Patent GB-273987-A (GB)
Title: Improvements relating to dynamo electric machines for electric welding and like purposes
IPC: H02K23/02
Filed: 1926-04-16
Abstract: 273,987. Creedy, F. April 16, 1926. Exciting; regulation of exciting machines; rotary converters and transformers; commutating poles and windings.-In a welding dynamo having a commutating circuit and separate or shunt and series excitation, the magnetic leakage between the commutator and shunt or separate excitation circuits is reduced to a minimum. This mav be done by reducing the armature inductance by means of short-circuited coils so placed that currents induced therein counteract the armature or by means of compensating coils which neutralize the armature flux. Transient induced voltages on changing load are thereby eliminated and the arc volt-ampere characteristic is rendered nearly the same for rapidly fluctuating load conditions as it is for slow variations. A separately excited field coil may also be used and the magnetic leakage between this, the shunt and the series coils may be minimized by sandwich windings. Fig. 1 shows a machine in which the stator slots contain a neutralizing winding N, preferably giving a slight over-compensation, and, in the slots shown, a differential series coil S and a shunt coil T and, optionally, a separately excited winding V. Similar windings are shown in the Specification for a salient pole machine having pole shoes slotted to contain a compensating winding and unwound commutating poles which are energized by the over-compensating effect of the compensating winding. The shunt - and series coils T, S may be sandwiched, as shown in Fig. 3, the series winding being made in two parallels, if necessary, each parallel being in one layer. When a separately-excited coil is used, it replaces half of the shunt turns, as shown at V. Where slot-wound fields are used, as in 'Figs. 1, and 5, it is preferable to wind the shunt and series coils in the same slots and to limit the whole shunt winding to one slot per pole. Fig. 4 shows the complete circuits for supplying an arc P through an inductance Q from a main machine C having compensating and series winding N, S and a shunt winding T excited by the sum of the voltages of the main machine and a separate exciter E. The exciter has compensating and shunt windings W, together with a counter series winding Y and an optional separate excitation, as shown at X. Fig. 5 shows a non-salient pole machine as described in Specification 249,579 adapted to act simultaneously as a converter from alternating to continuous-current and as a compensated welding generator. This has on its stator a winding adapted to excite a second or motor field and additional circuits on the rotor in which the motor field of the machine induces voltages while no voltage is induced in them by the generator field. Six slots are entirely devoted to the shunt, series and separately excited windings T, S, V (six being the pole number or a multiple thereof) and with end connections so arranged that the coils can be removed without interfering with the other windings, viz. the neutralizing coils N and the alternating-current windings L. The commutator segments are joined by equalizers F at points one-third of the circumference apart and the shunt winding T is connected in series with an exciter E of the same type as is shown in Fig. 4. The arc and steadying resistance are shown at P, Q. To improve the starting properties of the machine on alternating-current supplies the winding T may be made of three series-connected coils, each spanning half of the circumference. For starting, they are disconnected from the continuouscurrent side and are connected as a mesh group at the centre of the star-group alternating- current windings of the machine. In such an arrangement, the number of sections in the alternating-current winding may be a multiple of the number of poles of the generator field. For instance, with a 2 and 6-pole combination, a 3- phase alternating-current winding giving six sections has as many sections as there are generator poles, while with a 4 and 8-pole combination the relationship is obtained by employing a 2-phase 4-pole alternating-current winding.