Wow another topic- 3P 110/63V delta power

[grover]

Onboard ships, the most common electrical distribution is 110V delta (63V to ground), with two hot legs wired to every 120V receptacle and device. I've heard two reasons for this- one is safety; 63V to ground is a lot safer than 120+V when the sailor and the panel are both submerged in salt water. The other is ground fault tolerance; any one phase can fault out, and the power distribution system will continue to work. Pretty much every electric device ever made works fine with this.

I was just wondering if it blew any young engineers' minds that such a system existed?

 

[Wolverine]

Interesting. So the shorted leg collapses to zero, but you still maintain full V on the other? With the faulted leg isolated, would I want to run my 'lectric shaver?

 

[chaosiscash]

I've never had any experience with 110/63V delta, but the plant I worked for right out of school was predominately 480V delta (no 277). Delta is great from a keeping equipment running standpoint, but you've got to have a good ground detection system. While the delta system can accommodate a ground fault on one phase, like grover said, if you get that second ground fault you are in a world of hurt. A second ground (on a different leg) will cause a low impedance phase to phase fault, and will generally cause something to blow off the wall. I had a buss duct fill with water (at least that is the theory) on a system with no ground fault protection, and it subsequently blew up. Fortunately no one was hurt, but it caused some serious downtime.

The building I was in was WWII era, and had a lot of equipment that was "abandoned in place." This caused a lot of ground faults, and I spend many evenings with a couple of electricians thumping them out. Moral of the story is if you no longer need a piece of equipment, don't just turn it off and abandon it, at least air gap it. You'll save a lot of trouble for the guy following you 20 years down the road.

Chaos

 

[Freon]

I taught at Annapolis for a couple years. In Nimitz Hall, one of the main engineering buildings, we had a “museum” where some examples of older systems were displayed. You would be surprised how clever our grandfathers were....and they were using slide rules to do the math!

Freon

 

[grover]

Interesting. So the shorted leg collapses to zero, but you still maintain full V on the other? With the faulted leg isolated, would I want to run my 'lectric shaver?

Pretty much- normally, it's an ungrounded delta, and a single line ground fault would convert it into a corner-grounded delta. In either case, the transformers would still push 110V between the phases and it would be transparent to your shaver :multiplespotting:

 

[Art]

if I'm looking at this correctly, even if you 'ground' one line to the ship, all current still returns thru that line...not the ship...

and all line to lines stay 120...

the only way you would have current to ground is if it was less resistence than the line...and the source was grounded to the hull (ship)...

but aren't ship board systems isolated grounds for this very reason?...the source is not grounded to the hull (ship) so it can never act as a return path or current carrying conductor, ie, corrosion, interference or getting blasted when there is a fault somewhere...

so even if you grabbed a pipe that had a phase to it, no return path exists, so although it may be equipotential with the phase, since the hull is not grounded, no current can flow...

phase to phase is entirely another matter :17:

 

[grover]

but aren't ship board systems isolated grounds for this very reason?...the source is not grounded to the hull (ship) so it can never act as a return path or current carrying conductor, ie, corrosion, interference or getting blasted when there is a fault somewhere...

Yes, that's correct. The steel hull is configured as one gigantic ground wire that everything on the ship is grounded to, and power is completely isolated from the hull. There still exists the potential for ground loops, though, but no need for ground wires of any sort aside from isolated electronic grounds.

 

[FusionWhite]

You guys grounded out my ability to understand anything in this thread a long time ago. Yet for some reason I still read it all. EE's freaking rock because **** that stuff is hard as hell to understand.

 

[singlespeed]

You guys grounded out my ability to understand anything in this thread a long time ago. Yet for some reason I still read it all. EE's freaking rock because **** that stuff is hard as hell to understand.

Not only do we "freaking rock" but we do it with superposition too - just ask my wife :210: