Back in the 80's I quoted some military ships with 120 delta systems, I believe they were mine sweepers. I also remember a panel for a plastics company that had their process heaters in a 120V delta arrangement.
#66581 - 06/09/0603:33 PMRe: Strange Voltage Setup
120VAC delta systems, both 60Hz and 400Hz, are indeed used on Navy ships, as is 450VAC. It's pretty much like 240V delta systems except the voltage is half. I don't recall any actual 3 phase loads running at 120V.
I spent some time in Uncle Sam's Canoe Club, so maybe I can be of some help. What kinda info you looking for?
Radar - EM2(SS)
[This message has been edited by Radar (edited 06-09-2006).]
There are 10 types of people. Those who know binary, and those who don't.
#66582 - 06/09/0603:40 PMRe: Strange Voltage Setup
The carrier I was on, used the 120 V ungrounded delta to power up 120 V convience outlets and lighting. The delta requirement meant we could lose a single phase and still be able to power up 56% of the load. The ungrounded requirement meant that we could have one phase to ground fault and the system would still function. Both of these requirements were used to make the system fault tolerant.
We were repeatedly warned that just because the system was not referenced to ground, that is was _NOT_ safe to touch the energized phases. There was more than enough leakage current between each phase and ground to kill a person.
editted to add missing word
[This message has been edited by LarryC (edited 06-09-2006).]
#66584 - 06/09/0611:23 PMRe: Strange Voltage Setup
A friend of mine (electrician C-10) was asked to service a "target ship" that was had fried some sort of electronics circuit board. The Navy wanted Dan (my friend) to check the electrical system as they did no want to just fry another board (several thousand dollars for this board).
This is from "memory" so I may not have it all correct:
The boat had 480V 3-phase with each phase going to a separate transformer that put out 240/120V. Dan said that there was no “neutral”. He also said the voltages were really “strange” from phase to ground (I don’t recall the voltages) and were well under 120V.
I think he also said that phase to phase measurements were 120V.
I talk with him a second time and he said he had spoken to a “Square D” rep who when told of the particulars asked if it was a ship and especially if it was a navy ship.
What carrier were you on? I was on the USS Ranger (CV-61) with the Marine A6-E squadron for the 1987 and 1989 WestPacs.
Thanks for the info. One doesn’t get to see (and I didn’t get to personally) these sorts of strange things everyday, but it’s great to be able to toss out a question here and be able to get good answers.
#66585 - 06/10/0604:34 AMRe: Strange Voltage Setup
Not quite the same thing, but in the U.K. large building sites often employ a 3-ph transformer which has a Y secondary, 110V between phases, 63V each phase to ground. The neutral isn't used, with all the 110V power tools on site being connected across two of the three phases.
#66586 - 06/10/0611:41 AMRe: Strange Voltage Setup
US Naval ships use 110V 3-wire Delta power. I've heard variably that it's for safety (flooded compartments are safer with 64V than 120V live wires) and alternately for reliability in the marine environment (not sure why). Anything requiring wye or 220V, etc, is wired up with a dedicated transformer. The hull is always used as a safety ground; the only equipment that gets wired with an actual safety wire are plastic insulated cases that can't be directly bonded.
Distribution from the load centers is 440/255V delta for HVAC and distribution in general, with final step-down to 110V Delta. All 1-phase equipment onboard the ship (including convenience receptacles) is wired up 1-phase "delta" with two hot wires. This presents surprisingly few issues, despite being the white wire being live (not to mention 110V vice 120V); I can't recall a single issue with any commercial equipment and shipboard power from the neutral being hot.
And yes, it is 110V, not 120, and 440V vice 480. A lot of aircraft use 400Hz (220V wye IIRC, but don't quote me on that), so you see this a lot on ships as well, as it's often cheaper just to use aircraft equipment for a similar purpose onboard ship than to design something specifically for the ship. And no matter how many times I see it, the concept of an electric-powered generator always makes me chuckle
Also, NEC does not apply; the planning yard engineers have final say.
[This message has been edited by SteveFehr (edited 06-10-2006).]