Energy Losses in Transformer - UNSOLVED PRACTICE SET
Chapter: Alternating Current | Topic: Energy Losses in Transformer
ENERGY LOSSES IN TRANSFORMER - UNSOLVED PRACTICE SET
Topic: Energy Losses in Transformer
Multiple Choice Questions
Q1. The main cause of energy loss in a transformer due to alternating magnetic flux in the core is:
- Copper loss
- Eddy current loss
- Hysteresis loss
- Both (b) and (c)
Q2. Copper loss in a transformer is:
- Independent of load current
- Proportional to the load current
- Proportional to the square of the load current
- Inversely proportional to the load current
Q3. Eddy current losses in a transformer can be reduced by:
- Using a solid iron core
- Using a laminated core
- Increasing the frequency
- Decreasing the number of turns
Q4. Hysteresis loss in a transformer core is minimized by using:
- Soft iron core
- Steel core
- Copper core
- Aluminium core
Q5. The efficiency of a transformer is given by
- Output power / Input power
- Input power / Output power
- (Output power − Losses) / Input power
- Copper loss / Iron loss
Q6. At no load, the main loss in a transformer is:
- Copper loss
- Eddy current loss
- Hysteresis loss
- Both (b) and (c)
Short Answer Questions
Q7. Name the three main types of energy losses in a transformer. Which of these is load-dependent?
Q8. What are eddy currents? How do they cause energy loss in a transformer and how can this loss be minimized?
Q9. Explain hysteresis loss in a transformer. Why is soft iron preferred over steel for the transformer core?
Q10. Distinguish between copper losses and iron losses in a transformer. Which of these varies with load?
Q11. Why is the efficiency of a transformer very high compared to other electrical machines?
Q12. What is meant by 'flux leakage' in a transformer? How does it affect the efficiency?
Long Answer Questions
Q13. Describe the various energy losses that occur in a transformer. Explain the physical causes of each loss and discuss how each can be minimized in transformer design.
Q14. Explain why copper losses are called variable losses and iron losses are called constant losses. Derive the expression for the efficiency of a transformer and show that maximum efficiency occurs when copper loss equals iron loss.
Q15. Discuss the design features of an efficient transformer. How do laminations, choice of core material, and winding design contribute to reducing energy losses?
Numerical & Application-Based Problems
Q16. A transformer has an efficiency of 90% at full load. The primary voltage is 2000 V and the secondary voltage is 200 V. At full load, the secondary current is 50 A.
(a) Calculate the output power.
(b) Calculate the input power.
(c) Determine the total power loss in the transformer.
(d) If the copper loss at full load is 800 W, calculate the iron loss.
Q17. A 5 kVA transformer has iron losses of 50 W and full-load copper losses of 100 W.
(a) Calculate the efficiency at full load with unity power factor.
(b) Calculate the efficiency at half load with unity power factor.
(c) At what fraction of full load will the transformer have maximum efficiency?
(d) Calculate the maximum efficiency.
Q18. In your school's physics lab, a student is studying a small transformer used to power a 12 V, 24 W bulb from a 240 V AC mains.
(a) Calculate the turns ratio of the transformer.
(b) Calculate the current drawn from the mains when the bulb is operating at full brightness (assume 100% efficiency).
(c) The student measures the actual current drawn as 0.12 A and the bulb is slightly dimmer than expected. Calculate the actual efficiency of the transformer.
(d) The student then leaves the transformer connected to the mains with no load connected. After an hour, the transformer feels warm. Explain which losses are responsible for this heating and why.
(e) Large power transformers in India often use oil cooling. Explain why oil cooling is necessary and how it helps improve transformer efficiency.