GB159374A - Improvements in and relating to dynamo-electric machines - Google Patents

Abstract

159,374. British Thomson - Houston Co., Ltd., (General Electric Co.). Dec. 16, 1919. Exciting.-A commutating machine with a falling volt-ampere load characteristic, for example for arc welding, has two sets of poles, one set 6, Fig. 1, saturated and the other 7 unsaturated, and an auxiliary brush 4 between the main brushes 3, 13. The component AD of the armature reaction AR produces little effect on the poles 6 which give constant volts at the brushes 3, 4, to which the shunt coils 8 are connected. The component AE gives between the brushes 4, 13 a voltage which increases with the load current and is opposed between the brushes 3, 13 to that given by the brushes 3, 4. Thus, the load volts fall with increasing current. An adjustable number of series windings may be wound on the poles 7 to aid the armature flux AE or, alternatively, these poles may have windings in series with the coils 8 across the constantvoltage brushes 3, 4 and so wound as to oppose the flux AE so that at no load the volts between the brushes 4, 13 are added to those between the brushes 3, 4 but are decreased as the armature reaction increases. Fig. 4 shows a machine having both shunt and series coils 9, 10 of this nature differentially combined. By adjusting them so that at about half load the resultant flux in the poles 7 is zero, a decreasing voltage between brushes 4, 13 is added to that between brushes 3, 4 up to half load, whereafter an increasing voltage between brushes 4, 13 is subtracted from that between brushes 3, 4. Commutating-poles with ordinary series windings may be added.