Synchronous Motor with Different Excitations
Synchronous Motor with Different Excitations:
Fig: 1 Fig: 2
- A synchronous motor is said to have normal excitation when it’s Eb = V. If field excitation is such that Eb < V, the motor is said to be under-excited. In both these conditions, it has a lagging power factor as shown in Fig. 1.
- On the other hand, if d.c. field excitation is such that Eb > V, then motor is said to be over-excited and draws a leading current, as shown in Fig. 38.13 (a). There will be some value of excitation for which armature current will be in phase with V, so that power factor will become unity, as shown in Fig. 2 (b).
- The value of α and back e.m.f. Eb can be found with the help of vector diagrams for various power factors, shown in Fig. 3.