US2275118A - Alternating current braking circuit - Google Patents

Description

' March 3, 1942. F. w. WENDELBURG ET AL. 2,275,113

ALTERNATING CURRENT BRAKING CIRCUIT Filed Oct. 26, .1940

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Patented Mar. 3, 1942 ALTEBNATING CURRENT BRAKING CIRCUIT Frank W. Wend'elburg and Roy J. Wadd, Milwaukee, Wis., assignors to Barnischfeger Corporation. Milwaukee, Wis., a corporation oi Wisconsin Application October 26, 1940, Serial No. 362,986

Claims.

'a preparatory movement of a controller to a preselected position at which a solenoid friction brake is-released and simultaneously a moderate counter-torque opposing the lowering action of v the load is exerted by the motor, whereupon the system becomes potentially responsive to uninterrupted selection of graduated degrees 'of high speed, regenerative lowering, or low-speed counter-torque checking of the load at the will of the operator, whereby precision spotting or high-speed runway of the load may be effected at will.

This invention is in a sense related to and constitutes an improvement over the invention disclosed and claimed in our copending application Serial No. 307,456, filed December 4, 1939, patented May 27, 1941, No. 2,243,590, in which uninterrupted transition from one type of lowering to the other is described, but in which the preparatory movement of the controller brings about an immediate high-speed lowering of the load rather than a gradual and easily controlled descent thereof, with the result that the precision of spotting obtainable by this invention is diilicult of attainment- This invention is herein described by reference to the accompanying drawing forming a part hereof wherein there is set forth by way a of illustration and not of limitation one form of a circuit embodying this invention, said circuit being diagrammatically set forth therein.

In the drawing the single figure is a diagrammatic showing of a circuit embodying this invention.

The apparatus shown in the drawing will be shown by the detailed description set forth here-' inai'ter, to be composed of a three-phase, wound rotor induction motor, the resistance of the secondary of which is selectively controllable by a conventional drum controller. In conjunction with and as a part of this controller are segments which serve to bring into action magnetic contactors which control admission of current to a magnetic friction brake and the direction of admission of current to the primary of the motor. Through these latter instrumentalities the controller is provided with an open circuit center point, with a hoisting zone to the right and a counter-torque zone to the immediate left and a regenerative braking zone to the more remote left. These left-hand control zones are initially passive with the friction brake set and are rendered active only=by movement of the controller to one selected counter-torque position. Thereafter the friction brake remains re-. leased and all of the several regenerative (sometimes called running") positions as well as the counter-torque (sometimes called plugging") positions may be immediately selected and found active. Thus, in lowering a load the friction brake becomes initially released while the motor is exerting a torque which is positively resisting the descent of the load. Inertia and this countertorque combine to insure a very gradual starting of the downward movement of the load and if it is desired to check the lowering at once, so as to inch the load downwardly, the same may be accomplished by a quick return ofthe controller to the open circuit center point position where the friction brake will become set.

On the other hand, if rapid downward travel of the load is desired, the controller handle may be moved immediately into the regenerative braking zone in a single continuous movement of the controller handle. Thus both high-speed and precision control is available to the operator in a single control handle. This is in contrast with circuits heretofore described wherein it has been necessary to initiate downward movement by a preparatory selection of a regenerative (running) position, thus positively driving the load away at the outset, making a substantial overrun inevitable, or, in contrast with circuits where inching" must be accomplished by resort to a switch, or button, other than the controller handle.

The improved advantages indicated above are attained in this invention in the form herein described by an important but relatively simple change in the circuit of our copending application hereinabove referred to. The change consists in altering the length and position of the brake relay control segment only in the manner which clearly appears from the description which follows. I

In the drawing, a three-phase wound rotor induction motor is indicated at I. An adjustable external resistance 21s connected as shown in the secondary circuit of the motor I and is provided with taps-'3 leading to a controller 4 for a purpose hereinafter to be more fully described. A magnetically actuated friction brake 5 is mounted to act as shown upon the shaft of motor I. A primary lead 1 leads directly from the motor I to a line connection as shown, while the primary leads 8 and 9 of motor I lead to the magnetic contactors I and II, which together constitute a magnetically-actuated load reverser through which the sense of rotation of the primary of motor I may be reversed.

The magnetically-actuated brake is provided with a lead I2, which is in direct connection with lead 1 and thus in permanent connection with the line. The opposite side of brake 5 is connected through a lead I3 to brake and interlock relay I4, through which line supply is derived, as shown.

Magnetic contactor I0 is arranged to admit load current to the primary of motor I to produce forward rotation thereof and is provided with a forward closing coil I5 arranged to act upon normally open load contactors I6 and I1 and normally closed interlock contactor I8. The magnetically-actuated contactor II is arranged to produce reverse rotation of the primary of motor I and is provided with reversed closing coil I9 arranged to act upon normally open load contactors 20 and 2I, normally open interlock contactor 22, and normally closed interlock contactor 23.

Relay I4 serves to control the admission of current to brake 5 and additional purposes to be hereinafter described and is provided with relay closing coil 24, arranged to act upon normally open brake contactor 2B and normally open interlock contactors 21 and 28.

If it is assumed that motor I is to be applied to a hoisting or load-lifting duty, hoisting movement may be brought about by application of line supply to the primary of motor I through forward contactor I0 and in order to accomplish this controller current is drawn through supply lead 29 into a controller contactor finger 30,

.which is brought into contact with controller se ment 3| arranged on the hoisting side of the controller 4, which may be moved in the wellknown manner for that purpose. From segment 3I current passes through segment 32, contact finger 33, leads 34 and 35 to interlock contactor 23, which will be found closed with the controller 4 in the position now under consideration. Connection from interlock contactor 23 is then made through lead 36 with forward closing coil I5, which in turn is connected through lead 31, common return lead 38, and limit switch 39, to lead 1, which is in direct connection with the line. Forward closing coil I3 is thus energized and forward current supply is furnished to motor I.

To provide for release of brake 5 while load current is being provided to motor I, as above described, a controller segment 40 '5 provided, which comes into contact with the corresponding contactor finger 4I simultaneously with the engagement of segments 3I and 32 with their respective contactor fingers. Control current is thus supplied to lead 42, to closing coil 24 of relay I4, and from coil 24 return to the opposite line connection is made through common return lead 38,1imit switch 39, and lead 1, as previously described.

With the controller 4 in any of the several selected controller-hoisting positions indicated by the letters A to H, inclusive, adjusted amounts of external resistance 2 are placed in the secondary circuit of motor I through cooperation of the segment group 43 with corresponding contactor fin- .gers contained in contactor finger group 44 in the well-known manner. Upon the return of the controller to the open circuit center point position, closing coil I5 becomes deenergized and contactors I5 and I1 open. At the same time closing coil 24 of relay I4 becomes deenergized and brake 5 applied. The functional characteristics of the hoisting system hereinabove detailed are quite conventional, but are derived, in part at least, through the aid of instrumentalities which are specially adapted to produce the novel functional characteristics of the lowering control which characterize this invention.

With a load in hoisted position, lowering may be brought about by relatively moving the lefthand controller segments of controller 4 toward the controller contact fingers. In the initial stages of this movement segments 45, 46, and 41 come into contact respectively with contact fingers 30, 48, and 49. During the initialstages of this movement through positions a, b and c, nothing occurs. When movement reaches position d the initiating stage of lowering control becomes established as follows: Line connection established through lead 29 passes through segment 45 to segment 52, which is effective in the d position only. Connection thence continues through contact finger H and lead 42 to relayclosing coil 24 and thence through return lead 38 and limit switch 39 to line connection 1. As a result relay I4 moves from th normally open position to the closed position and when this occurs line supply is transmitted through contactor 25 and lead I3 to the friction brake 5, causing the same to be released.

While the above is occurring control current is also supplied to segment 46, contact finger 48, lead 50, contactor 28, lead 60 and lead 35 to contactor 23, which will be found in the normally closed position. From thence control current is supplied through the lead 36 to the closing coil I5 of the forward or hoisting switch I0 and from thence through the lead 31 and limit switch 39 back to line connection with lead 1. Line supply through the contactor Ifisand I1 thus causes the motor I to exert a torque in the hoisting direction which is modulated by the resistance 2 at its maximum value and a very gradual descent of the load begins to take place.

The bringing of the control to position d causes a further action to take place, namely, the establishment of a maintaining circuit for coil 24 of relay I4. This maintaining circuit may be traced from the line through conductor 29, contact finger 30, segment 45, segment 41, contact linger 49, and thence through lead 5I to contactor 21, which has been brought to the closed position a described above, and thence through leads 91 and 42 to closing coil 24, and thence back to line connection as previously described. It will thus be apparent that relay I4 will remain closed and brake 5 remain released so long a segment 41 remains in contact with contact finger 49, providing the controller has been initially moved as described above to position (1'.

By reason of the described circuit relationship, segments 53 and 45 may be brought, at the will of the operator, into contact with their respective contact fingers to product in positions a, b, c and d" regulated degrees of countertorque braking through circuit connections which have already been described and to positions e, j, g and h to produce regulated degrees or regenerative lowering in the manner about to be described.

Regenerative lowering is brought about in positions e to h, inclusive, when control supply entering through segment passes through 1621! normally closed ncontact'oriilfandtlead ifiato clos ing coil l9 or. reverse or regenerativev switchal lv From coil 19 directretum to the line is provideduz through lead 51 so thatrin :case. ofiover-runningzi and opening of limit switch139 lowering, can-.nev-f :1

ertheless be effected; The energizing ofcoil;i9; causes the closing of conta'ctors lflandll, causeing the motor I to be. driven in thereverse di-,. rection. Regulated amounts of resistance 2 are controlled by the. control segments of group 58 and various lowering speeds at speeds in excess of synchronous speed are thus brought about.

It will be observed that once the lowering action has been initiated through engagement of the short segment52 with its respective contact finger 4| that the operator is free to alternate at will between regenerative and counter-torque lowering, or to bring the descending load to a complete stop by movement of the controller to the open circuit center point where the brake 5 becomes applied. It will thus be apparent that the controller may be moved, if desired, to position (1' and then immediately back to the "ofi position, with the result that the load will descend a very small amount without appreciable over-running, or may be returned from position at to the off position gradually, resulting in a very slow descent of the load, which may be checked or stopped with great precision. On the other hand, if a speedy dropping of the load is desired, the controller may be moved without interruption into one of the positions e to h, inclusive, where the rapid descent characteristic of supersynchronous regenerative braking is obsaid brake in released position and for preservirigrall of said braking positions active after movement to said remote end of said countertorque' zoneand until said controller is moved to the oiI position.

*2. In abraking control system for wound rotor ":induction motors, the combinationcomprising a motor,-a brake, a movable controller, said controllerbeingprovided with an "01!" position, a zone for counter-torque braking and an adjacent zone'for regenerative braking, a switch responsive to connect said motor for counter-torque tained, at the end of which rapid drop, the

cushioning restraint, of counter-torque braking may be resorted to before the off" position and the application of brake 5 occurs.

It will thus be apparent that an improved control has been provided, having all of the versatility of controls heretofore proposed and having in addition the distinctly advantageous characteristic of being able to produce a small downward movement of the load without substantial overrunning.

It is intended that the protection of Letters Patent to be granted hereon be not unnecessarily limited by the illustrative example set forth hereinabove, but that the same shall extend to the limits of the inventive advance disclosed herein as set forth in the claims hereto appended.

That which we claim as our invention is as follows:

1. In a braking control system for wound rotor induction motors, the combination comprising a remote end of said counter-torque zone, a second switch rendered active only upon movement of said controller to said remote end of said counter-torque zone for causing release of said brake, means responsive to movement of said controller into said regenerative zone for connecting said motor for regenerative braking, and means in conjunction with said controller for maintaining braking only after movement of said controller -lo a preselected position in said counter-torque zone, a second switch rendered active only upon movement of said controller to said preselected position for causing release of said brake and for completing the circuit by which said first-mentioned switch responds, means responsive to movement of said controller into said regenerative zone for connecting said motor fo regenerative braking, and means in conjunction with said controller for maintaining said brake in released position after releasing the same and until said controller is moved to the off" position.

3. In a braking control system for wound rotor induction motors, the combination comprising a motor, a brake, a movable controller, said controller being provided with an off position, a zone for graduated degrees of counter-torque braking extending from said oif" position with the position of least counter-torque at the end of said zone remote from the off position and an adjacent zone for graduated degrees of regenerative braking extending from said remote end of said counter-torque zone, a switch responsive to connect said motor for counter-torque braking only after movement of said controller from the offi position to the remote end of said countertorque zone, a second switch rendered active only upon movement of said controller to said remote end of said counter-torque zone for causing release of said brake, means responsive to movement of said controller into said regenerative zone for connecting said motor for regenerative braking, and means in conjunction with said controller for maintaining said brake in released position and for preserving active all of said positions of braking after movement of said controller to said remote end of said countertorque zone and until said controller is moved to the off" position.

4. In a braking control system for wound rotor induction motors, the combination comprising a motor, a brake, a movable controller, said controller being provided with an "oif position, a counter-torque position, and an adjacent regenerative position, a switch responsive to connect said motor for counter-torque braking upon movement of said controller to said countertorque position, a second switch rendered active upon movement of said controller to said counter-torque position for causing release of said brake and for completing the circuit by which said first-mentioned switch responds, means responsive to movement of said controller into said regenerative position for connecting said motor for regenerative braking, and means in conjunction with said controller for maintaining said brake in released position after movement to said counter-torque position and until said controiler is moved to the off" position.

5. In a control for a hoisting motor of the wound rotor induction type, the combination comprising a motor, a brake, a movable controller, said controller being provided with a hoisting zone, an 011" position adjacent said hoisting zone, a zone for graduated degrees of countertorque braking adjacent said "01! position, and a zone for graduated degrees of regenerative braking adjacent said counter-torque zone, a switch responsive to connect said motor for hoisting upon movement of said controller into said hoisting zone, a limit switch for rendering said first-mentioned switch inoperative alter predetermined travel oi' said motor in a hoisting direction, said first-mentioned switch being also responsive to connect said motor for countertorque braking only after movement of said controller to a preselected position in said countertorque zone, a third switch rendered active only upon movement of said controller to said preselected position for causing release or said brake, means independent of said limit switch responsive to movement of said controller into said regenerative zone for connecting said motor for regenerative braking, and means in conjunction with said controller for maintaining said brake in released position after movement of said controller to said preselected position and until said controller is moved to the "01! position.

FRANK W. WENDELBURG. ROY J. WADD.

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