Power Angle Characteristics of Synchronous Generator

We have seen previously,

The relation between P_i  and δ is known as power angle characteristics of the machine. It is shown in the Fig. 1.

Fig. 1  Power Angle Characteristics

       The maximum power occurs at δ = 90^o . Beyond this point the machine falls out of step and loses synchronism. The machine can be taken up to P_{i max}  only by gradually increasing the load. This is known as the steady state stability limit of the machine. The is normally operated at δ much less than 90^o.