Current Flow for Insulation Failure Onboard Ship

What you say makes sense. GA.

The potential will be brought down to the level of the medium (seawater at 0 volts).

On a ship all electrix is connected to a singe point earth and it is a mandatory code requirement to interconnect all metal parts for an equipotential bonding. Use OHM's law if the resistance is 1K ohm.

If you have a place with bad insulation that shows a 1000 ohm path to ground, get it fixed ASAP, or the leak will get worse and there may be heating which will accelerate the process.

This can be very dangerous. Does the ship have an electrician or is it a small ship. For now, pull the breaker or fuse for that line, if you can

hi

you need to be carful if you do actually have a current leak as you could be turning the hull into part of a cathodic protection circuit.

I'm not 100% up to speed with detailed principals but you COULD find little holes appearing in the hull where the isulation has failed/broken down.

Try these links to get a better idea

http://en.wikipedia.org/wiki/Cathodic_protection

http://www.cathodicprotection101.com/

As previously in the other replies... if you have a current leak.. find it and repair it

Typically ship power is delta with a floating neutral. Current would have to have a return path thru other equipment. A 1000 path would do little and possible nothing. Your inside a metal shell, a faraday shield and thus would notice nothing. The answer is dependent on the supply voltage and power levels involved. 480 volts is a common voltage on older vessels and 1000 ohms on one leg would not be dramatic overall

THere would be no effect to the sea water, the power system is not earth referenced and would have no effect unless the hull current was high enough to create a potential drop to cause corrosion due to electrolysis.

Woody

To the best of my knowledge . . . the electrical systems on a ship are ISOLATED, thus ONE insulation failure does not result in any catastrophe. As the second insulation failure will result in a catastrophe, there are GROUND DETECTORS used to detect this FIRST grounding. Such ground detectors typically ground the "floating system" with a high value resistor . . in the order of 1,000 . . . 100,000 ohms. . . . . Oleh

You and everyone else are forgetting fuses and breakers with over current detection.

They trip and blow!!

Been there and done that and had the T-Shirt!!

You all need to think outside the box more often!!

GA

You bring common sense into being again. Thanks.

Next question; onboard our vessel we have the configuration as I have drawn. The neutral is floating with no reference to the hull. How is there a voltage measurable between the active conductors and the hull? How is it possible for someone to get a shock when coming in contact with the hull and a live conductor?

On all RN ships with three phase, neutral was always left floating......as 3 phase loads do not need it......

For single phase equiment, there were local transformers to produce single phase outputs, also with no neutral.

What they do with the neutral conductor (3 phase 415v) is use for domestic loads. Connecting any phase (red, white or blue) with the neutral phase will give 240v single phase, e.g. lighting, domestic power, etc...............or sometimes it is done by using step down transformers.

On all the AC ships I served on, that was simply not possible, due to the fact that the 3 Phase was set at 440 Volts. Which is NATO Standard since the 50's.....

Shore supplies for ships supply the same back so that a ship can shut its own generators down. I would be surprised if 380 VAC 3 phase was also on offer.....

To get nominal 220VAC 1 Phase, you need to have the 3 Phase at around 380 Volts....

Which is why generally speaking, 380V 3 Phase to 3 x local single phase transformers are used on ships to achieve either 220 or 120 Volts AC..

I do believe they were Delta/Wye transformers, but don't quote me.....

I do not remember what voltage can be measured between a single phase of 440 volts 3 phase and the neutral.....more than 240 I am pretty sure.....

This is a problem that Australian ships have (415v 3 phase 50 Hertz), however if you google "Cold Ironing" (a fl;ash name for shore power), its quite interesting.

The ship to shore power connex can be adapted to any power, frequency, voltage and phase..........at this point in time there are only a few ports where this is available........hopefully this will increase...........ships also require a retrofit of their shore power connection.

This is one of the Princess ships in Vancouver.

An illustration of one of the "Cold Ironing" units

To get nominal 220VAC 1 Phase, you need to have the 3 Phase at around 380 Volts....

Yep, that would be about right..........therefore we get 240v single phase from 415v 3 phase supply (any phase) via the neutral.