Line impedance measurement: a nondisruptive wideband technique

Line impedance is the basis for many power system calculations. This paper presents a technique for measuring line impedance as a function of frequency on an energized line in normal operation using commercially available equipment. A small sinusoidal current of predetermined frequency is injected into the line, and a network analyzer calculates line impedance at that frequency from the measured magnitude and phase of the injected current and resulting voltage. The measurement is repeated over a range of frequencies to produce a wideband impedance-versus-frequency characteristic. The element values for lumped equivalent circuit models are extracted from the measurement. These values are shown to be frequency dependent. Inexpensive portable equipment for performing this measurement is also briefly introduced.