Mutual inductance between wires in helically twisted power cables

The arrangement of the conductors in a multi-core power cable leads to a situation where various conductor loops are built up. One or several loops are formed by the phase and neutral conductors with the operational current flowing in these conductors. A further loop is built up by the protective earth conductor which is connected to the equipotential bonding system at several locations. The area of this loop is essentially arranged outside of the power cable. The inductive coupling from the phase conductor loops into that loop causes common mode voltages in the protective earth system with consequent common mode currents. It can be demonstrated that this effect even takes place in the case of balanced phase currents in the cable. Numerical simulations and parameter studies were carried out in order to describe this effect quantitatively and to investigate the influence of different cable parameters onto the resulting common mode voltages.