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Reg No.: Name:
APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY
Third Semester B.Tech Degree (S,FE) Examination January 2022 (2015 Scheme)

Course Code: EE205
Course Name: DC MACHINES AND TRANSFORMERS

Max. Marks: 100 Duration: 3 Hours
PARTA

Answer all questions, each carries 5 marks. Marks
1 Explain the role of dummy coils in the dc machine? (5)
2 Derive the e.m.f equation of a DC generator. (5)
3 What is the significance of back e.m.f in a DC motor? (5)
4 What is meant by an ideal transformer? Draw the phasor diagram of an ideal (5)

transformer on no load.

5 What are the losses in a transformer? How it can be reduced? (5)
6 Define all day efficiency of a transformer. What is done to improve the all-day (5)

efficiency of a distribution transformer?

7 Compare between a bank of 3 single phase transformers and a single unit of (5)
three-phase core type transformer.

8 Enumerate the purpose which detect the use of tertiary winding in a three- (5)
winding transformer.

PART ‏تا‎
‎Answer any two full questions, each carries 10 marks.

9 Explain the constructional features of dc machine with a neat diagram and (10)
explain the working of each part.

10 A short-shunt ‏عل‎ compound generator supplies a current of 100۸ at 220V. The (10)
resistance of the shunt field is 50Q, of the series winding 0.025Q and of the
armature 0.05Q. Iron and friction losses amount 10 1kW. Find (1) e.m.f generated
(ii) copper loss, (iii) the b.h.p of the prime mover (iv) commercial efficiency.

11 a) Explain the voltage build up in ೩ DC shunt generator. What are the conditions for (5)

voltage build up in a DC shunt generator?

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