US1802765A - Control system - Google Patents

Description

April 28, 1931. JAMES 1,802,765

CONTROL SYSTEM Filed Jan. 19, 1928 Forward /6 Reverse INVEVNTOR flew/y 9 James.

AT'TORNEY Patented Apr. 28, 1931 UNITED STATES PATENT OFFICE HENRY D. JAMES, OF EDGEWOOD, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELEC- TRIO & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA CONTROL SYSTEM Application filed January 19, 1928. Serial No. 247,890.

The invention relates to systems of control and has particular relation to systems in which a series of successively operable contactors are employed for automatically controllin the starting of electric motors.

The object of the invention, generally stated, is to provide in a control system for successively operating a plurality of contactors. 7

It is also the object of the invention to provide in a motor accelerating control systein for positively effecting the sequential operation of a'plurality of contactors.

A further object of the invention is to provide means in a motor control system, for short circuiting sections of a resistor disposed in the motor circuit in a predetermined sequence and at predetermined intervals, without reference to the current conditions of the motor circuit.

In order to obtain a clearer understanding of the invention, the following description should be read in connection with the accompanying drawing, in which:

Figure 1 is a diagram of the circuits of a control system arranged in accordance with my invention, and

Fig. 2 is a straight line diagram illustratin g the same system shown in Fig. 1.

In order to simplify the explanation of the invention, circuits shown in Fig. 2' will be designated by the same numerals as the corresponding circuits of Fig. 1.

In the system as illustrated, a motor 1, having an armature 2, and a series field winding 3 is connected in series circuit relation with a starting resistor 4 and across the supply conductors L1 and L2.

The reversal of the motor may be effected by appropriate operation of the reversing contactors 5, 6, 7, and 8. The starting resistor 4 is divided into sections 9, 11, and 12 and each of these sections is provided with a short-circuiting shunt. To control the shortcircuiting and, in consequence, the acceleration of the motor, electromagnetically operated accelerating switches 13, 14, and 15 having actuating coils 13a, 14a, and 15a, respectively, are associated with the respective shunts of sections 9, l1, and 12.

The accelerating switch 13, when closed, short-circuits section 9; the accelerating switch 14, when closed, short- circuits sections 9 and 11; and the, accelerating switch 14, when closed, short-circuits the entire starting resistor 4. The resistor in this instance is employed to protect the motor armature against the injurious eli'ect of excessive currents such as may occur when the motor is reversed by a reversal of the voltage applied to the motor armature while the motor is operating, which reversing operation is sometimes described as plugging the motor.

In order to prevent contactor 13 from closing to short-circuit a section of the resistor 4 until the current in the armature circuit of the motor has decreased to a safe value, current limit relays 17 and 18 are provided. These relays may be mounted in any convenient manner adjacent to the reversing switches 6 and 7. Arm members 26 and 27 may be provided on the armatures of the reversing switches and disposed to engage the armatures of the current limit relays, to maintain the relays in their circuit interrupting positions at all times when the reversing switches are open. Means, in the form of spring members 24 and 25 may be mounted under the bridging members of the relays to bias the relays to their circuit closing positions. These spring members should have suificient strength to effect the closing of the relays when the arm members on the reversing switches have been disengaged through the closing of the reversing switches. In other words, when, say, coils 6a and 17a are deenergized, the combined weight of arm 26 and the armatures of relays 6 and 17 overcomes the action of the spring 24, acting in the direction indicated by the arrow adjacent spring 24, and relay 17 will be in open-circuit position, but when coil 6a is energized and actuates relay 6, raising arm 26, then the spring 24, in the absence of counteracting energization of coil 1741, will close relay 17. A similar state of facts obtains for relay 18.

In order to prevent the immediate closing of the relays 17 and 18 thru the action of springs 24 and 25, after the reversing switches have been actuated, coils 17a and 18a, connected in series-circuit relation with the armature, series field, and starting resistor 4 of the motor, are positioned about the armatures 0t current- responsive relays 17 and 18, respectively. These coils 17a and 18a are so Wound about the relay armatures that their action, upon energization, opposes the action of springs 24 and 25. During starting of the motor, the initial rush of current, for well known reasons and in spite of the starting resistor 4, is heavy, and coils 17a and 18a, carrying this heavy current, are thus strong enough to maintain relays 17 and 18 open until the motor armature current has decreased to a predetermined safe operating value.

The energizing circuit for the actuating coil 13a on the accelerating contactor 13 is controlled by the one or the other of the current- responsive relays 17 and 18 the contacts of which are connected in parallelcircuit relation. The relay 13, therefore, will not close to short-circuit section 9 of the starting resistor 4 when the master switch 16 has been actuated to the one or the other of its operating positions unless the contact members of the one or the other of the relays 17 or 18 is closed. But the contacts of relays 17 and 18 remain open so long as the heavy starting current has not decreased to a predetermined safe operating value. The entire result is that section 9 remains in the armature circuit until the motor speed has built up some, the counter-electromotive force has increased, and the armature current has decreased to a desired value.

In order to control the sequence of operation of the accelerating switches 14 and 15,

time- delay relays 21 and 22 are provided. Actuating coils 21a and 22a, respectively, are mounted on the relays 21 and 22 and disposed to hold the'relays in their circuitinterrupting positions when the coils are energized. In order to delay the closing of the relays after the current thru the actuating coils has been shunted or by-passed around them, resistors 21?) and 225 are connected in shunt circuit relation to thecoils 21a and 22a, respectively. The purpose of the resistors 217) and 22b is to impede the changing of the magnetic flux that envelopes in these coils when energized by establishing a local circuit through the coils when the flux tends to collapse. The effect of prolonging the existence of the magnetic field is to prevent closing of the contact members of the relays for a short period of time after the motor current has been shunted or bypassed around the coils 21a and 22a.

The actuating coil of relay 21 in this instance is connected in series circuit relation with the starting resistor and, accordingly, is energized with the first rush of current through the motor. Thus, the relay 21 is actuated to open its contact members when the motor is started. Since as the actuating coil 14a of accelerating switch 14 is con nected in series circuit relation with the contact members of the relays 17, 18 and 21, the coil 14a of the accelerating contactor 14 will not be energized until the coil 21a of the time-delay relay 21 has been deenergized to allow the relay contact members thereof to close. The contact members of the timedelay relay 22, which is of similar construction to that of the relay 21 are, when closed, disposed to establish an energizing circuit for the coil 15a of the accelerating switch 15. lVhen the contact members of the acceler' ating switch 13, the time-delay relay 21, and the one or the other of the current- responsive relays 17 and 18 is closed, and the master switch 16 is in one of its circuit-closing positions, an energizing circuit for the coil 14a of the accelerating switch 14 will be established. This energizing circuit may be traced from the supply conductor L1, through the contact members of the one or the other of the current- responsive relays 17 and 18, conductor 20, the contact members of the relay 21, conductor 20 and the coil 14a of the switch 14, to the supply conductor L2.

It is to be noted that, so long as the contact members of both of the current- responsive relays 17 and 18 are open, the coil 13a of the accelerating switch 13 cannot be energized (see Fig. 2). Assuming now that the motor is operating in the forward direction and that the reversing switch 16 is actuated, then the heavy rush of current through the motor, caused by the reversal of the motor, eifects the opening of the relays 17 and 18 momentarily, thereby opening the switch 13 and reconnecting the resistor 4 into the motor circuit.

The moment the current in the motor drops to a predetermined value, the push of the spring 24 on the relay 17 will overcome the pull of the coil 17a of the relay and cause the contact members thereof to close. When they are closed, the coil 13a will again be energized to close the switch 13. Since the switch 13 has closed, the time-delay relay 21 will close, after a predetermined length of time, because the coil 21a and resistor 21?) and section 9 of the resistor 4 are shunted by a parallel circuit which extends from the junction of sections 9 and 11 of the resistor 4, through the contact members of the switch 13, the resistor 22b and coil 22a connected in parallel-circuit relation to each other, and the contact members of the switch 23. The length of time during which the contact members of the relay 21 will remain open, after switch 13 has closed, will depend upon the time constants of theclosed parallel circuits (see Fig. 2) comprising the coil 21a and resistor 21b, and section 9 of resistor 4, coil 21a and resistor 21?), coils 17a and 18a,

coil 22a and resistor 22?; and the contact members of the switch 18. These time constants will determine the rate of consumption of the energy stored in the magnetic field developed by the coil 21a.

lVhen the contacts of the relay 21 have closed, an energizing circuit for the coil 14a of the switch 14 is established in the manner hereinbefore set forth.

Since the contacts of the switch 14 have been closed, the section 11 of the resistor 4 and the coil 22a and resistor 22?) are shunted or by-passed by a circuit which extends from the junction of sections 11 and 12 of the resistor 4, through the contact members of the switches 14 and 23, to the supply conductor L2.

The length of time which will elapse befor the contact members of the relay 22 Will close is dependent upon the time required to dissipate the energy stored in the magnetic field developed by the coil 22a, in the circuits comprising the'coil 22a, the resistor 22b and the section 11 of the resistor 4, contact members of the switch 14 and the coil 22a and resistor 22?).

When the contact members of the relay 2 have closed, an energizing circuit for the 0011 15a is established, which circuit is in parallel relation with the circuit for the coil 14a (see Fig. 2). This circuit having been established, the switch 15 will close its contact members to thereby connect the motor directly across the supply conductors L1 and L2.

To start the motor from rest in the forward direction, the master switch 16 may be moved to its forward operating position establishing a circuit extending from line conductor L1 through the master switch 16, the actuating coils 5a and 7 a of reversing contactors 5 and 7 and the actuating coil 23a of line contactor 23 to line conductor L2 closing reversing eontactors 5 and 7 and line contactor 23. In this manner the motor is connected in a circuit which may be traced from line conductor L1 through reversing contactor 5, the armature 2 of the motor 1, reversing contactor 7, series field winding 3, resistor 4, the actuating coil 21a of relay 21 and actuating coils 17a and 18a of the current responsive relays 17 and 18 and line contactor 23 to line conductor 2 causing the motor to start to rotate. The current responsive relays 17 and 18 may be constructed in such a manner that they will close immediately when the motor is started from rest, thereby establishing a circuit to effect closing of accelerating contactor 13 simultaneously with the starting of the motor. The other accelerating eontactors will close in a predetermined sequence in accordance with the description given hereinbefore. It will be understood, however, that in the preferred embodiment discussed in detail above the current responsive relays 17 and 18 will be constructed so that they will delay the actuation of accelerating contactor 13 to short circuit section 9 of the starting resistor when the motor is being started. The main purpose of the current- limit relays 17 and 18 is to delay the short-circuiting of section 9 of the start ing resistor 4 to protect the motor against excessive currents in the armature when the motor is plugged across the line.

The usual practice would be to construct the current responsive relays so that they will be prevented from closing by the actuating coils 17a and 18a, until the current in the armature circ it has fallen to substantially the value that is drawn by the motor when the same is started. It will be readily seen that the reversal of the voltage applied to the armature of the motor may be effected by moving the master switch 16 to the reverse operating position in which position a circuit is established extending from conductor L1 through the master switch 16, the actuating coils 6a and 8a of the reversing switches 6 and 8 and the actuating coil 23a of line contactor 23 to line conductor L2, which circuit, when established, causes reversing switches 6 and 8 and line contactor 23 to close. The short-circuiting of the resistor 4 will follow in the same sequence as described hereinbefore.

It will be understood that the apparatus shown in this modification of the invention may be altered somewhat without departing from the spirit of the invention, as set forth in the appended claims.

I claim as my invention:

1. In a motor-accelerating system, in combination, a motor, a starting resistor for the motor, a plurality of separately actuated switches for sliort-circuiting sections of the resistor, coils for actuating said switches at predetermined intervals during the starting of the motor, motor-current responsive means for controlling the operation of one of said switches, a relay having an actuating coil disposed to be initially energized by motor current and subsequently deenergized when said one switch has been closed, a resistor disposed in shunt relation to said actuating coil for delaying the operation of the relay, said relay being disposed to establish an energizing circuit for the coil of another of said switches after said relay has operated.

2. In a motor-accelerating system, in combination, a motor, a starting resistor for'the motor, a plurality of separately actuated switches for short-circuiting sectionsof said resistor, coils for actuating said switches in a predetermined sequence during the starting'of the motor, current-responsive means for controlling the actuating coil of one of the switches, a relay for controlling theactuating coilof another of the switches, an actuating coil-and resistor connected in parallel circuit thereto for said relay, disposed to be energized when themotor is energized and subsequently deenergized responsive to the closing of the first-mentioned switch, said resistor being disposed to retard the closingiof the relay after said first-mentioned switch has been closed, a second relay having an actuating coil and a resistor connected in parallel-circuit relation thereto disposed to be energized when the first-mentioned switch closes and subsequently deenergized when the second-mentioned switch closes, said resistor being disposed to delay the operation of said second-mentioned relay, each of said relays being disposed to efiect the operation of one of said separately actuated switches.

' 3. In a motor-accelerating system, in combination,a motor, a source of power, a starting resistor for said motor, means for connecting said resistor in circuit relation'with said motor to said source of power, means for reversing the direction of application of said power to the motor, a plurality of accelerating switches for short-circuiting sections of the resistor, means responsive to the current flowing in the motor circuit for 'efiecting closing of one of the accelerating switches to short-circuit a section of the resistor when the motor is started from rest and disposed to prevent the operation of said accelerating switch when the power to the motoris reversed while the motor is running in one .direction, and a relay having an actuating coil and a'resistor connected in parallelrcircuit relation to the coil for effecting the operation of another accelerating switch after said relay has operated, saidparallel-connected resistor being disposed to retard the operation of said relay after it has been shunted by the first named accelerating switch.

4. In a control system, in combination, a motor, a starting resistor, a source of power, meansfor connecting the motor and starting resistor in series-circuit relation with the source of power, a plurality of accelerating switches for short-circuiting sections-of the resistor when the motor is being'started, a plurality of relays each having actuating coils responsive to motor current for controlling the operation of some of the accelerating switches, means responsive to the current conditions in the motor for effecting the actuation of one accelerating switch, said accelerating switch, when closed, being disposed to short-circuit the actuating coil of one relay and to effect energization of the actuating HENRY 1). JAMES.

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