GB820886A - Improvements in and relating to diesel electric and other electrical power transmission systems - Google Patents

Abstract

820,886. Electric motor control systems; electric motor controllers. METROPOLITANVICKERS ELECTRICAL CO. Ltd. Oct.10, 1956 [Oct. 25, 1955], No. 30536/55. Class 38 (3). [Also in Group XXXV] In an electric transmission system for, say, locomotives, the generator or the motor excitation currents alternatively are adjusted by variation in engine speed, depending on whether a means representative of the generator voltage is above or below a set value. A diesel engine E, Fig. 2, drives a generator G connected to one or more motors M through series generator and motor field windings DF, MF and current relay CLR. Conductors 1, 2 connected to a constant voltage source supply separately excited generator field differential winding GF through contacts G1, rheostat GFR, relay winding FCR and resistors 3, 4 which can be shorted by contacts G2, G3. Rheostat MFR and resistor 8 form a divertor across field winding MF. Contacts G1-G3 are sequentially closed in positions I-III of controller MC, with the engine speed set at, say, 350 r.p.m. Positions IV-X close contacts 12, 13 and progressively increase the speed of the engine, these speeds being regulated by an engine governor 7 which also supplies two hydraulic servomotors 6, 10, Fig. 3, coupled to rheostats GFR, MFR. When the engine speed is above the set value, pressure is applied to pipe Y, and when the speed is below, to pipe X. In positions I-III of the controller MC, coil OCA is energized through contacts 24-26, opening valve A, Fig. 3. Due to the load being below the engine output, the engine speed rises and pressure thus applied to pipe Y maintains the rheostats in their maximum resistance positions, hence acceleration will be dependent on the inherent characteristics of the equipment. In positions IV-X contacts 12, 13 are closed, energizing coil OCB, and also coil OCC through contacts 27, 28. Owing to the heavy accelerating current, relay CLR opens contacts 25 and closes valve A. This current gradually falls to its normal value, and the engine speed rises. Valve A is again opened by OCA and pressure applied to piston 16 from pipe Y decreasing the generator field resistance. If the movement is too rapid, relay CLR operates closing valve OCA. If the engine speed drops due to excessive load, pressure is applied through pipe X to piston 15, reducing the excitation. When the field current reaches a predetermined value, relay FCR operates, disconnecting OCA, OCC and connecting coil OCD of valve D. This value of current will be reached irrespective of temperature/resistance variations in the generator field. If the load on the generator is still below the engine output, pressure will be applied from pipe Y through valve OCD to piston 21 reducing the resistance of MFR, thus weakening the motor field. On the engine speed falling, pressure will be applied to piston 20 returning MFR to its illustrated position and closing contacts 26, 27 opening valve A hence applying pressure to piston 15 and reducing the generator excitation. In another embodiment, the motor field weakening is carried out in a series of steps by servomotor 10, two additional resistors being connected in series with the generator field at the same time, then sequentially cut out between each step. The operating current of relay CLR may be varied by an additional coil having a number of resistors in series controlled by contacts on the controller MC. Specification 703,649, [Group XXXV], is referred to.