3 Phase to 208Y/120 Service

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CBL65

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I have been given a problem I am a little confused on. I have a new set of trailers I need to power up. I have 4 100AMP main panels on these trailers.

I need to get 600V 3 phase down to 208Y/120 and then hook up these mains.

This will result in an imbalance to the transformer, I think.

Trailer one - A and B hots
Trailer two - B and C hots
Trailer three- A and C hots
Trailer four - A and B hots

So... I have 300 amps on A, 200 on B, and 200 on C. Is this kosher?

I'm really confused and could use some help. I'm not sure if I'm even approaching this right.

Thanks!
 
CBL65 said:
I have been given a problem I am a little confused on. I have a new set of trailers I need to power up. I have 4 100AMP main panels on these trailers.

I need to get 600V 3 phase down to 208Y/120 and then hook up these mains.

This will result in an imbalance to the transformer, I think.

Trailer one - A and B hots
Trailer two - B and C hots
Trailer three- A and C hots
Trailer four - A and B hots

So... I have 300 amps on A, 200 on B, and 200 on C. Is this kosher?

I'm really confused and could use some help. I'm not sure if I'm even approaching this right.

Thanks!
Click to expand...

Actually you will have 300A on line A, 300A on line B, and 200A on line C.
 
jim dungar said:
Actually you will have 300A on line A, 300A on line B, and 200A on line C.
Click to expand...

Yes, it would help if I could add!

One more question: If I use a 150 kVA transformer, is each phase good for 150 kVA or 50kVA?
 
CBL65 said:
One more question: If I use a 150 kVA transformer, is each phase good for 150 kVA or 50kVA?
Click to expand...
KVA adds like a normal human would expect. 50 KVA per phase, 150 KVA total.

This is as opposed to current: 30 amps on phase A, 30 amps on phase B, 30 amps on phase C, gives you a ?total? of 30 amps, not 90.
 
Correct me if i'm wrong. But if A&B phases carried two trailers 41600kw,B&C phases carried 1 trailer 20800 kw, C&A phases would carried 1 trailer 20800 kw, Then they would be delta connected and the amperage on phase A would be 259 amps,B phase would be 259 amps, C phase would be 173 amps. Total kw is 83200KW @ 208 volt.Full calculated load.Nominal amperage would be 300-300-200 but as calculations go would the above hold true?
Rick
 
actually the total would be whatever the actual load is. You can be pretty sure that those trailers aren't pulling 100 amps and the balancing of the phases on the transformer would only be true if the phases of the trailers panels are balanced.
 
cowboyjwc said:
actually the total would be whatever the actual load is. You can be pretty sure that those trailers aren't pulling 100 amps and the balancing of the phases on the transformer would only be true if the phases of the trailers panels are balanced.
Click to expand...
In other words, if you can determine that two trailers will be loaded less than the other two, parallel the two smaller loads.
 
I appreciate all the help... we're going to hook them up like I originally said, but then we are going to load balance at the panels in the trailers.

I feel like I should turn in my degree, but this one had me all turned around!
 
cowboyjwc said:
actually the total would be whatever the actual load is. You can be pretty sure that those trailers aren't pulling 100 amps and the balancing of the phases on the transformer would only be true if the phases of the trailers panels are balanced.
Click to expand...

The problem in many commercial projects is there are too many questions left unanswered. . I've been on way too many projects that get a couple weeks from being complete before you get good information on actual load.

When in doubt, size the transformer according to the total amperage of all mains and size your wye neutrals under the assumption that any one trailer will be occuppied at some point and under full load while all other trailers with be powered off.

David
 
David, of course worse case senerio is always the way to go and you can always go to big on the transformer and of course you're right at any given time there will be an unbalanced load on the transformer.

My real thought was I wouldn't worry that you were at 300-200-200, simply because your probably really weren't.
 
Thanks for the replies. I think I'm going to feed it with 600VAC 100A breaker stepped down through a 150kVA (Way oversized) transformer to make the stress on the transformer less. I'm going to install the cable as if the system was sized for 150kVA just in case someone ever finds a 150A breaker.

The breaker is the limiting factor. This is an old plant, and the MCC manufacturer is gone. We can't get 150A stabs for the MCC anymore, but I guess if it was urgent enough we could have them made in the future.

I just don't want to be accused of not future proofing the installation.
 
If they are single phase panels, then, load balancing the whole project would be necessary to balance the tub. But if the loads are dynamic, then it will be hit or miss at best. Not a huge issue, with an oversized xfmr., but you do need to look at the possability of the whole load going hot at once, and loading up the step down, and it's disconnect with inrush current.
 
Each panel will have a fused disconnect to protect against damaging the transformer or tripping all the way back to the high side feeder. I also am putting in a 400A distribution panel on the low side w/ a main breaker for additional protection.
 
I'm confused. If each trailer panel is 208Y/120, then there will not be an imbalance because each trailer will require all three phases.
 
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