Harmonic voltage measurements in the low voltage distribution grid

The supply territory of the company E.ON Distribution in the Czech Republic (run by the company E.ON Czech Republic) accounts for approximately 1.5 million customers. A problem was detected with harmonic voltage in approximately 14% low voltage (LV) distribution grids without the differentiation of harmonic order. This survey is based on the evaluation of approximately 1000 voltage quality (VQ) measurements which were taken in points of grid with known phase-earth system impedance and considers individual harmonics. This system impedance was measured in the each point of made VQ measurement and was compared with the reference value according to the standard IEC 60725. So it is possible to demonstrate the dependence of harmonic voltage level on phase-earth system impedance by means of graphs and therefore it is possible to answer these questions: Is the problem detected in the weak grids or even in the grids with better system impedance than reference value according to the standard IEC 60725? What is the cause that some harmonic voltages violate the limits according to the EN 50 160 standard?