Transformer sizing

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Glenn Becnel

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We have a new 10' X 12' Instrument Bldg. installed in our area. The bldg. was fabricated offsite & delivered as a package. The vendor design includes a 30 KVA transformer with a 480VAC, 3 phase, delta Primary/ 120-208 VAC, 3 phase, wye secondary. The loads on the 120-208 panel are L1=10.7KW, L2=10.2 KW & L3=6KW. The approx. total is 27 KW. We are experiencing power problems in the bldg. The vendor says these problems are caused by "transformer under sizing". The bldg. vendor wants to upsize the transformer to a 45KVA. Will this solution solve our problem?
Thanks in advance for your help.
 
Re: Transformer sizing

First of all, what kind of problems are you experiencing? I can't give you any real advice without knowing the nature of the problems.

Secondly, you appear to be using "KW" and "KVA" interchangeably. You say the total load is 27 KW. If the power factor is worse than 0.9, then you will be exceeding the 30 KVA rating of the transformer.

Next, when you list the loads on each of the phases, are you talking about measured loads, or the sums of the rated loads that are connected to each phase?

Finally, what types of load are being served by this transformer? If there are a significant amount of harmonic loads, then you could be seriously overloading the transformer.
 
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