Preliminary design of a multilevel converter based de-Icing application on the italian sub-transmission grid

The safe operation of high voltage overhead lines (OHLs) can be hampered by the accumulation of ice and snow on conductors. In this regard, the high voltage OHLs that cross the mountainous regions of the Alps and Apennines in Italy are of particular concern. Numerous utilities have also experienced this problem, requiring effective solutions to avoid and minimize the damages. The solution proposed by Terna S.p. A, the Italian Transmission System Operator, focuses on the relatively short (20-40 km) 132 kV and 150 kV OHLs of the Italian sub-transmission grid in the Alps and Apennines, which are generally equipped with small (15.75-22.8 mm diameter) conductors. The de-icing procedure is provided by a cascade connection of two multilevel neutral point clamped converters, capable to supply up to 1200 A at very low frequency. With the possibility to operate directly on the transfer bus of the substation with power electronic converters, this configuration exhibits high compactness and efficiency. This paper deals with the design of the multilevel converters based de-icing system operating across the Italian sub-transmission network in the Alps and Apennines. The electrical performance of the system is evaluated through a detailed model developed with the software ATP-EMTP. The thermal analysis of the de-icing procedure is also envisaged.