Power draw on 208V single phase ckt served by 208/120V t

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Re: Power draw on 208V single phase ckt served by 208/120V t

Originally posted by rattus: Consumed by the load, 2080VA, but the xfrmr thinks it is delivering 120x10x2, or 2400VA. If you are concerned about the xfrmr load, I would go with 2400VA. Whole nuther thread on this subject.
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I just made the following comment on that ?other thread.? But for completeness, I will repeat it here.
Originally posted by charlie b: The transformer thinks it is delivering 1 x 120 x I VA plus another 1 x 120 x I VA. But these two do not add up to 2 x 120 x I VA. Rather, they add up to 208 x I VA.
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The correct total load is 2080 VA, not 2400.
 
Re: Power draw on 208V single phase ckt served by 208/120V t

Charlie B.,

In this special case, one would have to consider the effect on the xfrmrs, then the answer would be 2400VA.

The question though asks how much (apparent) power to the load, and that is 2080VA.

In practice though, I think it won't matter much since this is such a rare case.

[ March 04, 2005, 02:47 PM: Message edited by: rattus ]
 
Re: Power draw on 208V single phase ckt served by 208/120V t

Burned again for answering too fast :eek:

Rattus is correct,
the load consumes 2080VA (2080W)
the transformer provides 2400VA (2080W)

This points out the importance in balancing loads.

There, I'm on both sides of the issue, so now I can't be wrong :D
 
Guys I think some of you are confused.

If you connect a 208VAC * 10A load to a transformer then the load seen by the transformer and power analyzer is 2080VA. That is the load, the transformer will need to support 2080VA not 2400VA.

The summation in the windings of the transformer assuming this load is connected AB is as follows:

(1200VA@30 degrees) + (1200VA@90 degrees) = (2080VA@60 degrees)

The transformer needs to be sized to handle 2080VA, that is the load.

As you can see, no matter how you look at it, the current is 10A. The transformer has to have enough copper in the windings to carry 10A but the load is 2080VA.

2080/208 = 10A
1200/120 = 10A
 
I am going to close this thread, just on general principles. Prior to the comment posted today, the most recent other comment was over two years ago.

If you feel there is a need to resume the discussion on this topic, please start a new thread.
 
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