GB827722A - Improvements in alternating current electric traction equipments - Google Patents

Abstract

827,722. Control of D.C. motors. METROPOLITAN-VICKERS ELECTRICAL CO. Ltd. May 14, 1956 [May 16, 1955], No. 14107/55. Class 38 (3). [Also in Group XXXV] The voltage supplied to a D.C. traction motion M from an A.C. supply through a transformer having secondary winding S and a rectifying arrangement comprising two or more anode-cathode paths in parallel, is varied on load by changing from one transformer tap to another, by means which includes depressing the anode volts of one path below that of the other to divert the current from one anode to the other. In the circuit of Fig. 1 the two paths are between main and auxiliary anodes A, C of a rectifier with a common cathode K. The motor M receives the algebraic sum of the voltages across part of the secondary winding S of the supply transformer from one of the taps 1, 2, 3 which may be distributed non-uniformly and part of the secondary winding SA of an auxiliary transformer whose primary winding PA is connected through reversing switch R and reactance TR to the taps on secondary winding S. The changes between the positions in which the supply is taken from taps 1, 2, 3 to provide the coarse adjustment of motor voltage, are made by appropriate operation of switches 1-3, 2a, 3a and Y. In changing from tap 1 to tap 2, the voltage supplied to the primary winding PA is first varied in known manner by sequential operation of switches 30-35 to increase the voltage at anode A until the voltage developed by winding SA is about half that between taps 1 and 2. Connection is then changed from tap 1 to tap 2, auxiliary anode C being momentarily supplied with the full voltage of tap 2 by closure of switch 2a, and switch R being reversed so that at the end of this step the voltage at anode A is little changed. Switch 2a is then opened and the load current again carried by anode A. The rise in volts to the motor while C carries current is only momentary. The voltage across primary PA is then reduced in steps by operation of switches 35-30 until the voltage at A is that at tap 2. The switching sequence for these and subsequent steps is given in a chart, Fig. 3A (not shown). Alternatively, the variable voltage supplied to winding PA may be derived from an induction regulator. The mercury arc rectifier may be replaced by ignitrons with or without exciter electrodes, or by semi-conductor rectifiers such as germanium or selenium rectifiers. The conductivity of the rectifiers may be controlled by the introduction into the rectifier circuit of a voltage from an auxiliary transformer, Fig. 4 (not shown).