Vlotage Limits for shore power connection to Naval Vessels 1

[Rodmcm]

Does anyone know of the standard that defines the voltage limits that must be normally maintained for a shore power connection to naval vessel at 60 HZ 460V nominal i.e what is the allowable+/- percentage

 

[Skogsgurra]

Since shore power usually comes from the normal grid, I would think that the same limits apply. In Europe that would be +/-10 % deviations maximum and trying to keep it within +/-5 % most of the time.

Most equipment onboard ships are fairly standard and probably designed for the same voltage tolerances as their firma terra counterparts.

But I do not know for sure. Must be someone out there that has the standards available.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[catserveng]

Just ran into this at a local shipyard, the US Navy Inspector said desired shore power voltage levels are between 440 and 480 VAC, appears the newer design ships have better electrical protection systems.

We were asked to readjust our normally 480 VAC output generator down to below 470 before ships crew would attempt close.

 

[Skogsgurra]

That is ridiculous. If nominal voltage is 480 V, which is a common voltage, then motors are 460 V motors. The 460 V motors can readily work with (they are designed to do that) 480 V.

Applying the narrow tolerance (5%) to 480 V gives upper and lower limits 504 V and 456 V. Standard tolerance limits give 528 V and 432 V.

That ship's crew were either bean counters or newbies.



Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Rodmcm]

I know that there are design limits provided by American Bureau of Shipping, DNV, and LLoyds. Some of them I have used for the luxury white boat industry. However, I am specifically interested in naval craft. Any chance of pushing the US NAvy Inspector catserveng?

 

[dpc]

Have you tried the NAVFAC website?

 

[mauner]

Standard navy voltage at source is 450 VAC, 60 Hz for type I power.

Mil-std-1399 section 300A or DOD-std-1399 section 300A or STANAG 1008 defines tolerances for normal power.

http://assist.daps.dla.mil/quicksearch/

 

[Skogsgurra]

I think I was too quick there. The Navy has 440 V as a standard voltage and the maximum voltage is 462, according to the standards in link by mauner. And the OP was saying Navy vessel.

This is confusing. Does that also apply to commercial ships? Or is it just the navy? I have seen installations on European ships that seem to follow normal "land" standards.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[catserveng]

I just came back off the ship today, asked Assistant Engineer what actual criteria was, he said stated nominal for US Navy Vessels is 450 VAC, and that a large amount of commercial equipment being allowed on the vessels due to cost reductions and other issues is nameplated for 460 VAC. Ship's crew goes by orders written by CHENG, so if he says between 440 and 480 VAC that's what they go by.

Most of the yardbirds agree that around 450 to 460 is normal for all the vessels that come in. That is my experience as well.

Hope that helps.

 

[Rodmcm]

Thanks for all of that, the Mil standard is interesting. I have been trying to find an equivalent British or IEC standard without luck. Can anyone point me in the right direction?

 

[catserveng]

The Marine classification societies, like Lloyd's of London, ABS, BV, DNV, etc is usually who defines the standards for mechanical and electrical system on ships. Several countries use modified versions of the commercial standards for their naval vessels.

 

[glendale]

In the UK the voltage limits to NATO ships is coverered bt DEF STAN 61-5 part 4. This covers steady state voltage limits and also transient limits, which is it you are interested in?

 

[glendale]

The NATO standard in the UK (DEF STAN 61-5 part 4) states:
440V +/- 5% steady state line to line
440V +/- 16% with a recovery time of 2 seconds

 

[Rodmcm]

Thanks all, that information is great. The reason I have been asking is that the shore side transformers we are dealing with are 6.6kV/440V with onload tap changes on them. This makes for an expensive solution. I keep wondering why we need the online taps, the 6.6kV is almost rock steady.

 

[glendale]

The more usual form of transformer is the regulator type with a buck/boost winding. An AVR is used to sense the ship supply voltage at the shore connection box. This type of transformer provides a stepless voltage regulated supply.
Where is your application (if you don't mind me asking)

 

[Rodmcm]

Thanks for that, I understand the options for either tap changer or buck boost, the question I am struggling with is why have them at all. I would have thought that the regulation (voltage drop) through the transfomer would be within the limits of the standards without tapchanging?
As always I am often perplexed by the design of others.

 

[glendale]

The purpose of a voltage regulating transformer is to maintain a constant, stepless voltage from no load to full load. This is deamed to be a requirement due to the often sensetive equipment on military vessels. We have regulating transformers on this site upto 2.5MVA and the volt drop from no load to full load would be unacceptable without the regulating action.

 

[Rodmcm]

Hi Glendale and others, Sorry but I am still confused. If you look at the voltage limits you've provided they are guite wide. If I had a 'standard' transformer with a 440V nominal secondary then it seems to me that you can extensively load it without going below the allowable voltage limits. So what is the reason for autotaps or buck/boost units to maintain the voltage at say 1.5 to 2%

 

[Skogsgurra]

"often sensetive equipment on military vessels"

What about mil-specs? Equipment are supposed to work under very adverse conditions. Is that not valid shoreside?

Considering what an on-board generator can do to the voltage when starting or dumping heavy loads, I do not believe that is a valid reason.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[SteveFehr]

The equipment IS supposed to work under adverse conditions. Ironically, I think you'll find that COTS is better able to handle an overvoltage, as much of it is designed for 480V, while the mil-spec is designed specifically for 440V shipboard power.

Most of the equipment onboard will work fine, but there are always those special pieces of equipment that will suffer abnormal failure rates if you feed them power outside the range. You might not outright blow anything up, especially for short term over/undervoltages, but long-term overvoltages is another thing entirely and it doesn't take too many premature failures of $100k components to justify strict compliance. A lot of this equipment is older than dirt and flakey enough as it is!

MIL-STD-1599/300A Table 1 states 440V +/-5%, which is 462V max, with some allowance outside the range for brief periods.