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Topic Title: Transformer Impedance Test & X/R Ratio
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Created On: 25 July 2013 09:14 AM
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 25 July 2013 09:14 AM
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jackdaniel

Posts: 69
Joined: 29 November 2012

So guys, please help me to verify my calculation,

From the short circuit Test of 4 kVA, 400/200 V, 50 Hz, 3-phase transformer has the following test data

SC test: 20V, 10A, 100W

Impedance % = (20/400) *100 = 5%

Z= V/I = 20/10 = 2 Ohm

R = P/3*I*1 = 100/(3*10*10) = 0.333 Ohm

X = SQRT(Z2 - R2) = 1.972 Ohm

So X/R ratio of the transformer is 1.972/0.333 = 5.922.

is it correct?
 25 July 2013 10:01 PM
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JonathanHill

Posts: 225
Joined: 09 September 2002

I may be getting a bit rusty, my recollection for sc testing is to short-circuit the secondary (assume the 200V windings) and then raise the voltage until full load current flows in the primary.

I get the primary FLC to be 5.797A which differs from your value. So unless my methodology is wrong, you can't deduce the impedance or X/R ratio from these test results.

Looking forward to hearing from others.

-------------------------
Jonno
 28 July 2013 04:12 PM
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jackdaniel

Posts: 69
Joined: 29 November 2012

Originally posted by: JonathanHill

I may be getting a bit rusty, my recollection for sc testing is to short-circuit the secondary (assume the 200V windings) and then raise the voltage until full load current flows in the primary.



I get the primary FLC to be 5.797A which differs from your value. So unless my methodology is wrong, you can't deduce the impedance or X/R ratio from these test results.



Looking forward to hearing from others.


John,

Act I pick randomly the value, my objective is to determine the X/R value from the test.
 29 July 2013 12:01 AM
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JonathanHill

Posts: 225
Joined: 09 September 2002

Apart from the SC issue and values, I think your approach was OK, but would appreciate a sanity check from others.

-------------------------
Jonno
 11 August 2013 06:40 PM
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sreeraasi94

Posts: 5
Joined: 11 August 2013

Correct!
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