Shore-To-Ship Power Supply System for a Cruise Ship

The power demand for a large cruise ship during berthing is close to 10 MVA. Such a power demand from the shore-to-ship requires multiple parallel feeds at medium voltage to match with the ship´s connection point voltage. The cruise ship authority required installation of a neutral grounding disconnect switch (DS) and insulated ground conductor (IG) at the shore power transformer neutral grounding resistor (NGR) such that during cold ironing the DS will be opened to complete the shore-side, line-to-ground fault current path through the equipment grounding conductor to reach the ship hull first before it returns to the transformer neutral via IG and NGR. Such an installation of the DS appears to violate National Electrical Code (NEC) [1] requirements of a power system grounding. For clarification of this issue, this paper provide example of a ground fault at the shore and a ground fault at the ship using DS and IG in the system. The need to know the ship´s on-board homo-polar grounding-equipment ratings and the ship´s system-charging current in designing shore-power-system grounding is discussed. This paper will provide input for the present IEEE and IEC draft standards on Cold Ironing.