Transformer question

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PowerdT

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120/208V Transformer is feeding 100A, 240V 1phase vessel at marina. They use 2 phases of conductor which is 208V plus or minus voltage drop while the vessel needs 240V.

What would that do to the transformer?
 
Etanuye said:
120/208V Transformer is feeding 100A, 240V 1phase vessel at marina. They use 2 phases of conductor which is 208V plus or minus voltage drop while the vessel needs 240V.

What would that do to the transformer?
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I do not understand the question. Yes the primary is two phases of a 208/120 system, and the secondary will likely be 240 with a center tap. The center tap would be grounded (even if you dont need 120 for anything. Another option is to ground one "side" of the 240 resulting in one ungrounded conductor and one grounded conductor.
 
electrofelon said:
I do not understand the question. Yes the primary is two phases of a 208/120 system, and the secondary will likely be 240 with a center tap. The center tap would be grounded (even if you dont need 120 for anything. Another option is to ground one "side" of the 240 resulting in one ungrounded conductor and one grounded conductor.
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Sorry. The transformer size is 112.5 kva - primary 480v, secondary 120/208v.
 
electrofelon said:
Ah ok, so you have 208 serving the vessel that supposedly needs 240v? The transformer does not care. The loads on the vessel may or may not care. I would guess probably not an issue, but we would need more details of the loads and equipment to know for sure.
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I see Thats why I can’t find much information I was just wondering if it damages the transformer. I dnt have detailed information about the loads
 
This would be the same as a 3ph service in a condo/apartment service. The loads would receive 120v L-N and/or 208v L-L. 240v-rated heating loads will operate at almost exactly 75% power.

While it's desirable to balance transformer loading, it's generally not detrimental if you don't, but do keep in mind that the available power will be lower than the transformer's rated capacity.
 
Etanuye said:
I see Thats why I can’t find much information I was just wondering if it damages the transformer. I dnt have detailed information about the loads
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The transformer will not be damaged. It is likely (over 50%, less than 100%) sure that the vessel will operate at 208. If 240 __TWO WIRE__ is required, a boost transformer is the solution. If 120-0-120 is required, 2 boost transformers are the solution.

With no doubt, you need the vessel requirements.
 
GeorgeB said:
If 120-0-120 is required, 2 boost transformers are the solution.
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Couldn't it also be done with a single transformer with a center tap grounded 240V secondary and two phases of the 208 with no neutral on the primary?
 
GeorgeB said:
The transformer will not be damaged. It is likely (over 50%, less than 100%) sure that the vessel will operate at 208. If 240 __TWO WIRE__ is required, a boost transformer is the solution. If 120-0-120 is required, 2 boost transformers are the solution.

With no doubt, you need the vessel requirements.
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The vessel needs 240V with 2Hot+1N+1G
 
Etanuye said:
The vessel needs 240V with 2Hot+1N+1G
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That statement requires further detail, as has already been commented. The vessel was obviously designed for 120/240V. But if all the loads are 120V, then it doesn't need 120/240V, it will run fine on 120/208V. If there are 240V 2-wire loads, then each one can be evaluated to determine if it really needs 240V, or would work fine on 208V. Likewise if there are 120/240V 3-wire loads.

Cheers, Wayne
 
GeorgeB said:
If 240 __TWO WIRE__ is required, a boost transformer is the solution. If 120-0-120 is required, 2 boost transformers are the solution.
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It's not clear to me how 2 boost transformers could be used to produce 120-0-120 (i.e., with the two 120V phases 180 degrees apart) when being provided with 120/208V.
 
wwhitney said:
That statement requires further detail, as has already been commented. The vessel was obviously designed for 120/240V. But if all the loads are 120V, then it doesn't need 120/240V, it will run fine on 120/208V. If there are 240V 2-wire loads, then each one can be evaluated to determine if it really needs 240V, or would work fine on 208V. Likewise if there are 120/240V 3-wire loads.

Cheers, Wayne
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That makes sense. I’m waiting for the information, the reason I opened the thread was to know if it has been damaging the transformer
 
Etanuye said:
That makes sense. I’m waiting for the information, the reason I opened the thread was to know if it has been damaging the transformer
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Well since you mentioned it is a 112.5kVA transformer and that you are only supplying something with two lines and the neutral that something can only be 75kVA maximum, you don't have the remaining 37.5 kVA of the unused phase available for utilization here. Proper overcurrent protection should open circuit if overloaded though.
 
ggunn said:
Couldn't it also be done with a single transformer with a center tap grounded 240V secondary and two phases of the 208 with no neutral on the primary?
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Yes. That is the best way.
Boosting the L-L voltage will also boost the L-N voltage.
 
synchro said:
It's not clear to me how 2 boost transformers could be used to produce 120-0-120 (i.e., with the two 120V phases 180 degrees apart) when being provided with 120/208V.
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They wouldn't. 120 volt loads would be supplied directly from the utility; no change. And the boost (auto)transformer(s) would supply only the 240-volt loads.

But the first step is to evaluate whether 240-volt service is needed at all, or if the boat will do just fine on 208.
 
ggunn said:
Couldn't it also be done with a single transformer with a center tap grounded 240V secondary and two phases of the 208 with no neutral on the primary?
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That would not be a buck-boost application but rather a separately derived system and will need to be full kVA rated and not just rated for the amount of boost like an autotransformer would be.
 
Etanuye said:
Two phases of the 208 is still 208V, not 240V
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Um, OK, on the primary side of the transformer, but what about on the secondary side? I am proposing a 208V ungrounded primary to 240V center tapped, grounded secondary transformer. I know that, for example, a 208V delta to 480/277V wye with a grounded neutral works; this seems similar to me.
 
kwired said:
That would not be a buck-boost application but rather a separately derived system and will need to be full kVA rated and not just rated for the amount of boost like an autotransformer would be.
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But it would work, right? My question was theoretical, not necessarily practical.
 
ggunn said:
But it would work, right? My question was theoretical, not necessarily practical.
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Yes.

Now if the 208/120 system were separately derived from say 480 volts, might be best to just put in 480 x 120/240 single phase transformer to begin with, of whatever rating the vessel needs. Add unless it is determined the vessel will be just fine with 208 instead of 240 and the 208 was already existing (which is what I think we have from OP).
 
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