Ship Power

[mbrooke]

I was at sea for 30 days several years ago on RV Sikuliaq. The generators we're 690V, but I don't know if delta or wye. I also don't know what the low voltage system was. I did see a fault detector during a tour of the ships systems so something was ungrounded. (I did ask if the system was grounded or not and I got laughed at. :ashamed1: The ships Electrician was not present during the tour)

I was always taught the ship's anchor was used for grounding it

 

[LarryFine]

I was always taught the ship's anchor was used for grounding it

No, that's for securing it.

 

[velocityloop]

Found this information, good overview: "NAVAL SHIPS’ TECHNICAL MANUAL CHAPTER 320 ELECTRIC POWER DISTRIBUTION SYSTEMS:
https://fas.org/man/dod-101/sys/ship/nstm/ch320.pdf

 

[mbrooke]

Found this information, good overview: "NAVAL SHIPS’ TECHNICAL MANUAL CHAPTER 320 ELECTRIC POWER DISTRIBUTION SYSTEMS:
https://fas.org/man/dod-101/sys/ship/nstm/ch320.pdf

Good stuff, this is why I post here. Much thanks

 

[RichB]

Ok all--10 years Navy Electrician's Mate First--

On the Kitty Hawk Class carriers (The Hawk and connie)

We ran a 450V60Hz distribution system--3 phase--consisting of 3 hots-- the ship's hull was used as a "ground" for grounding/bonding purposes--there was NO neutral-- the 120 volt circuits used 2 hots--it was "funny" to watch guys who were civilian electricians with no ship board experience turn off breakers till the lights went out then start to work on the circuit and get zapped!! retaught them the "always check for power first" before working on something

We used a ground fault test lamp system to find ground faults--If we had one we would go to the associated load centers for the affected switch-gear and start shutting off circuits till we found the bad circuit.

If there was a ground fault there was NO automatic trip--no matter how many you had unless it caused a phase to phase short--reason being--battle damage- You want everything to stay running in a combat scenario until it burns/blows up--don't want to lose weapons systems or flight deck systems in the middle of a shooting war.

 

[RichB]

And on the Eisenhower, a sister ship to the nuclear-powered carrier Nimitz, and the nuclear-powered cruiser Arkansas as well. But that part of my work life ended 35+ years ago. So don't rely too heavily on my memory.

The carriers had a 4160 volt delta connection for shore power service, and their generators produced the same voltage. There were step-down transformers to 480 volts for the large motors, but I don't recall whether the secondary windings were WYE or Delta. The cruisers had a 480 volt delta connection for shore power service, and their generators produced the same voltage. Both classes of ships had step down transformers with 120/208V WYE secondary windings. The neutral point of the transformers were not connected to any "ground," and in particular not to the ship's hull.

This was for reliability, as has already been mentioned. If a phase conductor contacted a metal enclosure, for example, it would not result in a short circuit, and no equipment would be out of service. A second phase-to-metal enclosure from a different phase would cause a breaker or fuse to terminate the short circuit. So it was important to discover and fix the first, before the second could happen.

I would like to clarify something said in post #6. The ships on which I served did have a ground detection system. But the ground indicator light did not immediately come on when a phase wire contacted a metal enclosure. Rather, an operator would push a "ground test" button once an hour, during the routine recording of temperatures, pressures, levels, and all other parameters that are monitored throughout the engineering plant. Once a ground fault was noticed, we did turn off circuits one-by-one until the fault was isolated.

I answered before I read the whole series--That is what I remember also Charlie--different boats different systems but about basically the same!

 

[mbrooke]

Ok all--10 years Navy Electrician's Mate First--

On the Kitty Hawk Class carriers (The Hawk and connie)

We ran a 450V60Hz distribution system--3 phase--consisting of 3 hots-- the ship's hull was used as a "ground" for grounding/bonding purposes--there was NO neutral-- the 120 volt circuits used 2 hots--it was "funny" to watch guys who were civilian electricians with no ship board experience turn off breakers till the lights went out then start to work on the circuit and get zapped!! retaught them the "always check for power first" before working on something

We used a ground fault test lamp system to find ground faults--If we had one we would go to the associated load centers for the affected switch-gear and start shutting off circuits till we found the bad circuit.

If there was a ground fault there was NO automatic trip--no matter how many you had unless it caused a phase to phase short--reason being--battle damage- You want everything to stay running in a combat scenario until it burns/blows up--don't want to lose weapons systems or flight deck systems in the middle of a shooting war.

Neat. 120 volt ungrounded delta?

 

[SceneryDriver]

Do ship power systems use a neutral? I see a lot of diagrams without them:

Depends on what type of ship you're on, and even where you are in the ship. My experience is on cruise ships. The type of power available depends on where you are in the ship, and who built the ship.

If the Italians build your cruise ship, you'll traditionally have delta-connected power, no matter the voltage. Usually ungrounded. 120V power came from the 120D delta transformers, and 230V came from the 230D transformers. Ground (green wire) was connected to the hull, but unreferenced to phase conductors except through capacitance. We always cautioned guest musicians to use our power strips and NOT their surge-protected power strips when they came onboard. The smart ones listened. The dumb ones got to watch their little surge protector strips try to become the star point for the entire ship. The MOVs typically went BANG! very quickly, and with extreme enthusiasm.

More recently, Italian-built ships have been supplying 120Y/208V grounded 5-wire power, at least in the Entertainment areas of the ships (main theatre, etc...) as NO Entertainment gear is happy running on delta power, especially without reference to ground. It's amazing how many fewer power supply failures there are now, now that the moving lights and sound equipment have the correct type of power. Regardless, it's all 60Hz, no matter the voltage.

The kitchen areas are all 120V ungrounded delta. They don't use GFCI's, so someone thinks ungrounded is safer. I don't really buy that, but it seems to work OK.



If the Germans build your cruise ship, it's 230Y/400V grounded 5-wire power, everywhere. They also have 120V available in almost all parts of the ship (guest cabins especially) for us electrical heathen Americans. Like the Italians, it's all 60Hz, no matter the voltage.



If the French build your cruse ship... it's not done yet, because they all went on strike again.



SceneryDriver

 

[jeremysterling]

Posted by iceworm "Puget sound Naval Shipyard - 1973 - 1980, Refueling overhauls, surface ships and submarines. All were 480D, ungrounded - even the reactor coolant pumps Except the last carrier that I cant remember, cause when it came - I was leaving. The Reactor Coolant Pumps were 4160D, ungrounded..." If you left in '80. you missed the S8G nukes. They had no neutral for the coolant pumps because there were no coolant pumps!

 

[mbrooke]

Depends on what type of ship you're on, and even where you are in the ship. My experience is on cruise ships. The type of power available depends on where you are in the ship, and who built the ship.

If the Italians build your cruise ship, you'll traditionally have delta-connected power, no matter the voltage. Usually ungrounded. 120V power came from the 120D delta transformers, and 230V came from the 230D transformers. Ground (green wire) was connected to the hull, but unreferenced to phase conductors except through capacitance. We always cautioned guest musicians to use our power strips and NOT their surge-protected power strips when they came onboard. The smart ones listened. The dumb ones got to watch their little surge protector strips try to become the star point for the entire ship. The MOVs typically went BANG! very quickly, and with extreme enthusiasm.

What is the electrical theory behind this? I'm assuming this is happening on 120/208 ungrounded Y systems and not 120 volt ungrounded delta?

More recently, Italian-built ships have been supplying 120Y/208V grounded 5-wire power, at least in the Entertainment areas of the ships (main theatre, etc...) as NO Entertainment gear is happy running on delta power, especially without reference to ground. It's amazing how many fewer power supply failures there are now, now that the moving lights and sound equipment have the correct type of power. Regardless, it's all 60Hz, no matter the voltage.

I'm curious why the failures.

The kitchen areas are all 120V ungrounded delta. They don't use GFCI's, so someone thinks ungrounded is safer. I don't really buy that, but it seems to work OK.

It is safer provided 1) the combined resistive and capacitive current (to ground) during a fault does not exceed 15 ma or some low level value. 2) There is some sort of ground fault indicator or line isolation monitor that goes off indicating a condition where a grounded phase/person will pass more than 15ma to ground.


Best bet is GFCIs, in theory they will work. But if your ship is blowing MOVs like you say, the GFCI may fry.

If the Germans build your cruise ship, it's 230Y/400V grounded 5-wire power, everywhere. They also have 120V available in almost all parts of the ship (guest cabins especially) for us electrical heathen Americans. Like the Italians, it's all 60Hz, no matter the voltage.



If the French build your cruse ship... it's not done yet, because they all went on strike again.



SceneryDriver

Why do the Germans ground their system? And why 60Hz in Europe?

 

[winnie]

If the Italians build your cruise ship, you'll traditionally have delta-connected power, no matter the voltage. Usually ungrounded. 120V power came from the 120D delta transformers, and 230V came from the 230D transformers. Ground (green wire) was connected to the hull, but unreferenced to phase conductors except through capacitance. We always cautioned guest musicians to use our power strips and NOT their surge-protected power strips when they came onboard. The smart ones listened. The dumb ones got to watch their little surge protector strips try to become the star point for the entire ship. The MOVs typically went BANG! very quickly, and with extreme enthusiasm.

What is the electrical theory behind this? I'm assuming this is happening on 120/208 ungrounded Y systems and not 120 volt ungrounded delta?

If you have a large ungrounded system, there is significant capacitive coupling to ground, which may not be perfectly balanced. Perhaps one phase or another is very close to ground potential, or perhaps all are at elevated potential.

Power strips with MOV 'surge suppressors' generally have these MOVs between the circuit conductors and ground. So if you connect one of these power strips to an ungrounded system the MOVs can become the elements trying to bring the entire system to balance.

This sounds similar to the problem that VFDs have when connected to ungrounded delta supplies.

-Jon

 

[mbrooke]

If you have a large ungrounded system, there is significant capacitive coupling to ground, which may not be perfectly balanced. Perhaps one phase or another is very close to ground potential, or perhaps all are at elevated potential.

Power strips with MOV 'surge suppressors' generally have these MOVs between the circuit conductors and ground. So if you connect one of these power strips to an ungrounded system the MOVs can become the elements trying to bring the entire system to balance.

This sounds similar to the problem that VFDs have when connected to ungrounded delta supplies.

-Jon

But that would mean reverse polarity would cause an MOV to flash over. 120 volt ungrounded delta... highest voltage to ground would be 120 volts, with 150 volt MOVs.

 

[SceneryDriver]

But that would mean reverse polarity would cause an MOV to flash over. 120 volt ungrounded delta... highest voltage to ground would be 120 volts, with 150 volt MOVs.

Because everything was (in theory) ungrounded on the Italian-built ships, there could be large voltage swings relative to ground (green wire / hull) due to capacitive coupling and inadvertent connections from a phase to ground (making it a corner-grounded delta until repaired). This would almost certainly create instances of more than 150V between the phase conductors and ground. Those poor MOVs would try valiantly to shunt the excess voltage to ground, and would die a hero's death in the process.


SceneryDriver

 

[mbrooke]

That would mean 120/208 ungrounded wye? A 120 volt delta system would be 120 volts to ground during a fault.

 

[Besoeker3]

That would mean 120/208 ungrounded wye? A 120 volt delta system would be 120 volts to ground during a fault.

If it's ungrounded, how do you get a ground fault?

 

[mbrooke]

Phase touches the ship's haul.

 

[Besoeker3]

Phase touches the ship's haul.

But if the system is ungrounded, how that that create a fault?

 

[winnie]

But if the system is ungrounded, how that that create a fault?

Definition. A ground fault is where a circuit conductor unintentionally contacts 'ground'. With a grounded system such a fault creates a short circuit and large current flow. In an ungrounded system the first fault does not create a short circuit, but the fault still exists.

Similarly, in a grounded system a neutral to ground fault is still a ground fault even though it doesn't cause large current flow.

Jon

 

[Besoeker3]

Definition. A ground fault is where a circuit conductor unintentionally contacts 'ground'. With a grounded system such a fault creates a short circuit and large current flow. In an ungrounded system the first fault does not create a short circuit, but the fault still exists.

Yes, quite. A fault. But my question remains. How can it be a ground fault if there is no ground?

 

[winnie]

Yes, quite. A fault. But my question remains. How can it be a ground fault if there is no ground?

On every ship, tucked away in the engine room, you will find a large flowerpot filled with soil that has a copper rod buried in it. The copper rod is connected by a copper braid to whatever needs to be grounded

Seriously, as you point out these are really faults to 'bonded metal not intended to carry current', not faults to the ground itself.