In this paper, a single-ended travelling wave-based fault location algorithm is presented with reference to HV (i.e. 60 kV) overhead unearthed operated lines. The main novelty of this contribution lies in the method of calculating the speed of the earth mode component of the travelling wave, which exploits the wave impedance and wave capacitance, and of simplifying the fault location procedure. The developed procedure has been applied to a real double-circuit overhead line modelled by EMTP-rv, whereas the fault location algorithm has been implemented in Matlab environment. In order to validate the proposed method, a sensitivity analysis has been performed by varying the fault position, the fault resistance and the fault inception angle. The proposed approach has proven to be independent of all these parameters.

In this paper, a procedure based on three-dimension matrices is presented: it is the generalization of multiconductor cell analysis to any transmission line where the positions of all the active and passive conductors may change with continuity along their length. A meaningful example of this is given by a three-core single lead-screened armoured cable where cores and armour wires are wound helically with different lay lengths. Therefore, this generalization is presented with reference to these cables but it can be applied to any transmission line. The proposed matrix procedures can be implemented in any standard computer by means of a mathematical software (e.g. Matlab). The computational complexity of this novel method is shown in comparison with the finite element method commercial software FLUX 3D which takes 70 h for meshing and solving a 3 m long model. On the contrary, the present matrix algorithms take from minute fractions to maximum 2 minutes (depending on subconductor number) to obtain results having negligible differences with respect to FEM FLUX 3D ones if paramagnetic materials are involved and differences up to maximum 7 % with ferromagnetic ones (which imply, for submarine cable installations, a current rating computation difference lower than 3%).

Single-phase positive sequence modelling is often used in power systems when power flows and short circuit analysis are assessed. Of course, the use of single-phase positive sequence modelling assumes purely three-phase configurations and perfectly symmetrical ones so that single-phase modelling considers that all the phase conductors behave in the same way. When considering the physical reality of power networks, this assumption can be questionable and the behaviors of all the system conductors including the passive ones (earth wires for overhead lines, metallic screens and armours for cables and enclosures for gas insulated lines) is completely unknown. Therefore, the present multiconductor cell analysis (MCA) becomes necessary, since it allows one to achieve great precision results on the regimes of both phase conductors and passive conductors. MCA offers a powerful tool in order to validate (or less) approximated and simplified computation methods. In particular, for single and double circuit overhead lines (OHLs), the current phasors induced in the earth wires and the ground return current alongside the line can be directly computed by MCA in steady state and faulty regimes. It is worth noting that, for faulty regimes, MCA allows also evaluating the approximation degree and validity field of screening factors k.

The knowledge of ground return current in fault occurrence plays a key role in the dimensioning of the earthing grid of substations and of cable sealing end compounds, in the computation of rise of earth potential at substation sites and in electromagnetic interference (EMI) on neighbouring parallel metallic conductors (pipes, handrails, etc.). Moreover, the ground return current evaluation is also important in steady-state regime since this stray current can be responsible for EMI and also for alternating current (AC) corrosion. In fault situations and under some assumptions, the ground return current value at a 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 analysis 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 on circuit parameters (cross-bonding box resistances, substation earthing resistances, soil resistivity) is presented in the paper.