Transformer Question

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pete m.

pete m.

Senior Member
Location
Ohio
I hope this is the correct place to ask this question....

Is there a standard formula for calculating "line losses" in amps per KVA for a dry type transformer? The one in question is a 75kva, 480 to 208y120 I am assuming the impedance is somewhere in the neighborhood of 5 to 6%.

Thanks for your help.
 
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mpross

Senior Member
Location
midwest
Transformer Losses

Transformer Losses

Pete,

Do you want the losses in terms of MW or MVARS? If you know the impedance (R and X) of the transformer, you should be able to calculate the losses based upon I^2*R or I^2*X

where I^2 = (P^2 + Q^2) / V^2...

...and of course P and Q are the real and reactive power flows through the xfmr.

Most times the transformer impedances are listed as a percent, or a per unit value. If this is the case, than you need to convert those values into actual impedance values.

Hope this helps.

-Matt
 
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templdl

Senior Member
Location
Wisconsin
Your question :"Is there a standard formula for calculating "line losses" in amps per KVA for a dry type transformer?" I am to assume that you are talking about efficiency. If so the manufacturer should have standard data for that transformer. It is stated in wattage at NL and FL with efficiencies given in % at 1/4, 1/2, 3/4. and FL. Z really doesn't have a lot to do with it.
If so the 75kva 150degC transformer would be around 499w and 2536w, and 97.2%, 97.6%, 97.2%, and 96.7% efficient.
A 115degC would be 400w and 2060w, and 97.1%, 97.7%, 97.8%, and 97.3% efficient.
An 80degC would be: 600w and 1855w, 96.5%, 97.8%,97.7, and 97.7w.
K-factor trransformers would be even different yet. remember amps in would be indirectly proportional to the primary and secondary voltages less the watts loss at a given load.
 
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