Evaluation of the uncertainties in the measurement of distorted power by means of the IEN sampling system

A method for the uncertainty evaluation in the measurement of power in distorted signals is described. The power is obtained by a sampling system, which acquires the voltage and current and computes the power from the harmonic components obtained by the best fit. An equivalent algorithm is applied to derive a simplified relation between the correlation matrix of the harmonics and that of the samples. The uncertainties are then evaluated by a model of the uncertainty of a single sample given by the manufacturer of the sampling voltmeters.