Shore Grounding

[Max9999]

I have a shore to ship supply. The shore transformer is delta to y(ungrounded) but the ship may be grounded(through the Hull or zig zag transformer?.) The connection is 13.8kV step down to 6.6kV to the ship. Any recommedations on modifying the grounding? I'm thinking of high impedance grounding the tx to comply with NEC any suggestions or refences?

 

[alehman]

To answer this question you need to know how the shipboard system is grounded. You may want to leave the shore trasf ungrounded and take a neutral to the shipboard neutral bus, if there is one. That way you don't interfere with the shipboard protection relays or create ground current in the hull. The NEC doesn't require any particular system grounding method for medium voltage. You need to consult an electrical engineer experienced in marine installations.

 

[Max9999]

I'm looking to comply with NEC 250.188. The ship has a zig zag tx.

 

[alehman]

250.188 is grounding requirements for portable equipment connections. Typically this is applied to large poewr equipment with trailing cables. As I said, marine installations are outside of my area of knowledge. Are you sure this applies to shore power supplies? Don't most shipboard systems fall under 46 CFR 110-113?

To comply with 250.188 your system will need to be grounded through an impedance which limits ground fault current to 100 amps and it must have ground fault relaying. As I said, in this case you would need to carefully analyze the shipboard ground fault protection system to be sure you don't intefere with its operation.

There must be a typical practice for this type of installation. You may want to consult an experienced marine architect/engineer.