Improvements in and relating to electric motor equipments for driving rolling mills

摘要

550,069. Control of two or more D.C. motors. HILL, E. P., and METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. March 19, 1941, No. 3770. [Class 38 (iii)] Varying E.M.F ; field control. Where, as in a rolling mill, one or more auxiliary motors 7 are required to follow the speed variations of a main motor 1 which is controlled in part by field weakening, a booster 12 connected between a variable voltage source, such as a Ward Leonard generator 2, and the armatures of the auxiliary motors are excited in part by a tachometer generator 16 sharing the speed variations of the main motor and the generator 16 has an excitation component which varies with the field strength of the main motor. As shown the tachometer generator has opposed field windings 18, 19 which balance at full field strength of the main motor, one winding being in parallel with a time-constant reducing resistance 4 in the motor field circuit. As shown, the tachometer generator is in series with the booster field 14 (which also has a time-constant reducing resistance 15) and with the variable voltage source 2. The booster E.M.F. is opposed to that of the source 2 and the tachometer voltage developed in proportion to main motor speed and to the degree of field weakening is also opposed to the variable voltage source. Other arrangements are possible and the booster may assist the variable voltage source.