Harmonics is a broadly used term to describe electrical distortion but as a subject is not universally understood within industry. Harmonic related issues became prominent with the proliferation of semiconductors and cause a variety of problems that are sometimes difficult to attribute and eliminate. Loads drawing their current through semiconductors have a non-linear characteristic and are primarily responsible for generating the harmonic distortion that is so damaging to supplies, equipment and sub-components.

What examples of loads are non-linear?
Single phase – switch-mode power supplies, PCs, monitors, photo-copiers, fax machines, high-frequency lighting, any electronic single-phase load in fact. Three phase – Variable-Speed Drives, Uninterruptable Power Supplies, 3 phase rectifiers.

Why are harmonics a problem?

  • Harmonic Current – causes overheating of conductors and their insulation, overheated transformers and increased losses, overloaded Neutral conductors, excess Neutral to Earth potential, overheating of capacitors and, ultimately, premature component failure. Additionally, exporting excessive harmonic distortion to the supply networks may well fall foul of the enforced requirements.
  • Harmonic Voltage – causes linear loads to draw non-linear current (resulting in current distortion effects), torque pulsation in motors, capacitor dielectric failure, insulation breakdown, PC monitor and power supply failure, electronic lighting failure, malfunction of sensitive electronic equipment and, again, excessive distortion in distribution supply networks.

How are harmonics dealt with?
There is no single solution because, depending on the circumstances, some harmonic mitigation techniques will be much more advantageous than others. A successful resolution depends on accurate assessment of the many variables that first need to be taken into account.