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Power factor: What it is, why it's important

  • January 2002
  • Number of views: 2493
  • Article rating: No rating

Cyndi Nyberg 
Former EASA Technical Support Specialist 

Power factor can be best explained with a short illustration. Figure 1 below shows the three ele­ments to consider. First, true power, measured in kW, is the power that does useful work. Reactive power, measured in kVAR, is the power that is stored and returned by all inductive machines, such as motors and transformers. The apparent power, measured in kVA, is the voltage multiplied by the current in the system. Even though the true power is doing the work, the power company has to dis­tribute the apparent power. 

Image

Mathematically, the power factor is the cosine of the angle between the true and apparent power. Power factor is defined as the ratio of true power used in an electric circuit to the apparent power, or the power that is apparently being drawn from the source. In a sense, apparent power is “bor­rowed” from the power company. Since AC power is continuously reversing, the borrowed power is sent back to the system every time the al­ternating current reverses. 

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EASA Technical Manual

More information on this topic can be found in EASA's Technical Manual
  • Section 5: Electronics

Related Reference and Training Materials

Principles of Medium & Large AC Motors (NEMA Standards)
  • Section 11: Motor Accessories & Terminal Boxes

Principles of Medium & Large AC Motors (IEC Standards)
  • Section 11: Motor Accessories & Terminal Boxes

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