"Salmon Egg" wrote in message news:C2A0AC46.8183C% snipped-for-privacy@sbcglobal.net...
------ True-no argument there
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------- I'm looking at this from an induction machine viewpoint-in fact two induction machines (assume linearity so one can consider superimposition). The first machine is the conventional machine with stator excitation in the forward (say CW direction) and this will produce supply frequency rotor voltage (and hence currents) in the shorted rotor at standstill. The field due to these currents rotates at synchronous speed in the CW direction. As the rotor speed increases, the rotor frequency drops but the rotor field is still CW at synchronous speed. If the rotor is moving above synchronous speed -say at twice synchronous speed, then the rotor frequency will be synchronous but the field it produces will still be at synchronous speed in the CW direction as seen from the stator. Generator action occurs which, in the absence of a mechanical driving force results in the rotor speed dropping back to synchronous speed or below as seen from the stator. Now consider the stator winding shorted and negative sequence applied to the rotor windings. This will cause a field rotating CCW with respect to the rotor and this will lead to stator currents trying to drive the stator CCW. The stator is fixed so the rotor will move CW. At standstill the induced stator currents will be at supply frequency and they will decrease in magnitude and frequency as the rotor speed rises but, as in the previous case, the field that the (induced) stator currents produce is always in synchronism with the rotor field. To make a long story shorter, negative sequence applied to the rotor will have the same physical action as positive sequence applied to the stator-producing CW motion and 0 torque at synchronous speed and generation at speeds above synchronous. If this came up about 15 years ago, I would have gone down to the lab and tried it. Now retired and far from the machines lab.
However, I will, if I have time, go over the basic model for steady state modifying it for dual excitation.