US1847081A - Control system - Google Patents

Description

W G. COOK CONTROL SYSTEM March 1', 1932 Filed July 7. 1928 r g .95 E

INVENTOR h M/ardG 600K WITNESS ATToRz s Patented Mar. 1, 1932 UNITED STATES PATENT OFFICE WILLARD G. COOK, OF PHILADELPHIA, PENNSYLVANIA, ASSIGNOB TO WESTING- HOUSE ELECTRIC & MANUFACTURING COMPANY, A COEPGBATION OF PENNSYL- VANIA CONTROL SYSTEM Application filed July 7, 1928. Serial No. 291,017.

This invention relates generally to motorcontrol s stems and particularly to control Systems or plugging or reversing the direction of rotation of a motor. i

'5 Heretofore, many schemes have been utilized for startin and reversing motors, but it has been foun generally that they do not satisfactorily meet all operating conditions. For example, when relays responsive to the counter-electromotive force of the motor are.

provided to shunt the starting resistors, and a load is imposed on the motor which prevents it from starting with the initial current that may flow through the resistors, then it cannot be connected directly across the line to develop the maximum torque. Therefore, a system which depends on the counter-electromotive force for short circuiting the starting resistors is not suitable for steel mills and other similar'installations where the mo-- tors are likely to be subjected to excessive loads. I

Motor-control systems, in which the well known lockout type of relay is utilized for shunting the resistors and iving the desired time element between the s ort circuiting of each section of resistor, are found unsatisfactory when the line voltage varies to any marked extent.

In some cases, current-limit relays have been utilized for shunting the starting resistors provided in motor-operating systems, but they have been found undersirable when,

for some reason, the motor will not start. i 7

part, be obvious and will, in part, appear hereinafter.

The invention, accordingly, is disclosed in the embodiment thereof shown in the accompanying drawings and comprises the features of construction, combination of elements and arrangement of parts which will be exemplified in the system hereinafter set forth, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description, taken in connection with the accompanying drawings, in which;

Figure 1 is a diagram of the circuitconnections ofa. control system embodying the fea- V tures of this invention, and

Fig. 2 is a view, partly in section and partly in side elevation, of a relay suitable to be utilized in the present control system.

In order that the control system may be readily understood, a description of the relay illustrated in Fig. 2 will be given first. As shown, the relay comprises a substantially U- shaped frame, that may be made from some suitable magnetic material, such as cast iron, and which is provided with a plurality of openings in the base thereof to facilitate mounting. The relay may be mounted in different positions but, in this instance, itis mounted in a horizontal position for reasons which will be explained hereafter.

In this particular showing, the relay is mounted on the panel 12 by means of screw bolts 13 and 14: which engage the threaded openings 11 provided in the base; The screw bolts may also be used as terminal members for connecting the frame in a circuit, if desired.

As illustrated, a core 15 is mounted in the frame 10 by means of a threaded end portion 16 which engages a threaded opening 17 provided in the base. The core member is centrally disposed in the frame and extends substantially the full height of the arms of the frame.

A main energizing coil 18 is mounted on the core and disposed inside of the frame 10. When the coil is energized, lines of magnetic force will be generated in the core memle which will divide at one end thereof and flow through the arms of the U-shaped frame, returning to the other end.

An armature 19 is pivotally mounted on the frame 10 by means of a pin 20. The lower end of the armature oiturcatcd and has an auxiliary coil 22 mounted between its arms 21 to fit over the end ot the core member 15 and be movable relative thereto.

As shown, a spring 23, which is mounted in a bracket provided on the frame 10, is disposed to engage the lower end of one arm oi the armature 19 to centralize it. The upper end of the armature is disposed between a pair of contact members 26 and 27, each of which is provided wi h a terminal by means of which they ma be connected into any circuit.

In order to energize the coil stationary contact terminals 29 are provided and mounted on the frame 10. The contact terminals 29 may be connected to the terminals of the coil 22 by means of flexible con ductors 30 which will permit a movement of the coil 22 relative to the core 15.

The relay is preferably mounted in a horizontal position so that the weight of the armature and coil 22 will tend to retain the upper end of the armature evenly spa ed between the contact members 26 and 27.

The operation of the control system will now be described in connection with 1. As illustrated, a motor, shown generally at 31 and provided with an armature 32 and series iield winding 32-3, disposed to be connected across the line conductors 3e and 35. A master switch, shown generally at 36, is provided for controlling the connection of the motor to the line conductors.

Assuming now that it is desired to operate the motor in the selected direction and that the master switch 36 is actuated upwardly to move the contact segments 37 and 38 into engagement with their respective contact fingers, circuits for operating the switches and 40 are established. These switch circuits extend from the line conductor 3%, through the limit switch 41, conductor 42, contact segment 3?, conductor the actuating coil of switch 39, conductor 45, the actuating coil 01'. switch 40, conductor 46, the actuating coil of the line switch -17, to the line conductor 35.

Therefore, the switches and 40 are closed, and a motor circuit is established which extends from the line conductor 34, conductor d9, switch 39, conductor 50. the armature 32 of the motor 31, conductor 51, switch 40, conductor 52, the motor field winding 33, starting resistor 53, switch 47 and the overload relay 5%, to the line conductor 35.

It will be readily understood that, unless the motor is excessively loaded, it will rotate and develop a counter-electromotive 22, a pair of force. Further, as shown, the main energizing coil 18 of the relay 55, which is similar to the relay illustrated in Fig. 2, is energized when the limit switch 11 is closed. The encrgizing circuit for the coil 18 extends from the line conductor 3%, through the limit switch ll, conductor 56, the energizing coil 18, conductors 57 and 58, interlock 59 on the overload relay to the line conductor As pointed out hereinbelore, the coil of the relay stands in a magnetic iield and, if a v0 is impressed across the coil to cause a current to flow, it will be moved either to the right or to the left in the same manner as a torque motor is actuated. its will be noted, the coil 22 of the relay 55 is connected across the armature 32. The circuit for the coil 22 may be traced from one tern'linal of the motor armature 32, through conductors and 60, the coil 22, and conductors 61 and. 51. back to the other terminal of the armature 32.

Therefore, when a voltage is impressed upon the armature, it is also iinpressed across the coil 22. Consequently, with the connecting of the motor armature across the line, a voltage is impressed on the coil 22, and it is actuated in predetermined direction. It will be assumed, for convenience in describing the operation of the system, that the coils 22 and 18 are so arranged that the armature 25 is actuated to the left to engage the contact member 27.

As has been explained hereinbeliore, a resistor 53 connected in the motor circuit to control t 1e current during the starting operation. In practice, the section 63, which is con trolled by the relay 5, will be constructed with a much higher ohmic value than the section 62.

In order to permit the desired starting current to flow in the motor, provision is inade for shunting the resistor section 63 immediately after the motor is connector. across the line, irrespective of whether or not it starts As explained hereinbetore, when the motor is connected across the line, both the coils l8 and 22 of the relay are energized, and the armature 25 is actuated into migagement with the contact member 21 In this manner. an actuating circuit for the switch 6 which shunts the resistor section 63, is es ablished and may be traced from the line conductor through limit switch ll, conductor 42, the contact segment 37 ot' the master switch 36, conductor 43, contact member 27, armature 25, conductor 66, the actuating coil of the switch or and conductor 6'1, to the line conductor 35. The switch (id is closed and a shunt circuit for the resistor section 63 is established, which may be traced from one terminal of the resistor section, through the actuating coil of the relay 69, switch 6s: and conductor 72, to the other terminal of the resistor section 63.

It will be readily understood that, upon the closing of the switch 64, which is effected almost instantaneously with the connecting of the motor across the line, there will be a heavy flow of current which will effect the operation of the relay 69 and prevent the closure of the switch 73. When the motor begins to rotate and a counter-electromotive force is developed, the current in actuating coil of relay 69 decreases and the relay closes. An actuating circuit for the relay 7 3 is immediately established which extends from the energized conductor 56, through the contact segment 38 of the master switch 36, conductor 74, the actuating coil of the switch contacts 7 3,relay 69, and conductor 76, to line conductor 35. Upon closure of the switch 73, a shunt circuit for the resistor section 62 is established which extends through the conductor 77, switch 73, conductor 70 and the actuating coil of the relay 69.

From the foregoing, it will be noted that the resistor section 63 of high ohmic value is shunted in order to connect the motor across the line and supply it with a high starting current, irrespective of whether or not the motor starts. The protection of the motor from excessive currents will depend on the operation of overload relay 54.

In he operation of motors of this type, in many applications, it is found necessary to provide for the quick plugging or reversal of the motor to perform the desired operations. Assuming now that it is desired to plug or reverse the motor when it is running at substantially normal speed, it is necessary to actuate reversing switches 80 and 81. It will be readily understood that, if the motor has been started by closing switches 80 and 81, the reversal could be effected by closing the switches 39 and 40. Therefore, the switches 39 and and 80 and 81 will be called the reversing switches.

In order to actuate the switches 80 and 81,

: the master switch 36 is actuated downwardly to move the contact segments 37 and 38 into engagement with the lower contact fingers. It will: be observed that the energizing circuit for the coil 18 is not interrupted by the operation of the master switch, but the actuating circuits of the switches 39, 40, 64 and the switch 47 are interrupted. Upon the opening of the switches 39, 40 and 47, the motor is disconnected from the line and the shunt of I the resistor section 63 is opened. Further, the

actuation of the mast-er switch 36 downwardly establishes an actuating circuit for the switches 80 and 81 which extends from the energized conductor 42, through contact segment 37, conductor 86, the actuating coil of switch 80, conductor 83, the actuating coil of switch 81, conductor 46 and'the actuating coil of switch 47, to the line conductor 35. In this manner, the switches 80 and 81 are closed to connect the motor across the line conductors so that the currentin the armature flows in the opposite direction to that in which it flowed in the circuit hereinbefore traced.

The motor circuit now established may be traced from the line conductor 34, through the conductors 49 and 84, switch 80, conductor 51, armature 32 of the motor 31, conductor 50, switch 81, conductor 52, motor field 33, the resistor sections 62 and 63, line switch 47 and the actuating coil of the overload relay 54, to the line conductor 35. If the motor armature is rotating at substantially normal speed when the reversing operation is effected, the line voltage will be applied cumulatively with the counter-electromotive force, and a voltage substantially double the line voltage will result. However, it will be noted that the resistor section 63, which is of high ohmic value, has been connected in series with the motor to limit the voltage applied to the motor armature.

In order to prevent the closure of switch 64 to shunt the high-resistance section 63 before the motor armature has substantially stopped, provision is made for utilizing the relay to prevent the establishment of its actuating circuit.

It will be noted that, since the coil 22 of relay 55, is connected across the motor armature, the application of voltage, caused by the counter-electromotive force developed by the rotating motor armature 32, will be in the same direction as the voltage applied to the coil when it is connected across the line conductors 34 and 35, upon the closure of the switches 39 and 40. Therefore, while the motor armature continues to rotate at a high speed, current will continue to fiow in the coil 22 in the same direction as when it was connected, across the line, to the switches 39 and 40. Consequently, the armature 25 will remain in engagement with the contact member 27 until the motor armature slows down to substantially zero, and the application of an excessive voltage to the motor armature is prevented.

Assuming now that the motor has substan tially come to rest and that the counter-electromotive force has decreased to substantially zero, the line voltage causes current to flow in the opposite direction in the coil 22. The energizing circuit for the coil 22 extends from the energized conductor 84, through switch 80, conductor 61, the coil'22, conductor 60, switch 81, conductor 52, the motor field 33, the resistor 53, the switch 47 and the actuating coil of the overload relay 54, to the line conductor 35. In response to the change of flow of current in the coil 22, the armature 25 is actuated to the right into engagement withthe contact member 26.

A new energizing circuit is, therefore, established for the switch 64 which extends from the energized conductor 86, through the contact member 26, armature 25, conductor (36, actuating coil of the switch 64 and conductor 67, to the line conductor 35. Upon the closure of the switch G l, the resistor section 63 is shunted in the manner hereinbefore described, and the starting of the motor in the opposite direction is effected.

If it is required to again reverse the motor, the master switch 36 is actuated to open the switches 80 and 81 and close the reversing switches 89 and 40. The functioning of the relay is the same as that hereinbetore described.

In the present system, in orcer to provide for the interruption of the control circuits upon a predetermined decrease in line voltage, a low-voltage relay 87 is provided. Further, ti o limit switch ll is connected across the relay 87' to control the operation of the latter when the line switch I? is closed. The switch 4-.1 may be actuated in conjunction with the line switch 47 in any suitable manner.

Since certain cl'ianges may be made in the above described system, and different embodiments of the invention may be made without departing from the scope thereof, it is intended that a l matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. In a motor-control system, in combination, a motor having an armature, a resistor disposed to be connected in circuit relation with the motor, reversing switches for the motor, a contactor for shunting the resistor, a relay provided with an armature for controlling the operation of the contactor, a main exciting coil on the relay and an auxiliary coil carried by the armature of the relay, said auxiliary coil being connected across the motor armature, thereby to prevent the immediate closure of the contactor when the reversing switches are actuated to effect a reversal of the motor.

2. In a motor-control system in combination, a motor, a source of power for the motor, reversing means for connecting the motor to the source oil power to operate it in either direction, a resistor for limiting the voltage applied to the motor, resistor-shunting means for shunting the resistor to increase the voltage applied to the motor, control means responsive to the line voltage for controlling the operation out the shunting means, means *esponsive to the counter-clectromotive forces 01": the motor cooperating with the control means to retain the control means in the position to which it has been actuated by an application of line voltage to prevent the operation of the shunting means when the reversing means is actuated to cause a reversal in the application 0t voltage to the motor.

In a motor control system, in combination, a source of power, a motor, means for connecting the motor to the source of power, a resistor for controlling the flow of current in the motor, means for reversing the motor, means for shunting the resistor controlled by the operation of the reversing means and control means for controlling the operation of the shunting means, said control means bein responsive to the line voltage and counrer-electromotive force of the motor,

In a motor-control system, in combination, a source of power, a motor, means for connecting the motor to the source of power, a resistor for controlling the How of current in the motor, means for rever 'ing the motor, means for shunting the resistor controlled by the operation oi the reversing means and electric control means having a pair of actuating circuits, one of said circuits being connected to the source of power and llllllSl'QSPOllSlVQ to the line voltage and the other of said circuits being connected to the motor armature terminals and thus responsive to the counter-electromotive force of the motor, for controlling the operation of the shunting means.

in a motor-control system, in combination, a source of direct current power, a direct current motor having a conventional armature and armature tern'iinals therefor, means for connecting the motor to the source of power, a resistor for controlling the low of current in the motor, means for reversing the motor, resistor-shunting means for shunting the resistor controlled by the operatioi'i of the reversing means, and electric control means for controlling the operation of the resistor-slmnting means, said control means having a pair oi actuating eircL'ts connected to be energized, respectively, by the voltage of the source of supply and the voltage drop across t ie motor armature terminals and designed to operate regardless of whether a counter-electromotive force be developed by the motor or not.

(3. In a motor-control system, in combination, a source of power, a motor, means for connecting the motor to the source of power, means for reversing the motor, a resistor for controlling the flow of current to the motor, a switch for shunting the resistor, a plurality of circuits for actuating said resistorshunting switch, and a relay disposed to interconnect said switch-actuating circuits with said resistor-shunting switch, said relay having a pa' r of actuating circuits responsive, respectively, to the voltage of the source of supply and to the coui'iter-electromotive force of the motor and means for inerrupting the actuating circuits of the resistorshunting switch.

7. In a 1not-or-control system, in combination, a source oi. power, a motor, means for connecting the motor to the source of power, means for reversing the motor, a resistor for controlling the flow of current in the motor, a switch for shunting the resistor, a plurality of circuits for actuating said resistorshunting switch, and a relay disposed to interconnect said switch-actuating circuits with said resistor-shunting switch, said relay having a pair of actuating circuits vresponsive, respectively, to the voltage of the source of supply and to the counter-electro motive force of the motor and means mechanically interlocked with the means for reversing the motor for interrupting the actuating circuits of the resistor-shunting switch each time the means for reversing the motor is moved through the OE position.

8. In a motor-control system, in combination, a source of power, a motor, means for connecting the motor to the source of power, means for reversing the motor, a resistor for limiting the voltage that may be applied to the motor, a relay for shunting the resistor, a pair of actuating circuits for said resistorshunting relay, means mechanically interlocked with the reversing means for interrupting the actuating circuit for the resistorshunting relay each time the means for reversing the motor is actuated, a relay disposed to interconnect the actuating circuits with said resistor-shunting relay, said relay being disposed to interrupt one of said pair of circuits and establish the other each time the reversing means is actuated, a pair of actuating circuits for said relay responsive, respectively, to the voltage of the source of supply and the counter-electromotive force of the motor, whereby said relay during normal reversing operation of the motor will stand in its circuit-closing position after the reversing means has been actuated until the counter-electromotive force of the motor has been decreased to a predetermined value.

In testimony whereof, I have hereunto subscribed my name this 26th day of June,

WILLARD G. COOK.

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