The report, based on the collaboration between RSE and the University of Padua, firstly provides a description of the methodology developed for estimating the overall costs of technological options for electricity transmission: among these there is, in particular, the conversion of high voltage overhead power lines from alternating current (HVAC, High Voltage Alternating Current) to direct current (HVDC, High Voltage Direct Current). This procedure can be used to support the preliminary identification of HVAC lines for which the conversion to HVDC can be taken into consideration (ex ante analysis), to be subsequently analysed in-depth, comparing the conversion against the installation of alternative technologies in HVAC.

In particular, the HVAC transmission technologies studied for comparison with conversion to HVDC include overhead lines with conventional conductors, overhead lines with high-performance conductors (reconductoring), cable lines, Gas Insulated Lines (GILs). The methodology allowed to identify crucial technical-economic and socio-environmental factors to identify potential candidates for line conversion from HVAC to HVDC. These include the length of the line and the cost of the land. A further element highlighted by the analysis is that respecting the voltage limits along the line can become limiting in certain cases of reconductoring.

Moreover, the report introduces an innovative approach for estimating the availability of network components for system reliability assessments. The approach, developed to overcome the challenges related to computational complexity and data uncertainty, is based on the theory of Markov state diagrams and allows the average unavailability of the components to be estimated starting from the failure and repair rates of the subcomponents that constitute it. To take into account the uncertainties on the input reliability parameters, the methodology is further extended to manage parameters expressed through intervals, with an appropriate use of the mathematics of the intervals.

Particular attention is paid to the application of this approach to HVDC systems.
The concepts and procedures described are an integral part of an innovative and more complete methodological approach for evaluating interventions on the network infrastructure, applicable to various technological solutions and in particular to support evaluations on the conversion of lines from HVAC to HVDC, which takes account of technical, economic and environmental aspects.

The Report is available on the Italian site