Analysis of harmonic current summation based on field measurements

Estimation of total harmonic current generated by a group of sources is a difficult task, because of time variations of loads and background harmonic voltages caused by the rest of the network. Several simulation techniques have been proposed in the past, which try to address the problem and estimate the maximal levels of current and voltage distortion, but with limited field measurements to verify the results. In this study, the subject of the summation of harmonic currents in industrial installations is reviewed and analysed based on field measurements. Harmonic magnitudes and phase angles of individual load currents and the total current were measured simultaneously, on four locations. The duration of each measurement was approximately 1 week, with a time resolution of 1 s. The assumptions made in probabilistic studies are discussed based on the results, and coefficients for simplified estimation are calculated together with their limit values. Lastly, some considerations about the measurement approach are made.