Patent GB-476901-A (GB)
Title: Improvements in ward-leonard type electric ship propulsion equipment
IPC: B63H23/24
Filed: 1936-06-29
Abstract: 476,901. Control of several D.C. motors. ENGLISH ELECTRIC CO., Ltd., CARNEGIE, H. S., and WILSON, J. C. June 29, 1936, No. 17970. [Class 38 (iii)] Varying E.M.F. ; field control.-In a Ward- Leonard system for ship propulsion, including mechanically separate and independently-operated port and starboard motor controllers each incorporating a resistance regulator for the corresponding motor excitation and a resistance regulator for varying the excitation of the common generator, step-by-step movement of both controllers together, over at least a certain range of positions, varies the generator excitation only, relative movement of the controllers varying the relative excitation of the port and starboard motors to vary their relation speeds. The generator field 1 and the port and starboard motor fields 2, 3 are connected in independent circuits by the port and starboard controllers 4, 5, having a central "off" position. The motor fields 2, 3 are connected through reversing switches 30, 31 and 32, 33, in circuit with the corresponding controller contacts 28, 29 or 25, 26 and with a variable resistance 18, 15 associated with the other controller. Thus, each motor field 2, 3 is weakened by the respective resistance 18, 15, inserted step-by-step by forward movement of the controller associated with the other motor, this resistance being cut out as the corresponding motor controller is moved, so that if both controllers are moved together the motor fields remain at maximum strength, whereas if one controller is advanced beyond the other, the motor corresponding to the lagging controller is reduced in speed by weakening of its field. Movement of either controller from the "off" position in either direction makes the generator field circuit at contacts 7 or 9 and then progressively cuts resistance 8 or 10 out of circuit. Resistances 11, 12 are included in the generator field circuit to prevent overloading when the motors are working at substantially different power outputs, and to prevent energy losses these resistances are cut out progressively by the controller contacts 23, 22. Potentiometer resistances 34, 35 are preferably connected across the fixed contacts 30, 32 of the motor field reversing switches to permit braking of the motors in the positions of the controllers corresponding to the gaps in the resistances 8, 10, that is, when the generator field circuit is broken. In this case the motors may be started on weak field by making the generator field circuit before the contacts 31, 33 engage the respective contacts 30, 32. Modifications. The generator unit may comprise a plurality of generators and the port and starboard propelling units may each consist of several motors. The controllers 4, 5 may, alternatively, regulate exciters for the generator and motors, and, to prevent overloading of the system, the generator or exciter therefor may have in addition a series decompounding field winding, and a third field winding, supplied by the voltage of the generator or exciter, for enhancing the effect of changes in excitation. The decompounding effect may be introduced only when a critical load is exceeded, for example, as described in Specification 472,472 in which case the third generator field winding may be regulated by both controllers similarly to the field 1. The resistances 11, 12 in the generator field circuit may then be permanent or omitted. The Provisional Specification also contains subject-matter proceeded with in Specification 477,443. Specification 349,012 also is referred to.