Download D. Electric Motor Used in Sugar Mill

International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
Design of 215kW DC Motor for Centrifugal
Machine Used in Sugar Mill (IJSETR)
Sis Sis Soe

Abstract— In designing the DC machine with appropriate
performance characteristics, it is essential that the designer is
fully conversant with the typical performance of the machine
that is needed to improve the design of DC motor. The field of
direct current usage being very wide, DC machines is produced
both as generators and motors for a large range of output,
voltage, speed etc. DC motors offer many distinct economic and
technological advantages in special application like rolling mills,
overhead cranes, lifts, electric vehicles and electric trains. The
DC motor basically works on the principle that when a
conductor carry current is placed in a magnetic field,
mechanical force acts on the current carrying conductor, as a
result the conductor starts rotating in a direction depending
upon the direction of current and the field is given by Flemings’
left hand rule. The e.m.f induced in the armature of alternates
with a frequency of f, Hz depending upon the number of poles in
the machine and the speed of the armature.
Index Terms—400V DC Supply, Compound DC Motor,
Design Calculation, Sugar Mill
II. SUGAR MANUFACTURING PROCESS
A sugar mill is a large factory used to produce raw sugar
and other products from sugar cane. Mills are made up of a
range of industrial plant such as boilers, storage and
processing vessels, crushing and hammer mills and a large
range of maintenance equipment. Mills operate in two distinct
modes, crushing and non-crushing, both of which introduce a
range of specific and general hazards to PCBUs, workers and
others. In essence, a sugar mill can be broken into the
following processes (see Fig. 1, for a diagram that shows the
sugar milling process). Sugar manufacturing process consists
of;
1. Cane handling (Preparation of Sugarcane)
2. Milling house
3. Clarification and evaporation
4. The pan stage
5. The fugal stage
6. Final sugar
7. Energy supply systems
8. Associated operations
I. INTRODUCTION
DC motors comprise one of the most common types of
actuator designed into electromechanical systems. They are a
very straightforward and inexpensive means of creating
motion or forces.
Electric motors are an essential component of our industrial
society with no less than 5 billion motor, built world wide
every year. The most wage two types of motor are AC motor
and Dc motor. DC motors are widely used in many industrial
applications such as electric vehicles, steel rolling mills,
electric cranes, and robotic manipulators. The direct current
motor is one of the first machines devised to convert electrical
power into mechanical power. When a conductor carrying
current is placed in a magnetic field, force is developed in the
conductor. If a number of conductors connected in series are
placed on a cylindrical rotor and current is allowed to flow
through the conductors, a torque will motor, two magnetic
fields can be found, i.e. the field produced by the magnets and
the field produced by the current flowing through the
armature conductors.
DC motors are classified such as shunt motor, separately
excited motor, series motor, compound motor, permanent
magnet DC (PMDC) motor and so on. AC motors are divided
into two groups such as induction motor and synchronous
motor. In this paper we are designed for the compound DC
motor for the use of centrifugal machine at fugal stage.
Figure.1. Raw and Refined Sugar Process
A. Cane Handling
The main objective of cane preparation is shredder from the
cane with the help of machine power before milling to the
smallest cane chip and which is sending with preparation to
cane milling. Thus, this smallest cane chip can be milled from
milling machine one to milling machine four and get not only
more juice but also good mill extraction for factory.
The main ambitions of cane preparation are
1. To increase in bulk density
2. To increase in crushing capacity
Manuscript received Oct 15, 2011.
Sis Sis Soe, Deperment of Electrical Power Engineering, Mandalay
Technological University, (e-mail: [email protected]).
3. To improve in pol extraction
4. To improve in primary juice extraction
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All Rights Reserved © 2012 IJSETR
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
5. To perform proportion load on mills
6. To obtain higher efficiency of imbibitions
7. To reduce in hydraulic pressure and thus less power
consumption
8. To reduce wearing of mill rollers
The followings are used for cane preparation
1. Cane feed table
2. Cane carrier
3. Cane leveler
4. Cane knives (cane cutter)
5. Magnetic iron separator
6. Cane shredder
7. Elevator
B. Milling House
The milling process essentially involves the removal of
juice from sugarcane by squeezing the cane between pairs of
large cylindrical rolls in a series of milling units collectively
called a milling train, as show in Fig. 2. The first milling unit
in the milling train is generally identified as #1 mill; the
second milling unit is generally identified as #2 mill, and so
on. The last milling unit is generally called the final mill. The
milling units between the first and final mills are collectively
known as intermediate mills.
After passing through a pair of rolls and expressing juice,
the remaining sugarcane material is known as bagasse. Only
the first milling unit in the milling train processes prepared
cane. The remaining milling units process bagasse. After
being processed by a mill, bagasse typically consists of 30%
to 50% of fiber, 45% to 60% of water and a diminishing
quantity of brix as subsequent milling units process the
bagasse. Although prepared cane and bagasse are defined as
different materials, bagasse as a general term to collectively
refer to both prepared cane and bagasse.
water or juice added to the bagasse is called imbibitions
process, called compound imbibitions, is shown in Figure 3.
Imbibition water is added to the bagasse entering the final
milling unit at a rate that is typically 200% to 300% of the rate
of fiber passing through the milling train. The juice expressed
from the final milling unit is used as imbibition juice for the
second last milling unit. The juice from the second last milling
unit is then used as imbibitions juice for the third last milling
unit. This process continues back to the second milling unit.
After first passing through a juice screen to remove most
of the fiber in the juice, the juice from the first and second
milling units, called mixed juice, is taken away for processing
into sugar. The fiber removed in the juice screen, called cush,
is returned to the milling train, usually before the second
milling unit. The bagasse from the final milling unit is taken
away for further processing, typically for burning in the boiler
furnace.
C. Fugal Stage
A fugal is a large electric centrifuge which spins up to 1200
revolutions per minute dependent on its function and stage of
operation. There are two types of centrifuge in use within
sugar mills, high grade centrifuges (usually batch, but
sometimes continuous) and low grade centrifuges which are
continuous. Continuous fugal maintain a constant flow of
product through them while batch fugal fill, operate and then
discharge the final product.
The fugal stage removes the remaining liquid product
which surrounds the crystal, washes the crystal and delivers it
into the final sugar system through a series of conveyors and a
drier. The material removed during the centrifuge process is
known as molasses and has a range of uses including sale as
stock feed, fermentation for distillery production and as a
component of cattle licks.
D. Electric Motor Used in Sugar Mill
At sugar mill, electric motors are used for cane feed table,
cane carrier, cane leveler, cane knives, magnetic iron
separator, cane shredder, cane elevator, mill tandem and
centrifugal machine. The electric motors used for sugar mill
are wound-rotor induction motor with slip ring, squirrel-cage
induction motor and DC motors such as separately excited
motor, shunt motor and series. Especially, compound DC
motors are used for centrifugal machine at fugal stage.
III. COMPOUND DC MOTOR
Compound motors are a combination of series and shunt
motors. A compound motor has two field windings, one is a
series with the armature winding, and which is therefore made
of thick wire of few turns. The second winding is called the
shunt field winding and is joined in parallel with the armature
and is made of thin wire of many turns (Figure.3). The series
field winding is wound above the shunt field winding on the
same pole shoe. In a compound motor the major portion of the
flux is produced by the shunt field winding.
Figure.2. Schematic diagram of milling train
To aid in the extraction of juice from the much drier
bagasse, water or diluted juice is added to the bagasse before
it enters the milling unit in a process called imbibition. The
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All Rights Reserved © 2012 IJSETR
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
loadings before the derivation of output equation. For the
specific magnetic loading, equation (1) is used and for the
specific electric loading, equation (2) is used. For number of
conductors, equation (3) is used and derivation of output
equation, equation (4) is used. For gross length of armature
and armature resistance, equations (5) and (6) are used.
Equations (7) to (21) are used for resistance of winding, flux
frequency reversal, speed, electromagnetic torque and
efficiency of DC motor.
A. Design of Armature Winding
pφ
B av 
Figure.3.Connections of a compound motor
There are two types of compound motors according to the
manner in which their field windings produce field flux;
1. Differential Compound Motor, and
2. Commulative (or addative ) Compound motor
IV. DESIGN THEORY
As compared to rotating machine, the design of DC motor
is simpler, because of complex inter relations between
magnetic and electric circuit. The aim, in designing the DC
machine is to obtain the complete dimensions of various parts
of the machine as lute below, to furnish these data to the
manufacturer.
1. Main dimensions of the armature structure
2. Design details of the armature winding
3. Main dimension of the field system
4. Design details of the field winding
5. Design details of the commutator and brushes
6. Design details of inter poles and its winding
7. Performance characteristics i.e. iron losses copper
losses, mechanical losses, efficiency and maximum
efficiency
In order to determine the above design information, for the
DC motor, designer needs the following.
1. Detailed specification of the DC motor
2. Limiting value of performance characteristics like
iron losses, copper losses, efficiency
3. Design equation based pm which design procedure
is to be initiated
4. Information regarding availability of material for
various parts
The above information needed to carry out the design has
been discussed in subsequent articles. Hence the design of DC
motor is carried out based on given specifications, using
available materials economically and to achieve lower cost,
reduced size and better operating performance. Important
specifications needed to initiate the design are given below
(input design data). Type of field excitation; rated output
power; rated output voltage; speed; type of enclosure; type of
duty (short time, inter mitten, continuous); field excitation
voltage; maximum temperature rise. After that we can draw
good design and we can construct efficiency good DC motor
for our load.
V. DESIGN EQUATION OF DC MOTOR
Design equation expresses the relationship between the
output of the machine and the main dimension of the armature
in terms of specific magnetic and electric loadings. It is
essential to define the terms specific magnetic and electric
(1)
πDL
Where,
B = Average gap flux density, Tesla
P= Number of poles
Ø= gap flux per pole, Wb
D = diameter of armature, m
L = gross length of armature, m
av
 Ia 
 Z
A
q
(2)
πD
Where,
q = specific electric loading
I = armature current
a
E
PZN
(3)
60 A
Where,
E = supply voltage, V
N = number of speed,r.p.m
Z = number of conductors
A = number of parallel paths
Pa  E a  I a  10
3
(4)
Where,
Pa = output power
Pa
1
2
D L

Co
N
(5)
Where,
C0 = output coefficient=0.164Bavq×10-3
πD
L  Kp 
P
Where,
Kp = ratio of pole arc and pole pitch
Ra 
ρL c Z
ac

1
2
A
Where,
ρ = resistivity of material, ohm-mm2/m
Lc = length of conductors, m
ac = cross sectional area of conductor, mm2
NP
f 
120
Where,
f = flux frequency reversal, Hz
(6)
(7)
(8)
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All Rights Reserved © 2012 IJSETR
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
N
Eb
Kφ
(9)
Where,
Eb= induced voltage
K = constant
φ = flux per pole of motor, wb
Where,
θ =temperature rise of field system
Pf=losses of field system per unit cooling
surface, W/cm2
vA=peripheral speed of armature in m/sec
C. Design of Commutator and Brushes
πD
S
(10)
θ
slot pith
Where,
S= number of slots
Di=D-2hs-2dc
Where,
Di=internal diameter of armature
hs=depth of slots
dc=depth of armature core
θ
(11)
120  lossesin W/cm
2
(18)
1  0.1Vc
Where,
θ =temperature rise of commutator
vc=peripheral speed of commutator
load current
'
Ib 
pair of po le
250 to 300 p
(12)
1  0.09 VA1.3
Where,
Ib′=current per brush
Nb 
Where,
θ =temperature-rise of armature
P′=total armature iron and copper losses per
sq.cm of the cooling surface, w/cm2
vA=peripheral speed of armature, m/sec
(19)
'
Ab
(20)
Ab
Where,
Nb=number of brush per spindle
Ab′=total brush area per spindle
Ab=area of brush
B. Design of field Winding
R sh 
η
ρL mtf Tsh
a sh
(13)
Where,
Lmtf = mean length of the turns of shunt exciting
coil
Tsh = total turn of shunt field winding
Ash = cross sectional area of conductor
ATf
Tsh 
I sh
Ap
(14)
(15)
Lp
Where,
ATse= ampere turn of series winding
Ise = armature current, Ia
1400 to 1600  p f
θ
1  0.07 VA
 100
(21)
Where,
η = efficiency
Design results can get as shown in table (2) by using input
table (1) and specific magnetic loading equation (1), specific
electric loading equation (2) and output power equation (4)
and equations (5) to (21).To calculate the proper size with
input data rating, gap flux density, core flux density and
specific electric loading are assumed. Note that every flux
density values never exceed 2.2 Tesla. One DC motor can get
good efficiency by making starting torque may be rise to
higher value. The main important fact is to reduce m motor
losses.
TABLE I
INPUT DATA
Where,
Ap = gross area of pole
Lp = axial length of the pole
I Z
ATse  0.15 to0.2  a 
 2P 
output  losses
VI. DESIGN RESULTS
Where,
Tsh = total number of turn
ATf = total ampere turn of the exciting coil
Ish = shunt field current
bp 
output
(16)
Specifications
Symbol
Unit
Design Value
Motor output
Po
W
215×103
Terminal voltage
V
V
400
Speed
Type
N
-
r.p.m
-
1200
Compound
(17)
TABLE II
DESIGN RESULTS
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All Rights Reserved © 2012 IJSETR
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
Specifications
MAIN DIMENSIONS
-Armature diameter
-Gross Length
-Peripheral speed
-Flux frequency
-Pole pitch
-Flux per pole
ARMATURE WINDING
-Type
-Total armature conductor
-Number of slots
-Conductors per slot
-Resistance of winding
-Armature copper loss
FIELD SYSTEM
-Axial length of pole
-Breadth of pole
-Height of pole
SHUNT WINDING
-Cross sectional area
-Exciting current
-Number of turns
-Resistance
-Copper losses
SERIES WINDING
-Ampere turns
-Current
-Turns per pole
-Resistance
-Copper losses
INTER POLE WINDING
-Ampere turn for inter pole
-Turn on each inter pole
-Cross sectional area
-Depth of winding
-Resistance
-Copper losses
OVERALL
PERFORMANCE
-Armature copper losses
-Series field copper losses
-Interpole winding copper
losses
-Shunt field copper losses
-Iron losses
-Commutator brush
contact loss
-Commutator brush
friction loss
-Bearing friction and
windage loss
-Total full load losses
-Full load efficiency
-Tem. rise of armature
-Tem. rise of commutator
Design
Value
VII. CONCLUSION
Symbol
Unit
D
L
VA
f
τp
φ
m
m
m/sec
Hz
m
wb
0.48
0.247
30
40
0.377
0.0577
Z
S
Zs
ra
Ia2ra
ohm
kW
Lap
336
58
6
0.0116
4.13
Lp
bp
hp
m
m
m
0.232
0.198
0.23
ash
Ish
Rsh
-
mm2
A
ohm
kW
1.31
2.2
2402
147
0.711
ATse
Ise
Rse
-
A
ohm
kW
1194
597
2
0.00059
0.210
ATcp
-
7729
acp
dcp
Rcp
-
mm2
cm
ohm
kW
13
260
2.1
0.00166
0.593
[1]
-
kw
kW
kw
4.96
0.210
0.596
[7]
-
kw
kW
kw
0.711
3.052
1.184
-
kw
1.013
-
kw
2.15
η
θ
θ
kW
%
°C
°C
13.876
93.9
39
13.6
This paper deals with main design of DC motor used in
sugar mill and study of the various functions of DC motor. DC
motor is composed of two main parts such that field winding
and armature section. All designers can make proper design
and construct DC motor for milling train. When this
compound DC motor to compare with other motor, it can
more produce high starting torque in short time to reach
maximum value than other motors. The series field provides
better starting torque and the shunt field provides better speed
regulation. To choose motor, 400V supply voltage compound
DC motor is the most suitable DC motor for centrifugal
machine used in sugar factory.
ACKNOWLEDGMENT
Firstly, the author wishes express her deep gratitude to His
Excellency Union Minister Dr. Ko Ko Oo, Ministry of
Science and Technology, for opening the Special Intensive
Course Leading to Master of Engineering at Mandalay
Technological University. The author would also like to thank
Dr. Myint Thein, Rector of Mandalay Technological
University for his motivation, supports and guidance. The
author would like to express her heartfelt gratitude to her
Supervisor U Thet Naing Htun, lecturer of Mandalay
Technological university, for his kind advice, permission and
his encouragement throughout this paper. His valuable
suggestions have been greatly appreciated. The author also
greatly thanks to Dr. Khin Thuzar Soe, Head of Department of
Electrical Power Engineering of Mandalay Technological
University for her support and encouragement through out
this paper. After that the author always thanks all teachers
from Electrical Power Engineering Department because of
their guidance, encouragement and advices and suggestions.
REFERENCES
[2]
[3]
[4]
[5]
[6]
Charles L. Hubert, “Electric Machine, Theory, Operation,
Application, Adjustments, and Control”
A.E. Fitzgeralad, “Generalized Theory of Electrical Machines”
Mark A. Juds, Earl F. Richards and Willion H. Yeadon, “Hand book
of Small Electric Motor”
Mandalay Technological University, “Electrical Machines, 1999”
Dr V. N. MITTLE, “Design of Electric Machines”
Geoffrey Alan KENT, “Increasing the capacity of Australian raw
sugar factrory milling units, 2003”
Allbest Creative Development Ltd. (ALLBEST), “Sugar Mill”,
Beijing, China
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