 38. The armature 34 carries a switch contact 39 at one end thereof, and this contact cooperates with a stationary but adjustable contact 40. The shim 41 of non-magnetic materialis supported by the armature 34 and is arranged to make engagement with the end of the core 30 of the electromagnet so as to provide a definite air gap between the armature 34 and the end 01 the core 30 when the armature is in the attracted position. The adjustable stationary contact 40 is carried by a strap 42 which is secured to the insulating support 32 by means of the bolt 43. Themanner &

electromagnet is considerably in excess of the value required to magnetically hold the arma ture in the attracted position. This is of advantage. since the timing action obtained by means of the relay will be substantially unindicated in the drawing will cause the coil of line switch 23 to be energized to close through a circuit from the segments 46 and 4 of the master controller 24, the coil of the line contactor 23 to the negative supply conductor. The closing of the line contactor 23 will produce no effect at this time, since the master controller is in the oil or neutral position. The closing of the line cont-actor 23 will also effect the closing of the auxiliary switch 48 associated with this line contactor, and this will establish a maintaining circuit for the feed conductor to the segment 47 of the controller so that the controller may be moved out of the off position, therebyopening the circuit to the controller segment 46 and the line contactor will nevertheless be maintained closed.

If the master controller is now moved from the of? position toward the left to its first operative position, the forward directional contactors 13 and 14 will be energized to close through a circuit from the plus supply conductor through the auxiliary switch 48, the segment 47 of the controller, segment 49 of the controller, through the coils of contac tors 13 and 14 to the negative supply conductor. The winding'of the relay 25 will be ener gized through the auxiliary switch 50 associated with the directional contactor 13 so that this winding will now be connected across the motor armature. 10 and the plugging rewill be energized by the drop in .of a sufficient value so that the relay will be energized to close its contacts. This will produce no effect at the present time until the master controller 24 is thrown toward the left to its second operative position, but when the controller is thrown to that position, the plugging contactor 20 is energized to close immediately, the circuit for the coil of this contactor being from the plus supply conductor, the auxiliary switch 48 associated with the plus supply conductor, the

line contactor 23, the segment 47 of the master controller, segment 49 of the controller, the contacts of relay 25, segments 51 and 52 of the master controller, through the coil of the plugging contactor 20 to the negative supply conductor.

It will be observed that as soon as the motor is connected to the supply circuit, the windings of relays 27 and 28 are immediately energized to open their respective contacts. This is because of the fact that the winding of relay 27 is energized in multiple relation with the plugging resistor 17 and the winding of relay 28 is energized in multiple relation with the accelerating resistor 18'. Since these relays are energized, the contacts controlled thereby are magnetically held in their respective open positions so that the resistor contactors 21 and 22 will not be energized until the proper interval in the starting of the motor. When the plugging resistor contactor 20 closes its main contactsas previously described, it also short circuits the winding of the relay 27 i v As before explained, the short-circuiting of the winding of this relay does notefiect the immediate release of the relay armature, 7

since it takes an appreciable interval of time for the flux in. the magnetic structure of the relay to decrease due to the inductive action of the relay winding, andthus an appreciable interval of time elapses before the biasing spring of the relay armature overpowers the v.magneticpull onfthe relay armature and effects the closing of the relay contacts.

When the relay contacts close, the resistor contactor 21 is energized to close, provided the master controller 24 has been moved to the left to its third operative position,.the circuit for the winding of this contactor being from the positive supply conductor, through the auxiliary switch 48.associated with the line contactor 23, the segments 47 and 49 of the master controller, the contacts of relay 25, segments 51 and 53 of the master controller, through the winding of the resistor contactor 21, the contacts of relay 27 to the negative supply conductor. The contactor 21 will thus be energized to close and short-circuit the accelerating resistor section 18 an interval of time after the shortcircuiting of the plugging resistor 17 The closing of the contactor 21 also shortcircuits the winding of the relay 28 so that after an interval of time, the springassociated with the armature of relay 28 will" overpower the magnetic attraction of the armature of the relay and the relay contacts will be permitted to assume their normal or closed position. The winding of contactor 2 2 is thus energized throu h a portion of the circuit previously traced y the winding of contactor 21, except that the winding of'contactor 22 is connected to the negative supply conductor through the contacts of the relay 40 arrested at an intermediate position.

28. The resistor contactor 22 is thus energiz'ed to close and short-circuit the accelerat ing resistor section 19.

The motor is thus accelerated from rest to the full running speed and it will be observed that the contacts of the plugging relay 25 Will be maintained in the closed position due to the fact that the coil of this relay is energized by the counter-electromotive force of the motor. Assume now that it is'desired to reverse the motor quickly and employ the plugging feature of the control system. The master controller will be thrown from the full running position forward toward the right to an operative position for the reverse direction of motor operation. i It is immaterial to which operative position the controller is thrown in so far as obtainin a quick reversal of the motor is concerned, hut

if the controller is thrown toward the right to the first operative position, the automatic progression of the closing of the resistor contactors will not be started. If the controller is thrown to the second reverse operativeposition, the automatic progression will be stopped when the resistor contactor 20 has been energized to close, but if the controller is thrown to the full running position reverse, the resistor contactors will all be ener gized to close in the previously mentioned succession so that the motor will be connectedfor full running speed in the reverse I direction.

It will be assumed for the present explanation of the operation that the motor conforward, the circuit for the windings of these contactors is broken at the segment 53 of the controller. When the master controller leaves the second forward operative position,

the plugging resistor contactor 20 is opened at the segment 52 of the master controller so that the resistance is all reinserted in the motor armature circuit before the reversing contactors 15 and 16 are energized to close in the first reverse position of the controller. 55 Ihe relays 27 and 28 are unelfected at this time by this operation of the master controller; that is, these relays are maintained in their closed osition until after the master controller has eenmoved to the first reverse position.

When the master controller is moved to the first reverse position or to a succeeding reverse position, the winding of the relay 26 is connected across themotor armature and the plugging resistor 17 by the closing of the income.

auxiliary switch '54 associated with the di- "rectional'contactor 16. However, by reason of the fact that the generated voltage of the motor armature is now in opposition to the voltage drop across the plugging resistor 17, the winding of relay 26 will not be sufficient- 1y energized to close the relay until after the motor decreases in speed and until the motor has come practically to rest, so that the volt- 1 age drop across the resistor 17 will be of a sullicient value to energize this relay to close.

The relay 26 is adjusted so that it will not be j limit the current in the motor armature circuit during a critical condition of the'motor during the plugging action.

When the relay 26 closes and provided the master controller is in its second operative .position reverse, the plugging resistor contactor 20 is energized through a circuit from the positive supply conductor, through the auxiliary switch 48 associated with the line contractor 23, the segments 47 and 55 of the master controller, contacts of relay 26, the

' segment 56 of the master controller, through segment 57 of the master controller and the coil of the contactor 20 to thenegative supply conductor. The relays 27 and 28 will have been energized to open when the directional contactors 15 and 16 closed after the opening of the' directional contactors-13 and 14 for the forward direction of operation, so

I that the contacts of these relays will be successively closed in the manner previously explained in connection with the forward direction of motor operation.

It will be observed that the relays 25 and 28 inclusive may be of identical construction and characteristics, the sole difference being that with respect to the relays 25 and 26 they shall have normally open contacts, whereas relays 27 and 28 should have normally closed contacts.

It be observed that we have provided a very simple and efiective control system in which-the acceleration of the motor is in accordance with a time interval action, a sub stantial time intervalbeing provided between the successive shunting of the accelerating, resistor sections due solely to the inductive efl'ect or magnetic inertia of the flux in the magnetic structure of the relays 27 and 28. By reason of the fact that it takes an appreciable time interval for the flux of each of these'relays to decrease to such a value that the holding efiectthereof is overpoweredby the biasing spring of the relay, the timing action is obtained ina very simple and efl'ective manner. If the time interval of operation of a particular relay is not of the desired value, the time interval may be adjusted by using a shim of different thickness than the shim 41. The time interval may also be adjusted by adjusting the nut 36 provided with each relay, thereby Varying the spring tension against which the attractive force of the flux of the electromagnet has to operate in holding the relay contacts closed for an interval of time.

What we claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination, two motor controlling resistors a contactor for shunting thesecond of saidiresistors, and a single winding elec-v tromagnetic time element relay for'controlling said contactor to control the shunting of the second resistor after the first resistor has been shunted, the said relay winding being connected in multiple relation with the first resistor so as to be shunted simultaneously with the shunting of the first resistor and delay the operation of the said resistor contactor to shunt the second resistor for an appreciable interval of time after the shunting of the first resistor due solely to the inductance of the relay.

2. A time-interval motor control system comprising a plurality of resistors in the motor armature circuit for limiting the motor armature current, an electromagnetic time element switch for elfecting the shunting of each of said resistors, each of said switches having a magnetic structure and a single winding for ener izing the structure, and connections where y the switches are caused to operate in a definite succession and each of said switches is caused to operate a substantial interval of time after a preceding switch of the successionhas operated due solely to the magnetic inductance of the switch, 7

. 3. A. time interval motor control system comprising a plurality of resistors connected in series relation in the motor armature circuit for limiting the motor armature cur rent, a plurality of successively operated single winding-electromagnetic time element switches for effecting the shunting of said resistors, the winding of each of said switches being connected to beenergized responsively to the voltage drop ofthe resistor preceding the resistor controlled by the switch, and means whereby each of said switches is caused to operate to efiect the shunting of the resistor controlled thereb a substantial time interval after the prece ing resistor is shunted due solely to the inductive efiect of the winding of the switch. 4. In combination in a motor control system, a plurality of resistors in the motor circuit arranged to be successlvelyshunted, a contactor for shunting each of said resistors,

a single winding electromagnetic time element relay for controlling. each of certain of said contactors, each of said relays having a magnetic structure, a Winding permanently armature to the attracted position and said contact to the open position until the preceding resistor is shunted and to then introduce a time interval in the closing of the relay directly in response to the inductance of said winding when the winding is shunted by the closing of the preceding contactor.

5. A motor control system comprising an accelerating resistor having a plurality of sections, a plurality of successively operated similar electromagnetic switches for controlling the successive short-circuiting of said sections, one of said switches being provided for each section of the resistor, each of said switches having a magnetic structure, a single winding connected in multiple relation with the resistor section preceding the section controlled by the switch for energizing said structure, a magnetic movable element carrying a switch contact, and a spring for biasing the said magnetic element to the unatt-r'acted position and the contact carried thereby to the closed position, the said winding being arranged to set up a magnetic flux in said structure considerably in excess of the value of flux required to hold the magnetic element in the attracted position, whereby upon the short-circuiting of the resistor section preceding the section controlled by the switch, the said-winding is also short-circuited and the switch is magnetically held in the open position for an appreciable interval of time due only to the time required for'the flux in said structure to decrease to a value that the said spring overpowers the magnetic holding efiect on said magnetic element.

6. In combination, in a' system of motor control, two motor controlling resistors, a contactor for shunting the second of sai resistors, a time element single winding electromagnetic relay for controlling said con tactor, the said relay having a magnetic movable member, a switch contact carried thereby and a spring which biases said member and contact to the closed position, the said winding being connected in multiple relation with ing the magnetic pull on said member of the temporarily persisting flux of the relay.

7. A reversing motor control system comprising reversing switch mechanism for the motor, a plugging resistor and a plurality of accelerating resistors in the motor armature circuit, acontactor for shunting the said plugging resistor, a pair of similar normally open electromagnetic relays for controlling the said plugging contactor, one of said pair for each direction of motor operation, each of said relays having a winding, the winding of the plugging relay for controlling the plugging-cont-actor for each selected direction of operation being connected across the motor armature and a portion of said resistors upon the closing of the reversing switch mechanism for the direction of motor operation selected, whereby the relay operates to effect the closing ofthe plugging contactor promptly when the motor is started from rest and only when the motor has practlcally stopped rotating when the motor 1s 8. A reversing motor control system com-' prising a plugging resistor and a'plurality of accelerating resistors in the motor armature circuit, a contactor for shunting each of said resistors, a pair of relays governed in accordance with the motor armature current for. governing the said plugging resistor contacto'r, an electromagnetic time element relay for governing each of said acceleratmg resis- .tor contactors, and connections whereby the contactor, one of said relays for eachdirection of motor operation, the said relays having each a winding and normally open contacts and the winding of the relay operative for each selected direction of operation being connected across the motor armature and the plugging resistor upon the closing of said reversing switch mechanlsm for the direction of motor operation selected, whereby the relay operates to effect the closing of the plugging contactor promptly when the motor is started from rest and only when the motor has practically: stopped, rotating when the motor is plugged, and a single winding time element relay for controlling the accelerating resistor contactor, the said accelerating relay having normally closed contacts and the winding of said accelerating relay being connected inshunt relation with the plugging resistor so as to be energized to open the relay contacts promptly with the closing of the reversing switch mechanism and to be shunted withthe shunting of the plugging resistor and delay the energization of the accelerating resistor for an interval of time determined solely by the inductance of the relay.

' 10. A reversing motor control system comprising reversing switch mechanism for the motor, a plugging resistor in the motor armature circuit, means responsive to the energization of the motor for shunting said plugging resistor immediately when the inotor is started substantially from rest, but delaying the shunting of said resistor when the motor is plugged until a predetermined period in the plugging operation.

11. A reversing motor control system comprising a plugging resistor, meansfor shunting said plugging resistor, reversing switching mechanism, and control means responsive to a voltage drop in the motor circuit and the counter E. M. F. of the motor for controlling said shunting means so that said plugging resister is shunted immediately when said switching mechanism is operated to close the motor circuit with the motor at rest, and is reinserted in the motor circuit when said switching mechanism is operated to the reverse running position for plugging whereupon said control means is held by the counter E. M. F. of the motor from again shunting said resistor until the motor is substantially at rest.

- 12. A reversing motor control system comprising a plugging resistor, a switch for controlling the starting and stopping of the motor for forward and reverse operation and the shunting of said plugging resistor, and 105 control means responsive to a voltage drop in the motor circuit for controlling the shunting of said plugging resistor jointly with said switch whereby said plugging resistor is shunted immediately when said switch is thrown to a running position with the motor substantially at rest, said control means being responsive also to the counter E. M. F. of the motor so that when said plugging resistor is reinserted in the motor circuit by the throwing of said switch from a running position in one direction to a running position in the reverse direction said control means is held by the counter E. M. F. of the motor from again shunting said resistor until the motor has de- 1 'celerated and is substantially at rest.

13. A reversing motor control system comprlsmg reversmg switch mechanism,'a plugging resistor and an accelerating resistor,

means responsive to the energization of said I motor for shunting said plugging resistor implugging resistor is delayed until a predetermined period in the plugging operation, and electro-responsive switching means for shunting said accelerating resistor, said electroresponsive switching means being provided with a winding connected acrosssaid plugging resistor.

14. A reversing motor control system comprising reversing switch mechanism, a plugging resistor and an accelerating resistor, electromesponsive switching mechanism actuated in response to the energization of the motor for shunting said plugging resistor immediately when the motor is started from rest, said electro-responsive switching mechanism being responsive to the counter-electromotive force of the motor so that when the motor is plugged said plugging resistor is shunted only after the motor has been brought substantially to rest, and inductive time switching mechanism controlled by said first switchlng mechanism for shunting said accelerating resistor. 7

EUGENE R. CARICHOFF. BENJAMIN W. JONES.

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