ISSN: 2277-3754
ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 5, Issue 7, January 2016
Designing of Three Phase Squirrel Cage
Induction Motor for Good Efficiency
1
Jagdish Singh, 2Khushdeep Singh, 3Harleen Kaur
are induction motors. The minimization of electrical energy
consumption through a better design becomes a major
concern. The aim of this work is to give a further contribution
in the design of a three phase induction motor for good
efficiency. In this work a conventional three phase
squirrel-cage type induction motor with specifications 10 hp,
415V, star-delta connected and 4 poles is chosen for
comparison with our motor, which is designed for good
efficiency.
Abstract— squirrel cage induction motors are mainly
employed in almost all applications. They always operate at low
power factor which ultimately results in less efficiency. Different
methods are employed to raise the power factor of the induction
motors for maximizing efficiency. Instead of making
arrangements to improve efficiency, design of induction motor for
good efficiency is better option. The significance of this work is
highlighted by the recent concerns in the various publications
stressing on the importance of designing motor for good
efficiency. This work is introducing the designing of new three
phase squirrel cage induction motor with an objective of getting
good efficiency. A motor rating of 10 horse power, 415 volts with
1440 rpm and 4-pole is selected for design problem and an
equivalent circuit model is developed to find out the various
performance parameters like efficiency, starting torque, torque
developed, efficiency at full load, rotor copper losses, stator copper
losses etc in ‘matlab’ using graphical user interface tool. Then the
results are compared with a pre-existed motor having identical
power ratings and presented the same. It is observed that new
design gives more efficiency (90.156%) than the pre-existed
designed motor (87.907%). One important application of this
model is that with the help of this model we can analyze the
performance of squirrel cage induction motor having any rating.
This model also helps to find the optimum parameters required
for design.
Fig (1) Energy Consumption Chart of Different Motors
Index Terms—IM, good efficiency, SCIM, MATLAB, GUI,
design
II. THREE-PHASE INDUCTION MOTORS
Induction motor is simply an electric transformer whose
magnetic circuit is separated by an air gap into two relatively
movable portions, one carrying the primary and the other
secondary winding. Alternating current supplied to the
primary winding from an electric power system induces an
opposite current in the secondary winding, when the later is
short-circuited or closed through external impedance.
Relative motion between primary and secondary structure is
produced by the electromagnetic forces corresponding to the
power thus transferred across the air gap by induction. The
essential features which distinguish the induction machine
from other type of electric motors is that the secondary
currents are created solely by induction, as in transformer
instead of being supplied by a dc exciter or other external
power sources, as in synchronous and dc machines [20] .
I. INTRODUCTION
Although the design procedures for induction motors are
well established, there are some areas which require special
attention. The manual design of induction motor is the
combination of lengthy calculations and special attention.
[16] And in order to get acceptable results redesign procedure
is sometimes needed. The design features of an induction
motor are classified as constructional wise and performance
wise and results are combined. The squirrel cage induction
motors are 90% used in various industrial, domestic and
commercial applications. Particularly, the squirrel cage type
is simplicity, robustness and low cost, which has always made
it very good-looking and therefore, captured the leading place
in industrial sector. The average load factor of electric motors
in both industrial and tertiary sectors is estimated to be less
than 60%. However, in some industrial sector, the average
load factor for some motor power ranges can be as low as
25%. Individual motors in those ranges have even lower load
factors. Because the motor load factor is an average of motor
load during a period. As a result of its extensive use in the
industry, induction motors consumes considerable amount of
electrical energy [15]. Approximately 65-70% of electric
energy is consumed by electric motors and over 90% of them
III. DESIGN
Design of three-phase induction motor is very tedious task.
The art of design lies in suitable and economic distribution of
space to iron, copper, insulation, stator diameter, rotor
dimensions, windings and air-gap in the machine. Basically
the design of electric motor involves the study of the voltages
40
ISSN: 2277-3754
ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 5, Issue 7, January 2016
induced in the windings, the load currents and terminal Z1
Stator impedance
voltages under different loading conditions, the power Vth
Thevenin voltage
received or given out by the machine, the speed at which the Zsh
Shunt impedance
machine is running, frequency and the torque produced under Zth
Thevenin impedance
Io
No Load Current
different loading conditions [11].
P
Air-gap power
A. Nomenclature
ag
T
Developed torque
d
IM
Induction motor
P
Gross mechanical power
m
SCIM
Squirrel cage induction motor
P
Stator copper loss
c
(stator)
MATLAB Matrix laboratory
P
Rotor copper loss
cu
(rotor)
GUI
Graphical user interface
Qkva
Required input in KVA
L
Rotor Length
L
Net Iron Length
i
Is
Stator Current
g
Slots per Pole per Phase
Ts
Stator winding turns
Lmt
Length of Mean Turn
Es
Voltage per Phase
λs
Stator Slot Permeance
Kw
Winding Factor
Kd
Distribution Factor
P
Poles
Kp
Pitch Factor
Bav
Specific Magnetic Loading
Prot
Rotational losses
D
Stator bore diameter
M1
Newly designed motor
ac
Specific Electric Loading
M2
Existed motor
Co
Output Coefficient
Tst
Starting Torque
Cosϕ
Power Factor
Tmax
Maximum Torque
Wb
Weber
To
Output Torque
A
Amperes
Pout
Output Power
θm
Temperature rise
KVA
Kilovolt Amperes
HP
Horse Power Rating
Zs
Total Stator Conductors
B. Rating of Motor
Ss
Stator Slots
Power ratings = 10Hp, Operating speed = 1440 rpm,
Zss
Conductors per Stator Slots
Synchronous speed = 1500 rpm, Poles = 4, Frequency = 50
As
Area of Stator Conductors
Hz, Operating voltage = 415 Volts, squirrel cage rotor type,
δs
Current Density in Stator Winding
Starting = star–delta, Efficiency = 0.94, Power factor = 0.90
Ass
Area of stator slots
dss
Depth of Stator Slot
Table 1: Constraints Data
Wss
Width of Stator Slot
S.N
Constraint
Variables
Value selected
Lg
Length of Air Gap
o
values
Sr
Rotor slots
1.
Air-gap flux density 0.3-0.65 Wb/m2
0.45 Wb/m2
Ib
Current in Rotor Bars
m
Motor Phases
5000-45000
2.
Ampere conductors
20000 A/m2
A/m2
Kws
Stator Winding Factor
Ab
Area of rotor bar
3.
Winding factor
0.955
0.955
δb
Current Density in Rotor Bars
Lb
Length of Rotor Bars
Current density
4.
3-8 A/mm2
3 A/mm2
(stator)
Rb
Resistance of rotor bar
Nb
Number of Rotor Bars
Current density
5.
4-8 A/mm2
4 A/mm2
Cub
Copper Losses in Rotor Bars
(rotor)
Ae
Area of End Ring
End ring current
6.
4-10 A/mm2
4 A/mm2
Ie
End Ring Current
density
δe
Current Density in End Rings
7.
Air-gap length
0.35-0.70 mm
0.5 mm
Do
Outside Diameter of End Rings
Dr
Rotor diameter
8.
Ratio of L and Tau
1.5
1.5
Din
Inside Diameter of End Rings
Dm
Mean Diameter of End Ring
Re
Resistance of End Ring
C. Design Procedure
Cue
Copper Losses in Two End Rings
Design procedure consists of the following steps:
Im
Magnetising Current
1. Input Rating:
Z2
Rotor impedance referred to stator
Input rating in KVA=Hp×0.746÷(η×Cos )
41
ISSN: 2277-3754
ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 5, Issue 7, January 2016
These are also called as rotational losses. They are assumed to
D 2L=KVA÷  Co ×Ns 
be equal to 1% of the rated output power. These losses are
2. Stator Turns Calculation
actually ranges between 1.5 to 3% of the rated output. But by
Number of Turns per Phase Ts =Es ÷  4.44×K w ×f×m 
using roller and ball bearings these can reduce upto 1% of the
3. Stator Conductor
rated output power [15].
Total stator conductors  Zs  =6Ts
18. Development of Equivalent Circuit Model using Matlab
4. Stator Current per Phase
GUI: A standard equivalent circuit model of an induction
Stator Current Is =  KVA×1000  ÷ 3×Es 
motor is developed with the help of matlab software, and
presented the same. Then it is solved to form Thevenin
5. Stator Slots
equivalent circuit. This simplified equivalent circuit allows us
Stator slots Ss =g×m×P
to calculate the operating parameters for an induction motor.
Conductors in single slot Zss = 6T S
SS
6. Area of Stator Conductor
Area of Stator Conductor As =Is /δs
7. Area of Stator Slots
Area of stator slots Ass =  As ×Zss  ÷0.4
8. Air-gap Length
Length of air-gap Lg =0.2+2×  D×L 
0.5
9. Rotor Slots
Following rules should be satisfied while selecting rotor slots:
1. To evade cogging and crawling: (a) Sr ≠ Ss
(b) Sr –Ss ≠ ±3P
2. To shun synchronous hooks as well as cusps Ss – Sr ≠
±P, ±2P, ±5P.
3. To Avoid raucous function Ss – Sr ≠ ±1, ±2, (±P ±1),
(±P ±2)
Therefore, the possible stator-rotor slot combinations for four
pole machine are: 24/34, 36/28, 36/44, 36/45, 48/35, 48/38,
48/36, 48/40, 48/57, 60/38, 60/48, 60/76, 72/60
10. Rotor bar Current
The value of rotor bar current is calculated by the relation:
Rotor bar current Ib =  2×m×K ws ×Ts ×Is ×Cos  ÷Sr
Fig (2) Equivalent Circuit Developed in matlab
The subsequent equations were considered to compute the
fitness function:-
Per phase resistance of stator winding R1 =0.021×Ts ×Lmts
Impedance of rotor referring towards stator Z2 =  R 2 /S +jX2
Stator winding impedance Z1 =R1 +jX1
Thevenin voltage Vth =  V1×Zsh  ÷  Z1 +Zsh 
11. Area of Rotor Bars
Area of rotor bar Ab =Ib ÷δb mm 2
12. Copper Losses in the Rotor Bars
Length of the rotor bar Lb = L+Skewing allowance
Total copper losses in the rotor bars Cub = I b2×R b×N b
13. Area of Each End Ring
Current in each end ring Ie = Sr ×Ib  ÷(3.14P)
Area of each end ring Ae =Ie ÷δe
14. Mean Diameter of End Ring
Outer diameter Do =Dr –  2×Total depth of rotor slots 
Inner diameter Din =Do –  2×depth of end ring 
Mean diameter of end ring Dm =  Do +Din  ÷2
15. Total Rotor Resistance
Total resistance of the rotor R 2 =R b +R e
16. Magnetizing Reactance
Fig (3) Thevenin Equivalent Circuit Developed in MATLAB
No load rotor current Io = I1 –I2
Air gap power Pag =3R 2 ×I 22
Magnetizing or acoustic reactance Xm =Es ÷I m
17. Friction and Windage Losses
Developed Torque Td =Pag /δs
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ISSN: 2277-3754
ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 5, Issue 7, January 2016
Table 2: Parameter Required for Equivalent Circuit (Motor 1)
Gross mechanical power Pm = 1-S Pag
Stator copper loss Pcu (stator) =3Is2 R1
Magnetization current Im =Es ÷Xm
Rotor Copper loss Pcu (rotor) =3I 2 2 R 2
Efficiency =
Output power
Input power
IV. RESULTS
QKVA = 8.81 KVA
Output Coefficient Co= 94.06
D2L = 3.746×10-3 m
L = 1.1775D m
D = 0.147 m
L = 1.1775×.147 = 0.173 m
Net Iron Length Li = 0.155 m
Stator flux = 9×10-3 Wb
Number of turns Ts = 216 turns
Type of winding used: Wave Winding
Total Conductors Zs = 1296 Conductors
Stator slots Ss = m × P × g = 3×4×3 = 36 slots
Conductors per Stator Slot Zss = 36 Conductors
Stator Current per Phase Is = 7.07 Amp
Area of Stator Conductor As = 2.356 mm2
Approximate area per slot (Ass) = 213.84 mm2
Area of stator slots = dss × Wss
Take dss/Wss = 2
Width of stator slot Wss = 10.34 mm
Depth of stator slot dss = 20.68 mm
Length of mean turn Lmt = 0.851mm
Stator winding resistance R1 = 1.63
Stator slot permeance = λs = 1.642 Ώ
Stator Slot leakage reactance X2 = 1.742 Ώ
Skewing angle = 20o
Distribution factor Kd = 0.9597
Stator winding factor Kws =0 .9597
Air-gap length Lg = 0.5 mm
Rotor diameter Dr = 146 mm
Select Rotor Slots = 45
Rotor bar Current Ib = 175.86 Amperes
Length of rotor bar after skewing Lb = 0.184 m
Area of rotor bar Ab= 44 mm2
Total resistance of all rotor bars = 3.861×10-3 Ώ
End ring current Ie = 629.140 Amp
The value of current density in end ring is taken as 4 A/mm2
Area of each end-ring Ae =157 mm2
Outside dia. of end ring = 121 mm
Inside dia. of end ring = 91 mm
Mean dia. of end ring Dm = 106 mm
Total end rings resistance Re = 8.904×10-5 Ώ
Total rotor resistance Rr = 3.95×10-3 Ώ
Resistance of rotor referred to stator side R2 = 1.63395 Ώ
Total permeance coefficient of rotor slots = 1.53 Ώ
Permeance referred to stator side λsr = 1.224 Ώ
Rotor’s seepage reactance referred to stator side X2 = 1.294 Ώ
Magnetizing reactance Xm = 162.936 Ώ
Rotational losses = 1% of rated output = 74.60 watts
S.No
Parameters
Obtained
Values
1.
Stator resistance R1
1.63 Ώ
2.
Stator reactance X1
1.742 Ώ
3.
Rotor side resistance referred to
stator side R2
1.6339 Ώ
4.
Rotor leakage reactance referred
to stator side X2
1.294 Ώ
5.
Rotational losses Prot
74.60 Watts
6.
Magnetizing reactance Xm
162.936 Ώ
Fig (4) Snapshot of Equivalent Circuit of Designed Motor
(Motor 1)
Fig (5) Results of the Model for Motor 1
In the graph, torque-speed characteristics of the induction
motor are plotted with the help of gui.m tool of the matlab. In
these results starting torque, maximum torque, losses, current
on no-load etc. are calculated with the help of Thevenin
equivalent circuit. From the above graph, it is clearly visible
that designed motor exhibits a maximum efficiency of
90.156%.These results will be compared with the results of
same rated machine. Parameters of the existing motor (i.e
motor 2) necessary from the equivalent circuit point of view
for analyzing its performance are arranged in below table.
43
ISSN: 2277-3754
ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 5, Issue 7, January 2016
Table 3: Parameter Required for Equivalent Circuit (Motor 2)
Recorded
S.No
Parameters
Values
Stator resistance R1
2.05 Ώ
Stator reactance X1
1.68 Ώ
Rotor resistance referred to
stator side R2
Rotor leakage reactance
referred to stator side X2
1.826 Ώ
5.
Rotational losses Prot
149.20 Watts
6.
Magnetizing reactance Xm
201.65 Ώ
7.
Slip S
0.033
1.
2.
3.
4.
Table 4: Comparison of Two Motors Having Same Ratings
1.249 Ώ
S.N
o
Name of
Parameter
Designed
Motor (M1)
Existing Motor
(M2)
1.
Stator slots
36
36
2.
Rotor slots
45
44
2.
Turns per phase
216
240
3.
Conductor area
2.376 mm2
2.0106 mm2
Stator
resistance R1
Rotor resistance
R2
1.63 Ώ
2.05 Ώ
1.6339 Ώ
3.87 Ώ
4.
5.
6.
Magnetizing
reactance Xm
171.77 Ώ
201.65 Ώ
7.
Efficiency
90.156%
87.907%
24.22 N-m
18.093 N-m
89.305 N-m
84.219 N-m
106.833 N-m
96.668 N-m
8.
9.
10.
Torque
developed Td
Starting torque
Tst
Maximum
torque Tmax
Fig (6) Equivalent Circuit of Existing Motor (Motor 2)
Fig (8) Comparison Graph of Two Motors
V. CONCLUSION
Firstly designing of three phase squirrel cage induction
motor for good efficiency is done; an equivalent circuit model
is developed in matlab with the help of graphical user
interface tool, then comparison a comparison is performed
between newly designed motor and a conventional existing
motor. Newly designed motor shows higher efficiency
(90.156%) as compared to existing motor’s efficiency
(87.907%).
Fig (7) Results of the Model for Motor 2
The comparison between the two motors is also shown in the
graphical as well as in tabular form as:
44
ISSN: 2277-3754
ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 5, Issue 7, January 2016
[16] Vincent, Deepa and R, Bindu (2013) “Three Phase Induction
Motor Design in Windows Programming Platform”, IJEIT,
Vol. 3, Issue 1, July 2013.
VI. FUTURE SCOPE
In future scope this work can be extended as optimization
process for designing of three phase squirrel cage induction
motor. Improvement of existing designs of other motors for
good efficiency can be carried out. Finite element analysis of
the developed motor could be carried out instead of GUI
analysis. Different designs for getting high torques, lowest
manufacturing cost can be carried out.
[17] Www.mathswork.com/help/matlab/gui_developement.
[18] Www.wikipedia.org/wiki/inductionmotor.
[19] Yanawati .Y and Daut .I (2012) “Efficiency Increment on 0.35
mm and 0.50 mm Thicknesses of Non-Oriented Steel Sheets
for 0.5 Hp Induction Motor”, IJME, 2(2), pp. 1-5.
[20] Ansari A A and Deshpande D M (2010) “Mathematical Model
of Asynchronous Machine in MATLAB Simulink”,
International Journal of Engineering Science and Technology
(IJEST) Vol. 2(5), 2010, 1260-1267.
REFRENCES
[1] ALMEIDA and C.N, Leandro Jose (2010) “Analytical Method
for the Design of the Skewed Permanent Magnet Machines of
High Performance”, International Journal of Electrical and
Electronics Engineering (IEEE), 978-1-4244-5697.
AUTHOR’S PROFILE
[2] Baranwal, Aanchal and Chahal, Neeshu (2014) “Designing of
Three-Phase Induction Motor Using MATLAB GUI”, MIT,
IJEIT, Vol. 4, No.1, January 2014, pp. 42-44.
Jagdish Singh is a post graduate student of M.Tech (Power Engineering)
in Electrical Engineering Department of Guru Nanak Dev engineering
[3] Çunkas, Mehmet, (2008) “Intelligent Design of Induction
Motors by Multi-objective Fuzzy Genetic Algorithm”,
Springer 21: pp. 393-402.
College, Ludhiana (Punjab). He is currently pursuing M.Tech. in power
engineering, and have done his Bachelor’s degree from M.B.S.C.E.T,
Babliana, Jammu. Email jagdish.singh177@gmail.com, 094195-92307.
[4] Faiz, Jawad and Sharifian, B.B, Mohammad (2001) “Optimal
Design of Three Phase Induction Motors and their Comparison
with a Typical Industrial Motor”, ELSEVIER, 27, pp.
133-144.
Khushdeep Singh is Associate professor in Electrical Engineering
Department of GNDEC Ludhiana. He has nearly thirty years of teaching
[5] GG, Veinott (2011) “Theory and Design of Small Induction
Motors”, McGraw-Hill, USA.
experience. He obtained his M.E in power system from GNDEC Ludhiana.
[6] Lonel, Dan and Popescu, Mircea (2007) “Computation of Core
Losses in Electrical Machines Using Improved Models for
Laminated Steel”, IEEE, Vol. 43, No. 6.
Khushdeep_singh2000@yahoo.co.in
[7] MG, Say (2014) “Performance and Design of AC Machines”,
Pitman, London UK.
Electrical Engineering Department of Guru Nanak Dev Engineering College,
He
has
numerous
publications
to
his
credit.
Email
Harleen Kaur is currently a student of M.Tech (Power Engineering) in
Ludhiana (Punjab). She has done her bachelor’s in GNDEC Ludhiana.
[8] Moses, Tutkun. N (2004) “Localized Losses in Stator
Laminations of an Induction Motor under PWM Excitation”,
ELSEVIER, 161, 79-82.
[9] Murthy, S.S, Mohammad (2000) “Energy Conservation
through Improved Design of Induction Motor”, EED, IIT
Delhi, India.
[10] P, Beckley (2002) “Electrical Steels for Rotating Machines”,
IEEE, No. 37.
[11] Raghuram, A and Shashikala, V (2013) “Design and
Optimization of Three Phase Induction Motor Using Genetic
Algorithm”, IJACST, Volume 2, No.6, June 2013.
[12] S.J, Chapman (2005) “Electrical Machinery Fundamentals”,
McGraw Hill.
[13] Sawhney, A.K (2015) “A Course in Electrical Machine
Design”, Dhanpat Rai and Co, New Delhi.
[14] Simons and Kelly, D.O (1968) “Introduction to Generalized
Electrical Machine Theory”, McGraw Hill.
[15] Sivaraju, S.S and Devarajan, N (2011) “G.A Based Optimal
Design of Three Phase Squirrel Cage Induction Motor for
Enhancing Performance”, IJAET, Vol. II, Issue IV, pp.
202-206.
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