‘Live’ mains impedance measurement and analysis

Since the 1980-ties, the asymmetric mains impedances have been defined by IEC CISPR 16-1-2 [1] and used in an artificial mains network (AMN) suited in the frequency range (10) 150 kHz to 30 MHz. The mains impedance has recently been extended by the definition of asymmetric or common-mode artificial networks (AAN) and coupling/ decoupling networks (CDN) which are defined to be used in the frequency range 150 kHz to 80 MHz. All power mains impedances defined with these networks represent mean values from statistical data gathered and these networks are formally used to demonstrate conducted mains RF emission (and RF immunity) compliance in a defined and reproducible manner. However, other international EMC standards like IEC 61000-3-2 [4] and 61000-3-3 [5] consider mains frequency harmonic emission and flicker from the same mains wall outlet sockets with other impedances, this from the mains frequency upwards to 2 kHz. The mains impedance in the intermediate/overlapping frequency range from 2 kHz to 150 kHz is considerably less as defined by IEC 61000-4-19 [3] which is opposed to the mean values as given by IEC 61000-4-7 [2] where the mains impedances are much higher. In this paper, two `live' mains impedance measurement techniques are given to obtain a detailed impedance behavior in time and/or frequency domain. Knowing the `real' mains impedances means that one is able to forecast resonances and derive the optimal way on how to apply mains filters effectively, while using their appropriate parameters. Mains distribution optimization can also be used inside a large system or installation.