3ph 400V/50Hz yacht can't connect to the Shore power

[Dsanduril]

In the delta-wye configuration with unbalanced load on the wye side, with an ideal transformer the system should measure zero imbalance. There will be circulating currents within the delta portion of the transformer. From the outside there will be a positive sequence and a negative sequence current on the primary wiring, but there should not be any zero sequence current.

Few transformers are ideal, which is why your relay allows for a few amps of measured unbalance. I am surprised, from your reports, that a 5A or 30A doesn't allow you to account for those (I would expect even the 1A to do so). I'd start to look at insulation in the shore power cables (since you have already tested the transformer primary) to see if you have a fault that is leading to an imbalance under higher loads. You could also try measuring each phase current at the shore end power connection point to see if you can measure/detect the imbalance, then again at the xfmr input. If the readings don't match then that points to a fault in the shore power cable.

[EngineerRetired]

Originally Posted by gubavac12345

You are saying: Minimal leakage through the ship's steel hull is tripping the ground fault breaker.

Are you refering to the leakage current on the secondary side? That shouldn't matter as there is an isolation transformer that will nullify any effect earth faults on the secondary side might have on the shore side.

There can only be some earth leakage on the primary side causing the earth leakage to trip...



How do people get electrocuted from neutral and ground being connected together on boats?

A pretty good article on it. https://abycinc.org/blogpost/1678504...Shock+Drowning


You are behind an isolation transformer but... isolation measured in m.a. can be pretty tricky, especially if the transformers internal/external grounds and neutrals are tied in anyway.

[s/v Jedi]

Originally Posted by EngineerRetired

You are behind an isolation transformer but... isolation measured in m.a. can be pretty tricky, especially if the transformers internal/external grounds and neutrals are tied in anyway.

Isolating the internal/external grounds is the primary function, giving the name to an isolation transformer. If this doesn’t work 100%, it needs to be fixed or replaced.

The only way around an issue like that is to remove the Neutral to Ground jumper on the ship side, which gets many all up in panic.

[EngineerRetired]

Originally Posted by s/v Jedi

The only way around an issue like that is to remove the Neutral to Ground jumper on the ship side, which gets many all up in panic.

And yet that is how all boats are wired in the US. The American Boat and Yacht Council (ABYC) set that standard years ago.


There have been many electrocutions (when tying ground and neutral together) of swimmers in waters near a boat wired as yours is. I would wager a fat chunk that if the insurance underwriter did an inspection and found it the polices would be canceled immediately.

[s/v Jedi]

Originally Posted by EngineerRetired

And yet that is how all boats are wired in the US. The American Boat and Yacht Council (ABYC) set that standard years ago.


There have been many electrocutions (when tying ground and neutral together) of swimmers in waters near a boat wired as yours is. I would wager a fat chunk that if the insurance underwriter did an inspection and found it the polices would be canceled immediately.

You don’t know how I wired my boat and it is impossible that anyone gets electrocuted around my boat.

ABYC compliance means you must jumper neutral to ground behind the isolation transformer… you info is wrong.

[EngineerRetired]

Originally Posted by s/v Jedi

You don’t know how I wired my boat and it is impossible that anyone gets electrocuted around my boat.

ABYC compliance means you must jumper neutral to ground behind the isolation transformer… you info is wrong.

Uh huh... I'm not here to argue with you. I am simply telling you what the ABYC requirements are, you are free to check them yourself. In fact, I encourage it.

[gubavac12345]

Originally Posted by s/v Jedi

Gubavac,

Please know that very few members here have knowledge about hi power 3-phase electrical installations.

Step back: minimum required conductors from shore are L1, L2 and L3, powering the transformer and thus only creating a magnetic field. The shore ground is connected to the shield around the primary windings of the transformer.

Disconnect shore power and measure primary side of the transformer: between each of the primary phases and shield around primary winding. They should show infinite resistance.

Now do the same measurement between each of those phases and the GND terminal on the secondary side of the transformer. Often this is a lug to the housing. Should all be infinite as well.

Now measure between primary shield GND and secondary GND. This should be infinite resistance as well.

Can you measure current for each primary phase? They should all be equal.

Dear Jedi, all well understood and I really appreciate everybody's help.

Unfortunately, I have now left the ship ans my colleague has taken over. Right now, the ship cannot connnect to the shore power to measure currents through the primary, but I hope they will be able to do it soon!

[s/v Jedi]

Originally Posted by EngineerRetired

Uh huh... I'm not here to argue with you. I am simply telling you what the ABYC requirements are, you are free to check them yourself. In fact, I encourage it.

ABYC requires that the neutral is grounded at every point where power is generated. This means in the genset, with a relay in an inverter, which engages whenever the inverter provides power and behind an isolation transformer, when it provides power.

It is how it is. When you take neutral from shore it should not be grounded aboard because it’s already grounded at the transformer ashore.