This measurement column addresses frequently asked questions received by our customer support center and provides answers to those questions.
Originally, commercial power frequencies are single sine waves of 50 Hz or 60 Hz. However, due to the pulsed circuit load of the equipment, the current flowing through it does not become a sine wave but contains large harmonic components. This harmonic current distortion flows into the power transmission and distribution system, causing abnormalities, malfunctions, and electrical noise in other connected equipment, among other adverse effects.
Furthermore, harmonics are also generated when generating electricity with solar cells.
The electricity generated by solar panels is direct current (DC) electricity. To use this DC electricity in a home or business, it needs to be converted to alternating current (AC) electricity using a power conditioner. However, the DC-AC conversion circuit within the power conditioner does not always produce a clean sine wave; it can result in a distorted waveform containing harmonic components, which can negatively affect connected electronic devices.
The indicator of how distorted a waveform is is the total harmonic distortion.
Generally, when the output waveform is formed by the fundamental frequency f1 and harmonic components such as the second harmonic f2, third harmonic f3, etc., if the effective values of each are | E1 |, | E2 |, | E3 |, ... then the overall distortion rate is
It is defined as
Furthermore, when focusing on an arbitrary nth harmonic component,
This term is used. (Sometimes it's simply called the distortion rate.)
The amount of harmonic current distortion components present can be analyzed using an FFT analyzer.
When harmonics are represented using the power spectra p1, p2, p3, etc., for each frequency, they are as follows:
For example, by capturing the power supply current with a clamp-on ammeter and performing frequency analysis with an FFT analyzer, the magnitudes of the fundamental frequency (50 Hz or 60 Hz) and higher-order components can be determined.
The FFT analyzer includes functions for calculating total harmonic distortion and harmonic content.
Once you set the fundamental frequency, it will automatically list the harmonics and display the total harmonic distortion and harmonic content.
The figure below shows an example of analysis using O-Solution*.
The total harmonic distortion is displayed at the top of the list, along with the individual harmonic content.
List display example
You can easily evaluate it using an FFT analyzer. Please consider it.
*O-Solution DS-5000 Sound and Vibration Analysis System
Example applications
Measurement and evaluation of motor current harmonic components
(Excerpt from the email newsletter issued on March 17, 2021)
