GB286762A - Improvements relating to dynamo-electric machines for converting electric currents - Google Patents

Abstract

286,762. Quasi-Arc Co., Ltd., and Musto, R. J. Dec 3, 1926. Rotary transformers. - An alternating - current dynamoelectric welding set comprises two machines or two machine elements of the induction motor type both supplied from a polyphase source, one acting as a transformer and the other as a motor driving the rotor of the transformer; the transformer has a single-phase output winding for supplying welding current and the electrical constants of the set are such that the output frequency is greater than that of the source of supply while the input phases of the transformer take a substantially balanced current. In a modification, the dynamo-electric welding set has a polyphase output winding supplying independent welding units which give rise to unbalanced output conditions whilst balanced currents are maintained in the phases of the input winding. In the arrangement shown in Fig. 1, the set comprises a motor Q having a three-phase two-pole primary winding 7 and a squirrel cage rotor 8, driving a transformer having a three-phase 4-pole primary winding 1 on the rotor connected to slip-rings 4 and a single-phase output winding 2 on the stator. Both primary windings are fed in parallel from a three-phase source 3. The welding arc 5 is connected to the winding 2 through an adjustable choking coil 6. The rotor 8 revolves in the same direction as the rotating field produced by the winding 1 so that the frequency in the ouput. winding 2 is three times that of the source of supply. In the modification shown in Fig. 2, the motor Q is provided with a wound rotor, the winding 10 being connected through slip-rings 11 to a throw-over switch 12, whereby the winding can be connected either to a starter 13 or to brushes 14 resting on a commutator 15 connected to a phase compensating winding 16. Fig. 3 shows the invention applied to multiple-arc welding. The output winding 2 of the transformer has three phases and feeds welding arcs 5<a>, 5<b>, 5<c> through adjustable choking coils 6<a>, 6<b>, 6<c>. The compensating winding in this case is connected to the secondary winding 2 of the transformer and has the additional effect of tending to maintain the output voltage upon increase of load current. In order to produce a sinusoidal flux distribution, the coils of the transformer primary winding are caused to overlap and the slots may be skewed by one slot pitch. The coils of the transformer secondary winding may embrace more or less than a complete pole pitch and the winding should have a high inductance except when connected to a compensating winding as in Fig. 3. The motor and transformer may constitute separate machines or both may be incorporated in one machine and the stator and rotor windings of each element may be interchanged.