GB566147A - Improvements in synchronous electric motors - Google Patents

Abstract

566,147. Dynamo-electric machines. MAcFARLANE, J. C., and MAcFARLANE, W. April 10, 1943, No. 5787. [Class 35] A rotor for a synchronous motor of the reluctance type is built up of parts 3, Fig. 1, presenting a low reluctance path for the main flux 6 and having faces 4 which form the cylindrical exterior of the rotor, the parts being separated by gaps 5 so to increase the reluctance of the rotor to the cross-flux 7 and being clamped between end plates by bolts 8 extending from end to end of the rotor. The bolts may, as shown, be located in the gaps and form in conjunction with the end plates a squirrel cage starting winding. Alternatively, the bolts may be of magnetic material and pass through the parts 3 adjacent their faces, in which case a starting winding or a D.C. exciting winding to improve the hold-in torque may be wound in the gaps. The rotor shaft may be formed in two sections, one section being carried by each end plate, or, as shown in Fig. 3, which illustrates the shapes of the different parts 20, 21 of a four-pole rotor, the shaft 26 may pass through the rotor, provided the parts adjacent it are so shaped as to leave a space 23 around the shaft. When starting under load is required, a separate squirrel cage starting motor may be provided, or the rotor may be divided midway of its length so that one section thereof may temporarily be displaced through 90 electrical degrees to increase the cross-flux permeance for induction starting. Alternatively, the motor may be supplied from a variable frequency supply, the frequency of which, during starting, is gradually increased from zero to the normal working frequency. According to the Provisional Specification, a rotor connected to an A.C. supply may be surrounded by a stator formed of parts so shaped and arranged as to increase its reluctance to cross-flux.