GB644893A - Improvements in control systems for dynamo electric machines - Google Patents

Abstract

644,893. Exciting dynamo-electric machines; automatic control systems for dynamo-electric machines. ENGLISH ELECTRIC CO., Ltd. Dec. 5, 1947, No. 32123. [Classes 35 and 38 (iv)] [Also in Group XXXVII] An electric drive for a reel on which strip material coming from or going to a treating machine, such as a rolling mill or calender, is being wound or unwound under tension, comprises in combination a main dynamo-electric machine operatively coupled to the reel, one or more additional direct-current dynamoelectric machines arranged to be coupled at will to the reel through positively-acting clutch means so as to extend the maximum torque which can be exerted on the reel and means for automatically varying the torque on the reel in accordance with the diameter of the coil in a sense to maintain the tension in the strip substantially constant. Two substantially identical D.C. reel motors 1 and 2 are connected in series with a booster 4 across busbars 5 which may be supplied from a Ward- Leonard generator. A motor 6, which is connected to the same supply, drives a rolling mill. The field windings of the motors 1 and 2 are supplied from an amplifying exciter 8 the field winding of whichis connected across a series resistor 9, so that the excitation of the motors is varied in accordance with the armature current to maintain strip tension substantially constant. The armature of the motor 2 is directly coupled to the reel-shaft, the motor 1 being coupled thereto through a clutch. For low ranges of strip tension the motor 1 is disengaged and its armature is disconnected from the supply. For high values of strip tension both motors are coupled to the reel and both are energized. A pilot exciter 12, which is coupled to the mill motor 6 is connected in series with a field winding 4a of the booster 4 across the bus-bars. The voltago of the exciter 12 opposes that of the bus-bars and is equal to it when the field excitation of the motor 6 is adjusted to a given value, so that, under these circumstances the field winding 4a is not excited. Any change in mill motor speed due to variation of its field excitation will effect energization of the winding 4a and cause the booster 4 to inject a voltage into the reel motor circuit whereby the speed of the reel is varied in correspondence with the change of speed of the mill motor. A variation of voltage of the bus-bars 5 equally affects the speeds of the mill motor and reel, the ratio of speeds remaining unchanged. The voltage of the pilot exciter 12 is altered in accordance with the number of reel machines in operation, the field winding 12a being connected in series with only one rheostat 14 when both machines 1 and 2 are effective, and a rheostat 15 being brought into circuit when the motor 2 alone drives the reel. A field winding 4b of the booster 4 enables that machine to afford compensation for voltage-drop due to the resistance of the armature circuit of the reel motor or motors. A rheostat 17 provides adjustment of the excitation of the winding 4b when both motors 1 and 2 are effective, a rheostat 18 is additionally connected when only the motor 2 is used. In a modification (Fig. 2, not shown), the reel and mill motors are separately supplied from variable voltage generators. The rheostats regulating the field excitation of the two generators are ganged, so that the speed of the reel is related to that of the mill. The field excitation of the generator supplying the reel motors is varied in accordance with the number of machines in use. An additional field winding of this generator compensates for resistance-drop. The arrangements referred to may provide for unwinding the strip from the reel, or a reversible drive, wherein the strip is alternately wound and unwound, may be afforded. To obtain a low voltage for the reel machines during unwinding an additional opposing field winding on the booster 4. excited from the pilot generator 12, is rendered effective. When the drive is used for winding strip only, series motors may replace the machines 1 and 2, the applied voltage being reduced with an increase of load current so as to maintain the horse-power substantially constant. Specifications 465,527, 474,287, 486,114, [all in Group XXXVII], and 644,868 are referred to.