Load Calculation for Transformer

How many phases?

I_(A) = 1000 × S_(kVA) / V_(V)

If PF = 1.0 (as would be the case for incandescent lights), 2500 ÷ 60 ≈ 41 lamps. If the PF is less, the number of lamps will be correspondingly fewer.

True, but...

"To achieve maximum transformer efficiency, maintain average transformer loading between 60% and 80%."

See this item:

http://www.grainger.com/tps/electrical_general_purpose_transformer_selection_guide.pdf

That differs from what I have seen elsewhere.

Since I did worked for a manufacturer, I remember the allowable maximum load is actually dependent upon on the designer / manufacturer. In my old company the auto-transformer types were designed to safely provide up to a 25% of its rated capacity. The added safety margin are computed for resistive loads, and applicable on transformers having kva ratings of 1 kva and above.

The Isolation type transformers were designed a bit differently due to physical (core and copper) limitations. They were hot tested them to provide 80% of its rated capacity, with 2 degrees C., maximum allowable temperature rise for 24 continuous hours.

In short, real performance mostly will be brand and/or manufacturer dependent plus the country of origin!

What will you be illuminating?

Assuming the pf is 1 ( lighting load ):

· 2500 VA can means 2500 watts power . So you can use - 2500 / 60w = 41 lamps as mentioned earlier .

· In another way , the transformer of 2500 VA , can deliver current of : 2500 / 25 ( approx 26 v ) ie., 104.16 amps

· A 60 watts lamp on 24 v , will take - 2.5 amps . So the number of lamps that can be connected to secondary is 104.16 / 2.5 = 41.66 .

Approximately the number of lamps that can be connected is 41 ( Bulbs of 60 w / 24 v each )

hey everyone i know all formulas which you are giving

the formulas which the members are suggesting is only applicable if the transformer efficency is 100% then you can say that 41 lamp..... i want to know the average load calculatiion i.e if transformer eff is 80% and pf is 1 then which formula is applicable..

note that transformer connection is Y-Y and line volt is

i/p volts = 415_____420v

o/p volts = 26.5____24v

I presume that if you have a 60 watt bulb that you have all ready decided what you are going to put on your transformer, or was the question you were given worded differently?