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Total Pages:2

Reg No.: Name:

APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY
THIRD SEMESTER B.TECH DEGREE EXAMINATION, DECEMBER 2017

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 What is the function of equalizer ring in a lap wound de machine? (5)

2 Derive the emf equation of a dc generator. (5)

3 What is starter? What is the necessity of starter in dc motor? (5)

4 Distinguish between core and shell type transformer? (5) 5 What is an auto
transformer? Derive an expression for the saving of copperin (5) an autotransformer as
compared to an equivalent two winding transformer?

6 Derive the condition for maximum efficiency of transformer. (5)

7 What are the necessary conditions for parallel operation of three phase (5) transformer?

8 What is the purpose of tertiary winding on transformer? (5)

PART 8
Answer any two full questions, each carries 10 marks.

9 With neat diagram explain the construction of 0൦ generator. (10)

10 a) A 250V short shunt compound generator is delivering 80A. Armature, series (5) and shunt
field resistances are 0.05Q, 0.03Q and 100Q respectively. Calculate the induced emf.

b) Define commutation. Explain the process of commutation with neat sketches. (5)

11 What are the effects of armature reaction on the operation of ‏عل‎ machine? What (10) are the

remedial measures taken to counter effects of armature reaction?
PARTC
Answer any two full questions, each carries 10 marks.

12 a) Explain with neat sketch how speed control of a 60 motor is done. (5) b) Draw the phasor
diagram of a single phase transformer supplying to inductive (5) load.

13 A 6 pole 250V series motor is wave connected. There are 240 slots and each (10) slot has 4
conductors. The flux per pole is 0.175mWb when the motor is taking 80A. The field
resistance is 0.05Q, the armature resistance is 0.1Q and the iron and frictional loss is 0.1kW.
Calculate (a) speed (b) BHP (c) shaft torque (d) the pull in newtons at the rim of the pulley
of diameter 25cm.

14 What are the different cooling methods used in transformer? (10)

PART D
Answer any two full questions, each carries 10 marks.
15 a) The following test results were obtained on a 20kVA, 2200/220V, 50112 single (5) phase

transformer
OC Test(LV side) 220۷ 1.16 125W
SC Test(HV side) 52.7V 8.4A 287W

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