What Is Power Factor Correction?
Power factor correction balances the reactive power demand of a facility and improves power factor. Correct design supports energy quality and reduces reactive penalty risk.
What Is Reactive Power?
Reactive power is the component required by motors, transformers and inductive loads to create magnetic fields, but it is not converted into active work.
Inductive and Capacitive Loads
Inductive loads
Motors, transformers and welding machines usually demand inductive reactive power.
Capacitive loads
Capacitors supply capacitive reactive power and balance inductive demand.
Harmonic loads
Drives and power electronics may require detuned or filtered correction.
What Is Cosφ?
Cosφ is the ratio of active power to apparent power. The closer it is to 1, the more efficiently the system uses apparent power.
| Cosφ range | Meaning | Approach |
|---|---|---|
| 0.70 - 0.80 | Low power factor | Correction demand is high |
| 0.80 - 0.90 | Moderate | Step sizing should be checked |
| 0.90 - 0.99 | Usually acceptable | Reactive limits should be monitored |
| Very close to 1.00 | Good, but overcorrection must be avoided | Watch capacitive operation |
Why Is Correction Needed?
Correction reduces reactive penalties, relieves transformers and cables, improves voltage quality and allows system capacity to be used more effectively.
Advantages
Improved power factor
Reactive demand from the grid decreases.
Lower losses
Cable and transformer current can be reduced.
Better capacity use
Existing infrastructure is used more efficiently.
Power quality
Correct design supports voltage stability.
Capacitor Selection
Capacitor selection depends on reactive demand, step structure, harmonic level, voltage rating and ambient temperature. With harmonics, detuned or filtered systems should be considered.
Reactive Power Controller Duties
Step control
Switches capacitor steps according to demand.
Cosφ tracking
Continuously follows the target power factor.
Alarm
Reports over/under correction and wiring errors.
Measurement
Uses voltage, current and reactive power values.
Panel Components
Capacitor
Supplies reactive power.
Contactor
Switches capacitor steps.
Reactor
Used in detuned systems to reduce harmonic stress.
Controller
Controls step switching.
Fuse/breaker
Provides protection and isolation.
Ventilation
Controls panel temperature.
Common Faults
Capacitor swelling
May indicate overvoltage, harmonics or ageing.
Contactor sticking
A step may remain connected.
Fuse operation
Check short circuit, overcurrent or capacitor fault.
Capacitive penalty
May be overcorrection or wrong controller setting.
Maintenance Recommendations
Visual check
Inspect swelling, heating and loose connections.
Cleaning
Dust and clogged filters increase temperature.
Step test
Each step should switch correctly.
Harmonic measurement
Periodic checks are needed in drive-heavy plants.
Conclusion
Power factor correction must be designed according to load profile and harmonic conditions. Poor design can increase both penalty risk and equipment failure probability.
FAQ
What does correction do?
It balances reactive demand and improves power factor.
What if harmonics exist?
Detuned or filtered correction should be considered.
What cosφ is targeted?
It depends on regulations and site conditions; around 0.95 is common.
Is maintenance needed?
Yes, capacitors, contactors, fuses and ventilation should be checked regularly.