For the electronic, electrical products powered AC mains; harmonic current is an important EMC test project. The electronic, electrical equipment which are used under low pressure mains network, the power supply voltage is a sine wave, but the current waveform is not surely a sine wave, there may be more or less distortion. Plenty of applications of such equipment may cause the wave distortion of network voltage, and decrease the power quality.
A periodic function can be decomposed to Fourier series, it can be expressed as the sum formula of multistage sine function, the cycle signal can be considered as synthesis of sine function and high order harmonic, so the distortion current waveform of equipment can be decomposed into base wave and high order harmonic, we can analyze the equipment’s current waveform distortion through the measurement of high order harmonic content by particular equipment, these high order harmonic current component is called harmonic current by us.
When there is excessive harmonic current in power network, it can not only decrease the generator’s efficiency lower, when it is serious, it can also cause the damage of generator and power network, at the same time, it can also affect the normal working of power network user equipment, such as the computer operation error, the roll-over of TV screen.
It is only for the sake of protecting the shared power quality, and make the power network and user equipment running normally, IEC puts forward the limit standard of harmonic current.
Harmonic current test does not apply to the electronic and electrical products powered by the low pressure AC/ DC and battery of non mains electricity.