Synchrounous Machine Dynamic Model

[oblomof]

Dear Friends
I faced a problem in Synchrounous machine dynamic model. I cant understand stator mutual inductance as follow: Lab=-Ms-Lm cos(2*teta+pi/3) , Lbc=-Ms-Lm cos(2*teta-pi) , Lac=-Ms-Lm cos(2*teta+5pi/3). Why does phase shift as follow: pi/3 , pi , 5pi/3 ?

 

[ijl]

Without going into details: (1) The cos-term tells how the mutual inductance between two stator windings depends on the rotor position. (2) The angle between the stator windings is 2pi/3. (3) The relative position of the rotor with respect to stator winding pairs is different for each pair. The rest is geometry, I think.