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Is Low Power Factor Costing You Money?

Key Points
  • Low power factor can increase your electric bill and reduce equipment performance.
  • Potential solutions include adding capacitors and adjusting equipment operations.
  • Adding capacitors requires careful planning and design by a qualified engineer.

Are you a little fuzzy on the concept of power factor? If so, that could be a problem. When power factor is too low, it can become a big factor on your electric bill and reduce equipment performance. By getting the facts on power factor, you'll have the knowledge you need to save money and improve your operations. Read on to find out what power factor is all about and how you can manage it.

The equation that can add up

Power factor is a calculation that's not easy to explain, but let's give it a shot.

  1. All electrical equipment requires power to do work. This is called "real" power and it's measured in kilowatts (kW).
  2. Some equipment, such as induction motors, require an extra current to create a magnetic field in order to operate. This is called "reactive" power and it's measured in kilovar (kVAR).
  3. "Apparent" power, expressed in kilovolt-amperes (kVA), is the vector sum (legs of a triangle) of real and reactive power in a circuit.
  4. To calculate power factor, divide real power by apparent power.

If your power factor is too low, you may be charged a penalty for it on your energy bill. Facilities with low power factor draw more apparent power, causing additional strain on the electric grid.

Get your power factor on

Correcting low power factor by reducing reactive power may not only reduce your electric bill, but can improve equipment performance and lower repair and replacement costs from damaged equipment as well. Here's how to make it happen:

  • Install capacitors in your alternating current (AC) circuit to decrease reactive power
  • Set synchronous motors to a leading power factor mode
  • Minimize the operation of idling or lightly loaded motors
  • Operate equipment only within rated voltage
  • Replace standard motors with energy-efficient units

If you use a lot of motors, you likely have a "lagging" power factor. Adding capacitors is typically the best solution. However, adding capacitors requires careful planning and design. Factors to consider include:

  • Too many capacitors can create "leading" power factor—excessive current and over-voltage conditions that can damage equipment.
  • For variable motor loads, the capacitance required to correct power factor will also vary. In these cases, use a switched capacitor bank rather than a fixed solution.
  • In systems with large amounts of capacitance running in parallel with inductance, harmonic resonance can result. This may reduce the performance of electrical controls and cause equipment damage. You'll need to either apply another method of kVAR compensation (filters or condensers) or change the size of the capacitor bank and live with the results (higher power factor).

To ensure safety and optimize performance, any power factor solution involving capacitor correction should be reviewed by a qualified electrical engineer.

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