Impedance Measurements on Underground Cables

To eliminate uncertainties arising from assumed constants involved in the calculation of sequence impedances, hield measurements of 60 cycle positive and zero sequence impedances of 2 sizes of 3-conductor underground power cable were made on the 27 kv system of a large eastern metropolitan company; the results are reported in this paper. While the principal results are applicable only to the particular system involved, they show that without the support of the experimental data the calculation of zero sequence impedance of feeder circuits in a system of this kind can be at best only roughly approximate.