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Which motor use as power factor improvement?
Induction motor
Synchronous motor
DC motor
Universal motor
Synchronous motor
A synchronous motor is uniquely capable of operating at leading, lagging, or unity power factor depending on its field excitation. When over-excited, it acts as a synchronous condenser, drawing leading current from the supply to compensate for lagging loads, thereby improving the overall power factor of the system.
A synchronous motor is uniquely capable of operating at leading, lagging, or unity power factor depending on its field excitation. When over-excited, it acts as a synchronous condenser, drawing leading current from the supply to compensate for lagging loads, thereby improving the overall power factor of the system.
Q=VIsin(╧Х) тАФ Reactive power calculation
EbтАЛ>V тАФ Condition for leading power factor (Over-excitation)
The power factor of a synchronous motor is controlled by its DC excitation. In an over-excited state, the induced back EMF (EbтАЛ) exceeds the terminal voltage (V), causing the motor to act like a capacitor. This generates reactive power (Q) which balances the inductive reactive power of other loads, bringing the system power factor closer to unity.
Over-excited synchronous motors supply lagging reactive power to the system.
A synchronous motor running at no load for power factor correction is called a 'Synchronous Condenser'.
Induction motors always consume lagging reactive power, hence they degrade power factor.
Power factor improvement reduces transmission line losses and improves voltage regulation.
Continuous control of power factor by adjusting field excitation
Can operate at a leading power factor unlike induction motors
Provides voltage regulation for the local bus
High efficiency in large capacity ratings
Requires a separate DC excitation source
More complex starting mechanism than induction motors
Costly for small industrial installations compared to capacitor banks
Large industrial power plants
Transmission substations
Heavy load factories with many induction motors
| Feature | Induction Motor | Synchronous Motor |
|---|---|---|
Operating Mode | Always draws lagging current | Leading, Lagging, or Unity |
DC motors and Universal motors are not used for power factor improvement as they are not connected to AC supply or operate on different commutation principles.
Capacitor banks are also used for PF improvement but are static devices, whereas synchronous motors are rotating machines.
B is correct тАФ Synchronous motors, when over-excited, provide leading reactive power to the network, effectively improving the system power factor.
Always remember: Over-excited Synchronous Motor = Capacitor (Leading PF), Under-excited Synchronous Motor = Inductor (Lagging PF).