Compensation circuit for asynchronous motor driving heavy load - makes torque increase with speed initially to smooth out torque variation

摘要

The compensation circuit, for turning a tower crane, varies the d.c. excitation of the magnetising coil in an electromagnetic delay device in order to alter the counter-torque on the sync. motor driving the load of large moment of inertia. The compensation circuit smooths out the torque variations experienced during starting (and braking) and normal running by only allowing full current to reach the motor once it has reached its constant wanted speed. The magnetising coil's (24) d.c. excitation circuit (63, 65) has a variable-time-constant circuit (61-68) that continuously alters the excitation current so that torque increases with speed during a part of the start-up curve.