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Topic Title: Current in a 2 phase transformer
Topic Summary: how do I calculate the current?
Created On: 25 September 2013 09:31 AM
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 25 September 2013 09:31 AM
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anoor

Posts: 2
Joined: 12 July 2010

I am a graduate engineer and have been set a small task to work out the current (primary side) in a 2 phase 30kVA 415:650 tranformer. The 2 phases have been utlized from a 3 phase source and are hence 120degrees out of phase.

I understand had it been a 3 phase 30kVA transformer I could calculate my current by 30kVA / 415 / route*3 = 42A.

If it was a single phase then simply 30kVA / 415 = 73A.

However if i am only using 2 phases from a 3 phase source yet still need to produce 30kVA of power, how do a calculate the line current?

Thanks in advance.
 25 September 2013 07:17 PM
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AdrianWint

Posts: 262
Joined: 25 May 2006

Hint .... think about what the transformer actually sees ....... does it really see two phases .... or is the transformer really a single phase transformer that just happens to find itself connected to a 415V source? How many sinewaves does it see?

What about the current in each of the supply legs? It is the same?

Adrian
 25 September 2013 10:30 PM
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anoor

Posts: 2
Joined: 12 July 2010

I would consider it a single phase with a 415V input yet at the same time it sees two sine waves phase shifted? As with a balance 3 phased load i would expect the current magnitude in each leg to be the same?
 25 September 2013 11:31 PM
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alancapon

Posts: 5786
Joined: 27 December 2005

Originally posted by: anoor
I would consider it a single phase with a 415V input yet at the same time it sees two sine waves phase shifted . . .

Does it really? Draw two sine waves, one shifted by 120°, then draw the two added together. It sounds like you will be surprised by the answer. . .

Regards,

Alan.
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