Effect of Power Frequency Harmonics in Conducted Emission Measurement

Conducted Emission (CE) measurement for AC operated equipment is carried out to quantity the amount of noise / interference generated by Equipment Under Test (EUT) and sent back to power supply input terminal through power cable. The increased use of non linear devices has resulted in increased 'power harmonics' and thus degradation of power quality. The interference generated by, the EUT will not only depend on its internal source (electronics) but also will depend on the input AC mains power quality. The presence of voltage harmonics at line impedance stabilization network (LISN) output significantly affects the conducted emission generated by EUT. This paper establishes the effect of voltage harmonics on CE measurement with experimental results and data. It also stresses the need for specification of maximum allowable voltage Total Harmonic Distortion (THD) in electromagnetic compatibility (EMC) standards.