Transformers open circuit and short circuit test confusion

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SUMMARY

The discussion centers on the efficiency calculation of a 50 KVA, 6360 V/230 V transformer using open circuit (O.C.) and short circuit (S.C.) tests. The O.C. test results indicate a primary voltage of 6360 V, primary current of 1 A, and a power input of 2 kW. The S.C. test shows a primary voltage of 180 V, secondary current of 175 A, and a power input of 2 kW. The calculated efficiency is approximately 0.88367 p.u., which differs from the book's approximation of 0.887 p.u., likely due to rounding in the power loss calculations. The confusion arises regarding the application of the O.C. test on the low voltage side, as it is traditionally performed on the high voltage side to determine core losses.

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Curiouschap101
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Homework Statement


A 50 KVA,6360 V/230 V transformer is tested on open and short-circuit to obtain its efficiency,the results being as follows:
O.C.:
Primary Voltage-6360 V,
Primary Current-1 A,
Power Input - 2 kW
S.C:
Voltage across primary winding-180 V
Current in secondary winding-175 A
Power Input-2 kW.
Find the efficiency of the transformer when supplying full load at a power input of 0.8 lagging.
Also make the phasor diagram (ignoring impedance drops)for this condition.

Homework Equations


Efficiency(η)=Pout/(Pout+POC+n2PSC)
n=applied load/full load

The Attempt at a Solution


n=1
Pout=50*0.8=40 kW
POC=2 kW
PSC=2 kW*(230/180)2=3.265432099..kW
η=40/(40+2+3.265432099)=0.88367...p.u.
The solution in the book is given to be 0.887 p.u.(Maybe they have approximated POC that's why.Please do check.)
But I am confused by the way the tests are conducted e.g. Why apply the open circuit test on L.V. side(kept as secondary in the first test if I am interpreting the problem correctly)?(My instructor told that O.C. test needs to be done with the H.V. side kept open(I forget the reason).On second thought power loss in core is said to be nearly invariant of the setup if I am correct right? ).As far as I know O.C Test can be used to determine the core loss and core impedance and the short circuit test is used to determine the copper loss and series impedance in circuit.Can you find the full load constraints(say full load current etc.) from any of these?
 
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Please help.
 
At least,is my approach correct?
 

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