Optimal Operation of Long Inhomogeneous AC Cable Lines: The Malta–Sicily Interconnector

This paper presents a new approach to optimal exploitation and reactive power control of long inhomogeneous high-voltage ac cable lines, such as submarine interconnectors including significant land cable stretches. Voltage and reactive power profiles are discussed, highlighting the requirements for full exploitation of power transmission capacity, and giving formulae for optimal voltage control. Capability curves for the lossy inhomogeneous cable line are discussed; this paper also proposes a simple algorithm for controlling the reactive power flow at one end of the line independently from active power, using variable shunt reactors and tap-changing transformers. The application of the presented treatment to a real inhomogeneous line, that is, the 118-km-long 245-kV–50-Hz Malta–Sicily interconnector currently under construction, yields maximum power and optimal voltage drop values in close agreement with detailed simulation results. Power-flow simulations also confirm the effectiveness of the proposed reactive power control algorithm. Finally, total transmission losses associated with the proposed optimal voltage control are evaluated and shown to be competitive with those of state-of-the-art HVDC–VSC systems.