# Electrical Machines Questions and Answers – Open Circuit and Short Circuit Test

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This set of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on “Open Circuit and Short Circuit Test”.

1. Power required during the open circuit and short circuit test is?
a) losses incurring in the transformer
b) executing the power requirements by measuring instruments
c) power for the core losses only
d) all of the mentioned

Explanation: The power measured while conducting the tests is the winding losses and the core losses.

2. The open circuit test results in finding which of the following parameters?

```I. core losses
II. shunt branch parameters
III. turns ratio of transformer
```

a) I, II, III
b) I, II
c) II, III
d) I, III

Explanation: OC test gives the shunt branch parameters as well as the turns ratio by connecting a voltmeter at open circuited secondary terminals.
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3. The open circuit test results in finding which of the following parameters?

```I. core losses
II. shunt branch parameters
III. series parameters
```

a) I, II, III
b) I, II
c) II, III
d) I, III

Explanation: Series parameters are obtained by short circuit test results.
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4. Which of the following informations are obtained from short-circuit test?

```I. Ohmic losses at rated current
II. Equivalent resistance and leakage reactance
III. Core losses
IV. Voltage regulation
```

a) I, II, IV
b) II, III
c) I, II, IV
d) II, III, IV

Explanation: Core losses are found from OC test.

5. Which of the below estimations require results of both open circuit test and short circuit test?
a) Efficiency
b) Equivalent impedance of one side of the winding
c) Voltage regulation for exact circuit
d) All of the mentioned

Explanation: All the estimations asked will need results of both the tests.

6. To conduct the open circuit test, test is conducted on the _____________
a) l.v. side
b) h.v. side
c) primary
d) secondary

Explanation: OC test is performed on the l.v. side of the transformer because the l.v. winding will have lower stress on the insulation and no damage will occur.

7. To conduct the short circuit test, test is conducted on the ___________
a) l.v. side
b) h.v. side
c) primary
d) secondary

Explanation: To circulate the rated current in the winding, we should opt for lower value of the current so that winding will not damage.

8. A single phase transformer of 2200/220 V having rated l.v. current of 150 A has to undergo open circuit test on h.v. side. Which of the below instruments range should be used?
a) 6A, 200V
b) 150A, 22V
c) 60A, 220V
d) 6A, 20V

Explanation: Open circuit test is conducted on l.v. side, so the measuring instruments will be on the h.v. side.
So the current in the h.v. side will be around 3-6% of the rated.

9. A single phase transformer of 2000/200 V having rated l.v. current of 100 A has to undergo short circuit test on l.v. side. Which of the below instruments range should be used?
a) 200V,10A
b) 20V, 10A
c) 300V,100A
d) 200V,50A

Explanation: Short circuit test is conducted on h.v. side, so the measuring instruments will be on the l.v. side.
Rated current on the h.v. will be 10A and voltage will be around 5-12% to account for winding losses.

10. A single phase transformer of 2200/220 V having rated l.v. current of 150 A has to undergo open circuit test on h.v side. The instruments used are voltmeter of 200V and ammeter of 1A. Then the results ___________
a) will be wrong
b) will be accurate
c) of ammeter will burn
d) none of the mentioned

Explanation: The current in the h.v. winding will be around 10 A but the ammeter is of 1 A rating. So, it will burn off.

11. Which of the following conditions have to ensured for a short-circuit test?

```A. L.v. is short circuited
B. It helps in calculation of voltage regulation
C. It is performed at rated voltage
```

a) A, B
b) A, B, C
c) B, C
d) A, C

Explanation: For conducting short circuit test, l.v. winding is short circuited and it is not performed at rated voltage.

12. Which of the following conditions have to ensured for a short-circuit test?

```A. h.v. winding is short-circuited
B. It helps in calculation of voltage regulation
C. It is performed at rated voltage
D. l.v. winding is short-circuited
```

a) B, D
b) A, B, C
c) B, C, D
d) A, C

Explanation: For conducting short circuit test, l.v. winding is short circuited and it is not performed at rated voltage.

13. Transformers with high leakage impedance is used in ___________
a) arc welding
b) power distribution
c) power generating terminals
d) none of the mentioned

Explanation: The feature of the high impedance is extracted in the arc welding applications.

14. Which of the following conditions have to ensured for a open-circuit test?

```A. Performed on L.V side
B. Leakage impedance can be obtained
C. It is performed at rated voltage
D. It gives magnetizing impedance
```

a) B, D
b) A, B, C
c) B, C, D
d) A, C, D

15. Which of the following conditions have to ensured for a open-circuit test?

```A. Performed on L.V side
B. Leakage impedance can be obtained
C. It is performed at 10-12% of rated voltage
D. It gives magnetizing impedance
```

a) B, D
b) A, B, C
c) B, C, D
d) A, D

Explanation: Leakage impedance is not found from open-circuit test. And it is performed on the rated voltage to account for core losses.

16. Which of the following informations are not obtained from short-circuit test?

```I. Ohmic losses at rated current
II. Equivalent resistance and leakage reactance
III. Core losses
IV. Voltage regulation
```

a) I, II
b) II, III
c) I, II, IV
d) II, III

Explanation: Core losses are found from OC test and the voltage regulation is not obtained from one single test here.

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