Measurement uncertainty in evaluating total harmonic distortion factor

In the last years power quality issues have been growing in more and more interest, and therefore the definitions of power quality indices are of increasing concern. Obviously the validity of an index is tightly correlated to its measurement uncertainty. Nevertheless, in the determination of these indexes the evaluation of the measurement uncertainty is often neglected. In the present paper an investigation for the evaluation of the measurement uncertainty is proposed for one of the more used indices: the total harmonic distortion factor (THD). The proposed analysis allows a choice of measurement instrumentation with the purpose to obtain THD measurement inside a band of preset uncertainty.