GB969475A - Improvements in or relating to rotary electric machines - Google Patents

Abstract

969,475. Dynamo-electric machines. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Jan. 11, 1961 [Jan.' 14, 1960; June 7, 1960], Nos. 1400/60 and 19955/60. Heading H2A. In a polyphase machine whose stator and rotor are both energized, so that the machine runs synchronously at double frequency (generally called " induction " machines), the stator carries an additional winding of higher polenumber and energized at a higher frequency, and the rotor winding is arranged to act as a short-circuited winding in respect of this higher pole number for the purpose of damping and running-up. Figs. 1 and 2 show one phase (between star-point 9 and slip-ring connection 10) of a 4-pole rotor winding in which the coil groups 1, 2, 3, 4 act in series-parallel between the terminals 9 and 10, but in a closed series loop for the 8-pole energization induced by the additional stator field. The stator carries the normal three-phase, 4-pole winding, and an additional 8-pole winding in the same slots and energized at quadruple frequency (i.e. double the pole-number, and double frequency because of the double speed of the machine). A modification is described (Fig. 6, not shown) in which a single, centre-tapped stator winding is energized at both pole-numbers by means of centretapped transformer windings. In a modification in which the higher pole-number is a third instead of a second harmonic of the main supply, Fig. 10, the rotor 90 is arranged as a 2-pole, delta-connected, three-phase winding, and also as a 6-pole, series-connected, singlephase winding which is used for starting and damping by the use of a resistor 88 and shorting switch 89 respectively,