GB495779A - Improvements in or relating to electric generators - Google Patents

Abstract

495,779. Exciting dynamos. HOLMES & CO., Ltd., J. H., and BAYLES, J. W. May 18, 1937, No. 13894. [Class 35] The invention relates to electric generators for purposes, such as welding, requiring a falling characteristic and is concerned with generators of the type having main poles B, C and auxiliary poles D, E arranged so that the flux in the former tends to be increased by armature reaction but is restricted by saturation, whilst the flux in the latter tends to be decreased and reversed by armature reaction ; an auxiliary brush F<3> is provided in addition to the main brushes F<1>, F<2> and the voltage between certain brushes varies comparatively little while that between other brushes is reduced or reversed. According to the invention the generator has on at least one auxiliary pole, for example the pole E, a shunt winding E<1> connected between brushes F1, F2 between which the voltage is reduced or reversed with increase of armature current and on at least one auxiliary pole a series winding D<2> or E<2> tending to increase the flux or to oppose its reversal with increase of armature current. The windings B<1>, C<1> on the main poles and the winding D<1> on the auxiliary pole D are connected across the constant voltage brushes F2, F3. In a modification, the winding D<1> is connected across the brushes F<1>, F<3> and the winding E' across the main brushes. The windings D<1>, E<1> may be connected in series or in parallel across the main brushes. Two or more auxiliary windings may be connected across brushes between which the voltage reverses with increase of armature current, but it is desirable to maintain stability by providing a winding through which the current is never reversed. More than one auxiliary brush may be provided, an auxiliary winding being connected across two such brushes or each auxiliary winding across a main brush and an auxiliary brush. Other arrangements described are: (1) windings B<1> and D<1> in series between brushes F2, F<3> and windings C<1> and E<1> in series between brushes F<1>, F3, additional compounding series windings being provided on the main poles ; (2) windings B<1> and D<1> in series across the main brushes and windings C and E<1> in series across brushes F', F<3> or F<2>, F3. A winding may be divided between different poles. The auxiliary poles are of greater section than the main poles and are saturated on open circuit but are unsaturated at short-circuit. Resistances which may be varied differentially or together may be connected in series with the auxiliary pole shunt windings. Control of the current may also be obtained by the provision of tappings on the auxiliary pole series windings and by brush rocking.