GB620468A - Improvements in electrical control systems for electric lift motors - Google Patents

Abstract

620,468. Exciting dynamos. WHEELER, H. D., and MOSSAY, P. A. H. Jan. 20, 1947, No. 1792. [Class 35] [Also in Group XXXVII] A Ward-Leonard generator, supplying an electric motor M, which may be a lift-motor, is provided with a fixed shunt field winding GS, a variable reversible shunt winding GV, a reversible separately-excited master winding GX, and a series winding S. Initially, the field winding GV is excited at full strength, in opposition to the field winding GX, so as to provide together with the field windings GS and S, a resultant generator excitation affording a steady slow hoisting speed for the motor, the field winding MF of which is at full strength. Generator field forcing, providing motor acceleration, is afforded by connecting the field winding GV in series with resistors R1 and R2 to assist the windings GX and GS, the series winding S being shunted. The time constants of the generator field windings are so chosen as to. provide a substantially uniform rate of acceleration. When the generator reaches its normal maximum voltage, a switch, responsive to such voltage, effects closure of a contactor short-circuiting the generator field winding GV to provide a stable motor speed. Operation of a slow-down switch connects the generator field winding GV in series with resistors R1 and R2 to provide self-excitation tending to maintain the existing voltage, and the winding GX is reversed to oppose the windings GV and GS. When the generator voltage reaches a minimum value, a switch, responsive to such voltage, operates to afford the circuit connections appropriate to the low-speed motor operation described above. For lowering operation the functions of switches 3 and 4, which control the generator field winding GX, are interchanged. The switches responsive to maximum and minimum generator voltages may be adjusted in accordance with the load on the lift-motor.