208 to 240 - Boat Yard

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I'm not familiar with a an SEC transformer. I'm looking into it now but I'm pretty sure there are spaces for individual breakers for the independent loads.


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Npstewart said:
.... I'm looking into it now but I'm pretty sure there are spaces for individual breakers for the independent loads.
Click to expand...
Supply wires would have to land on a single ocpd (i.e. main; pedestal is MCB). If pedestals are MLO, perhaps a back-fed breaker can be set up as a main in each. [240.21(C)]
 
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Your original idea may work

Your original idea may work

Hammond Transformers selection guide seems to have a buck/boost that will work.
Three Phase - Group B Selection Chart, wye connected, LV 219 / HV 249;
I expect that -10% in = -10% out, or 209 volts in should produce 239 volts out.
Use 3 Q003ESCF transformers to produce 70 KVA, connection diagram #12.
The questions section at the bottom of the PDF covers the neutral, from question #12:
"a three-phase ?wye? buck-boost transformer connection should be used only on a 4-wire source of supply"
Even if you decide this is not ideal for your application, the PDF has lots of good information,

http://www.hammondpowersolutions.com/files/HPS_Catalog_BuckBoost_Section2.pdf
 
I waited to long to edit a mistake in the selection of the transformers, but the idea is that without matching the exact voltages, you should be able to match a corresponding ratio. I didn't catch that my calculator was not actually subtracting the percentages I though I was entering.
 
I do believe the transformer selected is the correct one after all, it's just that it would be -5% in at 208 volts and that should give you the same -5% out for around 237 volts. A word of caution though, and someone may correct me here: but normally a transformer will react with an equal reduction out to the percent of the incoming voltage, but do these react the same way to the reduction since it is only changing a portion of the voltage?
 
under8ed...

It's good to see a new member posting. :thumbsup:

However, this is a little more complex than simply converting 208V to 240V, as the pedestals each require a 120/240V 1? 3W supply. There are no [feasible] buck/boost configurations that provide the required voltage configuration and also balance the load on the 3? supply.
 
I'm glad to finally quit just lurking here..been doing that for a few years now. But why does this situation need to be treated so particular? Once you have fed a 3 phase panel, you balance the loads the best you can with single & double pole breakers; with a little thought put into placement, it would seem you could do about as well as the average panel I usually see in a plant. The PDF appears to indicate that it can provide the correct voltages. I don't claim to know it will work, but it seems that it would.
 
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under8ed said:
I'm glad to finally quit just lurking here..been doing that for a few years now. But why does this situation need to be treated so particular? Once you have fed a 3 phase panel, you balance the loads the best you can with single & double pole breakers; with a little thought put into placement, it would seem you could do about as well as the average panel I usually see in a plant. The PDF appears to indicate that it can provide the correct voltages. I don't claim to know it will work, but it seems that it would.
Click to expand...
Look at any buck/boost diagram for 3?. Show me one that has a neutral for each 240V 1? connection, i.e. A-B, B-C, and C-A for balancing.
 
Smart $ said:
Look at any buck/boost diagram for 3?. Show me one that has a neutral for each 240V 1? connection, i.e. A-B, B-C, and C-A for balancing.
Click to expand...
Even if you came up with close to such a configuration, with three center taps, there is no way that you could ground them all.
Boom!
 
I'm wondering if we are thinking of two separate things. Linked below is a drawing that shows a 3 phase, wye output with a common neutral as any other normal system. The 240 volt loads needing none, but one is there for all the single phase 120 loads. The balancing would be a bit of creative placement & luck of where the boats tie up. Here a link discusses their 3 phase wye buck/boost selection with wiring diagrams showing neutral in & out. There are no cautions on how to use or not use the 3 ph. wye feed. From the link below:
"Q4 Can I use a Buck-Boost Transformer to provide an output of 208Y/120 (or any other wye combination)?
A4. This all depends on your source. If you have a wye source, you can feed the wye through the autotransformer. If you have a High-Leg Delta or a 3-wire source, you can not create the wye for your application........."
I believe the 208/3 the OP mentioned would also have a neutral..

http://www.automationdirect.com/static/manuals/buckboosttransformer/buckboostmanual.pdf
 
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under8ed said:
I'm wondering if we are thinking of two separate things. Linked below is a drawing that shows a 3 phase, wye output with a common neutral as any other normal system. The 240 volt loads needing none, but one is there for all the single phase 120 loads. The balancing would be a bit of creative placement & luck of where the boats tie up. Here a link discusses their 3 phase wye buck/boost selection with wiring diagrams showing neutral in & out. There are no cautions on how to use or not use the 3 ph. wye feed. From the link below:
"Q4 Can I use a Buck-Boost Transformer to provide an output of 208Y/120 (or any other wye combination)?
A4. This all depends on your source. If you have a wye source, you can feed the wye through the autotransformer. If you have a High-Leg Delta or a 3-wire source, you can not create the wye for your application........."
I believe the 208/3 the OP mentioned would also have a neutral..

http://www.automationdirect.com/static/manuals/buckboosttransformer/buckboostmanual.pdf
Click to expand...
You can boost a 208Y/120 to a 240Y/138 with no problems. But there will be no 120/240 combination available (i.e. center tapped).
You could still use the original terminals for 120V to neutral loads, but the 240 would not be an SDS and trying to use both voltage systems could be really confusing, and a minefield for the next person to work on it.
At a minimum the 120 wye and 240 delta will require separate breaker panels, and the 240 circuits may not work with slash rated breakers.
 
You guys are right, the set I up described will not serve all the loads of the pedestal. The same PDF finally states that on the next to the last page. It can be made to handle the problem described by the OP; but as pointed out, it will create a system that could confuse future work. A situation that could possibly be clarified by permanent marking & identification? Maybe not in this setting.
 
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