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Code No: W0221/R07
Set No. 1
II B.Tech I Semester Regular Examinations, November 2009
(Electrical & Electronic Engineering)
Time: 3 hours
Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
? ? ? ? ?
1. With the help of neat diagram obtain the expression for the energy stored in a
magnetic system for a simple attracted armature type relay. Explain the operation
(a) Explain the role of brushes in DC machines. What is the material used for
brushes? What is importance of brush pressure on performance of machine?
(b) A armature is wound with lap winding and 8 poles. There are 72 slots on the
armature surface and 8 conductors per slot. If the resistance of one conductor
is 2 mΩ, find the resistance of armature. Neglect the resistance of overhang.
Find the value of EMF induced if flux per pole is 60mwb and generator is
rotated at 300 rpm.
(a) With a neat sketch explain the function of commutator in a d.c. machine.
(b) A 2-pole, 25KW, 220V wave-wound shunt generator has 400 armature con-
ductors. Brushes are given a lead of 4 commutator segments. Calculate the
demagnetization amp-turns/pole if shunt field resistance is 110Ω. Also calcu-
late extra shunt field turns/pole to neutralize the demagnetization.
4. What is critical speed? How do you calculate the critical speed in laboratory. 
(a) What are the reasons for the parallel operation of DC generators?
(b) What are the conditions necessary for parallel operation of DC shunt genera-
(c) Explain the procedure of parallel operation of DC shunt generators. [4+4+8]
(a) Differentiate between generator action and motor action of a DC machin