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Synchronous motor can be operated at
Leading power factor
Lagging power factor
Unity power factor
All of above
All of above
A synchronous motor is a versatile machine that can operate at leading, lagging, or unity power factors depending on its field excitation. This unique characteristic is governed by the V-curve and inverted V-curve relationships between the field current and the armature current/power factor.
A synchronous motor is a versatile machine that can operate at leading, lagging, or unity power factors depending on its field excitation. This unique characteristic is governed by the V-curve and inverted V-curve relationships between the field current and the armature current/power factor.
P=XsтАЛVEbтАЛтАЛsin╬┤ тАФ Power developed per phase
EbтАЛ=VтИТIaтАЛ(RaтАЛ+jXsтАЛ) тАФ Phasor relationship for synchronous machine
The excitation level of the DC field winding controls the reactive power exchange between the motor and the supply. Under-excitation causes the motor to draw lagging reactive power (inductive behavior), while over-excitation causes it to deliver reactive power to the system (capacitive behavior). At normal excitation, the back EMF EbтАЛ matches the terminal voltage V, resulting in unity power factor operation.
Under-excited motors behave like an inductor (lagging power factor).
Over-excited motors behave like a capacitor (leading power factor).
Normal-excited motors operate at unity power factor.
Synchronous motors are widely used for power factor improvement in industries.
Constant speed operation
Ability to control power factor
Higher efficiency at low speeds
Requires DC excitation source
Not self-starting (needs auxiliary equipment)
Susceptible to hunting
Power factor correction
Large industrial drives (compressors, pumps)
Voltage regulation in transmission lines
A synchronous condenser is essentially a synchronous motor running at no load with high over-excitation to supply leading reactive power.
Option D is correct because the motor's power factor is controllable via the field excitation current.
D is correct тАФ A synchronous motor's power factor can be adjusted from lagging to leading by varying its field excitation, allowing it to operate at any power factor including unity.
Always remember the mnemonic: Over-excited = Over-capacitive (Leading), Under-excited = Under-inductive (Lagging).