Salient pole Synchronous generator

The first term is the same as for a round rotor machine with Xs = Xd and constitutes the major part in power transfer. The second term is quite small (about 10-20%) compared to the first term and is known as reluctance power.
P versus ? is plotted in figure below. It is noticed that the maximum power output occurs at ? < 90° (about 70°). Further dp/d ? (change in power per unit change in power angle for small changes in power angle), called the synchronizing power coefficient, in the operating region (? < 70°) is larger in a salient pole machine than in a round rotor machine.
The synchronous generator described previously can operate either as generators or as motors. When operating as motors (by connecting them to a 3-phase source), they are called synchronous motors. As the name implies, synchronous motors run in synchronism with revolving field. The speed of rotation is therefore tied to the frequency of the source. Because the frequency is fixed, the motor speed stays constant, irrespective of load or voltage of the 3-phase line