US2505281A - Antiplugging control for motors - Google Patents

Description

April 25, 1950 J. G. ELWOOD ANTIPLUGGING CONTROL FOR MOTORS Filed April 8, 1949 INVENTOR. JULIUS G. ELWOQD Y E N R o T T A Patented Apr. 25, 1950 UNITED TS TAT-ES "OFFICE 'ANTIPLUGGIN G CON TROL' "FOR MOTORS ,1 Julius G.qElwood, .ChiOflS'OrliIll-h assignor tonGar- '1' .nogie-Jllinois-Steel .Corporation,ia=corporation Application April 8, I-949,-Serial-No-. 86,352

2 Claims. 1

This invention. relates. particularly to an anti- :p'lugging control for :a hoisting motor and is a continuation-impart .01" my: copending application, -Serial No 658,054, filed .Mareh ZQ, 194.6, -=nowPatent'2-,494;611, issued January 17, 1950.

Previous to my invention, constanttrouble was experienced with crane hoist motors because the existing means of protection against plugging are ineffective under certain conditions. .plugging' of a motor means reversing the '.direction of rotation of the-motorbefore the .m'otor has come -to-a complete stop from its original di- -rection'orrotation. This causes: a greatly inten- The term sified currentto flow through the armature coils of thomotopwhioh; if not controlled, .may damagethe motor. The-high currentsaredue to the fact that the'C. "F. (counter eleotromotive force),-which isthe- 'stabilizing element of the motor speed; 'is-in the samedirectionas the apmotorarmature which often'W-reck the armature and also :the'field windings.

In case 1 the motor speed 'becomes excessive --;while lowering a heavy load", the operator usually becomes excited and hisfirst thought is to throw themotorinto the reverseflirectionin order to stop. theload. Mostcranes are built-without any protection againstplugging the hoist motor although in some .instances partial protection under certain conditions is provided for.

It is therefore an object of my invention to provide a control for preventing the harmful effects of plugging hoist motors.

Another object is to provide protection of hoist motor armatures against overloading stresses due to acceleration of the load being lowered.

These and other objects will be more apparent after referring to the following specification and attached drawings, in which the single figure is a schematic wiring diagram of my invention.

Referring more particularly to the drawing, the power circuit is shown in heavy lines and the control circuit is shown in light lines. Power is supplied to the motor armature E from the power source i, 5 through the knife switch 8. .c'

Power is supplied to the control circuit through combined knife switch and fuse it. The control circuit is provided with a master switch l2 havinga number of contacts operated by cams whose positions are controlled by the master switch -;handle. Asshown; the master switch is provided with three'lowering positions and four hoisting 1 positions. zThe switch is' provided, with contacts -16; 8,129, 22,124, 25' and 28. -:.places themaster switch .handlein'the first positionon the lowering-side, the contacts l6, I8, 22, '-:26- and128-.c1ose, 'this being indicated by the X adsjacent the contacts under position E. glass the contactor coils 3%, 32, 33, 34, 38, 42 and and 44:and to open contact 38.

tion 'the motor armatureZ-isconnected to'the power source-t;- 5 in series with the dynamic oral:-

When theoperator This ener- Mxtoclosecontactstli, 32, 33,34, 34','38, 42

In this posiing resistance'tfiwhich limits the armature current. The motor-series held 48 is connected to "the power line inserieswith the *magnetcofl 50 of the motor br'akeil and resistor 52. 1 Thus the :motor is connected and' operated as shunt motor which gives the series'motor the ability-to hold backthe load" in lowering by becoming-a "generator. The series brake releases when currentflowsthrou'gh its coil 59.

In thesecond' lowering position the contacts closed in the'fi-rst'lowering position remain closed with the=exception ofxcontact 28 which opens, thus'deenergizing coil 44 to open contact 44. This inserts theresistance 54 in series with the 'se1-'ies'field to-reduce the field current, thus increasingthelowering speed of the motor.

In the third position, contact 265 is open which -'-deenergizes-coil 42 toopen contact 4 2. This insertsresistor 56 inseries with the series field to reduce the field-currentstill-further, thus increasing the lowering speed of the motor.

"Forthefirst-position of the master switch on "the'hoistside, the switch contacts is, 2G and 22 close, thus energizing coils 30, 36 and 38 to close contacts 36 and 38 and open contact 38. This places the motor armature 2, series field 48, magnet coil 50 and resistances 52, 54 and 53 in series. The hoisting torque of the motor is limited by the resistances 52, 54 and 56.

When the master switch is placed in the second hoisting position, contact 24 is closed in addition to the contacts previously closed. This energizes coil 40 which in turn closes contact 40 to short out resistance 52 to increase the hoisting torque of the motor and accelerate it to a higher speed.

In the third position, the additional contact 26 is closed, thus energizing coil 42 which closes contact 42 to short out the resistance 56. This further increases the hoisting speed.

In the fourth position, contact 28 is closed in addition to the contacts previously closed. This energizes coil 44 which closes contact 44 to short contact 58.

Y will close contact 33.

tacts 58 and 58 in addition to normally open Contact 58 is in the line energized by the closing of contact 28 and contact 58 in the line energized by the closing of contact 22. As pointed out above, the motor is connected as a shunt motor during lowering of the load and the potential energy of the load is converted into electrical energy which is dissipated in the resistances in the armature and field circuits. When the switch is thrown to the lowering side the coil 34 will close contact 34 and the coil 33 This causes current to flow in the anti-plugging circuit so that the coil 58 will be energized, thus closing contact 53 and opening contacts 58 and 58. If the motor is suddenly plugged, that is, placed in the hoisting position, the relay 33 is deenergized, thus opening contact 33. However, relay 58 continues to be energized through closed contact 58 and holds the contacts 58 and 58 open, thus preventing the coils 35 and 38 from being energized and attempting to make the motor raise the load while it is still lowering. Since coil 38 is deenergized, normally closed contact 38 will be closed. Thus, the kinetic energy of the load is absorbed in the dynamic braking resistance 46 as heat energy, and also in the brake lining and brake Wheel as heat energy. Stopping the load in this fashion imposes the minimum strain on the motor. The relay 58 is pre-set at a predetermined potential which will occur at or just before the dynamic and mechanical braking brings the load and motor to a stop. When the motor comes to a complete stop the coil 58 deenergizes closing the contacts 58 and 58 and permitting the motor to hoist the load in accordance with the position of themaster switch. In the hoisting position relays 33 and 34 will always be deenergized so that the contacts 33 and 34 will be open. If desired the relays 3'2, 33, and 34 may be combined, it only being necessary that they be in a circuit which is energized only during lowering.

While one embodiment of my invention has been shown and described it will be apparent that other adaptations and modifications may be made without departing from the scope of the following claims.

I claim:

1. An anti-plugging control for a hoisting motor or the like having a power circuit for supplying power to the motor and a control circuit for controlling the direction of rotation of the motor which control comprises a dynamic braking re sistance in the power circuit, an anti-plugging relay coil connected across the motor armature, two pairs of normally open contacts in series with said relay coil and in parallel with each other, a relay in said control circuit energized during lowering only, one of said pair of contacts being operable by the anti-plugging relay and the other being operable by the second named relay, contacts in the control circuit operable by said anti-plugging relay, said last named contacts being closed during rotation of the motor in a hoisting direction, said anti-plugging relay coil being energized when lowering and remaining energized when the lowering circuit is interrupted to thereby hold said contacts open and prevent rotation of said motor in a hoisting direction until the kinetic energy of the load is absorbed.

2. An anti-plugging control for a hoisting motor or the like having a power circuit for supplying power to the motor and a control circuit for controlling the direction of rotation of the motor which control comprises a dynamic braking resistance in the power circuit, a magnet coil for a brake in series with said motor, an anti-plugging relay coil connected across the motor armature, two pairs of normally open contacts in series with said relay coil and in parallel with each other, a relay in said control circuit energized during lowering only, one of said pair of contacts being operable by the anti-plugging relay and the other being operable by the second named relay, contacts in the control circuit operable by said anti-plugging relay, said last named contacts being closed during rotation of the motor in a hoisting direction, said anti-plugging relay coil being energized when lowering and remaining energized when the lowering circuit is interrupted to thereby hold said contacts open and prevent rotation of said motor in a hoisting direction until the kinetic energy of the load is absorbed in the dynamic braking resistance and by the brake.

JULIUS G. ELWOOD.

No references cited.

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