Power Factor Improvement Methods
Power Factor improvement methods:
The low power factor is occurred mainly due to inductive load ( we know that most of the power loads are inductive in nature and draws lagging current). In order to improve the power factor we have to connect some device which takes leading power factor. Static capacitors, synchronous machines and synchronous condensers are some of the devices which takes leading power factor.
Various methods of power factor improvement are given below;
- Using Static capacitors
- Using synchronous motors
- Using synchronous condensers
- Using Phase advancers
- Using synchronous induction motors
- Using high power factor motors
Power Factor improvement: By use of static capacitors
- This method is followed in factories widely.
- By connecting the capacitors in parallel with the equipment working at low power factor, the power factor can be improved.
- The capacitors draw a leading current. So it partly or completely neutralizes the lagging reactive component of the load current.
- Consequently the power factor of the load is increased.
- For three-phase loads, the capacitors are connected in star or delta manner.
- They can be easily installed as they are light and require no foundation.
- They have low losses.
- As there are no rotating parts, they require little maintenance.
- If the voltage exceeds the rated value they are damaged easily.
- If the capacitors are damaged, their repair is uneconomical.
- They have short service life.
Power factor improvement - By use of synchronous condensers
- The over excited synchronous motor running on no load is known as synchronous condenser.
- When over excited, a synchronous motor takes a leading current, thus it act as a capacitor.
- So when it is connected in parallel with the supply, it draws a leading current which eliminates the lagging reactive component of the load.
- So the power factor of the circuit is improved.
- This method is generally used at major bulk supply substations for power factor improvement.
- Finer control can be achieved y varying the field excitation.
- Possibility of overloading a synchronous condenser for short periods
- System stability is improved.
- The faults can be easily removed.
- The cost is higher than static capacitors.
- Higher maintenance and operating cost.
- Lower efficiency due to losses in rotating parts and heat losses.
- Increase of short-circuit currents when the fault occurs near the synchronous condenser.
- Except in sizes above 500kVA, the cost is greater than that of capacitor method.
- An additional equipment is required to start the synchronous motor, as they has no self-starting torque.
Power factor improvement - By use of Phase advancers
- This method is used to improve the power factor of induction motors.
- In induction motor, the stator winding draws exciting current which lags behind the supply voltage by 90°. It leads to low power factor in induction motors.
- If the excitation is provided from some other source, then the stator winding will be relieved of exciting current.
- So the power factor of the induction motor can be increased.
- This additional excitation is done by phase advancers. It is simply known as ac exciter.
- It is mounted on the same shaft as the main motor and is connected in the rotor circuit of the motor.
- It provides the exciting ampere turns to the rotor circuit at slip frequency.
- By providing more ampere turns than required, the induction motor can be made to operate on leading power factor like an over-excited synchronous motor.
- Lagging KVAR drawn by the motor is drastically reduced due to supply of exciting ampere-turns at slip frequency.
- This method is conveniently used where the use of synchronous condensers are not possible.
- For motor rating below 200HP the phase advancers method is not economical.
Thanks for reading....