GB157723A - Improvements in and relating to alternating current electric motors - Google Patents

Abstract

157,723. British Thomson - Houston Co., Ltd., (Assignees of Altes, W. C. Korthals-). Dec. 22, 1917, [Convention date]. Void [Published under Sect. 91 of the Act]. Alternating-current commutator machines; exciting. - An alternating-current commutator motor has two sets of brushes, such as 8, 8<1>, 9, 9', Fig. 1, each connected with compensating windings 6, 6<1>, exciting windings 5, 5' and reactive coils 10, 10<1> in parallel on the commutator in such a manner as to avoid local short-circuits through the brushes. The compensating and exciting coils are wound in a slotted stator of the usual induction motor type, as shown in Fig. 6, and the brush studs need be arranged around a part only of the commutator, as in Fig. 8, where the brush pairs 58, 59 are arranged opposite handholes 60, 61 in the upper part of the motor casing. In the form shown in Fig. 1, the reactive coils 10, 10' form the secondaries of the transformer through which the motor is supplied with energy from the mains 12, but in an alternative arrangement each pair of brushes 8, 8<1>, 9, 9<1> is closed through a reactance, the mid-points of the reactances being connected to the mains, one directly and the other through the compensating and exciting coil groups connected in parallel. Or the compensating coils may be split into two parts each comprising two portions in series with one of the brushes. The two portions are joined together on their side remote from the brushes, and they are connected to the mains, one directly and the other through the exciting coils in series with a reversing switch. In the arrangement shown in Fig. 4, the brush pairs are connected to reactances 35, 35<1>, the mid-points of which are led to taps on the secondary side of the supply transformer 41, the exciting and compensating coils 37, 37' and 36, 36<1> being paralleled and connected in series with a portion 40 of the same secondary coil. The Specification also describes the application to a motor for starting a frequencychanging set comprising a synchronous motor coupled to a generator having a different pole number. This arrangement shows a throw-over switch for starting the commutator machine as a motor on the alternating-current mains on which the synchronous motor ultimately runs, and for subsequently throwing it over to a separate pair of mains to which it supplies continuous current as a generator driven by the frequency-changing set. The stator windings, Fig. 6, are of full pitch lap type and comprise exciting coils, shown in light lines, separated bv an unwound zone a, j somewhat greater than the angle between the brushes, and compensating coils, shown in heavy lines. Coils with different numbers of turns are used, whereby the armature reaction may be accurately compensated over a portion of the pole angle and over-compensated to ensure good commutation over the remaining angle. In the example shown, the full and dotted line coils have 5 and 7 turns respectively so that the slots c, h contain 14 compensating turns and the slots d, e, f, g 12 turns.