Important MCQ on Transformers with Explanations

Practice important power transformer MCQs with detailed explanations. Improve your understanding of transformer principles, testing, losses, and protection.

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Power Transformer (40 Questions)

Question 1

A transformer works on the principle of:

A. Self induction

B. Mutual induction

C. Eddy current

D. Hysteresis

Question 2

The core of a transformer is laminated to:

A. Reduce copper loss

B. Increase flux

C. Reduce eddy current loss

D. Reduce hysteresis loss

Question 3

Transformer rating is expressed in:

A. kW

B. kVA

C. kVAR

D. HP

Question 4

In a step-up transformer:

A. Ns < Np

B. Ns = Np

C. Ns > Np

D. Voltage decreases

Question 5

Copper loss depends on:

A. Voltage

B. Current

C. Frequency

D. Flux

Question 6

No-load current of transformer is about:

A. 50% rated

B. 25% rated

C. 2–5% rated

D. 80% rated

Question 7

Core loss depends mainly on:

A. Load current

B. Voltage & frequency

C. Resistance

D. Temperature

Question 8

Ideal transformer has:

A. Zero copper loss

B. Zero core loss

C. No leakage flux

D. All of the above

Question 9

Efficiency of transformer is maximum when:

A. Copper loss = Core loss

B. Copper loss > Core loss

C. Core loss > Copper loss

D. Voltage is maximum

Question 10

OC test is conducted on:

A. HV side

B. LV side

C. Both sides

D. Any side

Question 11

SC test measures:

A. Core loss

B. Copper loss

C. Iron loss

D. Hysteresis loss

Question 12

Transformer frequency increase will:

A. Increase core loss

B. Decrease core loss

C. Not affect core loss

D. Burn transformer

Question 13

Transformer works only with:

A. DC

B. AC

C. Pulsating DC

D. Both AC & DC

Question 14

In core type transformer:

A. Windings surround core

B. Core surrounds windings

C. Only LV winding present

D. Only HV winding present

Question 15

Shell type transformer has:

A. Single magnetic path

B. Double magnetic path

C. No leakage

D. No loss

Question 16

Voltage regulation is zero at:

A. Unity PF

B. Zero PF

C. Leading PF (slightly)

D. Lagging PF

Question 17

Oil in transformer is used for:

A. Insulation

B. Cooling

C. Arc quenching

D. Both A & B

Question 18

Buchholz relay is used in:

A. Dry transformer

B. Oil transformer

C. Distribution line

D. Generator

Question 19

Tap changer is provided to:

A. Increase current

B. Change frequency

C. Control voltage

D. Reduce losses

Question 20

Turns ratio is defined as:

A. Vp/Vs

B. Ip/Is

C. Ns/Np

D. Np/Ns

Question 21

Transformer core is made of:

A. Cast iron

B. Copper

C. Silicon steel

D. Aluminium

Question 22

Leakage reactance causes:

A. Voltage drop

B. Core loss

C. Copper loss

D. Hysteresis

Question 23

Transformer with 100% efficiency is:

A. Practical

B. Ideal

C. Possible

D. Used in PSU

Question 24

Transformer oil BDV test checks:

A. Viscosity

B. Insulation strength

C. Temperature

D. Density

Question 25

Cooling type ONAN means:

A. Oil Natural Air Natural

B. Oil Natural Air Forced

C. Oil Forced Air Forced

D. Air Natural

Question 26

Per unit impedance is important for:

A. Efficiency

B. Fault calculation

C. Core loss

D. Turns ratio

Question 27

Guaranteed impedance is specified at:

A. 20°C

B. 75°C

C. 100°C

D. Ambient

Question 28

Short circuit current is inversely proportional to:

A. Voltage

B. Impedance

C. Current

D. Power

Question 29

In parallel operation, transformers must have same:

A. kVA rating only

B. Impedance only

C. Voltage ratio & impedance

D. Color

Question 30

Vector group Dyn11 indicates:

A. HV delta, LV star, 30° shift

B. HV star, LV delta

C. No phase shift

D. 60° shift

Question 31

Auto-transformer saves copper because:

A. Lower voltage

B. Shared winding

C. No leakage

D. No loss

Question 32

Zero sequence current cannot flow in:

A. Star with neutral

B. Delta winding

C. Grounded star

D. Zig-zag

Question 33

Magnetizing current is:

A. In phase with voltage

B. 90° lagging

C. 90° leading

D. 180°

Question 34

Eddy current loss ∝:

A. f

B. f²

C. V

D. I

Question 35

Hysteresis loss ∝:

A. f

B. f²

C. I²

D. V²

Question 36

Regulation is highest at:

A. Unity PF

B. Leading PF

C. Lagging PF

D. No load

Question 37

SC test voltage is about:

A. Rated voltage

B. 50%

C. 5–10%

D. 100%

Question 38

Core loss during SC test is:

A. Full

B. Half

C. Negligible

D. Maximum

Question 39

OC test gives:

A. Copper loss

B. Core loss

C. Leakage reactance

D. Efficiency directly

Question 40

Transformer tank is earthed to:

A. Increase efficiency

B. Reduce losses

C. Ensure safety

D. Improve cooling

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Power Transformer (40 Questions)

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