The subscripts for the Wr terms correspond to those for the ° limits. That is, the
rotor speed Wr l corresponds to that at the angle 0 , and Wr2 corresponds to °2,
Since Wr represents the departure of the rotor speed from synchronous speed,
wereadily see that i f the rotor speed is synchronous at °1 and ° 2 , then,
correspondingly, Wr l = Wr 2 = O. Under this condition, Eq . (16.61) becomes