Where do harmonics come from? The general categories of harmonic producing loads (also called non-linear loads) are: 

  • Power electronic equipment (drives, rectifiers, computers, etc.)
  • Arcing devices (welders, arc furnaces, florescent lights, etc.)
  • Iron saturating devices (transformers)
  • Rotating machines (generators)

Today, the most prevalent and growing harmonic sources are:

  • Adjustable frequency drives (AFD)
  • Switch-mode power supplies (computers)
  • Fluorescent lightning


How do you know you have a problem? The only way to know is to identify symptoms of harmonics. Very often, if you recognize specific symptoms of harmonics, the problem has already created issues on your power system. The trick is to recognize “potential” symptoms and identify potential harmonic issues before they occur or to implement correction into the system design. Sometimes modeling and simple calculations will help identify the issues before they become a problem. Symptoms of harmonic problems can be divided into four major areas: Equipment failure and misoperation, economic considerations, application of power factor correction capacitors and other issues.

The following symptoms are examples of equipment failure and misoperation associated with harmonics on a power system.

  • Voltage notching
  • Erratic electronic equipment operation
  • Computer and/or PLC lockups
  • Overheating (motors, cables, transformers, neutrals)
  • Motor vibrations
  • Audible noise in transformers and rotating machines
  • Nuisance circuit breaker operation
  • Voltage regulator malfunctioning
  • Generator regulator malfunctioning
  • Timing or digital clock errors
  • Electrical fires

The following are economic considerations that should be evaluated with regard to harmonics.

  • Losses/inefficiency (motors)
  • kW losses in cables and transformers
  • Low total power factor
  • Generator sizing considerations
  • UPS sizing consideration
  • Capacity concerns (transformers, cables)
  • Utility imposed penalties

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Written By:

Daniel J. Carnovale, P.E.
Eaton | Cutler-Hammer
Moon Township, PA

Thomas J. Dionise, P.E.
Eaton | Cutler-Hammer
Warrendale, PA

Thomas M. Blooming, P.E.
Eaton | Cutler-Hammer
Minneapolis, MN