New methods of stabilising doubly fed slip-ring machines

When the stator and rotor windings of a slip-ring machine are connected to supplies of fixed frequency, one of the possible modes of synchronous operation is at a speed proportional to the sum of the supply frequencies. Such a doubly fed machine, in its basic form, possesses considerable peak power capabilities but is dynamically unstable and is not self-starting. The paper demonstrates how a 2-pole, 6000rev/min, 50c/s, doubly fed machine can be started and stabilised by incorporating a small auxiliary 8-pole winding on the stator and by using a single 8/2-pole-amplitude-modulated winding on the rotor.