GB312357A - Improvements in and relating to dynamo-electric machines more especially for electric arc welding - Google Patents

Abstract

312,357. Elin Akt.-Ges. f³r Elektrishe Industrie. May 25, 1928. [Convention date]. Dynamos, regulating; coils. - In a series excited dynamo feeding a load with an arc characteristic, for instance for arc welding with electrodes of different thicknesses several series coils are provided and these are connected in different ways for thin and thick electrodes so that they give a smaller effective number of ampereturns and a greater internal resistance for thin electrode work. The increase in resistance is not large enough to reduce the steady current appreciably but it reduces current surges. The following methods are described:-(1) A double armature generator with two series windings may have its two component machines, each comprising an armature and field coils, connected in parallel for heavy loads, one component machine being used for light loads, thus giving internal resistance values in the ratio 1 : 2. (ii) A single armature machine may have two series windings of different sections, or number of turns, the smaller one being used either alone or in series with the larger one for small load currents, and the thicker one either alone or in parallel with the thinner one for large currents. The field coils in this case are preferably strip-wound with the thin and thick-section coils sandwiched so that the thick ones when unloaded carry away heat from the thin ones; or the thin coil may surround the thick one to give it an increased length per turn. Fig. 4 shows a machine in which the arc 25 is connected in series either with the thin or thick series coils 21, 22 of a machine of the Rosenbeag type by throwing the switch on the contacts 29, 28 respectively, the thin coil having a smaller number of turns than the thick one. Alternatively, the two coils may have the same number of turns but a portion of the thin coil may oppose the remainder of its turns, thus giving a smaller effective number. Fig. 6 shows an arrangement in which the thick coils 22 are always in circuit. For a reduced load current and increased internal resistance, the thin coils 36, which have fewer turns, are connected in series with the coils 22 by removing the short-circuit at 37. In the form shown in Fig. 7, the machine has two field coils 41, 42 with different numbers of turns which are connected in parallel for heavy loads, as shown in full lines at 43, and in differential opposition for light loads, as shown in dotted lines. In all of the arrangements depending upon different conductor sections the same result may be obtained by supplying materials of different resistivities for the two coils. Specifications 17423/04 and 253,930 are referred to. Tbo Specification as open to inspection under Sect. 91 (3) (a) describes also the use in a machine with separate or any other type of excitation of a counter-compounding series coil consisting either of one winding or two windings which may be connected in series or parallel. This subject-matter does not appear in the Specification as accepted.