Is Low Power Factor Costing You Money?

What is power factor and how does it affect my energy costs? This is a common question among business owners and facility managers. The truth is, power factor is a complex issue—one that can have a negative impact on your bottom line. Facilities with low power factor require the utility to operate at a higher capacity resulting in a power factor charge. In addition, low power factor can lead to reduced equipment performance and premature failure. Understanding low power factor and how it may impact your facility can help you find the right solution to fit your needs.

What Causes Low Power Factor?

All electrical equipment requires power to do work. This is called real or active power and is measured in kilowatts (kW). However, commonly used induction equipment—such as motors and high-intensity discharge (HID) lights—requires additional current to create the magnetic field needed to operate the device. This is called reactive power and is measured in kilovar (kVAR). Reactive power is non-working power inherent in equipment that uses magnetic fields such as motors and transformers. Apparent power, expressed in kilovolt-amperes (kVA), is the vector sum (legs of a triangle) of active and reactive power in a circuit. Power factor is the percentage ratio of active power over apparent power. It is also exhibited as the current waveform lagging the voltage waveform.

While power factor is difficult to understand, the important thing to remember is that your electric bill may include a penalty for power factor. This is because facilities with low power factor draw more kVA, requiring additional transmission and distribution system capacity or utility distribution capacitors. 

Source: www.energy.gov

Correcting Power Factor

Correcting power factor by reducing reactive power helps facilities avoid the fees and extra charges associated with low power factor. Moreover, fixing voltage drops can increase motor starting torque, running torque, overload capacity, and lighting intensity—improving equipment performance.

There are a variety of potential solutions for increasing your power factor, including the following:

• Install capacitors in your AC circuit to decrease the magnitude of reactive power. 
  
• Set synchronous motors to a leading power factor mode.
  
• Minimize the operation of idling or lightly loaded motors.
• Avoid operating equipment that is above its rated voltage.
• As standard motors burn out, replace them with energy-efficient motors.

Typically, facilities with a large number of motors will have a lagging power factor. Adding capacitors to this inductive load can correct the power factor. Too many capacitors can create excessive current and over-voltage conditions, which can damage equipment. This is known as leading power factor.

Adding capacitors to correct power factor requires careful planning and design. For variable motor loads, the amount of capacitance required to correct power factor will also vary. In these cases, consider a variable or switched capacitor bank rather than a fixed solution. Care should be taken in the application of a switched capacitor bank. This is because a capacitor takes about one minute to discharge. When the motor is unloaded, power factor increases, as does voltage. It is always a good practice to disconnect capacitors when disconnecting motors.

Equipment that generates harmonics can cause problems on systems with large amounts of capacitance in parallel with inductance. A condition known as harmonic resonance can result, causing the electrical control equipment to perform erratically. In the worst case, capacitors can explode and equipment damage may occur. Any proposed application or modification involving capacitor correction should be reviewed by a qualified electrical engineer.

If your facility has a significant motor load or uses HID lighting, power factor correction can help you reduce your electric costs if your bill includes a power factor charge. Careful planning and design is necessary to optimize savings and protect your critical equipment.