YOKOGAWA WT500 User Manual page 338

Appendix 3 Power Basics (Power, harmonics, and AC RLC circuits)
Harmonics
App-18
Harmonics refer to all sine waves whose frequency is an integer multiple of the
fundamental signal (normally a 50-Hz or 60-Hz sinusoidal power line signal) except
for the fundamental signal itself. The input currents that flow through the power
rectification circuits, phase control circuits, and other circuits used in various kinds of
electrical equipment generate harmonic currents and voltages in power lines. When the
fundamental and harmonic signals are combined, distortion occurs in the waveform, and
interference sometimes occurs in the equipment connected to the power line.
Terminology
The terminology related to harmonics is described below.
• Fundamental signal (fundamental component)
The sine wave with the longest period among the different sine waves contained in a
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 a periodic complex wave. The
frequency of the fundamental signal.
• Distorted wave
A wave that differs from the fundamental signal.
• Higher harmonic
A sine wave with a frequency that is an integer multiple (twice or more) of the
fundamental frequency.
• Harmonic component
A waveform component with a frequency that is an integer multiple (twice or more) of
the fundamental frequency.
• Harmonic distortion factor
The ratio of the rms value of the specified n
wave to the rms value of the fundamental signal (or all signals).
• 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
all signals).
Some of the effects of harmonics on electrical devices and equipment are explained in
the list below.
• Condensers and series reactors
Harmonic current reduces circuit impedance. This causes excessive current flow,
which can result in vibration, humming, overheat, or burnout.
• Cables
Harmonic current flow through the neutral line of a three-phase, four-wire system will
cause the neutral line to overheat.
• Transformers
Harmonics cause magnetostrictive noise in the iron core and increases iron and
copper loss.
• Breakers and fuses
Excessive harmonic current can causes erroneous operation and fuse blowing.
• Communication lines
The electromagnetic induction caused by harmonics creates noise voltage.
• Controllers
Harmonic distortion of control signals can lead to malfunctions.
• Audio visual equipment
Harmonics can cause degradation of performance and service life, noise-related video
flickering, and damaged parts.
th
order harmonic contained in the distorted
IM 760201-01E