Mutual Inductive Interference of 400 kV Cable Systems

The paper proposes a suitable model for the calculation of the mutual inductive and ohmic interference of 400 kV cable systems particularly of the induced currents and voltages in cable shields, cross bonding joints and earthing systems. Based on practical relevant examples, typical scenarios were defined and the effects of parallel laid 400kV cable systems are shown and discussed. For the calculation of voltages and currents due to mutual inductive and ohmic coupling of parallel laid underground cable systems, the following parameters have to be considered: electrical symmetry of the cable systems, cable laying arrangement, distances between systems and phases, system and cross-bonding section length, influencing current, cross-section arrangement with detailed sub-section design, earthing configuration of the cable shields and joint cases, parallel earth continuity conductors, specific soil resistivity and laying depth. Considering the isolation materials of cables, the distances between phases and related cable shields, between phases themselves and between three-phase systems are much lower than the distances on overhead lines. Therefore, the mutual coupling, the symmetry of the entire system and the earthing arrangement play an essential role regarding induced voltages and currents. Not only the number of sections, but also the section length varies in many cases. For each of these sections, the impedance matrix is computed by using the self-impedances of all conductors and the coupling-impedances between all conductors using Dubanton’s approximation. These coupled cable sections are combined with the earthing resistances of the joints to form a chain model. The voltage and current distribution across 400 kV cable systems through the inductive interference can be finally calculated in all accessible places. Measurements at 400 kV cable systems of a DSO in Austria were carried out to validate the simulation model and the calculation results respectively. The presented results show a good correlation with the measurement results.