CALCULATION OF SAFE CLEARANCE DISTANCES IN AC POWER LINE REPOWERING USING HVDC TECHNOLOGY

Abstract

During the last decades, the combination of several factors (rapid growth of electricity consumption, deregulation of the electricity market and increase of distributed generation) has led to important changes in power flows in the Spanish Electricity System, overloading power lines that were not initially designed to withstand those levels of energy transmission. Considering the inherent difficulties related to building new power lines, repowering the existing lines emerges as a necessary solution. At the same time, the important development of power electronics based on new semiconductors has boosted the appearance of new technologies applicable to transmission and distribution systems, such as HVDC (High Voltage Direct Current). The technical and economic benefits associated to this technology represent an attractive alternative to AC power line repowering. However, AC-to-DC power line conversion requires converter stations at its ends, as well as adapting the insulation system to the new working conditions. In this regard, the lack of a specific regulation for DC lines and the last change of the existing regulation for AC lines have caused a regulatory gap, whose consequences are analyzed in this paper. Special emphasis is laid on the different criteria to calculate safe clearance distances, when converting AC power lines to DC. Keywords: HVDC, Repowering, Insulators, Safe clearance distances, DC line