| 摘要 |
1,198,199. Control of A.C. motors. HILGERS A.G. 30 Aug., 1968 [2 Sept., 1967; 8 March, 1968 ; 16 March, 1968], No. 41479/68. Heading H2J. [Also in Division G3] An induction motor ml is associated with a brake-release motor sl and has rotor resistances 1r1 which are switched out in steps by contactors 1c3-1c7 as a controller is moved to successive positions in a hoisting direction. In the first lowering position of the controller, the motor exerts a small hoisting torque but is over driven by the load. A speed-responsive device 1u1 responds to rotor voltage to control contactor 1c8 whereby the rotor resistance is varied at, intervals to stabilize the downward speed. At further lowering positions, contactors 1c4-1c6 are opened in succession to develop lower reverse torque and a higher rate of speed. Finally the motor m1 is reversed to provide a positive downward torque. A thyristor regulator Th is connected to the motor s1 and has a manually-regulated resistor 1 in series with a resistor 2 which is shunted by contacts 3 of a relay 4. This relay is energized by a rectifier 5 in series with a switch 17 which provides a pulse at each revolution of the hoisting motor to open the contacts 3. A signalling device 10 gives an indication of the speed of the motor ml. In another arrangement, the motor m1 develops a torque in the required direction of movement of the load under all operating conditions. A transformer is connected between the rotor of the motor m1 and the stator of the motor s1, so that, as the speed of the load increases, the braking action also increases, Fig. 4 (not shown). The speed-responsive circuit 1u1 may comprise a D.C. amplifier comprising a transistor and having its input connected to the slip-rings of the hoist motor through a transformer and rectifier as well as a voltage divider and a Zener diode. The output side of the amplifier is connected through another Zener diode to a relay which controls the contactor 1c8, Fig. 5 (not shown). The brake release is of the ball-screw-spindle type.
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