GB190526094A - Improvements in and relating to Alternating Current Dynamo-electric Machines. - Google Patents

Abstract

26,094. Allgemeine Elektricitõts-Ges. Dec. 15, 1904, [date applied for under Patents Act, 1901]. Field magnets; sparking, preventing.-The commutation of alterna. ting-current motors, having a transverse magnetic field f, Fig. 1, in addition to the main field F, is improved by providing a suitable magnetic field at the points where the rotor coils are short-circuited. One method consists in making the air gap between the stator and rotor either greater or less at those places where the rotor coils are short-circuited according as the commutation is arranged to take place at high or low speeds, or the magnetic saturation of the stator may be made greater or less at those places. An auxiliary coil may be employed upon the stator, the field of which may be either in phase with the field f, dependent upon the current to be commutated, or dependent upon both. In Fig. 4, this field is produced by an auxiliary coil H excited by an adjustable shunt transformer T and regulated by a variable resistance W. In modifications, the coil H may be excited by both shunt and series transformers, or it may be short-circuited either on itself or through a variable resistance W to weaken the fields f or F at the desired places, as shown in Fig. 6. In those cases in which the maximum field strength occurs at the places where the coils are short-circuited and where the field is weakened by the last-mentioned arrangement, the hysteresis loss is simultaneously reduced.