hi

1.Assume say singly fed IM .. imagine  steady state'' the stator windings and rotor windings are coupled through air gap flux. so we have a system of coupled coils . one set rotating .one stationary .

2. At the moment of opening the stator ( say ideally with zero arcing) the trapped flux linkage theorem can be applied to the rotor coils. Thus we get a decaying current in the rotor coils which decay with rotor time constant determined by Lrotor and R rotor..

3. The output stator voltage will depend on this decaying flux in the rotor.. and the frequency of the mechanical speed as it slows down..

4. It is wise to wait for transient to die down ( unless electronics are used to switch back) to avoid huge currents as a result of the varying phase/ freq of rotor opposing voltage..

5. Unified theory of machines would provide a good way of understanding this type of transient.

Cheers

hi

 From some work  done a long ..long time ago here is a simple formula formula:

1.Assume phase a voltage max at time of switching off.

2 Use hot resistance values Rr from standard single phase representation T eqt circuit.

3. Slip s=0 . Xr = Xmu +xleak2  (Xmu is unsaturated  value),w =rotor speed., t=time

Xs = Xmu +xleak1  wr = wrmech*poles/2 in electr rads/sec., Vs- =preswitcing

stator voltage.

4 The approx stator voltage is :

     Vstator =( Vs- ) .*(Xmu^2/(Xs*Xr )* exp(-  (Rr*w/Xr) *t)  *cos(w*t)

5. Re-switching normally after Vstator is< 40%

Hope it is useful

 Cheers

Simply, this bus has to be modeled as generator bus with residual flux linkages decaying with some constant (typically 1 s or more) and with some deceleration depending on previous load torque (and load characteristics). Thus, the mathematical model must include flux linkages decay, speed and angle time description!