C14 DIRECT CURRENT DC MACHINE Subject code : EE302
D.C.
MACHINES
Subject Title : D.C.
Machines
Subject
Code : EE302
Periods/Week : 04
Periods/Semester : 60
TIME SCHEDULE
Unit Test 1 Syllubus
Sl. No.

Major Topics

Periods

Weightage

Short Questions

Essay Questions

1.

Fundamentals
of D.C Generators

14

29

03

02

2.

Armature
Reaction and Characteristics of D.C Generators.

16

26

02

02


TOTAL

30

55

05

04

Unit Test 2 Syllubus
Sl. No.

Major Topics

Periods

Weightage

Short Questions

Essay Questions

1.

Fundamentals
of D.C Motors

12

26

02

02

2.

Speed
Control and Starters for D.C Motors

10

16

02

01

3.

Characteristics
and Testing of D.C Motors

8

13

01

01


TOTAL

30

55

05

04

UNIT TESTI
MODEL PAPERI
PARTA
NOTE
: Answer all questions
2 X 3=6
Each
question carries two marks
1. Write the working principle of DC generator.
2. Difference between lap and wave winding.
3. What is armature reaction?
PARTB
NOTE: Answer
any two questions
2 X 7=14
Each question
carries seven marks
4 . What are the essential part of dc generator and
explain.
5 .A shunt
generator delivers 200A at 250V.The armature and shunt field resistances
are
0.25ohm and 50 ohm respectively. The total stray losses
amounts to 900W.Calculate
a) Copper losses b) Commercial efficiency.
6. A 4pole lap wound dc Generator with 450 armature conductors supplies a
current of
150A.The brushes have been
displaced through 3 angular degrees from the geometrical
neutral axis. Calculate a) Demagnetising
AT/pole b) Cross magnetising AT/pole c)
The
additional field current for
neutralising the demagnetisation if the field winding has 1000
turns per pole.
UNIT TESTI
MODEL PAPERII
PARTA
NOTE :
Answer all questions
2 X 3=6
Each
question carries two marks
1. . State the Fleming’s right hand rule
2. Draw the schematic diagram of
separately excited dc generator.
3. Draw external characteristic curve
for a d.c shunt generator
PARTB
NOTE: Answer any two questions
2 X 7=14
Each
question carries seven marks
4. Derive the generated emf equation of a dc generator.
5. A short
shunt d.c generator supplies a current of 100A at a voltage of 220V.If the
Resistance of the shunt field is 50ohm,series field is
0.025ohm and armature is
0.05ohm.The total brush drop 2V and iron
and frictional losses amount to 1KW.
Find i)The Generated EMF ii)The CU losses
iii) The Generator efficiency.
6. .Describe various method to improve the commutation
UNIT TESTII
MODEL PAPERI
PARTA
NOTE :
Answer all questions
2 X 3=6
Each
question carries two marks
1. State the Flemings left hand rule.
2. State factor that affect the speed of a dc motor
3. What is meant by regenerative test
PARTB
NOTE :
Answer any two questions
2 X 7=14
Each
question carries seven marks
4. Derive the equation for armature torque and
shaft torque in D.C Motor.
5. A 200V
shunt motor has armature resistance of 0.04ohm and runs at 1000 rpm. When
the
armature current is 60A, if the torque
remains unchanged ,Find the speed and armature
current when
the field strength is reduced by 20% .
6. Explain
how break test is conducted on D.C shunt motor with a neat sketch and also
write
merits and
demerits of the test.
UNIT TESTII
MODEL PAPERII
PARTA
NOTE : Answer
all questions
2 X 3=6
Each question carries two marks
1. Why D.C series motor having high
starting torque?
2. State the necessity for starter in dc motor?
3. What are the disadvantages of
Swinburne’s test
PARTB
NOTE :
Answer any two questions
2 X 7=14
Each
question carries seven marks
4. A
250V,4pole shunt motor has wave wound armature with 600 conductors. The
armature
and
field resistance are 0.25ohm and 125ohm respectively and the flux per pole is
0.02weber.If the motor draws 15A from the
mains neglecting armature reaction,
Calculate i) Speed and torque developed in
the armature II ) Shaft torque when rotational
losses is equal to 300W
5. Draw the
schematic diagram of a 3 Point starter and Explain the working with protective
devices.
6. The Hopkinson’s test on two similar D.C shunt
machines gave the following results
Time voltage 220V
Time current excluding field current = 40A
Armature current of motoring machine = 200A
Field current of motoring machine = 6A
Field current of generating machine = 7A
Calculate the efficiency of each machine at
the given load conditions. The armature
resistances
of each of the machine is 0.05ohm
BOARD DIPLOMA EXAMINATIONS, (C14)
DEEETHIRD SEMISTER EXAMINATIONS
MODEL PAPERI
EE302 , D.C. MACHINES
Time:
3Hours Total
marks: 80
PARTA
NOTE: Answer all questions. 3 X 10=30
Each question carries three marks.
1. Write
about dynamically induced EMF?
2. Compare
Lap and wave winding in different aspects?
3. Draw the
separately excited D.C generator and name the parts?
4. List the
effect of armature reaction in D.C machines?
5. Draw the
external characteristic curve of a D.C shunt generator?
6. State the
Fleming’s left hand rule?
7. Why
series motor is having high starting torque?
8. State the
necessity of speed control of d.c. motor
9. State the
necessity of starter in d.c motor?
10. What is
meant by Regenerative Test.
PARTB 5 X 10=50
NOTE:
Answer any five questions.
Each question carries ten marks.
11. Explain
the working of simple loop D.C Generator?
12. A shunt
generator delivers 195A, at terminal p.d of 250V. The armature resistance and
shunt field resistance are 0.02ohm and
50ohm respectively. The iron and friction losses
equal 950 W .Find (i) Emf generated (ii) Copper
losses (iii) o/p of prime mover
(iv) Electrical efficiency?
13. Derive
the formula for Demagnetising AT/Pole & Cross magnetising A T/Pole for a
d.c
generator?
14. A 4pole
lap wound dc generator with 450armature conductors supplies a current of
150amps. The brushes have been displaced
through 3 angular degrees from the
geometrical neutral axis. Calculate (i)
Demagnetising AT/pole (ii) Cross magnetising
AT/pole (iii) The additional field
current for neutralising the demagnetisation is the field
winding has 1000 turns/pole?
15. (I)
explain the principle operation of D.C Motor with neat sketches?
(ii) Explain the significance of back
EMF in dc motors and its formula?
16. Explain
the different losses & power stages in d.c motor?
17. A 200V
shunt motor has armature resistance of 0.04ohm and runs at 1000 rpm, when
the armature current is 60A.If the torque
is unchanged; find the speed and armature
current when the field strength is
reduced by 20%?
18. Explain
how break test is conducted on d.c shunt motor with a neat sketch, also write
the merits and demerits of the test?
BOARD DIPLOMA EXAMINATIONS,
(C14)
DEEETHIRD SEMISTER
EXAMINATIONS
MODEL PAPERI
EE302 , D.C. MACHINES
Time: 3Hours Total marks: 80
PARTA
NOTE: Answer all questions. 3 x10=30
Each question carries three marks.
1. State the Fleming’s
right hand rule?
2. Define (a) Pole
pitch (b) Back pitch (c) Front pitch?
3. Draw the power
flow diagram of d.c generator?
4. State the causes
of sparking at brush of d.c generator?
5. List the
advantages of parallel operation of d.c generator?
6. A 4 pole 500V, shunt motor has 720 wave wound
armature conductors. The full load
armature
current is 60A, and the flux/pole is 0.03Wb.The armature resistance is 0.2ohm
and
the contact drop is 1V/Brush, Calculate the
full load speed of the motor?
7. State the
different losses in D.C motors?
8. State the
factors that affect the speed of a D.C motor?
9. Draw the
connection diagram for speed control of d.c.series motor
10. What are the
disadvantages of Swinburne’s Test.
PARTB 5 x10=50
NOTE: Answer any five questions.
Each question carries ten marks.
11. Explain the
construction of a dc generator with neat sketch?
12. . Classify the D.C generators based on excitation
along with voltage and current
equations, showing diagrammatically?
13. A100kw, 400V, 6pole dc shunt generator has a lap
wound armature with 36 slots and 28
Conductors
per slot. The shunt field resistance is 100 ohms. The brush is given a lead of
12°. Calculate the Demagnetising and
cross magnetising AT/Pole?
14. Explain O.C.C,
Internal and external characteristics of D.C Shunt generator?
15. (i) Classify
DC motors in to different types with figures of each. Also write voltage and
Current equation?
(ii) Derive an equation for armature
torque in dc motors?
16. (i) Derive the
condition for maximum efficiency of D.C motor?
(ii) A 220V, dc shunt motor takes 5A at
no load when running at 700r.p.m. the field
Resistance is 200ohms.aThe
resistance of armature is stand still gave a drop of 5V
Across armature terminals when
10Amps wave passed through it. Calculate (i) speed
on load (ii) torque in N.M (iii)
Efficiency.
17. Draw the schematic diagram of a 3point starter
and explain the working with protective
devices?
18. A 250V 15KW Shunt motor has a maximum efficiency
of 88% and a speed of 750 r.p.m
when
delivering 75% of its rated output. The resistance of its shunt field is 100ohms.
Calculate
the efficiency when the motor draws a current of 78Amp from mains?