Barge electrics

[lyledunn]

We have taken delivery of a 400ton steel-hulled dutch barge which has no less than 3 separate 3-phase 400/230v generators of around 40KVA. The control system is such that the generators cannot operate in parallel.
Setting aside the 24v dc installation, the electrical installation is as you might find it in any building with a number of 3-phase dist boards feeding lights sockets, compressors, pumps etc.
Noteworthy is that none of the gen-sets have had their neutral points connected to the steel hull of the vessel. I am not sure if this is deliberate since the frame of each set is connected to the neutral but the gen sets are mounted on rubber feed to reduce vibration.
I cannot think of any reason why we should not connect the star point of the sets to the hull.
I would appreciate any comments.

Regards,

Lyledunn

 

[waross]

Will this vessel ever goon shore power?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[cranky108]

Consiter that if there were a ground fault, there would not be any current, but the generator frame would then become hot. How does that not become a problem for the mechanic?

Not that I believe the generator should be effectivly grounded, but a high impedance ground would allow a ground fault detection. And a grounded frame would be safer for those who work on them.

Shore power would require an isolation transformer, and a set of three transfer switches.

With the generators electrically seprated, the combined fault current would never come into play.

 

[jimbofitz]

In my limited experience with shipboard electronics, they usually have delta transformers. Specifically we manufacture delta-delta isolation transformers. Hull corrosion due to circulating currents was the main reason for not grounding them. This was for military customers.

 

[waross]

There are reasons for grounding shipboard systems to the hull and reasons for running isolated.
The main reasons for running ungrounded are for safety and to avoid corrosion when on shore power. Search this site. Corrosion issues from shore power connection have been discussed several times.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rovineye]

That star point should not be earthed to the frame if on resilient mounts. Any ground fault (and capacitance) on the distribution system will result in potential across those mounts and a shock to anyone touching the generator frame.

I would disconnect that star point and make sure I have ground detection installed.

 

[lyledunn]

The issue on this vessel is not the loss of imperative equipment as any such equipment is derived from battery banks charged by an alternator on the main engine.
There will be no shore power, even though the facility exists. Given that consideration and the fact that the neutral is distributed, can you conceive of any reason why I should not connect the hull to Gen set neutral?
Many thanks for the replies. They have been very useful.

Regards,

Lyledunn

 

[rovineye]

I would not do it for reason waross stated: safety factor. With the neutral earthed, any touch contact to any phase will complete the circuit thru the body to hull. If ungrounded neutral, there may be a much lesser shock due only to inmperfect insulation and capacitance.

Similarly, a less than full bolted earth fault can result in a arcing fault that may not trip the protective device. If ungrounded neutral there will only be an indication on the ground detector and no resulting damage.