GB899624A - Improvements relating to single-phase alternating current electric motors - Google Patents

Abstract

899,624. A.C. commutator motors. MENSFORTH, T. Dec. 15, 1958 [Jan. 15, 1958; Sept. 2, 1958], Nos. 1411/58 and 28112/58. Class 35. In a single-phase commutator motor, the field flux is maintained substantially constant and in phase with the armature voltage to give a shunt characteristic over a wide speed range, by means of a phase-shifting capacitor g in series with the field winding e, and an autotransformer h through which the voltage applied to these is varied inversely with the armature voltage. The machine is provided with a shunt commutating winding o fed from a tapping on the speed-control transformer k, and at high speed this winding acts to oppose the voltage induced in the armature winding by transformer action from the main winding e, and so suppresses current circulating under the brushes. However, at low speed, the resultant current induced between the commutator segments by the main field interferes with the field current in winding e. This effect is overcome, according to the invention, by applying a higher voltage to the field winding circuit at low armature speeds, i.e. at low armature voltages. For this purpose, the auto-transformer h is connected, as shown, so that as the armature voltage is raised, progressively more voltage is subtracted from the excitation circuit. Known resistive armature connections c, series commutating windings n, and series armature-reaction compensating windings m are provided. The machine may be reversible. The stator winding layout, Fig. 2, having nine slots per pole comprises the field winding e in six slots in each pole at the edges thereof, the armature reaction compensating winding m distributed in six slots at the centre of each pole, while the commutating windings o and n are wound round one tooth and three teeth respectively, between the poles.