Abstract :
Low-speed electric elevators, using d-c. motors, came into use about 18.90. Later, a-c. motors were employed, but on account of the difficulty of speed control could not be used for the high speeds necessary in tall buildings. Since the height of buildings is dependent upon the elevator system, and in many districts only a-c. is available, the need for high-speed equipments that can be operated from a-c. is evident. A solution to the problem is found in the variable voltage system of control. In this system each elevator motor is supplied by an individual generator driven by a motor operating, from the a-c. or d-c. supply voltage. The generator´s voltage, and hence the elevator motor´s speed, are controlled by varying the field of the generator. The apparatus consists of: 1. An ordinary shunt-wound d-c. elevator motor. 2. A d-c. generator of special design for the elevator motor. 3. Control panel for the generator and elevator motor. 4. An a-c. or d-c. motor to drive the generator. 5. A starting device for the driving motor And if the supply is a-c. 6. A direct-connected exciter for the field, brake and control circuits. The control panel (1) makes the proper connections for up and down motion of the car; (2) releases, or sets, the brake: (3) controls the speed; (4) discharges the generator field during retardation, and on stopping (5) demagnetizes the generator and (6) opens the circuit between the armature of the generator and the armature of the elevator motor.
