# Electrical Machines Questions and Answers – Ideal Two Winding Transformer

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This set of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on “Ideal Two Winding Transformer”.

1. Which of the following statements support the ideal transformer features?

```I. Zero winding resistance
II. Zero leakage flux
III. Constant core losses
```

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

Explanation: Ideal transformer has zero or very small core or copper losses.

2. Which of the following statements support the ideal transformer features?

```I. Zero winding resistance
II. Zero leakage flux
III. Negligible core losses
```
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a) I, II, III
b) III
c) I, III
d) I

Explanation: All the statements support the ideal nature of a transformer.

3. Which of the following statements support the ideal transformer features?

```I. Zero winding resistance
II. Constant permeability
III. Constant core losses
```

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

Explanation: Ideal transformer has constant permeability so that the magnetization of the core remains linear.

4. Which of the following statements support the ideal transformer features?

```I. Zero winding resistance
II. Constant permeability
III. Constant core losses
Iv. Zero leakage reactance
```

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

Explanation: An ideal transformer should be free from all types of losses and must have a linear magnetization of the core material.

5. Which of the following statements support the ideal transformer features?

```I. Variable winding reactance
II. Constant permeability
III. Constant core losses
```

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

Explanation: There should not be any leakage reactance of the winding so that leakage flux is zero and complete coupling takes place.

6. The voltage induced at the end of primary terminals of a two winding transformer consisting of N turns is?
a) -N*dϕ/dt
b) N*dϕ/dt
c) -dϕ/dt
d) -N*dt/dϕ

Explanation: Emf is induced based on the electromagnetic induction principle for N turns winding.
Explanation: In an ideal transformer, the induced emf lags the flux by 90degrees.

8. Consider a 2-winding transformer as below. If the switch is open then the emf induced across the load ‘Zl’ having transformation ratio of 2 is?
a) zero
b) V1
c) V1/2
d) 2*V1

Explanation: As the secondary switch is kept open, the voltage across load will be zero.

9. Consider a 2-winding transformer as below. If the switch is open then the emf induced across the secondary having transformation ratio of 2 is?
a) zero
b) V1
c) V1/2
d) 2*V1

Explanation: V2/V1 = 2
S, V2 = 2*V1.

10. Consider a 2-winding transformer as below. If the switch is kept open then the emf induced across the secondary having transformation ratio of ‘2’ is? a) zero
b) 2E1
c) E/2
d) E1

Explanation: The induced emf lags the flux by 90degrees.

11. Which of the following statement is true?

```I. Core flux in an ideal transformer remains constant.
II. Core flux is independent of the load current.
```

a) I
b) II
c) I,II
d) none of the mentioned

Explanation: Any changes in the secondary circuit of the transformer is reflected automaticaly in the primary winding so the net core flux remains constant.
Explanation: I2 will lag behind the V2 by the angle θ.

13. Which of the following assumptions about the transformer supports the fact that the instantaneous power input and output of a transformer is equal?

```I. Zero winding resistance
II. Constant permeability
III. Constant core losses
Iv. Zero leakage reactance
```

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

Explanation: If the impedance overall is zero for a transformer, then the losses ocurring in a transformer will be zero. So the efficiency is 100%.

14. Which of the following statements are incorrect for an ideal transformer?

```I. Voltages - inverse ratio
II. Current - direct ratio
III. Impedance - direct ratio squared
Iv. Power - remains same
```

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

Explanation: Voltages are transformed in direct ratio of the turns ratio. and current as inverse turns ratio.

15. Which of the following statements are correct for an ideal transformer?

```I. Voltages - Direct ratio
II. Current - Inverse ratio
III. Impedance - Direct ratio squared
Iv. Power - Remains same
```

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

Explanation: All the matches are correct.

16. Which of the following statements are correct for an ideal transformer?

```I. Voltages - inverse ratio
II. Current - direct ratio
III. Impedance - direct ratio squared
Iv. KVA - remains same
```

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

Explanation: Voltages are transformed in direct ratio of the turns ratio. and current as inverse turns ratio in a 2-winding transformer.

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