Transformer impedance test calculations

[Mondy]

Hi All

Can anyone help me with the calculations involved in a transformer short circuit impedance test. I have the following data:

Transformer rated voltage =230v
Transformer rated power = 960VA
Secondary short circuited during test
ambient temperature during test = 22 deg.C

Measured impedance voltage Ez = 3.55v at 50% of rated current and at the transformers rated frequency (50Hz)

Supplied current = 2.188 average amps

Measured copper loss CuW = 7.51W at 50% of rated current and at the transformers rated frequency (50Hz)

Impedance voltage (Ez) and Load Loss (CuW) corrected to 100% of the rated current and a reference temperature of 80deg.C resulting in:

Short circuit resistance Er = 3.84%
Short circuit impedance Ez = 3.87%
Short circuit reactance Ex = 0.51%
Copper Loss CuW @ 100% load = 36.84W

I assume that the Ez of 3.84% is calculated from the 3.55v @ 50% of rated current (although I cannot get it to add up) and then the reactance Ex = 0.51 derived from

Sqr(Ez 3.87^2 - Er 3.84^2)

and Er = 36.84W * 10 /960VA

as usual, but I cant get it to add up. Or is the Ex = 0.51 calculated and then added in quadrature to come up with the Ez = 3.87%

Can anyone get these figures to make sense as I cannot get them to correlate and I can only assume I am not taking into account something in the correction of the parameters measured at 50% of rated load to 100% rated load and 80 deg.C reference temperature?

Cheers
Ray

 

[ScottyUK]

Glad to be of help. Sometimes it's nice just to sit down with a pencil and paper and do the calcs to prove to yourself that you still know. Let us know what the outcome of the dispute is.


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If we learn from our mistakes,
I'm getting a great education!

 

[garyvin]

Hey no problem, Like ScottyUK said glad to help. That's why we are here and I do hope you are able to resolve the situation.