Power Factor Correction

Power factor is the ratio of active power (the power flowing to a system/appliance) vs the amount it uses to perform its function. A device’s power factor represents how effectively that device is using the power supplied to it – essentially its electrical efficiency.

Devices with high power factors make better use of the power being supplied to them than devices with low power factors.  Power factors range from 0 to 1 where 1 represents 100% efficiency. A device that has a power factor of 1 is using all the power supplied to it.

Generally, a power factor of 0.8 or above is considered good.  Lower than 0.8 and it should be corrected to save on consumption and comply with the requirements of the electricity network operator.

Other key reasons for improving power factor:

  • Increases the efficiency of your power use
  • Reduces your power bills
  • Filters unwanted frequency harmonics
  • Reduces stress on your electrical equipment
  • Extra kVA available from your existing supply.
  • Extends equipment life as there is reduced electrical burden on cables and electrical components.


How do we measure Power Factor?

Power factor isn’t static – it fluctuates and can be influenced by changes in processes such as motor loading.

The power factor in a single-phase circuit (or balanced three-phase circuit) can be measured with the wattmeter-ammeter-voltmeter method, where the power in watts is divided by the product of measured voltage and current. The power factor of a balanced polyphase circuit is the same as that of any phase.


What causes poor power factory?

The main cause of low Power factor is Inductive Loads such as:

  • Electric motors
  • Transformers
  • Arc welders
  • HVAC systems
  • Molding equipment
  • Presses
  • High-intensity discharge lighting

Unlike resistive loads (i.e., incandescent lights, electric heaters, cooking ovens), which involve a more direct conversion to useful work in the form of heat energy, inductive loads operate off of the magnetic field that is created by reactive power.


How can you improve your power factor?

While low power factor can cause a significant increase in your plant expenses and a decrease in your system’s efficiency, you can take several steps to help correct your power factor, including:

  • Minimizing the operation of idling or lightly loaded inductive equipment, particularly motors
  • Replacing defunct motors with energy-efficient ones, and operating these near their rated capacity
  • Avoiding operating your equipment above its rated voltage
  • Installing capacitors to decrease the amount of reactive power used
  • Upgrading or replacing inductive loads that don’t operate close to their design capacity
  • Local power factor correction at the load
  • Centralised capacitive correction with a power factor correction unit.


The simplest way to improve power factor is to add power factor correction capacitors to the electrical system. Power factor correction capacitors act as reactive current generators. They help offset the non-working power used by inductive loads, thereby improving the power factor.

If you want advice on improving the energy efficiency of your plant get in touch with the EAS team today on 834 0505.




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