What is total harmonic distortion (THD)?

What is total harmonic distortion (THD)?

Question

When using a power meter, I noticed a THD setting in the harmonic settings. What is this? What’s the difference between THD-F and THD-R?

Answer

Total harmonic distortion, or THD, is one way to gauge power supply quality. It indicates how much of a harmonic component the voltage and current waveforms contain, and it serves as an indicator of the extent of the waveform distortion that is caused as a result. The Japan Industrial Standards define THD as the ratio of the harmonic component to the fundamental component. In addition to power waveforms, THD is used to analyze vibration and audio waveforms. THD-F (fundamental wave harmonic component) and THD-R (RMS harmonic component) differ in terms of the formula that is used to calculate them. THD-F is generally used to measure commercial power supplies.

Total harmonic distortion can be easily measured by the Power Analyzer PQ3198, Clamp On Power Logger PW3360, and Power Meters PW3336 and PW3337.