Frequency domain studies for the Malta-Sicily interconnector

Very long HV and EHV submarine ac cable lines can be an effective solution for bulk power transmission systems at distances up to 100 km, as demonstrated by several recent projects like the Malta-Sicily and the Mallorca-Ibiza interconnections. However the introduction of very long HV cable system can cause significant interaction between the existing network and the cable system itself. Most recent literature focuses about two main issues: • Switching transients, mainly due to the distributed nature of the line. • Low-order harmonic resonances, mainly due to the interaction of the cable capacitance with the (inductive) network impedance. Even if the first issue could be counteracted by proper selection of line-end surge arresters (SAs), the latter could result in temporary overvoltages, typically as a consequence of switching manoeuvres, especially troublesome to above mentioned SAs. The relative weakness of one or both interconnected networks, in terms of short circuit current, exacerbates the above issues; very long cable lines connecting weak nodes (such as offshore windfarms or small isolated networks) should thus be investigated by means of time and frequency domain studies, also due to the current lack of information about operating results of similar projects, most of which are presently under construction. The paper deals with the detailed frequency domain studies for the 118 km Malta-Sicily line, which will be the longest 245 kV cable in the world.