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What Is Low Power Factor and Why is It 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.

If you've heard of low power factor, you might be wondering how it affects your energy costs. If you haven't heard of low power factor, you might not know that it does. Power factor is a complex calculation that speaks to how you might be using more energy than you should and not even know it.  Not taking time to understand the concept of power factor can impact your bottom line, because when it's low it can beef up your electric bill while eating away at equipment performance. Read on to find out what it is, how it works and how to manage it. 

Power factor
The equation that adds up?

Power factor is a calculation that is not intuitive to define, 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 an induction motor, requires 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.  

While power factor may take time to fully understand, the important thing to remember is that your electric bill may include a penalty if it's too low. Facilities that have 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. There are a number of factors to consider:

  • Too many capacitors can create leading power factor—excessive current and over-voltage conditions that can damage equipment.
  • For variable motors 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.

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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