Understanding Power Factor

Power factor is a measure of how effectively the power delivered to a service is used. Certain rate classes, like Large Power, are susceptible to a power factor penalty. This page explains what power factor is in greater detail, how it's calculated, and how it can be improved to reduce penalties.

industrial

What is Power Factor?

All electrical equipment requires power to do work. This is called real power, and it's measured in kilowatts (kW). 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).

Apparent power, expressed in kilovolt-amperes (kVA), is the vector sum (legs of a triangle) of real and reactive power in a circuit. To calculate power factor, divide real power by apparent power.

At Boone Power, Large Power and Large-Large Power accounts incur a power factor fee on their bill if the power factor at the time of the maximum demand for the billing period is less than 93 percent. More information is available in our rate sheets, which can be found HERE.

Power factor is calculated is this way: 

kWD x (0.93/Measured Power Factor) = Demand for Billing Purposes

Improving Power Factor

Correcting low power factor by reducing reactive power will not only reduce your electric bill, it can also improve equipment performance and lower repair and replacement costs from damaged equipment.

Here are some suggestions:

  • 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 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.