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
View Answer
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
a) I, II, III
b) III
c) I, III
d) I
View Answer
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
View Answer
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
View Answer
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
View Answer
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
View Answer
Explanation: Emf is induced based on the electromagnetic induction principle for N turns winding.
7. Identify the phasor diagram for an ideal transformer at no load.
a) 
b) 
c) 
d) 
View Answer
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
View Answer
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
View Answer
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
View Answer
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
View Answer
Explanation: Any changes in the secondary circuit of the transformer is reflected automaticaly in the primary winding so the net core flux remains constant.
12. If it is happened to place an inductive load to a two winding transformer, then the phasor diagram for such a loading will be?
a) 
b) 
c)
d) 
View Answer
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
View Answer
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
View Answer
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
View Answer
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
View Answer
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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