Evaluation of the Impact of the Cable Model on the Distance Protection Performance in a Submarine Transmission System

Distance protection is widely used to protect transmission systems due to its simplicity and selectivity. The line sequence impedances, which are required for setting the distance relay before its field implementation, depend on the chosen cable models. This paper assesses the accuracy of distance protection for a power system comprising both land and submarine cables. A comparison is made between two approaches for calculating the line sequence impedances of the cables, one with DIgSILENT PowerFactory and one entirely based on the manufacturer’s data. The findings from the fault tests conducted on the power system under study show that the distance relay performs better when the line sequence impedances are calculated using the cable manufacturer’s specifications. While PowerFactory allows the specification of the cross-section layers as provided by the manufacturer, its internal routines neglect some parameters used for the sequence impedance calculations, ultimately compromising their accuracy. When computing the sequence impedances used for the relay settings, the obtained results underline the need to accurately model the actual cross-section layers of transmission cables in order to obtain a better performance of the distance protection.