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New Member
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Apr 6, 2007, 12:59 PM
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Step down transformers
How many amps, at 400 volts, can I get from a 300 kva [ 480v/ 400v] transformer?
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Full Member
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Apr 8, 2007, 06:12 AM
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Originally Posted by Nathonian
How many amps, at 400 volts, can I get from a 300 kva [ 480v/ 400v] transformer?
This answer can vary depending on the type of load. Assuming a non-inductive load,(no large motors) then your answer would be 300kva/400volts output=750 amps. This is in an ideal situation. In reality you have a less then perfect energy transfer, the "standard" for industrial applications is usually to caclulate for a 60% efficiency or Power Factor(PF). In this case 300kva*.6PF =180000/400volts yields you approximatley 450 Amps.
Hope This Helps,
Morrowrj
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Uber Member
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Apr 8, 2007, 08:12 AM
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The expression Volt Amps of AC power, will include any power factor consideration on the circuit. A transformer rated in KVA will not need to be derated for any inductive or capacitive load.
Assuming this is a 3 phase transformer, due to the size and voltages involved, the amps available on the 400 volt secondary side is calculated:
300,000 VA / 400 volts * 1.73= 1297.5 or 1300 amps
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Full Member
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Apr 8, 2007, 04:30 PM
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Hmm, I normally work single phase... However it still seems like your calculation is off? Is it possible that the equation is KVa divided by the quantity of volts times 1.73 ?
300,000VA / (400 V * 1.73)
or
300,000Va / 692 = 433 Amps.
Please see here : Rex Power Magnetics - Home Page
Or here : How To Size Phase Transformers
Please let me know if I am missing something.
Morrowrj
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Uber Member
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Apr 10, 2007, 01:26 AM
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Sorry I missed this, thought I would get subscribed just by answering.
You are right ,I can't believe I said that. The brackets mean to calc phase to phase voltage of 692, then divide.
Morrow is correct, the amps is 433.
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New Member
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Jun 1, 2007, 05:52 PM
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Hello There
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New Member
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Jun 1, 2007, 05:54 PM
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Sorry New, What Would Be The Right Size Transformer.
Power Coming In Would Be Single Phase 480
Output Is 120v , About 4.2a
I Figure About 1kva Would Be Plenty
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Full Member
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Jun 3, 2007, 05:55 AM
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Yes, I agree 1kva should be good. Did you check the links I referenced above?
Morrowrj
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