Legacy Shipboard DC System Now Operating on AC

[crshears]

Hello all,

In the past I've posted about my volunteer involvement aboard a historic vessel. For the interested, those posts can be found at:

http://www.eng-tips.com/viewthread.cfm?qid=341551

http://www.eng-tips.com/viewthread.cfm?qid=342485

and

http://www.eng-tips.com/viewthread.cfm?qid=343198

Moving on...

I've recently agreed to take on the task of assessing said vessel's electrical system, principally because nobody more qualified can be found to do the job, and the need is desperate.

The vessel was originally powered with two steam-engine-driven dynamos, each rated to provide a 30 kW output at 125VDC. I'm in the very early stages of gathering information, but the electrical system appears to have been operated ungrounded; the three distribution panels I've looked at so far all have two bus bars running down the centre, with lateral double pole single throw switches supplying each branch circuit. The load sides of said switches are fused in both legs.

Since the vessel's retirement and transition into a museum, the electrical system has been converted to a 120/240 VAC configuration with a grounded neutral, which is where it gets interesting...

The aforementioned panels are thus now wired with one bus bar hot and the other at effective ground potential. However, in two of the panels the hot bus bar is on the left while in the third it is on the right...

In many cases I found fuses of too high a rating for the circuit they were protecting, and these I promptly replaced with fuses of the correct rating...with a caveat:

I was horrified to find that in numerous cases the 'neutral' fuse was of a lower rating than the 'hot' fuse, meaning that if a branch circuit 'neutral' fuse were to blow for any reason the circuit itself [depending on fault magnitude] could remain live via the higher rated 'hot' fuse. In these instances I placed a fuse of the correct rating in the 'hot' side with a deliberately higher-rated fuse in the neutral side in an effort to achieve some level of fuse co-ordination.

Another concern I have yet to investigate is whether any attempt was made to observe the correct polarity when converting the system to AC, in other words if for example the shells of all the lamp sockets are connected to neutral and all centre 'buttons' are connected to hot...or whether any attention was even paid to this when the vessel was first laid down, meaning that some lamp socket shells might now be hot while others are connected to neutral...

I'm posting this here because it was in this forum that the question of whether a distribution system should be grounded or ungrounded was once discussed. The vessel has essentially been put to bed for the [northern-hemisphere] winter, so nobody will be working on board until the spring. I'm wondering whether I should even consider going to an ungrounded neutral system [since this requires added vigilance which might not avail over the winter], or if it would be better to stick with a grounded neutral and swap branch circuit polarities as needed to clean up the safety issue of hot shells.

Based on what I've provided, I'd appreciate any advice on how to proceed in the short term to keep the old girl safe and from catching fire which, considering she has a supertructure with wood overlay, would be disastrous...

I'm also looking for a recommendation as to how best to proceed with insulation assessment; a hand-crank megger rated at 300 volts would probably be ideal, as well as historically authentic...if I can even locate such a beast; but I don't want in any fashion to let that stop me if employing more modern metering techniques would enhance my abilities to detect the presence of problems I might otherwise miss.

Thanks.

 

[waross]

Thanks for the update. It is much appreciated.

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

 

[crshears]

Things are looking up...

Had a first 'Electrical Team' meeting yesterday with my 'supervisor' among the attendees...

One of my team's associate members is a recently electrical engineer; he reported starting out as an electrician before going back to university, something I love hearing because there's nothing like hands-on-the-tools background to provide a solid no-nonsense foundation for a career in engineering.

[Short digression: a friend of mine was an auto mechanic for four or five years before he went back to university to take mechanical engineering. He admitted he barely passed, but I later heard from other sources that the place he ended up at [designing highway service vehicles like snowplows, salters/sanders, etc.] practically fell in love with him. Reason? feedback from the field; district maintenance supervisors started calling in asking who was designing the new equipment. The manager asked why, fearing he was about to get an earful; instead he's told, 'Whoever it is, hang on to him, whatever it takes; we're finally getting machinery that's easy to repair!' End of digression.]

Although this gentleman is an associate because his primary interest is ham radio, he will spend part of his time working on the electrical system as well. The icing on the cake is that he attends to the electrical needs of another vessel in the area, and is well acquainted with galvanic/electrolytic corrosion, isolating transformers and the like, as well as the applicable / prevailing electrical codes pertaining to the project. And though he will not be doing very much of the labour himself, he will work with me to ensure whatever we undertake is done to code and well-found.

It's still early days, but from what he's seen on board so far, we may be better advised to continue to follow marine practice as regards circuit-breaker-protected neutrals and so on, rather than having getting into developing some manner of bastardized wiring scheme that is neither fish nor fowl, namely, consisting of some marine-certified wiring that does not satisfy land-based codes and vice versa.

I could hardly have asked for a better advisor.

Another attendee, also a ham radio enthusiast, is willing to assist with determining lamp socket polarities and the like, along with troubleshooting as the need arises.

Additionally, my supervisor will be running interference for me, and has already been in touch with a shipbreaker to see if we can purchase some used but serviceable equipment [such as an isolating transformer] from them, thus controlling costs.

CR

 

[waross]

Thank you very much for the feedback.
Glad to hear that you are on track.
Yours
Bill

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

 

[crshears]

You're most welcome, Bill, and thanks to you all for the help; it's much appreciated.

And now, unless there are howls of protest from those who want to be kept apprised on progress from time to time, I think we can call this thread closed...after all, I can always start another one on a different topic in the future

CR

 

[crshears]

Oops...

Line above reading

'One of my team's associate members is a recently electrical engineer'

should have been

'One of my team's associate members is a recently RETIRED electrical engineer'

Another case of brain faster than fingers...

CR