Quality evaluation of virtual instrumentation for power system harmonics investigations-multichannel signal conditioning problems

In the paper the signal conditioning and A/D conversion problems in multichannel power signals acquisition are discussed. The power signals are relatively difficult to process as they need to be isolated from the line, and conditioned by different construction voltage and current transducers. In special situations the voltage and current paths have to be as close as possible: the tolerated level discrepancy is of 1 per cent and relative phase shift is of a few degrees in the 10 kHz frequency range. To get such channel accuracy, special attention should be given to any stage of signal processing: analog signal conditioning, interchannel crosstalks, signal multiplexing etc. The problems of high accuracy channel realizations are discussed, and illustrated with experimental data. Three channel voltage and three channel current conditioning circuits, targeted to three phase power system observations in 10 kHz frequency range, have been compared. The presented paper is focused on problems, which are commonly neglected in standard DSP.