Hi all, I am facing the problem with shore power supply for the vessel. At our ship yard, sometimes we need to arrange temporary electric supply for the vessel meanwhile their generators are overhauled. For 440 V 60 Hz i am using portable generator supply and for 415 V 50 Hz supply i am using National power gird supply which is 415 V 50 Hz and neutal earthing system). The incoming from power grid to our HT side is 22 kV and there, we use 3 pase 3 MVA transformer to step down to 415 V 50 Hz supply. Our transformer secondary connection is Y connection. When I supply 415V 50 Hz three phase to the ship, alomot all vessel i found out that bus bar insulation were showing low inulation. But our cables insulation test was showing infinite. Whatever there is nothing problem for the vessel during shore power using periods but sometimes it is very difficult for me to explain to chief engineer or captain of the vessel. I suspect that it is because of neutral earthing system and i told them that is the reason. So pls i need all of your help to explain. Most of the ship the neaul is not needed. But only need to supply three phase with earth only.