D

Reg No.:_ Name:

THIRD SEMESTER B.TECH DEGREE EXAMINATION(R&S), DECEMBER 2019

Max. Marks: 100

b)

10

11 ஐ

b)

C192042 Pages:2

APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY

Course Code: EE205
Course Name: DC MACHINES AND TRANSFORMERS

Graph sheets shall be provided
PARTA
Answer all questions, each carries5 marks.
Dummy coils are not used in lap winding. Justify with suitable example

What is armature reaction? What are the effects of armature reaction on the
performance of 60 machine?
Derive the condition for gross mechanical power developed by motor is
maximum?
Draw the phasor diagram of a practical transformer under no-load condition.
Name the no-load components and write its equation.
A 11000/230V, 200kVA, 50Hz single phase transformer has core loss of 1200 W
and copper loss of 1700 W at full load condition. Find the load in kVA at which
maximum efficiency occurs?
What are the essential and desirable conditions to be satisfied for parallel
operation of single phase transformers?
What is vector grouping? Name the vector groups commonly used in three phase
transformers?
What is tertiary winding?
PART B

Answer any twofull questions, each carries10 marks.
There are 60 conductors in a 4 pole 60 machine. Whether lap winding or wave
winding is preferred? What type of coil arrangements needed in this armature
core?
i. ‏ولا‎ and ‏علا‎ should be odd number for simplex winding. Why?
ii. Find the back pitch and front pitch of a simplex 2-layer lap winding with 12
coils. Average pitch = 6, Resultant pitch = 2.
The open circuit characteristics of a dc shunt generator running at 850 rpm is
ivenbelow. ..._.

0 0.8 1.6 2.4 3.2 4
Calculate
i. emf to which the machine will excite, when the shunt field resistance 15 2262
1. emf when an additional resistance of 8Q is included in the shunt field circuit
111. shunt field resistance for a normal voltage of 100V
iv. Critical speed with shunt field resistance for a voltage of 100V
What is equalizer rings? Why it is generally used in lap windings instead of wave
windings?

A long shunt compound generator supplies a load at 250V. The load consists of
five motors each drawing 60A and a lighting load of 250 lamps at 100W each.
The armature, series field and shunt field resistances are 0.01, 0.02 and 75Q

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Duration: 3 Hours

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