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Join Date: Jan 2012
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Load Calculation for Transformer

02/04/2012 2:04 AM

Can some one help me about load calculating i.e i have 24 volt step down transformer for lighting purpose (2.5 kva input 415v output 26v ) the bulb I am using is 60watts 24v now what is formula for load calculating i.e how much bulb i can use on that transformer?

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Guru

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#1

Re: load calculation for transformer

02/04/2012 3:10 AM

How many phases?

I(A) = 1000 × S(kVA) / V(V)

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#2

Re: Load Calculation for Transformer

02/04/2012 9:45 AM

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.

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#3
In reply to #2

Re: Load Calculation for Transformer

02/05/2012 12:06 AM

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

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#5
In reply to #3

Re: Load Calculation for Transformer

02/05/2012 3:54 AM

That differs from what I have seen elsewhere.

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#9
In reply to #5

Re: Load Calculation for Transformer

02/05/2012 9:26 AM

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!

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#4

Re: Load Calculation for Transformer

02/05/2012 3:26 AM

What will you be illuminating?

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Associate

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#6
In reply to #4

Re: Load Calculation for Transformer

02/05/2012 4:37 AM

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 )

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#7
In reply to #6

Re: Load Calculation for Transformer

02/05/2012 8:09 AM

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

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#8

Re: Load Calculation for Transformer

02/05/2012 9:00 AM

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?

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