GB642695A - Improvements relating to excitation control systems for d.c. dynamo electric machines - Google Patents

Abstract

642,695. Exciting dynamo-electric machines. ENGLISH ELECTRIC CO., Ltd. Feb. 6,1948, No. 3500. [Class 35] [Also in Group XXXVIIJ In a system for introducing compound excitation into a D.C. machine at a predetermined load current, a separately excited field winding on the machine is arranged to provide a component of excitation depending on the current in a circuit connected to a source of voltage varying with the load current, one or more counter E.M.F. cells being connected in series with the circuit to prevent the current flow until the voltage exceeds a predetermined value. The counter E.M.F. cells produce an opposing voltage to the current whatever the direction of the current flow. The invention is described as applied to a reversible and regenerative Ward- Leonard set, and in the form shown, the generator G having a separately excited field winding G1 feeds a motor M. The field G1 is energized by an exciter 11 excited partly (lla) from the D.C. mains 12 through a rheostat 13, and partly (11b) with a current flowing through the counter E.M.F. cells 14 due to the voltage developed across the generator series field winding G2 dependent on the load current. For load currents up to a predetermined value, no current passes the cells, but when the drop across the series winding G2 exceeds the maximum voltage of the cells, the winding 11b is energized and changes the excitation of the generator G to reduce the load current. Contactors 15, 16, 17 which short-circuit the cells, alter the load current setting. The field winding 10b of the motor exciter 10 is similarly controlled by the same cells or a separate bank, and reversing switches or rectifiers may be provided if the generator voltage is reversible.