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Final report RSE 18000006

Project T&D-C.C.:Transmission and Distribution in Continuous Current. Synthesis Report of 2017

The document presents a summary of the results achieved in the research activities relating to the integration into traditional grids of direct current connections and grids at all voltage levels. The results are related to both simulation activities of MVDC and HVDC networks and of experimental activities of LVDC microgrid and components for LVDC and HVDC applicazioni

The document shows the main results obtained in the last year of a three-year research program to evaluate the opportunities to introduce portion of Direct Current (DC) networks in Alternating Current (AC) networks at different voltage levels. The activity was based on experimental activities and studies. The context is related to the growing of production from renewable sources and the need to manage power flows to offer ancillary services to the grid.

For the distribution grids, the possibility of meshing the AC networks with DC connections (MVDC) was evaluated in collaboration with Unareti. The approach is also supported by the improvements that have occurred in the last period from power electronics converters used to interface renewable sources generation systems, storage systems and a growing share of DC loads: all of these elements can be simplified by the adoption of a DC distribution grid, bringing advantages to the system also from an energy point of view. Furthermore, technological developments related to the world of DC grids have been considered: a hybrid switch prototype was developed for LV networks in DC (LVDC), in collaboration with the Milan Polytechnic, and experimented within the DC microgrid available in RSE.

Then, as far as concerns the transmission grid, to analyze the possible conversion of overhead lines from AC to DC, different types of insulators (polymer or glass with RTV coating) have been experimentally characterized with aging tests and multi-stress DC power supply. It emerged that polymeric solutions offer a better behavior in terms of aging and damage to the material, also considering that DC power supply more stresses the materials compared to the AC power supply. At the same time studies have been carried out on the acoustic emissions of these types of lines and on the ionic currents.

Finally, in collaboration with the UE project Best Paths, the issues related to the control logic of the power electronics converters, which constitute the HVDC-VSC conversion stations, have been simulated evaluating the effectiveness for the power flows regulation and also for the support of the system in terms of inertia, LVFRT, black-start.

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