Patent GB-191402822-A (GB)
Title: Improvements in or relating to the Conversion of Electric Current.
Inventor: ARTHUR SCHERBIUS
IPC: H02K29/00
Filed: 1914-02-03
Abstract: 2822. Scherbius, A. Feb. 3, 1913, [Convention date]. Void. [Published under Section 91 of the Act.] [Addition to 24,306/13.] Arc and spark-gap apparatus, arrangements of; vapour and vacuum or low-pressure apparatus, arrangements of.-In dynamo-electric machines in which the usual commutators or collectors are replaced by electric valves, as described in the parent Specification, the completion of the wave is effected by generating electromotive forces in the alternating-current circuit which eliminate the current when the valves are thrown out of action. The principle of the invention is illustrated in Fig. 1, in which a represents a coil passing beneath a main pole S at the end of which is an auxiliary pole-piece h of greater strength. On closing the valve v, current flows through the coil a in the direction i, while a back electromotive force is induced in the direction e, which increases and neutralizes the current as the coil passes beneath the pole-piece h, the ignition device in the valve v being rendered inoperative immediately before the current is neutralized. The invention can be applied to machines with open or closed armature windings, the back electromotive forces required being produced by local variations of the field strength or by providing auxiliary pole-pieces. In applying the method to transformers or the like with stationary windings, the reduction of the current in the coil or coils to be switched off may be effected by generating a current in an auxiliary winding wound with a higher number of poles. In the arrangement shown in Fig. 4, a special commutating-transformer is used, the armature windings a connected in parallel between the bars c1, c2 of a continuous-current network being in series with windings f1, f on a ring t having a winding h2 carrying currents having the calculated commutation periodicity. The currents required for operating the valves and the auxiliary alternating commutating currents are generated in the same machine or in two machines coupled together mechanically or electrically. In applying the invention to alternating-current machines, the auxiliary commutating current may be taken from a synchronous machine excited by the main current, or the generator may be provided with a second winding for this purpose. In machines such as motors, which start slowly, and in which the back electromotive force is small at the beginning, the motor may be arranged, during its initial movements, to tension a spring or lift a weight, by means of which an auxiliary armature can be intermittently rotated to generate electromotive forces of sufficient strength to eliminate the valve currents, the auxiliary armature being cut out automatically as the motor speeds up. In a modification, the individual armature windings may be passed to a commutating transformer of the type shown in Fig. 4, the necessary starting voltages being produced by armatures driven intermittently by means of changes in the magnetization brought about by the switching impulses. In other cases, a stationary transformer is arranged between the network and the motor, and the valves are placed between the transformer and the network, the voltages for eliminating the current being transmitted from the motor to the transformer.