Transformer Losses and Efficiency Free MCQ Practice Test with Solutions

Test: Transformer Losses and Efficiency - Question 1

The efficiency of a 20 KVA, 2000/200 V, single phase transformer at unity pf is 98%. The total losses at this condition is?

A.
408W
B.
4.08kW
C.
204W
D.
2.04kW

Detailed Solution for Test: Transformer Losses and Efficiency - Question 1

Efficiency = 1 - (losses/input) = 1 - (losses/output + losses)
0.98 = 1 - (Losses/20000 + losses)
Losses = 408 W.

Test: Transformer Losses and Efficiency - Question 2

Mutual flux __ at the lagging loading and it _ at the leading power factor.

A.
decreases, increases
B.
increases, increases
C.
decreases, decreases
D.
increases, decreases

Detailed Solution for Test: Transformer Losses and Efficiency - Question 2

The mutual flux falls when the transformer is working at lagging p.f. and it increases at leading p.f.

Test: Transformer Losses and Efficiency - Question 3

The full load voltage drop in a 1-phase transformer is 2% and 4% respectively due to resistance and leakage reactance. Then the voltage drop is zero at __________

A.
0.45 lagging
B.
0.45 leading
C.
0.9 lagging
D.
0.9 leading

Detailed Solution for Test: Transformer Losses and Efficiency - Question 3

Z = 4.47; cosθ = percentage x/percentage z = 4/4.47 = 0.89.

Test: Transformer Losses and Efficiency - Question 4

The efficiency of a 20 KVA, 2000/200 V, single phase transformer at unity pf is 98%. The given total losses at full load is 200 W. The pu resistance is?

A.
0.01
B.
0.1
C.
1.0
D.
0.0196

Detailed Solution for Test: Transformer Losses and Efficiency - Question 4

pu resistance = Ohmic losses/KVA = 200/20000 = 0.01 pu.

Test: Transformer Losses and Efficiency - Question 5

It is possible to attain maximum efficiency in a transformer when the ______

A.
core losses are equal to rated full load copper losses
B.
core losses are more than rated full load copper losses
C.
core losses and full load copper losses are constant
D.
copper loss also becomes constant

Detailed Solution for Test: Transformer Losses and Efficiency - Question 5

Maximum efficiency is achieved at the condition when fixed core losses and copper losses at rated condition are equal.

Test: Transformer Losses and Efficiency - Question 6

Which of the following mentioned losses occur in a transformer?

A.
Hysteresis losses; Eddy current losses; Dielectric losses; Stray load losses
B.
Hysteresis losses; Eddy current losses;
C.
Dielectric losses; Stray load losses
D.
Hysteresis losses; Eddy current losses; Stray load losses

Detailed Solution for Test: Transformer Losses and Efficiency - Question 6

Hysteresis losses-due to magnetic material; Eddy current losses-on the core area; Dielectric losses- due to insulation material; Stray load losses- due to leakage through the parts of the transformer.

Test: Transformer Losses and Efficiency - Question 7

Which of the statements made here are incorrect regarding the transformer?

I. Maximum voltage regulation occurs at the leading p.f.
II. Maximum voltage regulation occurs when load p.f. angle and impedance angle of the leakage impedance are same.
III. V.R. at zero p.f. is always zero.
IV. V.R. of a transformer may be negative at leading p.f.

A.
I, II, III
B.
IV
C.
I, III
D.
I, IV, III

Detailed Solution for Test: Transformer Losses and Efficiency - Question 7

Let's analyze each statement carefully:

Statement I:

"Maximum voltage regulation occurs at the leading power factor."

Voltage regulation ( $V.R.$ ) is a measure of the voltage drop in a transformer under load conditions. It is maximum at lagging power factors (e.g., inductive loads), not leading power factors.
At leading power factors, the voltage regulation can even become negative.

This statement is incorrect.

Statement II:

"Maximum voltage regulation occurs when the load power factor angle and impedance angle of the leakage impedance are the same."

This is true. The maximum voltage regulation occurs when the phase angle of the load current matches the impedance angle ( $\tan^{-1}(X/R)$ ) of the transformer.
This is because the voltage drop due to leakage reactance ( $IX$ ) and resistance ( $IR$ ) aligns with the load current, maximizing the overall voltage drop.

This statement is correct.

Statement III:

"Voltage regulation at zero power factor is always zero."

At zero power factor (purely reactive load), the voltage regulation is not zero. Instead, it is dominated by the reactive component of the impedance ( $IX$ ).
The voltage regulation at zero power factor is typically the highest because the reactive drop is maximum.

This statement is incorrect.

Statement IV:

"Voltage regulation of a transformer may be negative at leading power factors."

At leading power factors (e.g., capacitive loads), the reactive voltage drop ( $IX$ ) becomes negative, leading to a rise in terminal voltage rather than a drop.
Hence, voltage regulation can indeed be negative.

This statement is correct.

Summary of Correctness:

Statement I: Incorrect
Statement II: Correct
Statement III: Incorrect
Statement IV: Correct

Final Answer:

The incorrect statements are:

\boxed{\text{I and III}}

Test: Transformer Losses and Efficiency - Question 8

Which of the statements made here are correct regarding the transformer?

I. Maximum voltage regulation occurs at the leading p.f.
II. Maximum voltage regulation occurs when load p.f. angle and impedance angle of the leakage impedance are same.
III. V.R. at zero p.f. is always zero.
IV. V.R. of a transformer may be negative at leading p.f.

A.
I, III
B.
II, IV
C.
1, III
D.
I, IV, III

Detailed Solution for Test: Transformer Losses and Efficiency - Question 8

V.R. is always negative at leading p.f. and the load p.f. angle and impedance angle of the leakage impedance should be same for maximum V.R.

Test: Transformer Losses and Efficiency - Question 9

From the above graph of the core losses per cycle is, the eddy losses per phase for a transformer at a operating frequency of 40 Hz is?

A.
15 W
B.
20W
C.
35W
D.
32W

Detailed Solution for Test: Transformer Losses and Efficiency - Question 9

Pe = k2 * f²;
Using the slope of the line, (k2) * 50 = 0.8 – 0.5 = 0.3
(k2) = 0.006
Pe = 50*50*0.006 = 15 W.

Test: Transformer Losses and Efficiency - Question 10

The full load voltage drop in a 1-phase transformer is 2% and 4% respectively due to resistance and leakage reactance. Then the voltage drop is maximum at __________

A.
0.45 lagging
B.
0.45 leading
C.
0.9 lagging
D.
0.9 leading

Detailed Solution for Test: Transformer Losses and Efficiency - Question 10

Z = 4.47; cosθ = percentage r/percentage z = 2/(4.47) = 0.45.

Test: Transformer Losses and Efficiency - Electrical Engineering (EE) MCQ

10 Questions MCQ Test - Test: Transformer Losses and Efficiency

The efficiency of a 20 KVA, 2000/200 V, single phase transformer at unity pf is 98%. The total losses at this condition is?

Mutual flux __ at the lagging loading and it _ at the leading power factor.

The full load voltage drop in a 1-phase transformer is 2% and 4% respectively due to resistance and leakage reactance. Then the voltage drop is zero at __________

Statement I:

Statement II:

Statement III:

Statement IV:

Summary of Correctness:

Final Answer:

Top Courses for Electrical Engineering (EE)

Top Courses for Electrical Engineering (EE)

Schools

Competitive Examinations

Quick Access Links

Technical Exams

Important Questions for Transformer Losses and Efficiency

Transformer Losses and Efficiency MCQs with Answers

Online Tests for Transformer Losses and Efficiency

Test: Transformer Losses and Efficiency - Electrical Engineering (EE) MCQ

10 Questions MCQ Test - Test: Transformer Losses and Efficiency

The efficiency of a 20 KVA, 2000/200 V, single phase transformer at unity pf is 98%. The total losses at this condition is?

Mutual flux ______ at the lagging loading and it _____ at the leading power factor.

The full load voltage drop in a 1-phase transformer is 2% and 4% respectively due to resistance and leakage reactance. Then the voltage drop is zero at __________

Statement I:

Statement II:

Statement III:

Statement IV:

Summary of Correctness:

Final Answer:

Top Courses for Electrical Engineering (EE)

Top Courses for Electrical Engineering (EE)

Important Questions for Transformer Losses and Efficiency

Transformer Losses and Efficiency MCQs with Answers

Online Tests for Transformer Losses and Efficiency

Mutual flux __ at the lagging loading and it _ at the leading power factor.