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COURSE PLANNER
SUBJECT: DESIGN OF DC MACHINE AND
TRANSFORMER [2160912]
B.E. – THIRD YEAR
Class – Electrical 2014
Term: 16/2 (DEC-16 to APR-17)
Faculty: Prof. P.D.SOLANKI Prof. P.T. PATEL
Prof. S.P.SHAH Prof. S.R.PATEL
CONTENTS:
1. Course Outcomes
2. Course Contents [Syllabus]
3. List of Reference Books
4. List of Experiments
5. Major Equipment Required for Experiments
6. List of Open Source Software and Learning websites required for experiments
7. Active Learning Assignment and Tutorial.
INSTRUCTIONS:
1. This set of Assignment-Tutorial consist the collection of questions of past GTU
Question papers.
2. Attend the questions which are frequently asked in GTU exams and/or the
questions which are Bold Marked.
3. Students should make a separate Chapter wise Files [Write in File Pages] to solve
these Questions.
4. Students must solve these given set of Assignments by themselves only.
5. Assessment of given assignment should be done regularly after completion of each
chapter by Students from the respective faculty members.
2
1. Course Outcomes
After learning the course the students should be able to:
1. Design the DC machine of given specifications.
2. Prepare the detailed sketches of the designed machines.
3. Prepare the detailed sketches of the designed machines.
4. Design the various parts of DC machine with magnetic and electrical specification.
5. Design the various parts of Transformer with magnetic and electrical specification.
3
2. Course Contents
[Syllabus]
Subject Code: 2160912
Subject Name: Design of DC machines and Transformer
Sr.
No
Topics Total
Hrs.
%
Weightage
1
GENERAL DESIGN ASPECTS:
Specific Electric Loading and Specific Magnetic Loading, Output Co-
efficient, Output Equations for Transformers and Rotating Machines,
Factor Affecting Size of Machines, Criteria for selection of Specific
Loadings, Heating and Cooling of Transformer and Rotating Machines.
6
20
2
DESIGN OF THREE PHASE TRANSFORMER:
Types of Transformers, Position of HV and LV windings and its
importance, Relation between core and yoke cross section area and its
significance, Different types of Transformer windings, Different
Positions of tapping, Window Space Factor, Factor Affecting Window
Space Factor, Relation Between EMF per turn and transformer rating,
Stacking Factor.
MAIN DIMENSIONS:
Design of Window Dimensions, Yoke Dimensions and Over All Core
Dimensions, Numerical Examples.
DESIGN OF WINDINGS:
Design of HV and LV windings (No. of turns and area of cross section),
Selection type of Winding.
PERFORMANCE PARAMETER ESTIMATION:
Primary and Secondary Winding Resistance and Leakage Reactance
Calculation, Calculation of No Load Current, Losses and Temperature of
Transformer, Design of Tank with Tubes, Calculation of Dimension of
Tank, Numerical Examples, Variation of Output and Losses in
Transformer with Linear Dimension, Basic Design Aspect of Dry
Transformer and High Frequency Transformer, Basic Design Aspect of
Welding Transformers and Instrument Transformer.
18
40
3 DESIGN OF DC MACHINES:
Introduction, Output Equation, MMF Calculation, Selection of Number
of Poles, Design of Core length and Armature Diameter, Carter’s
fringing curves and its significance, Design of Length of Air Gap,
Numerical Examples.
ARMATURE DESIGN:
Choice of Armature Winding, Armature Conductor, Number of
Armature Slot, Slot Dimension, Slot Loading, Design of Armature Core,
Numerical Examples,
18
40
4
DESIGN OF FIELD SYSTEMS:
Pole Design, Design of Field Winding of Shunt, Series and Compound
Machine, Design of Inter Poles, Effect and Minimization of Armature
Reaction, Design of Commutator and Brushes, Numerical Example,
Performance Parameter Evaluation.
5
3. List of Reference Books
1. A Course in Electrical Machine Design - A.K. Sawhney
2. Electrical Machine Design – R.K. Agrawal
3. Design of Electrical Machine – V.N. Mittle
6
4. List of Experiments
Sr.
No. Experiments
1 To Study About Insulating Material, Heating and Cooling of Machines.
2 DESIGN SHEET 01: Different Parts of DC MACHINE.
3 Theory and Tutorial on Three Phase Transformer Design – I.
4
DESIGN SHEET 02: Sectional View of THREE PHASE
TRANSFORMER Based on Numerical And Sectional View of SINGLE
PHASE TRANSFORMER without Measures.
5 DESIGN SHEET 03: Constructional and Sectional View of DC
MACHINE.
6 Theory and Tutorial on Main Dimensions and Armature Winding Design of
DC MACHINE.
7 DESIGN SHEET 04: Design Layout of CORE TYPE DISTRIBUTION
TRANSFORMER.
8 Theory and Tutorial on Three Phase Transformer Design – II.
9 Theory and Tutorial on Field Winding Design of DC MACHINE.
10 DESIGN SHEET 05: Design Layout of CURRENT TRANSFORMER.
7
5. Major Equipment Required For
Experiments
Lab set up following machines
1. Cut Section Model of a) Transformer b) DC Machine
2. Charts to Explain Various Parts of Machine
6. List of Open Source Software and Learning Websites
Required for Experiments
1. http://www.electrical-engineering –portal.com/
2. http://nptel.iitm.ac.in/courses.php
3. Virtual Lab Website www.vlab.co.in
8
7. Active Learning Assignment and Tutorial.
1. Preparation of Power Point Slides which Include Videos, Animation, Pictures and Graphics for
better Understanding theory and practical work. 2. Tutorial
Chapter-1 GENERAL DESIGN ASPECTS:
Specific Electric Loading and Specific Magnetic Loading, Output Co-efficient,
Output Equations for Transformers and Rotating Machines, Factor Affecting Size
of Machines, Criteria for selection of Specific Loadings, Heating and Cooling of
Transformer and Rotating Machines
ATTEMPT ANY THREE
Sr.
No. QUESTION YEAR
MARK
S
1 Write short note on classification of insulating materials.
Nov-11
June-14
DEC-15
07
2 Define specific electric and specific magnetic loading. Also
state advantages and disadvantages of these loadings. Nov-11 07
3 Prepare a technical note on classification of insulating
materials. May-13 07
4
Briefly explain cooling methods of transformer.
Explain diff. cooling methods used for oil immersed
transformer
May-13
Dec-14
DEC15
07
5 Write a Short Note on : Duty Cycle Dec-13
June-14 07
6 Explain how temperature rise affects the life of electrical
Machine? Also explain Intermittent with starting duty cycle Dec-14 07
7 Explain criteria for selection of specific loading May-16 07
8 Write a short note on heating of electrical machine. MAY-16 07
9 How area of core is affected by weight of copper and iron. MAY-16 07
9
ATTEMPT ANY EIGHT
Sr.
No. QUESTION YEAR MARKS
1
Derive equation Et = k√Q where Q = kVA rating of a
transformer. Explain how service condition of
transformer affect the value of K.
NOV-11
MAY-15
JUNE-
14
DEC-15
OCT-16
07
Derive output equation of 3 –Φ Transformer. Write the
significance of constant ‘K’. DEC-13 07
Derive the output equation of a 3-phase core type
transformer. JUN-12 07
Explain in brief the factors affecting the value of K in
the expression of volt per turn in transformer design.
𝑬𝒕 = 𝑲 𝑲𝑽𝑨
JUN-12 07
Chapter-2
DESIGN OF THREE PHASE TRANSFORMER:
Types of Transformers, Position of HV and LV windings and its importance,
Relation between core and yoke cross section area and its significance,
Different types of Transformer windings, Different Positions of tapping,
Window Space Factor, Factor Affecting Window Space Factor, Relation
Between EMF per turn and transformer rating, Stacking Factor.
MAIN DIMENSIONS:
Design of Window Dimensions, Yoke Dimensions and Over All Core
Dimensions, Numerical Examples.
DESIGN OF WINDINGS:
Design of HV and LV windings (No. of turns and area of cross section),
Selection type of Winding.
PERFORMANCE PARAMETER ESTIMATION:
Primary and Secondary Winding Resistance and Leakage Reactance
Calculation, Calculation of No Load Current, Losses and Temperature of
Transformer, Design of Tank with Tubes, Calculation of Dimension of Tank,
Numerical Examples, Variation of Output and Losses in Transformer with
Linear Dimension, Basic Design Aspect of Dry Transformer and High
Frequency Transformer, Basic Design Aspect of Welding Transformers and
Instrument Transformer.
10
2
Answer the following questions with respect to transformer
design. (Be brief and to the point).
(1) Explain the reason for using stepped core construction.
(2) If a designer selects higher value of flux density what
will be its effect on performance and cost of the
transformer?
(3) Why tapings are usually provided on the h.v. winding
side?
NOV-11
07
3 What is design optimization? Derive necessary condition
fordesigning a transformer with minimum cost.
NOV-11
DEC-15
MAY-16
OCT-16
07
4
Define : (1) Window space factor (2) Stacking factor. NOV-11 07
What is window space factor? Explain how it varies
with (i) KVA rating and (ii) KV rating.
JUN-12
DEC-13
DEC15
07
5
Discuss the importance of mitred joints in the core
assembly of transformers. NOV-11 07
Explain :
(a) Significance of mitered joints in transformer.
(b)Design difference between power & distribution
transformer
DEC-13
MAY-15
JUNE-
14
DEC-15
Oct-16
07
6
Obtain the expression of leakage reactance of a 3-phase
core type distribution transformer
JUN-12
MAY-15
OCT-16
07
Estimate the leakage reactance of concentric winding in
core type transformers clearly stating the assumptions
used.
DEC-12
DEC-13 07
7
Explain the steps involved to calculate no load current of a
3-phase transformer from its design data.
OR
From design data discuss how no load current can be
estimated in 3-phase core typ transformer.
JUN-12
MAY-16 07
8
Answer the following in respect to transformer design:
(i) Why cores are stepped?
(ii) Why yoke is designed for low flux density?
(iii) Why circular coils are preferred in transformer
winding?
JUN-12 07
Why yoke is designed for low flux density DEC-13 02
Why cores are stepped? DEC-13 03
11
Explain technical reasons for :
(1) Low flux density is selected for yoke of a three phase
transformer.
(2) Circular coils are preferred in transformer winding.
(3) Tappings are usually provided on h.v. side of
transformer.
MAY-13 07
9 From the design data discuss how no load current can be
estimated in 3 phase core type transformer. MAY-13 07
10
Transformer A and B are of same type and have equal
current density, flux density, frequency and window space
factor. Their linear dimensions are in the ratio of 2:1.
Prove that their losses will be in the ratio of 8:1.
MAY-13 07
11 Explain types of mechanical forces are developed in
transformer windings?
MAY-13
MAY-16 07
12
What is design optimization? Derive necessary
condition for designing a transformer with minimum
cost.
DEC-13
DEC-14
JUNE-
14
07
13
Transformer A and B are of same type and have equal
current density, flux density, frequency and window space
factor. Their linear dimensions are in the ratio of 2:1.
Prove that their losses will be in the ratio of 8:1.
JUNE-
14 07
14
Explain effect of change in frequency on losses, voltage,
leakage impedance, resistance of winding & losses on
transformer.
DEC-14
MAY-15
DEC15
07
15
Explain different types of windings used in core type
power transformer. MAY-15 07
List out diff. types of winding used in 3- phase
transformer with its voltage rating. Also explain
continuous disc type winding for 3- phase transformer.
DEC-14 07
16 Make a list of losses in transformer. Derive the condition
for maximum efficiency of transformer. MAY-15 07
17 Define Window Space Factor. Explain role of it to improve
transformer regulation . DEC-14 07
18 How will the output and losses in a transformer vary with
the linear dimensions.
MAY-15
MAY-16 07
12
EXAMPLES
ATTEMPT ANY SEVEN.
1
The tank of a 1.25 MVA natural oil cooled transformer
has the dimensions of 155cm x 65 cm x 185 cm (length,
width and height). The full load losses are 13100 watts.
Estimate the number of cooling tubes required for this
transformer. Assume: W/m2--0C due to radiation = 6
and due to convection = 6.5; improvement in
convection due to provision of tubes = 40%. ;
Temperature rise = 40 0C. ; Length of each tube = 1 m;
diameter of tubes = 50 mm. Neglect top and bottom
surfaces of the tank as regards cooling.
JUNE-
14 07
2
Determine the main core dimensions for a 250 KVA,
6600/500V, 50 Hz, 3-phase star/delta core type
transformer from the following data:
Window space factor = 0.27
Current density = 2.5 A/mm²
Max. flux density = 1.25 Wb/m²
Volts per turn = 8.5 V . Use 4-stepped core limb section
which has the area factor = 0.62
Height of window / width of window = 2
JUNE-
14 07
Determine the main core dimensions for a 250 KVA,
6600/500V, 50 Hz, 3-phase star/delta core type
transformer from the following data:
Window space factor = 0.27
Current density = 2.5 A/mm²
Max. flux density = 1.25 Wb/m²
Volts per turn = 8.5 V. Use 4-stepped core limb section
which has the area factor = 0.62
Height of window / width of window = 2
JUN-12 07
3
Design a 250 KVA, 2000/400 volt, 50 Hz , 1- phase, core
type oil immersed self cooledpower transformer with
following data:
Induced emf per turn = 15 Volt
Maximum flux density Bm = 1.25 wb/m2
Current density = 2.75 A/mm2
Window space factor= 0.3
Hght of the window Hw/ Width of the window Ww = 3
Assume 3 stepped core and Ai = 0.6 d2, a= 0.9 d
Determine the main dimension of yoke and core.
MAY-15 07
4
Calculate approximate overall dimensions for a 500 KVA,
6600 / 440 V, 50Hz, 3-phase core type transformer. The
following data may be assumed ;emf / turn= 10 V, max.
flux density = 1.3 wb/m2 , current density = 2.5 A/mm2,
window space factor = 0.3 , overall height = overall width,
DEC-14 07
13
stacking factor=0.9, Use 3 stepped core.
For core, width of largest stamping = 0.9 d and net iron
area= 0.6 d,
where d= dia. of circumscribing circle.
5
A 200 KVA, 6600/ 400 Volt, 3 phase core type
transformer has a total loss of 4800 W at full load. The
transformer tank is 1.25 m in height and 1 m ⤫ 0.5 m in
plan. Design a suitable scheme for tube if the average
temp. rise is to be limited to 35˚C. The diameter of tube is
50 mm and are spaced 75 mm from each other. The avg.
height of tube is 1.05 m. Specific heat dessipation due to
radiation and convection is respectively 6 and 6.5 w/m2
˚C. Assume that convection is improved by 35 % due to
provision of tube.
MAY-15 07
6
A 200 kVA, 6.6kV/440volts, 50Hz, three phase core
type transformer has the following design data:
Max. flux density : 1.25 wb/m2
Emf / turn : 10 volts
Stacking factor : 0.9
Window space factor : 0.32
Current density : 2.4 A/mm2
Overall width and overall height are same. If three
stepped core is used determine overall dimensions. Also
show them on a sketch.
NOV-11
MAY-16 07
7
Estimate the number of cooling tubes for a 250 KVA,
6600/400 V, 50 Hz, 3-phase delta / star core type oil
cooled transformer from the following data:
Temp rise = 50° C
Total losses at 90° C are 5.0 KW
Tank size = 125 x 100 x 50 cms. (h x l x w)
Oil level = 115 cms.
Sp-heat dissipation of plain tank = 12.5 W/m²/°C
Diameter of cooling tube = 5.0 cms.
Show the tube arrangement by sketch.
JUN-12 07
8
Estimate the per unit regulation, at full load and 0.8 power
factor lagging, for a 300 kVA, 50 Hz, 6600/400 V, 3
phase, delta/star, core type transformer. The data given is:
H.V. winding: outside diameter=0.36m, inside
diameter=0.29m, area of conductor=5.4mm2
, L.V.
winding: outside diameter=0.26m, inside diameter=0.22m,
area of conductor=170mm2
, Length of coils=0.5 m,
voltage per turn=8V, resistivity=0.21 Ω/m/ mm2
.
DEC-12
DEC-15 07
9
Calculate approximate overall dimensions for a 200
kVA, 6600/440V, 50 Hz, 3 phase core type transformer.
The following data may be assumed: emf per
turn=10V; maximum flux density=1.3 Wb/m2
, current
DEC-12 07
14
density=2.5 A/mm2
, window space factor=0.3, overall
height=overall width, stacking factor=0.9. Use a 3
stepped core.
For a 3 stepped core,
Width of largest stamping=0.9d and
Net iron area= 0.6d2
, where d=diameter of
circumscribing circle.
10
An 11 kV, 25 Hz transformer has I2R ,hystersis and eddy
current losses 1.6, 0.6 and 0.4 percent of the output. What
will be the percentage losses if the transformer is
connected to 22 kV, 50 Hz supply assuming the full load
current to remain the same?
DEC-12 07
11
A 40 Hz transformer is to be used on a 50 Hz system.
Assuming the Steinmetz’s coefficient as 1.6 and losses at
lower frequency 1.2%, 0.7% and 0.5% for I2R ,hystersis
and eddy current respectively. Find (a) losses on 50 Hz for
the same supply voltage and current (b) Output at 50 Hz
for the same total losses as on 40 Hz.
DEC-12 07
12
Estimate the main dimensions of complete core frame,
winding conductor areas and no. of turns of a 3-phase
core type delta-star transformer which is rated at 300
kVA, 6600/440 volts, 50 Hz. Use three stepped core with
the diameter of circumscribing circle of 0.25 m. Assume
volts/turn = 8.5 , current density of 2.5 A/mm2, window
space factor of 0.28 , stacking factor of 0.9 and height to
width ratio for window =3.
MAY-13 07
13
Find out main dimensions and number of armature
conductors for 350 KW, 440 Volts, 720 rpm, 6-pole D.C.
Generator. Assume square pole face, ratio of pole arc to
pole pitch 0.66, efficiency 91%, 4% of rated voltage for
brush drop. Use data obtained from the following machine.
250 KW, 500 Volts, 600rpm DC generator with 720 lap
connected armature conductors, 0.75m armature diameter
and core length of 0.3m.
DEC-13 10
14
Determine the main core & yoke dimensions for a 200
KVA, 50 Hz, 1-phase core type transformer. Window
space factor = 0.32 Current density = 3 A/mm² Max.
flux density = 1.1 Wb/m² Volts per turn = 14 V
Stacking factor = 0.9 Net iron area = 0.56*d2
Cruciform core with distance between adjacent limbs =
1.6 times width of core
DEC-13
DEC-15 07
15
A 40 Hz transformer is to be used on a 50 Hz system.
Assuming the Steinmetz’s coefficient as 1.6 and losses at
lower frequency 1.2%, 0.7% and 0.5% for I 2R ,hystersis
and eddy current respectively. Find (a) losses on 50 Hz for
the same supply voltage and current (b) Output at 50 Hz
for the same total losses as on 40 Hz.
DEC-13 07
15
16
Determine the main dimensions of the core for a 5 kVA,
11000/400 V, 50 Hz, single phase core type distribution
transformer. The net conducterrea in the window is 0.6
times the net cross section of iron in the core. Assume a
square cross-section for the core, a flux density 1 Wb/m2, a
current density 1.4 A/mm2, and a window space factor 0.2.
The height of window is 3 times its width.
OCT-16 07
17
The current densities in the primary and secondary
windings of a transformer are 2.2 and 2.1 A/ mm2
respectively. The ratio of transformation is 10 : 1 and the
length of the mean turn of the primary is 10 percent greater
than that of the secondary . Calculate the resistance of the
secondary winding given that the primary winding
resistance is 8 Ω.
OCT-16 07
16
Chapter-3
DESIGN OF DC MACHINES:
Introduction, Output Equation, MMF Calculation, Selection of Number of
Poles, Design of Core length and Armature Diameter, Carter’s fringing curves
and its significance, Design of Length of Air Gap, Numerical Examples.
ARMATURE DESIGN:
Choice of Armature Winding, Armature Conductor, Number of Armature Slot,
Slot Dimension, Slot Loading, Design of Armature Core, Numerical Examples,
DESIGN OF FIELD SYSTEMS:
Pole Design, Design of Field Winding of Shunt, Series and Compound
Machine, Design of Inter Poles, Effect and Minimization of Armature
Reaction, Design of Commutator and Brushes, Numerical Example,
Performance Parameter Evaluation.
ATTEMPT ANY EIGHT:
Sr.
No. QUESTION YEAR MARKS
1
Explain various factors affecting choice of Average flux
density and Ampere conductors per meter for D.C.
machine.
DEC-13
MAY-15 07
Discuss the factors affecting the selection of specific
magnetic and specific electric loadings in dc machine
design
JUNE-12
DEC-15 07
2
List the various losses occurring in DC machine. Also derive
the relationship between armature power developed (Pa) and
the output power (P) for both- DC generator and DC motor.
DEC-12 07
3 Derive the output equation of a D.C. machine and explain its
significance. DEC-12 07
4 Discuss the criteria for separation of D and L for d.c.
machine. NOV-11 07
5 Discuss factors to be considered while deciding the length
of air gap in the design of a d.c. machine.
NOV-11
MAY-15
DEC-14
DEC-15
OCT-16
07
6 Explain various factors affecting selection of number of
poles for D.C. machine
DEC-13
MAY-15
DEC-15
07
17
MAY-16
OCT-16
State the factors to be considered while selecting the
number of poles in the design of DC machine. DEC-12 07
7
Explain how the choice of number of poles in a d.c.
machine affects
(1) Losses in the machine
(2) Weight of machine
NOV-11
JUNE-14
07
Discuss the factors in brief how the number of poles
affects the weight of iron and weight of copper in dc
machine.
JUNE-12 07
8
Explain guidelines used for the selection of number of
armature slots in d.c. machine design.
NOV-11
MAY-15
JUNE-14
DEC-15
OCT-16
07
Explain guiding factors for choice of no of armature slots.
Also show the slot view with insulations. DEC-14 07
Explain various factors affecting selection of Numbers of
armature slots for D.C. machine. DEC-13 07
State the guiding factors while selecting the no. of
armature slots in DC machine. DEC-12 07
9 Discuss design procedure for designing a commutator and
brushes of a dc machine.
JUNE-12
JUNE-14
MAY-16
07
10
Explain how pole body height is fixed while designing field
system of a d.c. machine. MAY-13 07
Explain how pole body (shank) height is fixed while
designing field system of a dc machine. JUNE-12 07
11 Derive the expression of obtaining the number of coils of dc
machine armature from design parameters. JUNE-12 07
12
Explain steps to design shunt field winding of a d.c.
machine.
MAY-13
MAY-16
OCT-16
07
Discuss the steps for designing a shunt field winding of a JUNE-12
JUNE-14 07
18
dc machine.
13 Describe steps to calculate AT required for each part and
total magnetic circuit of a dc machine. JUNE-12 07
14 Explain the various steps while designing the DC machine, to
reduce armature reaction. MAY-15 07
15 With the help of neat sketch, explain the effect of
armature reaction on air gap flux in case of DC machine.
DEC-13
JUNE-14 07
16
Explain Commutation in dc machine. Explain how
interpole improves it ?
DEC-14
OCT-16 07
Describe the different methods adopted to reduce the
effect of armature reaction in DC machine.
DEC-12
DEC-14
DEC-15
OCT-16
07
17
Explain how following points affect the dimensions of slots
in a d.c. machine armature design.
(1) Excessive flux density
(2) Flux pulsations
(3) Eddy current losses
(4) Mechanical issues.
MAY-13 07
18 Describe steps to calculate AT required for each part and
total magnetic circuit of a D.C. machine. JUNE-14 07
19 Define Field Form Factor. Explain Carter’s Fringe Curve. DEC-14 07
20
Explain how following factors influence the main dimensions
of a d.c. machine.
(1) L/ζratio,(2) Peripheral speed,
(3) Moment of inertia,(4) Voltage between adjacent
segments.
MAY-13
DEC-15 07
21 The length of the air-gap is not uniform under the entire pole
face. Why it is so? MAY-16 07
22
Explain technical reasons for:
1.Circular coils are preferred in transformer winding.
2.Tapping’s are usually provided on H.V. Side of
Transformer
MAY-16 07
19
EXAMPLES
ATTEMPT ANY EIGHT.
1
A 4 pole generator supplies a current of 140 A. It has 480
armature conductors (a) wave connected, (b) lap
connected. The brushes are given an actual lead of 10°.
Calculate the cross and demagnetizing mmf per pole in
each case. The field winding is shunt connected and takes
a current of 10 A, find the number of extra shunt field
turns to neutralize the demagnetization.
DEC-12
DEC-13 07
2
Calculate the main dimensions of the armature of a 400
KW, 500V, 180 rpm, 16 poles dc generator. Use square
pole-face.
Efficiency = 90 %
Pole-arc to pole pitch ratio = 0.7
Average gap density = 0.6 Wb/m²
Ampere-conductors per metre = 35000.
JUNE-14
JUNE-12 07
3
Calculate main dimensions of 50 KW, 4-pole, 600 rpm, dc
shunt generator with full load terminal voltage 220 V. The
max. gap flux density is 0.83 wb/m2 and the specific electric
loading is 30,000.
Assume that the full load armature voltage drop is 3 % of
rated terminal voltage and field current is 1 % of rated full
load current. Ratio of pole arc to pole pitch is 0.67& pole
face is square.
DEC-14
OCT-16 07
4
The armature of 12 pole ,500KW, 550 V, generator has a
simplex lap winding consisting of 2484 conductors. There
are 621 commutator segments & ratio of pole arc to pole
pitch is 0.7.
(a) Calculate the demagnetizing & cross magnetizing
mmf / pole at rated full load current if brushes are shifted
through 3 segments from G.N.A.
(b) Calculate no. of conductors that must be provided in
each pole face if a compensating winding is used.
DEC-14 07
5
The following particulars refer to the shunt field coil for 440
V, 6 pole, dc generator.
mmf/ pole = 7000 A, depth of winding =50 mm, length of
inner turn = 1.1 m, length of outer turn = 1.4 m, loss radiated
from outer surface excluding ends =1400 W/m2, space factor
=0.62, resistivity = 0.02 ohm/ m &mm2
calculate :
(1) dia of wire, (b) length of coil (3) no of turns (4) exciting
DEC-14 07
20
current
Assume a voltage drop of 20 % of terminal voltage across the
field regulator.
6
A 400 kW, 500V,500 rpm, 6 pole d.c. generator is built with
an armature diameter of 90 cm and core length of 36 cm. The
lap wound armature has 700 conductors. Determine specific
magnetic and electric loading of the machine. Efficiency
80%
NOV-11
MAY-16
07
7
Determine main dimensions(D and L) of a 12 kW, 230V,
2 pole, 1500 rpm D.C. shunt generator if the required
data is : full load efficiency = 82% polearc/pole pitch =
0.63 avg. flux density = 0.4 Wb/sqr m. Ampere
conductors / m =19000. Machine is designed to have
square pole face.
NOV-11
MAY-15
07
8
Discuss the criteria for separation of D and L for d.c.
machine. The tank of a 1.25 MVA natural oil cooled
transformer has the dimensions of 155cm x 65 cm x 185 cm
(length, width and height). The full load losses are 13100
watts. Estimate the number of cooling tubes required for this
transformer. Assume: W/m2—0C due to radiation = 6 and
due to convection = 6.5; improvement in convection due to
provision of tubes = 40%. ; temperature rise = 400C. ; length
of each tube = 1 m ; diameter of tubes = 50 mm. Neglect top
and bottom surfaces of the tank as regards cooling.
NOV-11 07
9
The given details refer to the shunt field coil of a 440 volt , 6
pole d.c. machine.
Mmf per pole = 7200 A
Depth of winding = 50 mm
Length of inner turn = 110 cm
Length of outer turn = 140 cm
space factor = 0.6
resistivity = 0.02 Ω/m and mm2
loss radiated from outer surface excluding ends = 1400
W/m2 20% of the terminal voltage drops across the field
regulator. Determine: The diameter of wire, length of coil,
number of turns and exciting current.
NOV-11 07
21
10
Determine the main dimensions, number of poles and
length of air gap of a 600 KW, 500 V, 900 rpm dc
generator from the following data:
Average gap density = 0.6 Wb/m²
Ampere-conductors per metre = 35000
Pole-arc to pole-pitch ratio = 0.7
Gap contraction factor = 1.15
Diameter of armature core = 0.81 m
Length of armature core = 0.325 m
MMF for air-gap = 50% of armature mmf, =91 %
JUNE-12
DEC-12 07
11
Calculate the diameter and length of armature for a 7.5 kW, 4
pole, 1000 r.p.m. 220 V shunt motor. Given: full load
efficiency=0.83; maximum gap flux density=0.9 Wb/m2 ;
specific electric loading=30,000 ampere conductors per
meter ; field form factor=0.7. Assume that the maximum
efficiency occurs at full load and field current is 2.5% of
rated current. The pole face is square.
DEC-12
MAY-16 07
12
The following particulars refer to the shunt field coil for a
440 V, 6 pole, DC generator: Mmf per pole=7000 A; depth
of winding=50mm; length of inner turn=1.1m; length of
outer turn=1.4m; loss radiated from outer surface excluding
ends = 1400 W/m2
; space factor=0.62; resistivity= 0.02 Ω/m
and mm2
. Calculate (a) the diameter of wire (b) length of coil
(c) number of turns and (d) exciting current. Assume a
voltage drop of 20 % of terminal voltage across the field
regulator.
DEC-12 07
13
The output coefficient of a d.c. machine is 200 kVA/m3-
r.p.s..Its armature power (Pa) is 1000 kW and speed is
300 rpm. Determine main dimensions (D and L) of the
machine and also find main dimensions if:
(1) Specific loadings are decreased by 10% each without
changing speed.
(2) Speed is decreased to 150 rpm without changing
specific loadings.
Assume L/D ratio = 0.2 in all cases. Comment on your
answers.
MAY-13 07
14
Determine the main dimensions, no. of poles and the length
of air gap of a 500 kW, 500 V, 960 rpm d.c. generator.
Assume:
1. Bav = 0.58 wb/m2.
MAY-13 07
22
2. ac = 36000
3. Pole arc/pole pitch = 0.75
4. Efficiency = 90%
The mmf required for air gap is 50% of armature mmf and
gap contraction factor is 1.15.
Design constraints (limiting values):
1. Peripheral speed : 40 m/s
2. Frequency of flux reversals : 50 Hz
3. Current per brush arm : 400 A
4. Armature mmf per pole: 7500 A.
15
A 350 KW, 500 Volts, 450 rpm, 6 pole d.c. generator is
built with an armature diameter of 87 cm and core length
of 32 cm. The lap wound armature has 660 conductors.
Determine specific magnetic and electric loading of the
machine.
DEC-13 07
16
Find out armature demagnetizing & cross magnetizing mmf
per pole if brushes are given a lead of 90 electrical for a 500
KW, 375 RPM, 8 Pole, D.C. Generator with flux per pole of
88.5 mwb. Assume that the power developed
by armature is equal to rating of machine.
DEC-13 07
17
A 150 KW, 230 volt, 500 RPM, DC shunt motor square
field coil. Find the number of poles and main dimensions
and air gap length.
Assume the avg gap density over the pole arc is 0.85
wb.m2 and the ampere conductor per meter is 29000. The
ratio of width of pole body to pole pitch is 0.55 and the
ratio of pole arc to pole pitch is 0.7. The efficiency is 91
%. Assume that mmf required for air gap is 55 % of the
armature mmf and the gap contraction factor is 1.15.
MAY-15 07
18
A 100 kW, 500 V, 300 rpm generator has the main
dimensions. D = 1.5 m, L =0.4 m, flux density in the airgap =
1 Wb/m2 voltage drop at full load is 7 volts and from factor
kf = 0.7. calculateemf/conductor, number of conductors in
series, total flux.
MAY-16 07
