Instrumentation for measurement of line impedance

This paper presents instrumentation for nondisruptively measuring the impedance of a normally operating line. A small sinusoidal current of known frequency is injected into the line, and line impedance at that frequency is calculated from the magnitude and phase of the injected current and resulting voltage as measured by a network analyzer. Line impedance as a function of frequency is found by repeating the measurement over a range of frequencies. Lumped equivalent circuit models are extracted from the measured line impedance and applied to an example analysis of line voltage distortion