Voltage induced in PE conductor by phase currents in twisted conductor cable with finite length

Abstract

The phase currents in twisted wires in power cables can induce through magnetic coupling the common mode voltages in the twisted protective earth conductor (PE) with consequent common mode currents in the protective earth system. Due to geometrical asymmetry of the PE conductor with respect to phase conductors, the inductive coupling exists even in case of balanced phase currents in the cable. The voltage induced in the PE conductor can be calculated if mutual inductances between twisted conductors are known. Taking into account that each of the cable conductors can be represented by a helical line, the calculation of the mutual inductance of finite length coaxial helical thin conductors is studied using the Neumann's formula. Furthermore the inductive coupling between twisted wires in cables with grounded conductor is considered and the voltage induced by phase currents in the PE conductor is calculated.