Ground return current behaviour in HVAC insulated cables by means of MCA

Abstract

The knowledge of ground return current in faulty occurrence plays a key role in the dimensioning of the earthing grid of substations and cable sealing end compounds, in the computation of rise of earth potential at substation sites and in electromagnetic interferences (EMIs) on neighbouring parallel metallic conductors (pipes, handrail, etc.). Moreover, the ground return current evaluation is also important in steady-state regime since this stray current can be responsible for EMIs and also for AC corrosion. In faulty situation and under some assumptions, the ground return current value at substation site can be computed by means of k-factors. The paper shows that these simplified and approximated approaches have a lot of limitations and only multiconductor approaches can show the ground return current behaviour along the cable (not only the two end values) both in steady-state regime and in short circuit occurrence (e.g. phase-to-ground and phase-to-phase-to-ground). Multiconductor Cell Analysis (MCA) considers the cable system in its real asymmetry without simplified and approximated hypotheses. The sensitivity of ground return current to circuit parameters (cross-bonding box resistances, substation earthing resistances, soil resistivity) is throughout presented.