System Capacitance and its Effects on Cold Ironing Power System Grounding

To minimize air pollution emissions generated by ocean-going vessels calling on ports, recently some ports are justifying powering such vessels by shore-power when they are docked. This method of providing shore power to the vessel by shutting down its on-board generators is called cold ironing. Increased power demand of the vessels during the docking period requires a cold ironing power supply system with multiple and relatively longer medium voltage cables. Inherent capacitance of such cables raises safety issues of handling the power plugs and receptacle assemblies that are part of the shore-to-ship power supply system. This paper provides the cable capacitance and its stored energy calculations for an actual cold ironing project. A cable capacitance voltage discharge profile and the need for a special grounding device for the safety of personnel are included in this paper. To maximize safety and protection of equipment and personnel, ship owners require a shore power supply system grounding design that will inject minimum ground fault current flow through the ship hull in case of a ground fault at the ship. To meet such grounding criteria and to maximize system protection, this paper reviews how system capacitance affects the power system grounding design requirements. This paper concludes that industry recommended guidelines should be developed for cold ironing power system design