App-30
IM 253710-01E
Harmonics
Harmonics are sine waves that have frequencies that are integer multiples of the
frequency of a fundamental signal (generally a 50/60-Hz sinusoid in the field of power).
The current power that flows through the power rectification circuit, phase control circuit,
and other circuits that are used in various electrical devices, generates harmonic
voltages and currents on the power line. When the fundamental signal and harmonic
signals are combined, the waveform is distorted, and this can cause interference to
devices that are connected to the power line.
Terminology
The following terms are related to harmonics.
• Fundamental wave (fundamental component)
Periodic complex waves are divided into different sinusoid groups. The
fundamental wave is the signal with the longest period. It is the sinusoid that has
the fundamental frequency among the periodic complex wave.
• Fundamental frequency
This is the frequency corresponding to the period of the periodic complex wave. It
is the frequency of the fundamental wave.
• Distorted wave
The distorted wave has a waveform that is different from the fundamental wave.
• Higher harmonic
Sinusoids that have frequencies that are integer multiples (2 or greater) of the
fundamental frequency.
• Harmonic component
The signal component of the waves that have frequencies that are integer multiples
(2 or greater) of the fundamental frequency.
• Harmonic distortion factor
The ratio of the rms value of the nth harmonic signal contained in the distorted
waveform to the rms value of the fundamental signal or total signal.
• Harmonic order
The integer ratio of the harmonic frequency with respect to the fundamental
frequency.
• Total harmonic distortion
The ratio of the rms value of all harmonics to the rms value of the fundamental
signal or total signal.
Appendix 7 Power Basics (Power/Harmonics/Three Constants Related to the AC Circuit)