Question

Which of the following statement is not correct with respect to short circuit test on transformer ?

• A. It is used to find out the copper losses in the transformer
• B. The short circuit test is most conveniently made by short circuiting the LT winding
• C. It is used to determine the core loss in the transformer
• D. Short circuit test is performed at rated current

Hint:

Transformer tests:
• Open circuit test \(\rightarrow\) Core loss
• Short circuit test \(\rightarrow\) Copper loss

Answer 1

The Correct Option is C

Concept: Transformer short circuit test is mainly performed to determine:
• copper losses,
• equivalent impedance,
• equivalent resistance and reactance. Core loss is determined using the open circuit test, not the short circuit test.

Step 1: Understanding short circuit test arrangement. In short circuit test:
• one winding is short circuited,
• low voltage is applied to the other winding,
• rated current is allowed to flow. Usually: \[ \text{LT winding is short circuited} \] for convenience and safety.

Step 2: Checking statement (1). Statement: \[ \text{It is used to find copper losses} \] This is correct. During short circuit test:
• applied voltage is very small,
• flux produced is very small,
• iron loss becomes negligible. Hence wattmeter reading approximately equals copper loss.

Step 3: Checking statement (2). Statement: \[ \text{LT winding is usually short circuited} \] This is correct because:
• LT winding carries high current,
• HV side requires smaller current supply for testing,
• practical handling becomes easier.

Step 4: Checking statement (3). Statement: \[ \text{It is used to determine core loss} \] This is incorrect. Core loss is measured using: \[ \text{Open circuit test} \] not short circuit test. In short circuit test, flux is very low and iron loss is negligible.

Step 5: Checking statement (4). Statement: \[ \text{Short circuit test is performed at rated current} \] This is correct. The applied voltage is adjusted until: \[ I=I_{\text{rated}} \] Hence statement (4) is correct.

Step 6: Selecting the incorrect statement. The incorrect statement is: \[ \boxed{(3)} \]