GB546084A - Improvements in or relating to electric generators - Google Patents

Abstract

546,084. Dynamos. REYROLLE & CO., Ltd., A., and BAYLES, J. W. Dec. 18, 1940, No. 17822. [Class 35] A generator having a falling characteristic, as for welding, has shunt windings B<SP>1</SP>, C<SP>1</SP> on the main poles B, C, shunt windings D<SP>1</SP>, E<SP>1</SP> on the auxiliary poles D, E, and series windings B<SP>2</SP>, C<SP>2</SP> on the main poles which reinforce the shunt windings, all the shunt windings being connected between the main brushes or terminals of the generator. The auxiliary poles are preferably of larger cross-section than the main poles. When a short-circuit occurs armature reaction tends to increase the flux in the main poles (but is restricted by saturation) and to decrease the flux in the auxiliary poles, so that the voltage drops to a small value necessary to maintain the desired short-circuit current. Series windings D2, E<SP>2</SP> may be provided on the auxiliary poles. The shunt and series windings reinforce one another so, that the transformer effect between them during transient current changes enhances the falling characteristic. For this purpose there should be a greater number of series windings on the main poles than on the auxiliary poles and means may be provided for increasing the leakage flux linking the windings. As shown, the shunt coils are all in series across the main brushes ; in a modification the shunt coils are series-connected pairs connected in parallel across the output terminals. The auxiliary poles may be saturated on open circuit. Specification 495,779 is referred to.