Power angle characteristics
When the synchronous generator feeding power to the infinite bus-bar at constant terminal voltage Vt as shown in single line diagram in Fig: 1.22 the phasor diagram for lagging power factor is shown if Fig: 1.23. For large size of generator armature resistance ra is negligible.
The per phase power delivered to the infinite bus is given by
Substitution of value of Ia cosqin power equation
The variation of power as derived above with respect to power-angle is plotted in Fig; 1.24. The power versus load angle characteristic curve has a sinusoidal shape and is usually called power-angle characteristic of the cylindrical-rotor synchronous machine. The power P, for generator is taken as positive and therefore, for motor as negative.