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Reg No.: Name:____ 02
APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY
THIRD SEMESTER B.TECH DEGREE EXAMINATION, APRIL 2018
Course Code: EE205
Course Name: DC MACHINES AND TRANSFORMERS (EE)
Max. Marks: 100 Duration: 3 Hours
PART A

Answer all questions, each carries 5 marks Marks

1 Point out the necessity of equalizer rings in a lap wound 60 machine. Why this is (5) not
applicable in wave wound machines

2 What is armature reaction and how it is eliminated in DC machines (5)

3 Compare the electrical and mechanical characteristics of a DC shunt motor with (5) those
of a DC series motor. Based on this point out the application areas of these motors.

4 What is the principle of operation of a transformer? Show how the flux is (5) balanced
when the transformer is supplying a load.

5 With supporting phasor diagrams, derive the expression for secondary side (5) voltage
regulation of a transformer for lagging and leading power factor loads.

6 What are the necessary and desirable conditions to be satisfied for parallel (5) operation
of two single phase transformers?

7 Distinguish the vector groupings Yy0, Dd0,Dy1,Yd11 in three phase transformer

(5) connections

8 Show how three phase power is obtained by using two single phase transformers (5)

connected in open delta.
PART B
Answer any two full questions, each carries 10 marks

9 For a 6 pole DC armature with 16 slots having two coil sides per slot and single (10) turn
coils, calculate the relevant pitches for a wave winding and draw the developed winding
diagram.

10 Draw the magnetisation characteristics of a DC shunt machine. Point out the (10)
conditions for voltage build- up of a DC shunt generator. Give the significance of the
terms critical resistance and critical speed as applicable to a DC shunt generator.

11 A short shunt compound DC generator supplies a current of 100۸ at 220%. If (10)

theresistance of the shunt field is 50 Q, of the series field is 0.02 Q, of the armatureis 0.05
६2, the iron and friction losses amount to 1K W. Find: i) The generated emf ii) The
copper losses iii) Output power of theprime-mover driving the generator iv) The
generator efficiency.

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