Engineering Transformers open circuit and short circuit test confusion

AI Thread Summary
The discussion revolves around the efficiency calculation of a 50 KVA transformer using open-circuit (O.C.) and short-circuit (S.C.) test results. The efficiency is calculated to be approximately 0.88367 p.u., while the book states it as 0.887 p.u., leading to questions about the approximation of power losses. There is confusion regarding the application of the O.C. test on the low-voltage side, with a mention that it should ideally be conducted on the high-voltage side to accurately measure core losses. The participant seeks clarification on whether their approach to calculating efficiency and understanding test setups is correct, as well as how to derive full load constraints from these tests. Overall, the discussion highlights the importance of understanding transformer testing methodologies and their implications on efficiency calculations.
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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