25 MCQs On Transformers

25 MCQs on Transformers: set of 25 Transformer MCQs covering fundamentals, construction, EMF equation, losses, efficiency, voltage regulation, tests, impedance, and transformer ratings.

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Contents

25 Multiple-Choice Questions on Transformers

1. What is the basic working principle of a transformer?

A) Self-induction
B) Mutual induction
C) Electrostatic induction
D) Resonance

Correct Answer: B) Mutual induction

2. A transformer is primarily used to:

A) Convert AC into DC
B) Convert DC into AC
C) Increase or decrease AC voltage
D) Increase frequency

Correct Answer: C) Increase or decrease AC voltage

3. A transformer can operate on:

A) DC only
B) AC only
C) Both AC and DC
D) Pulsating DC only

Correct Answer: B) AC only

4. The frequency of the secondary voltage of a transformer is:

A) Higher than the primary frequency
B) Lower than the primary frequency
C) Equal to the primary frequency
D) Zero

Correct Answer: C) Equal to the primary frequency

5. Which part of a transformer provides a path for magnetic flux?

A) Insulation
B) Transformer oil
C) Magnetic core
D) Bushing

Correct Answer: C) Magnetic core

6. Transformer cores are generally made of:

A) Copper
B) Aluminium
C) Laminated silicon steel
D) Cast iron

Correct Answer: C) Laminated silicon steel

7. Why is the transformer core laminated?

A) To increase copper loss
B) To reduce eddy-current loss
C) To increase weight
D) To increase frequency

Correct Answer: B) To reduce eddy-current loss

8. The EMF equation of a transformer is:

A) $E = 2.22 fN\Phi_m$
B) $E = 4.44 fN\Phi_m$
C) $E = fN/\Phi_m$
D) $E = 4.44 N/\left(f\Phi_m\right)$

Correct Answer: B) E=4.44fNΦmE = 4.44 fN\Phi_m

9. A transformer that increases the output voltage is called a:

A) Step-down transformer
B) Step-up transformer
C) Isolation transformer
D) Current transformer

Correct Answer: B) Step-up transformer

10. In a step-up transformer:

A) Secondary turns are fewer than primary turns
B) Secondary turns are equal to primary turns
C) Secondary turns are greater than primary turns
D) There are no secondary turns

Correct Answer: C) Secondary turns are greater than primary turns

11. Transformer rating is generally expressed in:

A) kW
B) kWh
C) kVA
D) HP

Correct Answer: C) kVA

12. A transformer is rated in kVA rather than kW mainly because:

A) It has no losses
B) Its losses depend on voltage and current
C) It operates only at unity power factor
D) Its output power is always constant

Correct Answer: B) Its losses depend on voltage and current

13. Which of the following is a copper loss in a transformer?

A) Hysteresis loss
B) Eddy-current loss
C) $I^2R$ loss
D) Dielectric loss

Correct Answer: C) I2RI^2R loss

14. Core losses in a transformer consist mainly of:

A) Copper and mechanical losses
B) Hysteresis and eddy-current losses
C) Friction and windage losses
D) Stray load and copper losses

Correct Answer: B) Hysteresis and eddy-current losses

15. Which test is commonly used to determine core loss in a transformer?

A) Short-circuit test
B) Open-circuit test
C) Load test only
D) Polarity test

Correct Answer: B) Open-circuit test

16. The short-circuit test of a transformer is mainly used to determine:

A) Core loss
B) Copper loss and equivalent impedance
C) Frequency
D) Turns ratio only

Correct Answer: B) Copper loss and equivalent impedance

17. Transformer efficiency is given by:

A) Output power / Input power
B) Input power / Output power
C) Output voltage / Input voltage
D) Input current / Output current

Correct Answer: A) Output power / Input power

18. Maximum efficiency of a transformer occurs when:

A) Copper loss = zero
B) Core loss = zero
C) Copper loss = Core loss
D) Output power = zero

Correct Answer: C) Copper loss = Core loss

19. Voltage regulation of a transformer indicates:

A) Change in frequency
B) Change in secondary voltage from no-load to full-load
C) Change in primary current
D) Change in core flux

Correct Answer: B) Change in secondary voltage from no-load to full-load

20. The percentage impedance of a transformer is commonly expressed as:

A) Percentage of rated current
B) Percentage of rated power
C) Percentage of rated voltage
D) Percentage of rated frequency

Correct Answer: C) Percentage of rated voltage

21. If a 2400 V transformer has an impedance rating of 3%, its impedance voltage is:

A) 24 V
B) 48 V
C) 72 V
D) 120 V

Correct Answer: C) 72 V

Calculation:

$V_Z=\frac{3}{100}\times2400=72V$

22. If the impedance voltage is 72 V and the rated current is 90 A, the equivalent impedance is:

A) 0.4 Ω
B) 0.8 Ω
C) 1.2 Ω
D) 8 Ω

Correct Answer: B) 0.8 Ω

Calculation:

$Z=\frac{V}{I}=\frac{72}{90}=0.8\Omega$

23. An autotransformer has:

A) Two completely separate windings
B) A single continuous winding with a common portion
C) No winding
D) Only a secondary winding

Correct Answer: B) A single continuous winding with a common portion

24. Which device is used to measure very large AC currents safely?

A) Potential transformer
B) Current transformer
C) Autotransformer
D) Isolation transformer

Correct Answer: B) Current transformer

25. The main function of a transformer cooling system is to:

A) Increase frequency
B) Reduce voltage
C) Remove heat produced by losses
D) Increase magnetic flux

Correct Answer: C) Remove heat produced by losses

Quick Answer Key

Q.No.	Answer	Q.No.	Answer	Q.No.	Answer
1	B	10	C	19	B
2	C	11	C	20	C
3	B	12	B	21	C
4	C	13	C	22	B
5	C	14	B	23	B
6	C	15	B	24	B
7	B	16	B	25	C
8	B	17	A
9	B	18	C