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Theoretical Questions

1.   What is a transformer? How does it transfer electric energy from one circuit to another?
2.   Explain the principal of operation of a transformer.
3.   What is meant by transformer action? Under what conditions will it take place?
4.   If an alternating current is impressed on one coil, what will be the frequency of the induced voltage in another coil with which it is coupled?
5.   Enumerate the various kinds of transformers.
6.   Explain the need for stepping up and stepping down voltages in a power system. How does a transformer accomplish?
7.   Why are transformer windings divided into several coils?
8.   What properties should a good transformer oil possess?
9.   What purposes are served by placing transformers in oil-filled tanks?
10.                Why are the tanks of some large transformers corrugated?
11.                Write a short note on ‘transformer cooling’.
12.                Enumerate and explain briefly different types of windings.
13.                Derive an expression for induced e.m.f. in a transformer in terms of frequency, the maximum value of flux and the number of turns on the windings.
14.                Derive an expression for the e.m.f. of an ideal transformer winding.
15.                Explain the function of the active and reactive components of the no-load current of a static transformer.
16.                Why are some transformers constructed with primary and secondary windings divided into two halves?
17.                Distinguish between power and distribution transformers.
18.                Draw and explain the no-load phasor diagram for a single-phase transformer.
19.                Draw the vector diagram of a power transformer under full-load condition.
20.                What is meant by equivalent resistance of a transformer? How may it be calculated in primary terms and secondary terms?
21.                What is meant by the equivalent reactance of a transformer? How may it be calculated in primary terms and secondary terms?
22.                How can the equivalent impedance of a transformer be determined?
23.                Outline carefully the procedure for performing the short-circuit test.
24.                What useful information is obtained from the short-circuit test?
25.                Outline carefully the procedure for performing the open-circuit test.
26.                What useful information is obtained from open-circuit test?
27.                What are the two components of the core loss?
28.                How is the hysteresis loss affected by a change in flux density?
29.                Develop the equivalent circuit of a single phase transformer.
30.                Draw the equivalent circuit of a transformer and show how the constants of the primary and secondary windings may be combined to give a simplified equivalent circuit with the values of constants given in terms of the secondary winding.
31.                Describe the method of calculating the regulation and efficiency of a single-phase transformer by open circuit and short circuit tests.
32.                Distinguish between the ‘efficiency’ and the ‘regulation’ of a transformer. Show how power factor affects both of them.
33.                Explain with circuit diagram, the open-circuit and short-circuit tests to be carried out in the laboratory for the determination of the parameters of a single-phase transformer. Derive t7he condition for maximum efficiency.
34.                What is Sumpner’s test? Draw a circuit diagram to conduct this test and explain its principle.
35.                Define all-day efficiency.
36.                What is an auto-transformer? What advantages are possessed by auto-transformers?
37.                Derive an expression for saving of copper when an auto-transformer is used.
38.                State the applications of auto-transformers. Why is this transformer not used as a distribution transformer? Prove that for the same capacity and voltage ratio, an auto-transformer requires less copper than an ordinary transformer.
39.                What are the sources of heat in a transformer? Describe briefly the various methods used for cooling of transformers.
40.                To what does the ‘polarity’ of a transformer refer?