Measuring of harmonics with extremely low amplitudes

Due to their interference on the telecommunication and signalling equipment, the harmonic emissions of power electronics must be limited to extremely low values. To inspect if these limits are exceeded, the harmonics must be measured very exactly. The widely used FFT method can not fulfil this demand, if the fundamental frequency of the signal can not be determined very exactly. In this work the harmonics are measured by special active band pass filters whose frequency response are given for every to be measured harmonics depending on the characteristics of the signaling systems. For measuring of the high frequency current harmonics Rogovski-coils are used. In the paper, the principle, calibrating and test results of the measuring system are presented.