Multiconductor analysis of underground power transmission systems: EHV AC cables

It is widely ascertained that the multiconductor analysis is a powerful tool which can solve any structurally complex circuit (e.g., high-speed railway supply system, gas insulated lines, etc.). Moreover, this method can be also used as an in-depth analysis of the electric networks after the power-flow studies when they introduce simplifying hypotheses especially in the presence of asymmetry. In this paper, the multiconductor cell analysis has been applied to AC underground cable lines (UGC). This multiconductor procedure based on the use of admittance matrices, which account for the line cells (with earth return currents), different types of sheath bonding, possible multiple circuits, allows predicting the steady-state (and faulty) regime of any cable system. The method calculates the proportion and behavior of the phase currents carried by each parallel conductor, the circulating current in the sheath of each cable and the stray current in the earth. Moreover, some comparisons have been made with traditional programs showing the great accuracy of multiconductor cell model.