IEC Std. 61000-3-2 harmonic current emission limits in practical systems: need of considering loading level and attenuation effects

The paper deals with the harmonic emission limits provided by International Electrotechnical Commission (IEC) Std. 61000-3-2 for appliances with current absorption less than or equal to 16 Amps. To this aim attention is focussed on personal computers (PC) as a sample of the wide non-linear appliance class D as regulated by the Standard. Results of some laboratory tests on a PC supplied from the low voltage (LV) grid show that: 1) IEC limits expressed in mA/W are exceeded by actual PCs operating in practical systems; 2) the LEG limits are stated for nominal load even though lower loading conditions produce higher specific (mA/W) harmonic contents. The problems are assessed by means of a testing activity performed in laboratory. To this aim, an experimental layout providing harmonic monitoring of a PC supplied from a system with variable impedance has been implemented in laboratory