Review and Assessment of Main Influencing Factors Affecting Cable Sequence Impedances

The accuracy of underground cable sequence impedance computations and measurements is critical to relay setting studies, transient overvoltage analyses and planning studies. The factors which impact the accuracy of cable sequence impedance values are widely dispersed in the worldwide technical literature. This paper seeks to assess and draw together in summary form, the main factors which influence cable sequence impedance values. The objective is to create an awareness of the factors that impact the accuracy of sequence impedance amongst cable engineers, asset managers, protection engineers and relay specialists. The study shows there is potential for inaccuracies to occur in site measurements of cable impedances as well as inaccuracies at the calculation stage and later during the lifetime of cables due to network installation changes