US1396101A - Electric system - Google Patents

Description

A. J. DREYER.

ELECTRIC SYSTEM. APPLICATION FILED AUG.I2, I920.

1,396,101, Patented Nov. 8, 1921 3 SHEETS-SHEET l.

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MQ Q W A. J. DREYER. ELECTR|C-SYSTEM. APPLICATION FILED AUG.I2, 1920.

1,396, 1 O1 Patented Nov. 8, 1921.

3 SHEETSSHEET 2.

Clftozneq A. J. DREYER. ELECTRIC SYSTEM.

APPLICATION FILED AUG. 12, 1920- 1 ,396, 1 O1 Patented Nov. 8, 1921.

3 SHEETS-SHEET 3- E: G Fl 5 5 3 uwntoi 21M i M a citizen of the United States, residin UNITED STATES PATENT OFFICE.

ALFRED I. DREYER, OF IIILW AUKEE, WISCONSIN, ASSIGNOR TO PAWLING &; HARNISCHFEGER 00., OF MILWAUKEE, WISCONSIN, A. CORPORATION 01:

Wisconsin.

ELECTRIC SYSTEM.

Patented N 0v. 8, 1921.

Application filed August 12, 1920. Serial No. 403,018.

To all whom it may concern.

Be it known that I, ALFRED J. DREYERt,

ilwaukee, county of Milwaukee, and tate of Wisconsin, have invented new and useful Improvements in Electric Systems, of which the following is a specification.

This invention relates to electric systems and is particularly directed to improvements in systems for controlling electric motors in which dynamic braking is a prominent feature.

The invention will be described as applied to hoisting motors for electric cranes and, for the sake of clearness, the description will be confined to this application of the invention. It is to be understood, however,

. that thisinvention relates broadly to systems for controlling .electric motors, and that it may be applied to motors serving a variety of purposes. It is, therefore, to be understood that the invention is not limited to systems in which the motor is employed as a hoisting motor for electric cranes.

In former systemsof the above general type, when applied to electric cranes and similar apparatus. the practical, final result attained, is that the current consumption and correspondingly the energy required for lowering the loads is actually in. excess of that required for raising the same loads. This obviously is a defective and inefficient organization and is not a logical arrangement. It is obvious that in an efiicient hoisting apparatus, for instance, more current would. be expected to be used during the hoisting period than during the lowering period for the same loads ;that is to say, energy would be converted from electrical energy: into mechanical energy to hoist the load and less energy should be required in lowering the load. However, in the standard systems, in which the motor is dynamically braked, it is found that more current is used while lowering the load than while raising the load, and that the speed cranes, allows high lowering speeds, which speeds are at all times,contro1led;-which reily under all conditions,

light loads,-although permitting intermedii ate or lower speeds; in which small starting currents are required when lowering; which is automatically protected against excessive speeds'under all conditions; and which is fool-proof.

Other objects of this invention are to provide a system which is adapted for use with a standard equipment; which when used with standard equipment is still ierotected against excessive speeds; and in whlch the electric motor brake releases readwhen it is supposed to release, and thereby prevents abusing the motor by subjecting it to excessive starting curren Other objects are to provide a syllsemior controlled electric motors which willioperate with an instant response even if the controller operating member or handle is thrown completely over on the lowering side; and to provide a system in which the logical operation of the controller is the only operation that is required, so that an unskilled operator may readily handle or operate the system. I

Other objects are to provide a duplex control for a single electric motor and hoisting mechanism so that some of thefunctions of the auxiliary hoisting mechanism with its attendant modest current consumption and high speeds may be performed bv the main hoisting mechanism, easily, efiiciently and readily.

Other objects are to provide a duplex system of control which is automatically selective; which is automatically controlled by the weight of the load without requiring any special skill or judgment'on the. part of the operator; and in which a pluralityof different lowering speeds may be easily attained.- I

Other obje ts are to provide a duplex system which is automatically selective but which may be manually changed by the operator from high speed'lowering to low v speed lowering even with a light load.

Other objects are to limit the generation of dynamic braking currents to values well within'the rating of the motor when controller handle is moved quickly from full lowering position to neutral, or off position, with light hook or light loads while motor is running at high speed, thereby preventing blackenlng of the commutator with the consequent reduction in speed and increase in current consumption.

In electrlc cranes, it has been customary where dynamic braking is provided, to connect the field winding, the brake winding,

and a resistance, across the mains and at the same time to connect the motorarmature and one or more resistances in parallel to the first set of elements, or in parallel to a portion thereof.- This practice is followed, in dynamically braked electric cranes, partly for the reason that it is necessary provide a substantially direct circuit through the brake winding and the field winding to insure the release of the brake and the maintenance of the field strength, and partly to adapt standardequipment to dynamic braking. This connection gave the motor a shunt characteristic, that is to this discrepancy in the logical operation of the crane is particularly pronounced in handling light loads where high lowering speed is desirable. In addition to this, two other features of marked disadvantage present themselves when lowering, viz: a very high starting current'and also excessive operating current, which sometimes is substantially 200% of that required for operating the 7 motor while raising the load.

This invention contemplates a system for controlling electric motors in which dynamic braking is provided while yet maintaining a series characteristic of the motor, thereby securing high speed during lowering, and

also without altering standard equipmentupon electric hoists,

This invention further contemplates a system for controlled dynamically braked electric motors in which a single motor and a single controller are so associated through a selective mechanism that either. of two sets of conditions may be automatically maintained to suit the requirements of the particular load being handled. That is to say, a duplex electric control is secured without the necessity of using two controllers or two motors.

In this invention a standard double throw controller may be employed and the same variable resistance ma beutilized on both the hoisting and the iowering side of the controller. Broadly stated, the invention includes a dynamically braked series motor-in which the series characteristic of the motor is retained, thereby lessening the electrical load placed upon the mains'when lowering the mechanical load and yet, bydynamic braking, insuring perfect control of the motor.

Embodiments of the invention as applied to cranes are shown in the accompanying drawings which illustrate electrical systems for the control of the hoisting motor and which also show a diagrammatic view of a portion of a crane.'

In the drawings: I

Figure 1 is a diagrammatic View illustrating an embodiment of my invention.

Fig. 2 is a simplified diagrammatic view showing the connections as established during the hoisting period.

Fig. 3 is a simplified diagrammatic View showing the connections as established when lowering a heavy load.

Fig. 4 is a simplified diagrammatic view showing the connections as established when lowering a light load.

Fig. 5 is a simplified diagrammatic view showln the connections in a further form of the invention as established when lowering a light load. 7

Fig. 6 is a diagrammatic View of a portion of the electric crane showing the trol- 95 ley, hoisting drum, load switch, and bottom block. i

Fig. 1, showing one form of the invention, will first be described. In this figure, the controller segments on the hoist side of the controller are shown at 1 to 11 inclusive and on the lowering side at 12 to 26 inclusive. Both sets of segments are carried upon one rotatably mounted drum. The stationary contact fingers are indicated by reference characters 27 to 43 inclusive and the controller resistance by the reference character 44. This controller, through certain of the contact fingers and contact segments, is connected at appropriate times with the positive main 45 and thereafter with the field winding 46, brake winding 47, and armature 48, and .through other contact fingers and segments with the negative main 49. 7

50 indicates broadly an electromagnetic 115 switch which is controlled by a load switch 51. The load switch 51 is controlled by the load handled by the crane, and uponloads of predetermined weights, it separates contacts 52 and 53, therebyopening an auxil- 12c iary circuit which in turn causes the electromagnetic switch 50 to move to the position shown in Fig. 1 thereby establishing a certain set of connections for the motor as shown in Fig. 1. The opening, of the load 1 25 switch gives a slower speed of lowering than would be obtained if the load switch were closed with the automatic switch in the position indicated in do'ttedlines. This change in the position of the switch occurs automat- 113a icallly when the load exceeds a predetermined va ue.

It may be found desirable to secure a low lowering speed when handling light loads and this may be obtained by removing the plug 54 to withdraw the connecting portion 55 from between contacts 56 and 57, thereby opening the auxiliarycircui The hoisting operation will not be described in detail other than to state that the current passes from the positive main through contapt finger 29, segment 1, conductor 58, segment 2, contact finger 30, wire 59, through armature 48 (from left to right in the diagram), wires 60, 61, contact 62, switch member 63, wire 64, through field winding 46, brake winding 47, wire 65,

switch member 66, contact 67, wires 68 and 69, resistance 44, through such contact segments and fingers as are then engaged, conductor 70, segment 9, contact fingers 40, 41, segment 10, conductor 71, segment 11 to the negative side 49 of the mains. As the controller is moved toward the extreme limit of the hoisting 'side, the resistance 44 is gradually cut out in the usual 'manner by the segments 3 to 9 and the corresponding contact fingers. The motor in this case operates as a series motor and the entire current flows through the armature, field winding, and brake winding. A simplified diagrammatic view of this connection is shown 1n Fig. 2.

When the controller is moved to first point lowering and a light load is being handled, such for example, as will allow the load switch 50 to remain closed, that is to'say, with the contacts 52 and 53 together, an auxiliary circuit will be established as follows: from the positive main 45, contact finger 29, segment 14, conductor 72, segment 12, contact finger 27, conductor 73, through solenoid 74 of the electromagnetic switch 50, conductor 75, contacts 53, 52, contacts 56,

Y55 and 57, and conductor 76 to negative main 49. This causes the electromagnetic switch to move to the dotted line position.

Under the conditions last described, current also passes from the positive main through contact finger 29, segment 14, conductor 72, segment l3, contact finger 28, conductor 77, field winding 46, brake winding 47, switch member 66, contact 78, conductors 79, 61, 60, through armature 48 (from right to left in the diagram), through resistance.

- 80, conductor 81, contact finger 32, segment 15, conductor 83, segment 16, resistance 44, contact finger 41, segment 24, conductor 84, segment 25, contact finger 42 to negative main 49. A second circuit is established from the point 86, through resistance 85, conductor 87, contact finger 43, segment 26, conductor 84, segment 25,- contact finger 42 to negative main 49.

In addition to these circuits, a further circuit is established from the point 90 (which point, it will be noted, is connected to the point 91, that is to say, the right hand brush of the armature), through a resistance 92, conductors 68, 69, to contact finger 33, segment 16, conductor 83, segment 15, contact finger 32, conductor 81, to point 86.

The last described connection forms a shunt across the armature connecting the resistances 92 and 80 directly across the armature while maintaining a series connection. between the armature and field. As the controller is moved farther toward the lowering side more resistance 44 is cut into this shunt circuit and more resistance 44 is removed from the straight series circuit of the motor. As this feature is of primary importance it will now be described in greater detail.

F ig. 4 shows these connections in simplified form. The current passes from the positive main 45 through the field winding 46, brake winding 47 conductor 65, movable member 66 of the electromagnetic switch, contact 7 8, conductor 79, contact 62, through the armature 48, (from right to left in the diagram), through resistance 80, and then divides, one portion passing through conductor 81,'and the right hand portion of resistance 44 to negative main 49, and the other portion passing through resistance 85 and conductor 87 to negative main 49. Under this condition, the motor is operating as a series motor,'with, however, a portion of the field current passing through resistance 92, and resistance44, to negative main 49. Under these conditions, the motor will rapidly speedup and attain a high lowering speed for the light'load.

' If, however, the speed of the motor becomes very high, the counter electromotive force generated by the motor will oppose the electromotive force urging the current through the armature and will gradually diminish the current flowing in the armature circuit. This, however, cannot weaken the field below a predetermined point for the reason that the additional field current passing through resistance 92 and resistance 44 to the negative main continues, and is sufficient to maintain field strength of the motor and also maintain the brake in open position. But if the speed of the armature continues to increase, the motor will act as a separately excited generator and the current generated by the revolving armature passes through conductor 79, member 66, resistance 92, the left hand portion of resistance 44, conductor 81, and resistance 80, back to the armature. This provides automatic dynamic braking for the motor while maintaining a series characteristic of the motor :that is to say, the motor operates as a series motor until the speed arrives at a predetermined point and thereafter there is a gradual shifting to dynamic braking without any new connections being established. A complete and certain control for lowering light loads, and also a high speed of the motor is thus obtained during this period. The ipherent danger when operating a motor solely as a straight series motor is overcome by this electrical-control, and no mechanical governor nor any mechanical movement of the switch members to efiect this control is required.

This dynamic control of the motor is easily regulated by the operator by moving the controller to the point corresponding to the speed desired. It will be seen that on the first point lowering the resistance 44 is not in the dynamic circuit of the motor, but is in the series circuit thereof, although this resistance is inparallel to the resistance 85. The resistance 85 prevents any but relatively small currents passing therethrough so that the actual manual control remains in the resistance 44. When it is desired to secure a higher lowering speed, the controller is moved so as to bring more of the resistance 44 into the dynamic circuit of the motor, thereby requiring a higher rotative speed of the motor and a correspondingly higher counter electromotive force to secure the same current flow through the motor and consequently the same resistance torque of the motor. This allows a substantial change in the difi'erent. speeds of the motor to be effected as desired'and such changes are secured by a logical manipulation of the controller lever. By moving the controller lever toward the extreme lowering point, the higher speeds of lowering the light loads may be obtained and as it returns toward the zero point the desired lower speed is obtained.

Even if the operator becomes excited, the logical manipulation of the controller is the one which he most probably would attempt, that is to say, he would move the controller toward zero point which would immediately slow down the speed of the motor and secure the result desired. On the other hand, if he should not move the controller toward the zero point, it would still be impossible for the motor tov attain an excessive speed, inasmuch as the dynamic braking control exists in all positions of the controller when lowering'a light load with the load switch closed. Fig. 3 shows the condition that exists when a heavy load is being lowered. Under this condition, the load switch separates the contacts 52 and 53, thereby opening the aux-. iliary circuit through the solenoid 74 and causing the electromagnetic switch to assume the position shown in Fig. 3. The current now passes from positive main through the field winding 46, brake winding 47 through member 66 (the resistance 92 being now short circuited) through resistance 44 to the negative main 49. Current also passes from the positive main through member 63, contacts 62, armature 48, resistance 80, and here divides, a portion passing along conductor 81 through the right hand portion of resistance 44 to the negative main, and the remaining portion through resistance.85 and conductor 87, to the negative main. The resistance 44 has the predominant effect.

Under these conditions the motor has two main independent paths for the current, one through the field and brake windings, and the other, (a parallel path), through the armature 'and" re;sistances. If the. motor speed now increases above a predetermined value, dynamic braking is secured; the current generated bv the revolving armature passing from the armature to contact 62, through member 63, through field and brake windings 46, 47, member 66, contact 67, a portion of resistance 44, conductor 81, resistance 80, back to the armature. A rela- 'tively small portion ofthe' current may also pass from resistance 44, through conductor 87, resistance 85, and resistance 80, back to the armature. In this manner, dynamic braking is again secured whilelowering ,a heavy load and excessive speeds of the motor 'are prevented.

Although these are the preferred connections for the motor, it may be, desirable under certain conditions to have a straight series motor connection without dynamic braking when handling a light load. In this case, the load switch is set to open at a predetermined load below that which would produce excessive motor speed. Thiscondition may be secured by the arrangement shown diagrammatically in Fig. 5, in which the load switch is shown in closed position. 5 The current now'passes from the positive main through the field winding 46, brake winding 47, conductor 65, member 66, contact 78, conductor 79, contact 62, through armature 48, resistance 80, conductor 81, a portion of resistance 44 to negative main. Also a certain amount of current passes through resistance 80. and resistance 82 to the negative main. This form of the invention does not employ the resistance 92 0011- 1 5 nected between member 66 and contact 67 and does not therefore provide dynamic braking while lowering light loads. If, however, a heavy loadis encountered and the motor is connected on the lowering side, the load switch opens the auxiliary rircuit through the solenoid 74 and the systemv is immediately connected as shown in Fig. 3, thereby protecting the equipment from excessive motor speeds.

In all forms of he invention, a plug 54 may be employed to open the auxiliary circuit through the solenoid 74, thereby causing the electromagnetic switch to assume the position indicated in Fig. 3. This is often 130 desirable when a slow speed is required while lowering a light load that will not open the load switch, as for example, lower- .ing a light core into a mold. Under these conditions the operator may remove the plug 54 and thereafter manipulate the controller in the usual manner. When these slow speeds are no longer desired for handling light loads, the operator may reinsert the plug and the system is again restored to a condition adapted for high "speed light load lowering.

Itis to be noted that on the lowering side of the controller, segments 12, 14, 15, and 15, are elongated so that they contact with their corresponding contact fingers in neutral position. The object of this arrangement is to insure modest dynamic braking currents when the controller is moved to neutral position while the motor is running at high speed as while lowering a light load.

When the controller is in neutral position, the auxiliary circuit is maintained as follows :from the positive main 45, throu h contact finger 29, segment 14, conductor $2, segment 12, contact finger 27, conductor 73, solenoid 74, through load switch, back to negative main,-the load switch being closed as the motor is lowering a light load. Also, the dynamic braking circuit of the motor is maintained in closed condition by the elongated segments 15 and 15, and their corresponding contact fingers. Under these conditions the circuit, diagrammatically shown in Fig. 4, is maintained with the difference, however, that the controller resistance is wholly cut out of the circuit, leaving resistances, 92, 80, in series with the motor armature. These resistances, 92, 80 are so pro-- portioned to the controller resistance that only a modest dynamic brakingcurrent is allowed tofiow in this circuit, under the above defined conditions. If, for example,

the segments 12 and 14. had passed from contact 'with their corresponding contact fingers 27 and 29 in neutral position while the motor was lowering a light load at high speed, the auxiliary circuit through the solenoid of electromagnetic switch 50 would be open, and the main circuits would be as shown in F i 3. That is to say, the motor running at %i h speed would suddenly be connected in s liuntwith the field, and the entire controller resistance cut out, thereby leaving only the sum of the resistance of the motor, brake, line and resistance 80 in this motor circuit. These resistances are comparatively small, and an excessive dynamic braking current would flow, thereb the circuits associated therewith.

causing Even if the controller was suddenly thrown from full point lowering while a light load was being handled into first point hoisting, an excessive dynamic braking current would not flow, for the reason that the dynamic circuit itself has been opened and the motor has been reversed so as to provide a straight series hoisting connection for the motor. In this case the only current that would-flow would be the starting current of the motor, which might be a fairly high starting current, but would be very much lower than the usual excessive dynamic braking current that has been such a serious handicap to prior systems of dynamic braking, and which is wholly avoided by this invention.

It is obvious that less energy consumption, better control, and a quicker lowering'of the load are secured when the series character istic of the motor is maintained during the lowering of light loads than when the shunt characteristic of the motor is the pronounced one as in the usual forms of dynamic braking. This invention accomplishes that result as it secures for light loads a series characteristic of the motor and maintains this series characteristic although allowing the motor to be dynamically braked without changing any connections. It is also obvious from the foregoing description of the invention as applied to cranes, that the invention can be utilized for the control of any motor which requires dynamic, braking control under varying conditions of speed and load.

I claim: .1. A system for controlling electric motors comprising a field winding, a brake winding, an armature arranged'to. be connected in series therewith in one position, a resistance arranged to be simultaneously connected across said armature in said position to establish a local circuit exclusive of said field winding whereby a dynamic braking circuit is provided, and means for insuring the response f said brake.

2. The method of electrically operating a hoist, which method comprises connecting upan electric motor with its field and armature in series for hoisting purposes, in shunt for lowering heavy loads, and in series for lowering light loads, by-passing a portion of the field current across the armature when lowering light loads, and interposing suflicient resistance in the by-pass to cause the motor to operate with a predominant series characteristic.

3. In combination, an electric motor for handling a mechanical load, a manually operated controller therefor, and means controlled by the mechanical load for selectively connecting said motor in either of two distinct circuits of which the manual controller forms a part. l I

4. A system for controlling electric motors, comprising-a manually operated controller; an electric motor; connections between said controller and motor for allowing a dynamic braking circuit to be established under predetermined conditions; and

an automatic, mechanically operated load switch for altering said connections and dynamic braking circuit.

6. The method of controlling electric motors, which method comprises connecting the armature and field of a motor in series' across supply mains in one position, connecting a resistance across the armature, whereby the motor will operate substantially as a series motor below predetermined speeds and as a dynamically braked motor above such speeds, and automatically alter- -ing these connections for loads ofpredetermined values to connect said field and armature 1n series w th resistances and n .sub-

stantial parallel to each other across the sup-- ply mains.

7. In combination an electric motor, a

-manual1y operated controller connected thereto, anelectromagnetic switch for alter- .in the presence ing connections between said manually op erated controller and said motor, and load responsive means for controlling said electromagnetic means.

8. A load switch for electric hoists com-- prising a pair of contacts, resilient means tending to hold said contacts together, and means for separating said contacts for loads of predetermined values, said means arranged for direct connection with the load handled by said hoist.

9. In combination an electric motor, a manually operated controller connected thereto, an electromagnetic switch for altering connections between said manually operated controller and said motor, and means controlled by variations in the load for controlling said electromagnetic means.

10. A system for controlling electric motors, comprising a manually operated controller; an electric motor;-connections be tween said controller and said motor for allowing a dynamic brakin circuit to be established under predetermined, conditions, and for maintaining a rotective dynamic braking circuit when sa d controller is in neutral position; and an automatic, mechanically operated load switch for altering said connections and dynamic braking circuit.

In testimony whereof I aflix my signature of two witnesses.

ALFRED J. DREYER.

Witnesses:

. A. R. Woonronx, Jr.,

M. J. YocoM.

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