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

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