In the very last years, the High Voltage Shore Connection (HVSC) has represented one of the best technical solutions to supply ships at berth without operating shipboard prime movers, thus reducing air pollution in city ports. Taking into account the potentiality of this technology, on one hand it is possible to notice the interest of several city ports throughout the world, on the other also the shipyards have started to design shipboard power systems capable of supplying ships at berth. Considering a single ship, the requested power may be about 10 MW in order to keep certain services running during berthing.

Therefore, when multiple megawatt-HVSC installations are exercised, electric power has to be delivered to the port from a primary high-voltage (HV) line (voltages higher than 100 kV). In this case, large earth fault currents can arise on the HV side, flowing through the port earthing system and the bonded ship hulls. Indeed, the hull of a shore-connected ship is a very peculiar type of ground rod, which acts as an appendix in parallel to the port earthing system. Due to possible phase-to ground faults, dangerous voltage gradients in sea water around the bonded ship hulls may occur. To investigate this particular phenomenon and to identify safety issues, the EPGC Lab. has developed several tridimensional models with the final aim of computing the potentials of an energized metallic structure with respect to a remote earth. The tool used (CDEGS from Safe Engineering Services & Technologies) is capable of including different soils (along with their different resistivities) in order to correctly model the different subsystems that constitute a HVSC (i.e. Port Earthing System, Ship’s Hull, Port Soil and Sea Water).

 

 

More info: prof. Giorgio Sulligoi