Variations in the electromechanical torque result in corresponding variations in the torque angle , RF ,as seen from Eq.5.1. The relationship is shown in the from of a torque-angle curve in fig .5.1, where the field current (rotor mmf) and resultant air-gap flux are assumed constant. Positive values of torque represent generator action, corresponding to positive values of RF for which the rotor mmf wave leads the resultant air-gap flux