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 Post subject: 3-Phase Transformer Model
PostPosted: Wed Jul 28, 2010 8:08 pm 

Joined: Wed Jul 21, 2010 7:54 am
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Location: OK
If I have a 300 kVA utility transformer bank made up of 3 single phase 100 kVA transformers each with an impedance of 1.9%, is the equivalent impedance of the 300 kVA transformer simply 3 x 1.9, or is it the square root of 3 times 1.9?


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PostPosted: Thu Jul 29, 2010 9:51 am 
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Location: Spartanburg, South Carolina
RJohnson wrote:
If I have a 300 kVA utility transformer bank made up of 3 single phase 100 kVA transformers each with an impedance of 1.9%, is the equivalent impedance of the 300 kVA transformer simply 3 x 1.9, or is it the square root of 3 times 1.9?

1.9%. The impedance is a per phase value.


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PostPosted: Fri Jul 30, 2010 8:04 am 
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How are the transformers connected? Wye or delta?


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PostPosted: Sat Jul 31, 2010 10:42 am 

Joined: Wed Jul 21, 2010 7:54 am
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Connected delta-wye.


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PostPosted: Mon Aug 02, 2010 8:52 am 
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Edited: Sorry I misremembered. Connections make no difference. 1.9% using 100 kVA and line to neutral voltage to get ohms secondary equates to 1.9% using 300 kVA and line to line voltage.


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PostPosted: Tue Aug 03, 2010 6:38 am 

Joined: Fri Jan 30, 2009 10:04 am
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Location: Toronto
RJohnson wrote:
Connected delta-wye.


No matter how the 3 single phase transformer connected, the impedance should be the same as the single phase tested value


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PostPosted: Tue Jun 07, 2011 12:32 pm 

Joined: Mon Apr 13, 2009 11:54 am
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Location: Midland, Tx
What is one of the transformers has a different nameplate impedance?


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PostPosted: Fri Jun 10, 2011 8:35 am 
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Then there is no equivalent three phase impedance.


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PostPosted: Sun Jun 12, 2011 6:08 pm 

Joined: Fri Jan 30, 2009 10:04 am
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Location: Toronto
Can 3 single phase transformers with different IZ% be connected to a transformer bank?


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PostPosted: Sun Jun 12, 2011 10:33 pm 
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Joined: Mon Mar 29, 2010 5:02 am
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J.T wrote:
Can 3 single phase transformers with different IZ% be connected to a transformer bank?


It is my understanding that they can be, but they still have to be within a very tight range..


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