New method for noninvasive measurement of utility harmonic impedance

The new, noninvasive method of measurement for power system harmonic impedance is presented in the paper. The method is based on the observation of variations of voltage and current harmonics caused by natural load variability. The novelty of the method lays in a way the method rejects segments of data containing insufficient or false information about the identified power system. Segment selection/rejection uses logical conditions applied to RMS values of measured voltage and current. Harmonic impedance of the power grid is then calculated using modified power spectral method. The method was validated in a field test conducted at 30 kV feeder bus of HV/MV substation. Details of the experiment and the results are discussed the paper. Obtained results confirm that the method copes with temporal, band-limited excitation as well as with deep, sudden changes of utility background voltage.