Improvements in or relating to control systems for electric motor-driven overhead travelling cranes

摘要

653,181. Control of D.C. motors. KUKA, K. S. March 18, 1948, No. 8074. [Class 38(iii)] A hoist motor is connected respectively as a series and a shunt machine for raising and lowering operation, its control circuit comprising a relay ALR having a coil ALR3 adapted to compare voltages respectively o b - tained across resistor 143 in the motor armature circuit and across resistor 111, which is connected to the main power line and in series with the parallel circuits formed by the motor armature and field winding during lowering. Coil ALR2 is adapted to increase the sensitivity of the relay ALR and is connected in series with resistor C and across resistor 143. The relay ALR operates as a compound relay during hoisting and non-overhauling lowering operation, but as a differential relay when an overhauling load is lowered, and controls contactors 1A and 4FA, which regulate resistors in the armature and field circuits, in such manner that the lowering speeds with no-load and full-load are substantially equal. The resistor 111 is connected in series with both the armature and field winding and diverts more current to the latter so as to enable the motor to handle heavy loads when operating as a shunt generator with weakened field excitation.