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Home > Science > Engineering   »   How am i going to size my 3 phase X'mer with 1 phase load using current as reference

 
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Old May 11, 2007, 03:43 AM
Peping
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How am i going to size my 3 phase X'mer with 1 phase load using current as reference

Hi, I'm Peping:

I have 90 pieces of single phase loads with current of 2 Amperes. This will be loaded to a 3 phase transformer, Wye connected having a line to line voltage of 220 Volts. What will be the size of the transformer required for the mentioned loads?

Many thanx,

Peping

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Old May 11, 2007, 11:45 AM   #2  
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Assuming the load needs 220 volts, 90 units at 2 amps each at 220 volt 1 phase will require 22.890 KVA minimum.

180 amps x 220 volts = 39600 VA 1 phase / 1.73 = 22890 VA or 22.89 KVA

Add at least 25% KVA to arrive at the minimum size transformer. If the loads are motors and will be started at the same time, add the locked rotor KVA to size the transformer.
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Old May 22, 2007, 03:28 PM   #3  
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This seems to me like it is a question for school; however, I would add that in North America 220V line-to-line three phase is not a readily available voltage. The Three phase voltage which is readily available near 220V would be 208 line-to-line / 120V line-to-neutral and that transformers (around this size) are available in 30kva and 45kva (i.e. you can't get a 28kva transformer).
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Old May 22, 2007, 03:29 PM   #4  
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Also, the 1.73 comes from the square root of 3 in case you are trying to show your work.
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