# Transformers open circuit and short circuit test confusion

• Engineering
• Curiouschap101
In summary, a 50 KVA, 6360 V/230 V transformer was tested on open and short-circuit to obtain its efficiency. The open circuit test was conducted on the secondary side with a primary voltage of 6360 V and a primary current of 1 A, resulting in a power input of 2 kW. During the short circuit test, the voltage across the primary winding was 180 V and the current in the secondary winding was 175 A, with a power input of 2 kW. To find the efficiency of the transformer when supplying full load at a power input of 0.8 lagging, the efficiency equation was used with n=1 and the power output of 40 kW (50*0
Curiouschap101

## 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)

## 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?

At least,is my approach correct?

## 1. What is the difference between an open circuit test and a short circuit test for transformers?

The open circuit test is used to determine the no-load losses of a transformer, while the short circuit test is used to determine the full-load losses.

## 2. Can the open circuit test be used to accurately predict the full-load performance of a transformer?

No, the open circuit test only provides information about the no-load losses and does not take into account factors such as load current and temperature that can affect the full-load performance.

## 3. How is the open circuit test conducted?

The open circuit test involves applying a rated voltage to the primary winding of the transformer while the secondary winding is left open. The resulting no-load current and power are measured to determine the no-load losses.

## 4. What is the purpose of the short circuit test?

The short circuit test is used to determine the full-load losses of a transformer by applying a reduced voltage to the primary winding while the secondary winding is short circuited. The resulting current and power are used to calculate the full-load losses.

## 5. Can the short circuit test be used to determine the efficiency of a transformer?

No, the short circuit test only provides information about the full-load losses and does not take into account factors such as no-load losses and input power that are necessary for calculating efficiency.

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