Active power measurement uncertainty modelling and propagation analysis in case of harmonically distorted signals

Abstract

The harmonic distortion of electrical waveforms results in a need for instruments’ performance evaluation in non-sinusoidal conditions. Specifications, which are valid for sine-wave input signals, are not supposed to be applied directly for uncertainty determination in case of harmonics, due to the non-linear dependence between the measured quantities and the single harmonic components’ magnitudes and phase shifts. Uncertainty calculation is especially challenging in case of power and/or energy measurements, because the corresponding instruments are used for legal metrology purposes i.e. in the regulated trade of electrical energy. The starting point for the concrete evaluation is related to determination of influence factors, which affect the recording of single harmonics’ magnitudes and phase shifts. For overall power and/or energy uncertainty calculation, mathematical modelling, based on analytical relations between single harmonic components and the measured quantity, will be performed. A GUM based perspective for uniting single influence factors is implemented and a simplified approach for the correlation coefficients calculation is adopted. The validation of the model, as well as, the uncertainty propagation analysis due to single harmonic components alteration, is backed up by real time measurements, conducted with high accuracy class measurement equipment.