Synchronous electric motors have two plausible excitation factors:
– direct current in the field winding;
– from the three-phase source of alternating current in the armature. Gates Rubber 16/A42
The synchronous electric motor when operated in the overexcited and empty condition is called the synchronous capacitor and performs the same function as a capacitor bank, being more efficient than the static capacitors. If its field current is sufficient to compose the essential magnetomotive force, not requiring magnetization current or reactive power, the motor acts with unit power factor.
If your field current is less than is said necessary, saying that the motor is underexposed, the magnetomotive force deficiency needs to be completed by the armature, so the motor works with a delayed power factor. If your field current is greater than is declared necessary, we say that the electric motor is overexcited, the surplus of magnetomotive force must be carefully balanced in the armature and an advanced current device is present, the motor works with power factor in advance.