GB169694A - Improvements in and relating to apparatus for converting electric currents - Google Patents

Abstract

169,694. Coninck, M. de. Sept. 30, 1920, [Convention date]. Commutator switching - arrangements.- In an apparatus for converting alternating current into direct current or vice versa in which commutator segments are connected to resistance elements, magnetic means are provided for limiting the amplitude of the harmonics of the alternating current. The arrangement shown in Fig. 1 comprises a rotating commutator C with brushes F1, F1<SP>1 >&c. connected to the polyphase leads I, I<1> &c., the segments of the commutator being connected to a resistance winding R, which rotates with the commutator and is connected at two or more points P, P<1> to slip rings B, B<1> whose brushes are connected to the direct current leads. The resistance is given decreasing values when approaching the direct current taps, and the commutator segments near these taps may be short-circuited or replaced by a larger segment. The number of taps may be increased by connecting them in parallel, the number of brushes for each phase of the polyphase current being correspondingly increased and connected in parallel. The third harmonic current and its multiples are limited by means of a reactance coil A, Fig. 3, having a single closed magnetic circuit and windings A' - - A' in series with the phases of alternating current. The higher harmonic currents may be limited by providing sufficient leakage reactance in the transformer or other apparatus connected to the alternating-current side of the converter. The resistance R may be wound around insulating-pegs G, G<1> carried by a metallic wheel E, Fig. 5, secured to the commutator shaft. Highvoltage direct current may be obtained by mounting several converters C1 - - C3 on the same shaft and connecting them in series as shown in Fig. 7, in which only the connections and brushes for the phase I are shown. When converting direct current into polyphase current, the converter may be used for driving synchronous motors at variable speeds by varying its speed of rotation. In order to obtain approximate equality of the counter E.M.F. of the motor and the voltage at the brushes of the converter at different speeds, the excitation or grouping of the windings of the motor may be varied, or resistances may be inserted on the direct-current side. Synchronous motors may also be driven at varying speeds from a polyphase supply by the use of two converters, the first of which rectifies the supply, while the second converts the direct current thus obtained into alternating current of varying frequency.