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App-21
IM 760301-01E
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App App
Index
Appendix
Harmonics
Harmonics refer to sine waves whose frequency is an integer multiple of the fundamental
wave (normally sine waves of commercial frequency 50-Hz or 60-Hz) excluding the
fundamental frequency. The input current that flows through the power rectification
circuit, phase control circuit, and other circuits used in various electric and electronic
equipment generate harmonic current or voltage on the power line. When the
fundamental and harmonic waves are combined, distortion occurs in the waveform, and
interference sometimes occur in equipment connected to the power line.
• Terminology
Terminology related to harmonics is described below.
• Fundamental wave (fundamental component)
The sine wave with the longest period among the different sine waves derived from
the periodic complex wave. Or the sine wave that has the fundamental frequency
within the components of the complex wave.
• Fundamental frequency
The frequency corresponding to the longest period in the periodic complex wave.
The frequency of the fundamental wave.
• Distorted wave
A wave that differs from the fundamental wave.
• Higher harmonic
A sine wave with frequency that is an integer multiple (twice or greater) of the
fundamental frequency.
• Harmonic component
A waveform component with frequency that is an integer multiple (twice or greater)
of the fundamental frequency.
• Harmonic distortion factor
The ratio of the rms value of the specified n
th
order harmonic contained in the
distorted wave to the rms value of the fundamental wave (or all waves).
• Harmonic order
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
wave (or all waves).
• Interference Caused by Harmonics
Below are some of the effects on electric devices and equipment caused by harmonics.
• Condenser and series reactor
Harmonic current reduces the circuit impedance causing excessive current to flow.
This results in vibration, beat, overheat, or burnout.
• Cable
Harmonic current flows through the neutral line of a three-phase, four-wire system
causing the neutral line to overheat.
• Transformer
Causes magnetostrictive noise of the iron core and increases iron loss and copper loss.
• Breaker and fuse
Excessive harmonic current causes erroneous operation and fuse to blow.
• Communication line
Electromagnetic induction causes noise voltage.
• Controller
Distorted control signal causes erroneous operation.
• Audio visual equipment
Causes degradation of performance and service life, flickering of video caused by
noise, and malfunction of parts.
Appendix 4 Power Basics (Power, Harmonics, and RLC of AC Circuits)