GB738705A - Improvements relating to electric motor control systems - Google Patents

Abstract

738,705. Automatic tension control systems. BRITISH THOMSON-HOUSTON CO., Ltd. June 28, 1954 [July 13, 1953], No. 19361/53. Class 38 (4). In a constant tension control system for a Ward-Leonard strip-coiler drive, both the generator and motor excitation is controlled through magnetic amplifiers, the generator being controlled to maintain constant current and the motor to maintain a constant ratio between motor voltage and strip speed. Provision is made to limit the rise in generator voltage when, for any reason, the mechanical load is removed from the motor. Generator control.-As shown, the generator G has its field FG supplied by a main magnetic amplifier A, which is controlled (i) by a magnetic amplifier Al (having a reversible output) in accordance with the difference between a reference voltage B and the drop across a resistance R in the Ward-Leonard loop, and (ii) by a tachometer generator T responsive to strip speed, in order to relieved the burden on the current-control-amplifier Al and increase its accuracy over the range of mill speed. Motor control.-The motor field Fm is supplied through a main magnetic amplifier A3 controlled by a resistance RH which is operated by a reversible motor M1 energized by a magnetic amplifier A2 in accordance with the difference between the output of the tachometer generator T (strip speed) and the motor B.E.M.F. obtained from a potentiometer R1, R2 plus 1R drop compensation. Voltage limiting.-A magnetic amplifier A4 having a unidirectional output is connected in series with the amplifier A2 and is normally inoperative unless the motor B.E.M.F. exceed the voltage from generator T, when it provides an output to a control winding on the amplifier A to limit the generator excitation. Specification 738,662 is referred to.