US1961822A - Control system - Google Patents

Description

C. H. FREESE CONTROL SYSTEM June 5, 1934.

Filed Jan. 23 1932 DYNAMIC LOWER/N6 lvm/cantor` I P0 WER es! S e U., D! P w Ht e A d .m ISH C Patented June 5, 1934 CONTRQL SYSTEM Clyde H. Frecce, Moscow, Union of Soviet Socialist Republics, assigner to General Electric Company, a corporation of New York Application January Z3, 1932, Serial No, 588,369

5 Claims.

ltiy invention relates to systems of control for Ylectrio motors, and more particularly to such ysteins intended for the control of a motor subject under certain conditions to overhauling loads,

and has for an object the provision of a siniple and reliable system in which the direction and speed ci rotation is governed by a pair of pushbutton switches or the like.

Heretoore certain types of electrically driven hoists have been controlled by means oi ropes operatively connected to a drum switch carried by the hoist. These ropes dangling from the hoist constitute a hazard inasmuch as they sornetirnes catch on machinery causing unexpected changes in thCl operation of the hoist. Furtherrnore, both hands of the operator were required to operate the ropes. Should the operator lose his footing, the hoist might proceed on its way, endangering the lives of other workmen as well as the machinery located in the path of the hoist.

Therefore, it is a further object of my invention provide normally open pushbuttons for the hoisting and lowering operations so that the operator may control the hoist with one hand, leavthe other free to guide the work, and in case he removes the pressure from a selected pushbutton the motor is quickly brought to standstill.

In case or power failure the resistance across the supply lines may be any value with zero and iunity asliinits. Heretofore, under certain conclu ons oi line resistance, the hoist dropped overhauling loads. Accordingly, a further object of iny invention is to provide for the controlled lowering of a heavy load in the event of power failure regardless oi the line resistance together with protective features for the motor.

For a more complete understanding of my invention reference should now be had to the drawing wherein i have shown in Fig. l a control *ein embodying rny invention, while in Fig. 2 shown curves explanatory of the operation niy invention. Fig. 3 shows the lowering ciri 1 in simpliied orrn.

@eferring now to the drawing, I have shown y invention in one forrn as applied to the control. oi a hoisting motor l0, one side of the armature of which is connected through a field winding l1 to the accelerating resistors 12, 13 and i4. @ne side oi a braking resistor 16 is cont: l to the midpoint 17 between the acceleratc l2 and The braking circuit the resistor 16 may be traced from one i8 provided on a hoisting direction normally closed contact 21 of the (Cl. 17E-152) direction switch and to the other side of the motor armature. A lowering direction switch 22 is arranged to complete an energizing circuit cr the motor 10 through a resistance 24 so that current is supplied to a parallel circuit, one

branch or" which includes the armature of motor 10, normally closed contacts 21, the coil 18, and the braking resistor 1G, while the other branch of the parallel circuit includes the eld winding l1 andthe acce erating resistor 12. The parallel circuits described are in series with the aoceleratu ing resistors i3 and 14, which resistors are controlled by means of the accelerating contactors 27 and 28. The accelerating contacter 26 serves to short c' fcuit the resistor 12 only during the hoisting of the motor. A pair of time closing relays 29 and 30 serve to complete energizing circuits for the accelerating contactors under certain conditions of operation so that the motors speed may be increased to insure the safe hoisting or lowering of a load. A brake 32 normally exerting its maximum braking force on the motor 10 arranged to be released through an energizing ci controlled by a bra-ire relay 33.

A pair of supply lines 35 and 36 are arranged to be connected by the line switches 37 and 38 to a suitable source of direct current supply as indicated by the well known symbols for direct current. A lowering pushbutton 40 and a hoisting pushbutton 41 are normally biased to their open positions in engagement with their respective contacts 42 and 43. A second pair of contacts 44 and 45 is provided on each pushbutton, the circuit therethrough being completed whenever a pushbutton is depressed. These contacts` 44 and 45 are arranged to be connected to the supply line 35 by means of relay 4'?, the operating coil of which is arranged to be energized from the supply line 35 through a circuit which may be traced by conductor 48, normally closed contacts 43 on the hoisting pushbutton 4l, coneither oi the overload relays 51 or 53 has been operated to its open position and the motor is srought to a standstill. As soon as the pushbuttons are released an energizing circuit is again Acompleted for the relay 47. A line contacter 56 is also provided to disconnect the motor circuit from the supply line 36 whenever both of the direction switches have been operated to their open positions.

With the above understanding of the elements and their organization with respect te each other in the system, the operation ef the system itself and the manner in which the various circuits are completed to secure complete control of the motor 10 under normal or abnormal operating conditions will be readily understood from the description which follows:

With the various parts in the positions shown in the drawing it will be assumed that the line switches 37 and 38 are operated to their closed positions to connect the supply lines 35 and 36 to a. suitable source of direct current supply. The relay 47 is immediately operated te its closed position inasmuch as the energizing circuit traced above is complete for the operating coil of the relay 47. This relay thereupon closes te energize a conductor 60 and te complete a holding circuit for the coil of the relay 47. This circuit may he traced from the supply line 35, contacts of relay 47, operating coil of this relay, conductor 50, contacts of overload relay 51, conductor 52, contacts of the overload relay 53 and te the other supply line 36.

As soon as the conductor 60 is energized circuits are completed for the time closing er accelerating relays 29 and 30. The energizing circuit for the accelerating relay 29 may be traced from the supply line 35, contacts of relay 47, conductors 60 and 62, .contacts 63 of the hoisting switch 29, conductor 64, operating coil of the accelerating relay 29 and by conductors 65 and 66 te the other supply line 36. This relay is thereupon operated to open its contacts. It will be observed that the closing of the relay 29, after the deenergizatien of the operating coil, is delayed by reason of a normally short circuited coil 67.. The energizing circuit for the accelerating relay 30 may be traced from the supply line 35, contacts of the relay 47, conductors 60 and 68, contacts 69 of the lowering direction switch 22, conductor 70, contacts 71 of the first acoelerating contacter 26, conductor 72, operating il of the accelerating relay 30, and by conductor 66 to the other supply line 36. This relay immediately operates te open its contacts. If it be desired to operate the motor 10 in a direction to hoist the load, it is only necessary te depress the pushbutten 41 until the conducting member of the pushbutten engages the contacter 45. A circuit is thereby completed for the hoisting direction switch 20 which circuit may be traced from the supply line 35, contacts of relay Y47, cmductor 60, contacts 45 of the pushbutten switch 41. conductor 74, interlocking contacts 75 of `the lowering direction switch 22, operating coil of the direction switch 20, and by conductor 76 te the other supply line 36. The hoisting direction switch 20 thereupon operates te open its contact 2.1 breaking the loop circuit through the meter armature, the field Winding and the resistances 12 and 16, and to close its contact 77 partially to complete an energizing circuit for the motor 10. This circuit may be traced from the supply line 35, conductor 78, series coil 79 of the overload relay 51, conductor 80, contact 77 of the hoisting direction switch 20, the armature of the motor 10, series field winding 11, accelerating resistors 12, 13 and 14 and to the line contacter 56. It will be observed that the closing of the contacts 73 of the hoisting direction switch completed an energizing circuit for the contacter 56. This circuit may be traced from the supply line 35, contacts ef relay 47, conductor 60, contacts 45 of the hoisting pushbutten 41, conductors "I4 and 83, contacts 73 of the hoisting direction switch 20, conductors 84 and 85, operating coil of the contacter 56 and to the other supply line 36. The contacter 56 is thereupon operated te complete the motor circuit through the series coil 82 of the overload relay 53 to the supply line 36. At the `same time the brake 32 is released due to the closing of the contacts 73, which serve te complete an energizing circuit for the brake relay 33. This circuit may be traced from the supply line 35, contacts of the relay 47, conductor 60, contacts 45 of the hoisting pushbutten 4l, conductors 74 and 83, contacts 73 of the hoisting direction switch 20, conductors 84 and 85, operating coil of braking relay 33, conductors 87 and 88 to the other supply line 36. The brake relay immediately operates to close its contacts thereby connecting the operating coil of the brake 32 in shunt with the motor by the conductor and te one side 90 of the accelerating resistor 14.

The motor new rotates at low speed in a direction to hoist the lead as indicated by curve H1 of Fig. 2. It will be observed that the contacts 63 of the hoisting switch 20 were opened as this switch was operated te deenergize the accelerating relay 29. After an interval of time determined by the short-circuited winding 67, its contacts close to complete an energizing circuit for the rst accelerating contacter 26. This circuit may be traced from the supply line 35, contacts of relay 47, conductor 60, pushbutton contacts 45, conductors 74 and 83, contacts 73 of hoisting switch 20, conductors 84 and 92, contacts of time delay relay 29, conductor 93, operating coil of the lrst accelerating contacter 26 and by conductor 88 to the other supply line 36. This contacter immediately operates to short circuit the resistance l2 thereby accelerating the motor 10 as indicated by curve Hz. The contacts 71 operated with this contacter are opened to deenergize the second accelerating relay 30. After a predetermined time interval this relay operates to clesc its contacts thereby completing an energizing oircuit for the second accelerating contacter 27. This circuit may be traced from the supply line 35, contacts ef the relay 47, conductor 60, pushbutton contacts 45, conductors 74 and 83, contacts 73 of the hoisting direction switch 20, conductor 95. contacts of the accelerating relay 30, conductor 96, operating coil of the second accelerating centactor 27 and by conductor 38 to the other supply line 36. The motor 10 is again accelerated as indicated by H3 by reason ef the short circuiting of the resistor 13 by the contacter 27. The closing of this contacter also serves to complete an energizing circuit through its contacts 97 for the third accelerating contacter 28. This circuit is derived from the conductor 96, contacts 97 of the second accelerating contacter 27, operating coil of the third accelerating contacter 28 and by conductor 88 to the other supply line 36. The motor 10 is new connected to normal line voltage for operation as indicated by curve H4,

It is important te here observe that the operation of the accelerating contacters, the contacter 56, the hoisting direction switch 20, and the brake relay 33 were all traced through the hoisting pushbutton contact 45. Therefore, if this pushbutton is released at any time it will be observed that these devices will be deenergized and are operated to their open positions.

As seen as this occurs, assuming that the motor is operating at its full speed in the hoisting direction, it will be observed that the motor 10 quickly comes to rest by reason of the force of gravity exerted upon the load which is being hoisted and because the brake 32 is immediately released to exert its maximum braking force on the motor. The brake 32 also serves to hold the load at rest in its hoisted position.

As soon as the hoisting direction switch 20 and the accelerating contactor 26 operated to close their respective contacts 63 and 7l the energizing circuits for the accelerating relays 29 and 30 are again established-` These relays are therefore operated to open their respective contacts.

In order to operate the motor 10 in a direction to lower the load, it is only necessary for the operator to depress the pushbutton 40 to close the contacts 44. As in the case of the hoisting operation, it will be observed that the energizing circuits which are to be traced are all completed through the contacts 44 of the pushbutton switch 40 so that the load may be stopped in any position by merely releasing the pressure on the pushbutton. It will also be seen that the speed oi the motor 10 is controlled Whether a heavy load or a light load is to be lowered so that the speed of the motor 10 is always limited to a safe value irrespective of whether there is power failure, or any condition in which the resulting line resistance may be zero or iniinity, or any value between these two limits. The motor 10 is also protected at all times against unduly large peak values of current.

As soon as the lowering pushbutton 40 engages its contacts 44, a circuit is completed for the lowering direction switch 22. This circuit may be traced from the supply line 35, contacts of the relay 47, conductor 60, contacts 44 of the pushbutton 40, conductor 98, interlocking contacts 99 of the hoisting direction switch 20, operating coil of the lowering direction switch 22 and by conductor 88 to the other supply line 36, The direction switch 22 thereupon closes to initiate power lowering as indicated by curve L1 of Fig. 2. A circuit is completed through its contacts 100 for the contactor 56, which circuit may be traced from the supply line 35, contacts of relay 47, conductor 60, contacts 44 of pushbutton 40, contacts 100 of lowering direction switch, conductors 84 and 85, operating coil of contactor and to the other supply line 36. The closing of the contacts 101 of the direction switch 22 serves to connect at all times the resistance 24 in series with a par-- allel circuit which includes the armature of the motor 10, coil 18 of direction switch 20, and the braking resistor 16 in one branch while the eld winding 11 and the accelerating resistor 12 is included in the other branch. Therefore, for lowering a load the motor 10 is connected as a shunt motor and current may iow from the supply line 35 by conductor 78, series coil 79 of the overload relay 51, conductors and 102, contacts 101 of the direction switch 2 2, resistance 24, the current dividing at the point 103, through the armature of the motor 10 and the braking resistor 16, and through the series eld winding 11, accelerating resistor 12. The armature and iield current then iows through the accelerating resistors 13 and 14, contactor 56, series coil 82 vof the overload relay 53 and to the other supply line 36. The brake operating coil of the brake 32 is again energized by the closing of the brake relay 33. This relay is closed by reason of an energizing circuit which may be traced from the supply line 35,

contacts of the relay 47, contacts 44 of the pushbutton 40, contacts of the lowering direction switch 22, conductor 84, operating coil of the brake relay 33 and by conductors 87 and 88 to the other supply line 36.

The motor 10 is accelerated in a direction to lower the load in accordance with the curve L1 of Fig. 2. The contacts 69 of the lowering direction switch 22 are opened as this switch is operated to its clos-ed position, thereby deenergizing the accelerating relay 30. Aiter a predetermined time interval the accelerating relay 36 closes its contacis to complete an energizing circuit for the second accelerating contacter 27 to indicate the power lowering as indicated by curve L2. This circuit may be traced from the supply line 35, contacts oi the relay 47, contacts 44 of the pushbutton station 40, contacts 100 of the lowering direction switch, conductors 84 and 95, contacts of accelerating relay 30, conductor 96, operating coil of the accelerating contacter 27, and by conductor 88 to the other supply line 36. The motor 10 now operates according to the curve L2 of Fig. 2. As soon as the accelerating contactor 27 closes the contactor 28 is closed by reason of the closing of the contacts 97 operated with the accelerating contacter 27. The motor 1G thereupon is connected to exert its maximum torque in a direction to lower the load as shown by the characteristic curve NO of Fig. 2.

In the case of an overhauling load such as when the hook is heavily loaded, the initial exertion of the torque of the motor is suiiicient to start the load in a downward direction. The tendency is for the motor 10 to be accelerated to high speed. However, the effect of the counter-electromotive force generated by the motor 10 is to decrease the current flowing to the motor armature. For a heavy overhauling load, the current through the' armature is actually reduced to zero and is reversed so that the motor 16 operates as a generator. The current flowing through the iield winding 11 is thereby increased to further limit the motor speed, The resistors 12 and 16 proportioned so that the speed of the motor 10 ze never exceeds a safe value.

If it is desired to bring the motor 10 to a standstill, itis only necessary to release the pushbutton 4Q which is immediately operated to its open position. It will be observed that the opening of 4 applied` to the motor 10 in addition to the brako ing effort applied oy the brake The current flowing through the coil 18 included in this loop circuit causes a force to be exerted on the hoisting direction switch 2o in a direction to apply pressure to the contact 21 thereby minimizing ,-1 sparking at these contacts and insuring a minimum resistance therethrough for the flow of current.

Assuming that the lowering pushbutton 4Q is maintained depressed with its contacts 44 closed e and there should be a power failure, the motor l0 will continue to lower a heavy load at substantially the same speed as before. If the motor 10 is operating on a tie-in system or a system in which there are a great many loads connected It will be observed that 1' n. in.;

sin)

to the line, the equivalent resistance of the line may be quite low, approaching zero as a limit. In this case, the motor 10 acting as a generator by reason of the heavy overhauling load, may supply current through the resistance 24, contacts 101 of the lowering direction switch 22, to the supply line 35 and through the external circuit LR (Fig. 3) to the other supply line 36, and by contactor 56, accelerating contactors 27 and 28, resistor 16, coil 18 of hoisting switch 20, contact 21 and to the other side of the motor amature. The resistance 24 also serves to limit the current now produced by the motor 10 through the supply lines 35 and 36 and serves to give the motor a desirable characteristic curve.

For example under the assumed conditions of power failure if the line resistance were zero and the resistor 24 had not been included in the circuit no difference in potential would be produced between the points 17 and 103. Therefore no current would flow through the iield winding 11 to maintain dynamic braking.

By including the resistance 24 however the line resistance may reach its lower limit of zero without causing the' loss of dynamic braking of the motor. Thus it will be seen that the voltage drop across the resistance 24 causes a difference in potential across the points 17 and 103 and insures a relatively strong field for dynamic braking so that the load is lowered at substantially the speed of normal operating conditions. This will be seen by reference to Fig. 2 where the curve NO represents normal operating conditions and the curve LO represents the condition when the line resistance reaches zero as a limit and the motor is connected as shown in Fig. 3. The line resistance will rarely, if ever, actually reach its lower limit but even if it should the curve LO shows that the system will safely lower very large overhauling loads.

However even if the line resistance does not approach zero as a limit, it may be low enough so that without the resistance 24 the motor field winding would no longer receive sufficient current to insure a safe lowering speed although sufiicient voltage (ten to fifteen per cent normal voltage) would exist to maintain the control devices in their energized positions. Because of the resistance 24 however and the correct selection of the resistance values for each branch of the parallel circuits suiiicient field current is insured to prevent excessive speed on an overhauling load.

If it is desired to stop the motor at any time, it is only necessary to release the pushbutton 40 so that its contacts 44 are opened. The direction switch 22 is thereupon operated to its open position to disconnect the motor and the resistance 24 from the supply lines 35 and 36. The contactors 27 and 28 and the braking relay 33 are immediately operated to their open positions. The motor 10 thereupon supplies current through the dynamic braking circuit including the field winding 11, the resistor 12, and the braking resistor 16. Consequently the motor 10 is quickly decelerated and the brake 32 is applied to assist the deceleration of the motor to a standstill and thereafter serve to hold the load in its new position.

It will now be assumed that the motor is connected as a shunt motor for lowering a heavy overhauling load and there is a power failure due to the opening of the supply circuit, or where there is a power failure on an isolated system so that the line resistance approaches infinity as a limit. It will be observed that the motor 10 acting as a generator may supply current by the resistance 24, contacts 101 of the lowering direction switch 22, series coil 79 of the overload relay 51, supply line 35, contacts of the relay 47, conductor 60, contacts 44 of the lowering pushbutton 40 and through the various energizing circuits traced above, including the operating coil of the direction switch 22, the operating coils of the accelerating contactors 27 and 28 and the coil of the brake relay 33, to the other supply line 36 and by resistor 16 to the other side of the motor armature. These devices remain in their closed positions if only a small fraction of their pickup current continues to flow through their respective operating windings. Consequently the C. E. M. F. of the motor is sufficient to maintain these devices closed, so that the lowering operation of the motor 10 is continued with its speed controlled within safe limits. In fact under this condition it will be observed from Fig. 2 that the curve LI, representing the condition when the line resistance approaches infinity as a limit, indicates that the speed of the motor is somewhat less than under the normal operating condition as represented by the curve NO. This is due to the increase in field excitation caused by substantially the total motor current flowing through the field winding 11.

Should there be a failure of the brake it will be observed that even for a heavy overhauling load, the load will not be dropped because the circuits described above will be completed and the motor will continue to .lower the heavy load at a speed less than normal as indicated by the curve NO.

Though it will, of course, be understood that the values of the various resistances and resistors may be varied as desired, the curves shown in Fig. 2 represent a highly satisfactory combination of hoisting and lowering characteristics. curves were obtained by proportioning the resisters as follows, the line volts divided by the full load current of the motor representing the base value of 100% ohms. The resistance 24, nineteen per cent; the braking resistor 16, twenty-eight per cent of the base value; resistor 12, eighty per cent of the base value and the accelerating resistors 13 and 14, respectively, thirty and twenty per cent of the base value.

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

1. A control system for a motor provided with a field winding and subjected to overhauling loads, comprising connections for connecting the armature of said motor and said field winding in parallel circuits. normally energized supply lines, means for limiting the lowering speed ofsaid motor in case of power failure irrespective of the line resistance comprising a resistance connected at all times in series with said parallel circuits, the resistances of each of said circuits being so proportioned with respect to said resistance as to produce suflicient field excitation to limit said motor speed to a safe value even though said line resistance approaches zero as a limit.

2. Means for controlling the speed of a motor subjected to an overhauling load when a power failure occurs, comprising a eld winding for said motor, a braking resistor, an accelerating resistor and a resistance, a lowering direction switch for energizing said motor through parallel circuits, one circuit including the armature of said motor and said braking resistor and the other circuit including said field winding and said accelerating These resistor, said resistance being connected at all times in series relation with said parallel circuits.

3. A control system for a motor provided with a field winding and subjected to overhauling loads, comprising connections for connecting the armature of said motor and said neld Winding in parallel circuits, normally energized supply lines, means for limiting the lowering speed of said motor in case of power failure when the value of line resistance is any value between zero and innity as limits comprising a resistance connected at all times in series with said parallel circuits to insure suflicient excitation on said motor to limit said motor speed when said line resistance approaches zero as a limit, the resistance of said parallel circuit being so proportioned as to produce a safe lowering speed with normal voltage on said feeders.

4. A control system for hoisting apparatus and the like including a direct current motor provided with a iield winding, accelerating resistors therefor, a braking resistor normally connected in shunt with said motor armature and said field winding, a series resistance, a lowering direction switch, a manually operable control switch for completing an energizing circuit for said lowering direction switch, the said direction switch serving to connect said resistance in series with a parallel circuit including said motor armatiue and said braking resistor in one branch and said eld winding and one of said accelerating resistors in said other branch, the resistance of said branches of said parallel circuit and of said series resistances being so proportioned as to produce a safe lowering speed of said motor on an overhauling load in the event of power failure with the value of the line resistance any value between zero and innity as limits.

5. The combination with a hoisting apparatus of a direct current motor provided with a eld winding, an accelerating resistor therefor, a braking resistor normally connected in shunt with said motor armature and said field winding, a series resistance, a lowering direction switch, a manually operable control switch biased to its open switch :for completing an energizing circuit for said lowering direction switch, said direction switch serving to connect at all times said series resistance in series with the parallel circuit including said motor armature and said braking resistor in one branch and said eld winding and said accelerating resistor in said other branch, the values of said resistance and of said resistors being selected so as to insure the safe lowering speed of an overhauling load in the event of power failure with the Value of line resistance any value between Zero and innity as limits.

CLYDE H. FREESE.

Images