How to adjust a synchronous motor from underexcited to overe

How to adjust a synchronous motor from underexcited to overexcited?

Solution

Synchronous motor excitation refers to the DC supply given to rotor which is used to produce the required magnetic flux.

When the Field current is not sufficient enough to produce the required air gap flux, additional magnetizing current or lagging reactive VA is drawn from the AC source. This magnetizing current produces the deficient flux. In this the motor is said to operate under lagging power factor and the is said to be under excited.

If the field current is more than the normal field current, motor is said to be over excited. This excess field current produces excess which must be neutralized by the armature winding. Hence the armature winding draws leading reactive VA or demagnetizing current leading voltage by almost 90o from the AC source. Hence in this case the motor operate under leading power factor.

For adjusting a synchronous motor from under excited to overexcited increase the field current above the normal filed current by reducing the resistance value connected in the field circuit.