Q7Electrical Machines II

The Power-Angle Characteristic describes the relationship between the active real power ($P$) transferred by a synchronous machine and the load angle (or power angle, $\delta$). The load angle is the electrical phase difference between the induced internal EMF ($E$) and the terminal voltage ($V$).

For a cylindrical rotor machine with synchronous reactance $X_s$, the relationship is: $P=\frac{EV}{X_s}\sin \delta$.

This equation reveals that the power transferred follows a sine curve, reaching a theoretical maximum limit at $\delta =90^{\circ }$. This characteristic is crucial for determining the static stability limit of the machine. If the mechanical load forces $\delta$ beyond $90^{\circ }$, the machine will lose synchronism (pull out of step) and stall.