Basics of Electrical Engineering
Question Bank
TO
EIE Department
UNIT-II
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Part – A ( 2 Marks excepted Questions):
1. What is the necessity of Transformer.
2. Write down the EMF equation of Transformer
3. What are different types of Transformers.
4. What is an Ideal Transformer
5. What are the properties of an Ideal Transformer
6. Draw the phasor diagram of an Ideal transformer on NO Load
7. How Eddy current losses can be reduced Transformer.
8. How Hysteresis losses can be reduced in a Transformer.
9. What is Voltage regulation of a Transformer?
10. What is the condition for maximum efficiency of a Transformer?
11. Why Transformers are rated in KVA?
Part – B ( 8 Marks excepted Questions):
12. Explain the principle of operation of a Transformer. .
13. Derive an expression for EMF of a Transformer.
14. What is an Ideal Transformer, what are its properties, Draw its phasor diagram on No load.
15. What is a practical Transformer, Explain its No Load and Load operation with Phasor diagram
16. Explain equivalent circuit of a Transformer with phasor diagram for different loadings.
17. Discuss losses in a Transformer, derive a condition for maximum efficiency of a transformer.
18. Explain Open circuit and Short circuit Tests of a Transformer?
19. How constant losses and variable losses obtained for a Transformer? Discuss.
20. Derive an equation for maximum current drawn and KVA drawn by a Transformer at its
maximum efficiency?
21. Draw equivalent circuit diagram of a Transformers, refereed to Primary and Secondary?
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Numerical Problems:
(1.) A 1-ф, 50 Hz transformer has 80 turns on the primary winding and 400 turns on the secondary
winding. The net cross – sectional area of the core is 200 cm2. If the primary winding is connected to
240V, 50 Hz supply, determine: (a) the EMF induced in the secondary winding, (b) The maximum
value of the flux density in the core.
(2.) A 1-ф, 50 Hz transformer 250 KVA, 11 kV/415V, has 80 turns on the secondary determine: (a) the
approximate value of the primary and secondary currents
(b) The approximate number of turns of primary
(c) The maximum value of the flux.
(3.) A 40KVA T/F 2000/250 V has R1 = 1.15 ohms, R2 = 0.0155ohms. Calculate
(i)total Resistance in terms of secondary side , (ii) Total Cu losses on Full load
(4.) A 350 KVA, single phase Transformer has constant losses of 1.8 KW, and full load copper
losses 2KW. Calculate (i) efficiency at full load at 0.8 lagging pf , (ii)KVA supplied at
maximum efficiency, (iii) maximum efficiency at 0.8 lagging pf
(5.) The efficiency of 200 KVA single phase Transformer is 98% when at full load 0.8 lagging
pf, while iron core losses of 2 KW, Calculate (i) full load copper losses, (ii) half load copper
losses, (iii) efficiency at half load.
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