Design of a low-frequency impedance measurement system applicable to LV grids in live conditions

The design of an impedance measurement system isdiscussed for application in low-voltage power grids in operation,addressing the presence of the grid voltage. A shunt injectionarrangement is preferred, relying then on the measurement ofthe port voltage and current. A Twin-T passive filter is designedto buffer the isolating injecting transformer, suppressing the50 Hz fundamental and avoiding excessive magnetizing currentand voltage the signal generator connected to the secondaryside. Before construction, the system has been simulated andparameters values optimized, showing good performance evenwith very large-power grids with impedance Zg of tens of mΩ.Zg estimate uncertainty is < 1 % at coverage factor k = 1.