Design of Five Phase Induction Motor
Sanket M. Bhimgade#1 Swapnil C. Chaudhari#2 Roshan B. Durge#3 Vabeihrohnei Chozah#4 Parag P. Salunke#5
Department of Electrical Engineering
Dr. Babasaheb Ambedkar Technological University, Lonere, Raigad (MS - 402 103) sanketbhimgade@gmail.com , 2swapnil.28492@gmail.com , 3roshan.durge16@gmail.com , 4pawhrohnei@gmail.com ,

1

Abstract: The conversion of electrical energy into mechanical energy has been and continuous to be a dominant form of power transmission for industrial purposes. The alternating current (AC) electric induction motor has been an industry workhouse for electromechanical conversion for over 100 years. This paper introduces the fundamental electric and mechanical principles of 5 phase AC induction motor. In this paper, a generalized formula is proposed for the selection of number of slots required for 5-phase alternative current (AC) machine design and the criterion for selecting the starting points of each phases.
Keywords: Induction motor. Five phase, Stator winding.

current. The power per phase is P = VP IP cosϕ and the total power is the sum of the amount of power in each phase. If the currents are equal and the phase angles are the same as in Fig. 1, then the load on the system is balanced, the current in the neutral is zero and the total power is [1],
=3
cos ∅
Or
Or

= √3
= 1.73

cos ∅ cos ∅

I. INTRODUCTION
In general, the induction machines having three-phase windings are normally used, since the standard power supply is three phase. However, when fed by an inverter, there is no need for a fixed number of phases, some other phases being possible and advantageous. A multiphase machine can operate normally after loss of one or more phases. An important aspect of machines with a higher number of phases is their improved reliability, since they can operate even when one phase is missing. An increase in number of phase can result in an increase in torque/ampere relation for the same volume of the machine, such that five-phase machines can develop torque using not only the fundamental, but also using higher harmonics of the air gap field.
Multi-phase machines have attracted increased interest in recent years. This is due several advantages that they offer as compared to the conventional three-phase ones. In the presence of a power electronic converter which is needed for variables speed ac drive, the number of phases is essentially not restricted and multiphase machines are nowadays considered as potentially viable solutions for high power and high current applications. Apart from their applications in traction and electric ship propulsion, some investigation is going on for a more-electric aircraft concept, because of their fault tolerance which enables disturbance-free mode of operation in case of loss of one or more phases.

Fig. 1 Phase relationship between voltages and currents for 3 phase

B. Five Phase Supply:
The Phasor diagram for five phase system is shown in
Fig. 2. A, B, C, D and E are the five respective phases.

II. COMPARISON BETWEEN
THREEE PHASE AND FIVE PHASE SUPPLY
Fig. 2 Phase relationship between voltage and current for five phase

A. Three Phase Supply:
In star connected loads to a three phase four wire supply system, if VRN = VYN = VBN (R = red, B = blue, Y
= yellow, N = neutral) and they are equally spaced, then the system of voltage is balanced. Let VL be the voltage between any pair of lines (the line voltage) and VP = VRN
= VYN = VBN (the phase voltage), then VL = √3 VP and IL
= IP; where IL is the line current and IP is the phase

If VAN = VBN = VCN = VDN = VEN and they are equally spaced (i.e., 720 each phase), then the system of voltage is balanced. Let VL be the voltage between any pair of lines
(the line voltage) and VPh = VAN = VBN = VCN = VDN =
VEN (the phase voltage), then VL= √1.38 VPh or VL =
1.175VPh and IL = IP, where IL is the line current and IP is the phase current. The power per phase is P = VP IP cosϕ

and the total power is the sum of the amount of power in each phase. So,
=5
∅
Or
= 4.25
∅

C. Comparison between Three-Phase & Five-Phase
Supply:
Voltage relation for Three - Phase:
= √3 or = 1.73
Voltage relation for Five - Phase:
= √1.38 or = 1.17
Current relation for Three - Phase:
IL = Iph
Current relation for Five - Phase:
IL = Iph
For the Three – Phase balanced system, Power is given as:
= √3 cos ∅ or = 1.73 cos ∅
For the Five – Phase balanced system, Power is given as:
=5
∅ or = 4.25
∅
Hence it is observed that five phase power output is 2.46 times more than three phase power and 4.25 times more than single phase power

III. MECHANICAL DESIGN:
The stator is that part of the AC induction motor’s magnetic structure that does not rotate. It ontatins the primary winding and is made of laminations with a large hole in the centre in which the rotor can turn. There are slots in the stator in which the windings of the coils are inserted. The rotor is the rotating member of the AC induction motor and is made up of stacked laminations. A shaft run through the centre and a squirrel cage made of aluminium or copper bars holds the laminations together. The squirrel cage acts as one assembly of bars, endrings, and fan blades. The manufacturing process is controlled to produce a homogenous void-free rotor casting. Casting quality is controlled by using quality ductile aluminium and proper injection modelling techniques. Cast rotors provides three times faster conduction of heat form the bars to the laminated core than the copper bar rotors. The bars are in direct contact with the core, which allows for faster heat conduction. The rotor fan blades, which are cast integrally with the end ring and bars, prvide rapid heat dissipation to the air at the end of the rotor. This characteristics of rapid heat dissipation allows for acceleration of large iertia’s without thermal distortion and overstressing of the aluminium rotor cage.
A. Design of Stator:
1. Output Equation:
Output equation for AC machines is
=
Output coefficient
= 1.11 .
. . . 10
=

.

ℎ .∗ 0.746
=
cos( ) cos( )
Where D = armature diameter or stator bore, m;
L = stator core length, m;
=

ns = speed, r.p.s;
Bav = Average flux density, Wb/m2; η = efficiency; cos ( ) = power factor
2. Choice of Average Flux Density in Air Gap:
Power Factor:
The value of flux density in air gap should be small as otherwise the machine will draw the large magnetizing current giving a poor power factor. However in induction motors the flux density in air gap should be such that there is no saturation in any part of the magnetic circuit. Iron Loss:
An increased value of gap density results in increased iron loss and decreased efficiency.
Overload Capacity:
The value of air gap flux density determines the overload capacity. The high value of Bab means that the flux per pole is large. Thus for the same voltage the winding requires less turns per phase and if the number of turns is less the leakage reactance becomes small. With small leakage reactance the machine has the large overload capacity. Most induction motors have an overload capacity of twice its horsepower but as the speed gets lower and lower it is very difficult to get this capacity and still get a reasonable good power factor. There has to be a compromise between two.
For 50 Hz machine of normal design the value of Bab lies between 0.3 and 0.6 Wb/m2. For machines used in cranes, rolling mills etc. where large overload capacity is required value of 0.65 Wb/m2 is used.
3. Shape of Stator Slots:
The stator slots may be completely open or semienclosed. When open slots are used, the winding coils can be formed and insulated completely before they are inserted in the slots. Also the windings are reasonable accessible when individual coils must be replaced or serviced in the field. On the other hand the coils must be taped and insulated after they are placed in the slots for machines with semi-enclosed slots.
Semi-enclosed slots are usually preferred for induction motor because with their use the air gap contraction factor is small giving the small value of magnetizing current.
The use of semi-enclosed slots results in low tooth pulsation loss and a much quieter operation as compared with that of open slots. Therefore open slots are used where it is desirable to complete the coils outside the armature and drop them into the slots. An advantage of open slot is that their use avoids excessive slot leakage thereby reducing the leakage reactance.
4. Number of Stator Slots:
The following points help to serve as guidelines in the selecting the no of stator slots.
Tooth pulsation loss:
In motor with open type slots, the slot opening have a considerable influence on the air gap reluctance. The slot

should be so proportioned that minimum variations in the air gap reluctance are produced as effect of these variations produces tooth pulsation losses and noise.
These effects can be minimized by using large number of narrow slots.
Leakage reactance:
If there are large no of slots, there are larger no of slots to insulate. Therefore the width of insulation become more i.e. the leakage flux have the longer path through air which results in its reduction and hence leakage reactance is reduced. In fact the slot leakage reactance is inversely proportional to the no of slots per pole per phase. Also with small value of leakage reactance due to large no of slots the overload capacity of the machine increases.
Ventilation:
The larger the no of slots for a given diameter the smaller will be the slot pitch. If the slot pitch is small the tooth width is also small as small width of stator slot is generally about one half of the slot pitch of the gap circumference. So with large no of slots the thickness of the teeth become smaller and the teeth may become mechanically weak and they may have to be supported at the radial ventilation ducts by welding. This obstructs the flow of air in the ducts thereby impairing the cooling.
Magnetizing current and analysis:
Use of larger no of slots result in excessive flux density in the teeth giving rise to higher magnetizing current and higher iron losses.
Cost:
With large no of slots there are large no of coils to wind, insulate and install involving higher cost.It is good practise to use as many slots as economically possible.
However the no of slots per pole per phase should not be less than 2, otherwise leakage reactance becomes high.
The slot pitch at the air gap surface for open type of slots should be between 15 to 25 mm. for semi-enclosed slots the slot pitch may be less than 15 mm. the stator slot pitch is: gap surface πd y =
=
total number of stator slots
S
Where Ss is the number of stator slots. total no of stator conductors = 5 ∗ 2T = 10
10T
conductors per stator slot Z =
S
5. Area Of Stator Slots:
When the no of conductor per slot has been obtained an approximate area of the slot can be calculated. copper area per slot
Approx area of each slot = space factor
Z ∗a approx area of each slot = space factor
The space factor ordinarily obtained varies from 0.25 to 0.4. High voltage machines have lower space factors owing to large thickness of insulations.

6. Stator Teeth:
The value of flux density in the teeth is determined by the dimension of the stator slot. A high value of flux

density in the teeth leads to higher iron loss and a great magnetizing mmf which is undesirable. The maximum value of mean flux density (Bts) in the stator teeth should not exceed 1.7 Wb/m2 ϕ minimum teeth are per pole =
1.7
tooth area/ pole = no. ofslots/pole ∗ net iron length
∗ width of teeth.
S
= ∗ L ∗W
P
Minimum width of stator tooth ϕ (W ) min =
1.7 ∗ (S /p) ∗ L
A check for minimum tooth width using above equation should be applied before final deciding the dimension of stator slot.
7. Stator Core:
The flux density in the core should not exceed about
1.5 Wb/m2. Generally it lies between 1.2 to 1.4Wb/m2.
From figure it is clear that flux passing through stator core is half of the flux per pole. ϕ flux in the stator core =
2
area of stator core =

flux through core ϕ = flux density in stator core 2B

Area of stator core = Li + dcs where dcs = depth of stator core. Thus
L ∗ d d =

2

=

2

∗

Fig 3 – Stator Lamination Dimensions

Outer diameter of stator laminations:
D = D + 2(depth of stator slots + depth of core)
= D + 2d + 2d

8. Winding Design:
The winding used for induction motor stators are mainly double layer lap type winding with diamond shaped coils. Small motors with small number of slots and having large number of turns per phase may use single layer mush winding. The five phases of the winding are connected in star.
For a five phase AC machine the phase angle between any two consecutive phases is given as:

360
(elect. ) = 72 (elect. )
5
= 36 (mech. ); for 4 pole AC machine
In general, the numbers of slots required are
[20+10K] = 10 * [2+K] where K = 0,1,2,3… ϕ= Therefore per slot angle =

∗[

]

=[

(
]

ℎ. )

And required phase angle between any two consecutive phases in terms of slots =
= [2 + ]
.

If phase A starts from slot no. 1 then phase B will start from [2+k]th slot, phase C from 2*[2+K]th slot, phase D from 3*[2+K]th slot & phase E will start from 4*[2+K]th slot. In general for P number of poles of five phase AC machines, the numbers of slots required are
5
S = P[2 + K]slots where K = 0,1,2,3 …
2
Consider a 5 phase induction squirrel cage machine having the following data:
Power 5 HP
No. of Pole = 4
Frequency 50 Hz
Speed 1500 rpm.
Stator slots 30
Since it is possible to have a four-pole five–phase fractional slot-stator winding, the stator winding is a double-layer five-phase stator fractional slot winding. The stator has thirty (30) slots.

This connection algorithm can be expressed in a general form as q =
= = I + where M and d have no common divisor. Thus for a fractional slot winding:
i.
ii. iii. iv.
v.

Number of poles in a unit is d = 2
Number of slots per phase in each unit is
M = qd = 3
Number of total slots in each unit is mM = 5× 3 = 15
Number of units = = = 2 , which is the maximum number of parallel paths.
Each phase, in a unit, contains d − n groups of I coils each and n groups of I +1 coils each

Now, dividing the table in five vertical parts, each having (15/5) = 3 columns and 2 rows, and the mark the cross (X) in the upper left square and move from left to right continuously in every second square, the result is as shown in Table 1.
The sequence of coil groups is shown in Table 2, whereas Table 3.3 shows the distribution of slots in a unit.
Figure 3.2 shows a winding layout and Figure 3.3 shows a clock diagram of the stator winding.
Table 1: sequence of coil Groups
A D B E C A D

Phases

Winding Configuration:
The average number of slots per pole per phase, q , is given by q =
=
= in which 3 and 2 are the lowest pair of whole numbers, where Ss is the number of stator slots, P is the number of poles and m is the number of stator phases. As each pole phase groups must have an integral number of coils, q = = 1 , can only be obtained if the 2 (the denominator of q ) phase groups under 2 poles have different number of coils totalling up to 3 coils (numerator of q ).
Now 3 coils for each phase lying under 2 poles can be obtained, if we have one pole phase group of one coil and one pole phase group of two coils. This gives an average
∗
∗ value of q =
= 1 . Two poles make one basic unit of this winding. As this winding has four poles, there are two units of two poles, each covering three slots of each phase. The (1+1) = 2 pole phase groups of each phase in a unit must be connected in series and as there are 2 such units, the maximum number of parallel paths is equal to two (2), which is the same as the number of units.

No. of coils in phase group

2

1

2

1

2

1

2

Table 2: Distribution of slots in a Unit
Phase
Slots
A

1,2

9

D

3

10,11

B

4,5

12

E

6

13,14

C

7,8

15

Consider q in the form of 3/2, where the numerator and denominator have no common factor, we have
i.
number of poles in a unit = 2 (denominator of q ) ii. number of slots per phase in each unit = 3
(numerator of q ) iii. number of units = [total number of poles /
(poles/unit)] = [P/ denominator of q]
Considering the form,q = 1 we observe that there are
i.
2-1=1 group of 1 coil each and ii. 1 group of 1+1=2 coils each.

Fig 4: Layout out of Fractional Slot Winding

B

E

C

1

2

1

IV. ADVANTAGE OF FIVE PHASE
INDUCTION MOTOR:

REFERENCES:
1.

P.S.N. De Silva, J.E. Fletcher, B.W.Williams, “Design of Five
Phase Induction Motor using Flux Distribution Optimization”,
IEEE Transaction, pp – 331 - 335

2.

P.C.Krause, O.Wasynczuk, S.D.Sudhoff, “Analysis of Electrical
Machines and Drive systems.”, IEEE Press, A John Wiley & Sons,
Inc. Publication, Second Edition, 2002.

3.

A.K.Sawhney,
“Electical
Machine
Publications, pp. – 10.1 to 10.13

4.

Sosthenes Francis Karugaba, “Thesis on - Dynamics and control of
Five phase Induction machine”

5.

Edward J. Thornpton, J. Kirk Armintor, “The Fundamental of AC
Electric induction motor design and application”, Proceeding of the twentieth international pump users symposium, 2003, pp.95-106

6.

M. Rizwan Khan, Atif Iqbal, “Multiphase alternative current machine winding design”, International Journal of Engineering,
Science and Technology, Vol. 2, No. 10, 2010, pp. – 79-86

7.

K.P. Prasad Rao, B. Krishna Veni, D. Ravithej, “Five Leg inverter for five phase supply”, International Journal of Engineering Trends and Technology – Vol. 3, Issue 2, 2012

8.

Palak G. Sharma, S. Rangari, “Simulation of Inverter fed Five Phase
Induction Motor”, International Journal of Science and Research,
Vol. – 2, Issue 2, 2013

Some of the advantages of multiphase machines when compared to their three-phase counterparts are
1. Fundamental stator currents produce a field with a lower space-harmonic content.
2. The frequency of the lowest torque ripple component being proportional to 2m increases with the number of phases. 3. Since only two currents are required for the flux/torque control of an AC machine, regardless of the number of phases, the remaining degrees of freedom can be utilized for other purposes. One such purpose, available only if the machine is with sinusoidal MMF distribution, is the independent control of multi-motor multiphase drive systems with a single power electronic converter supply.
4. As a consequence of the improvement in the harmonic content of the MMF, the noise emanated from a machine reduces and the efficiency can be higher than in a three-phase machine. All multiphase variablespeed drives share a couple of common features.
5. For a given machine’s output power, utilization of more than three-phases enables splitting of the power across a larger number of inverter legs, thus enabling use of semiconductor switches lower rating.
6. Due to a larger number of phases, multiphase machines are characterized with much better fault tolerance than the three-phase machines. Independent flux and torque control requires means for independent control of two currents. This becomes impossible in a three-phase machine if one phase becomes opencircuited, but is not a problem in a multiphase machine as long as no more than (m − 3) phases are faulted.
V. APPLICATIONS:
Five phase induction motor is mainly used in special applications where high reliability is demanded.
It is used in,
1. Electric Vehicles and Hybrid Electric Vehicles
2. Aerospace applications in Electric aircraft
3. Electric ship propulsion
4. Railway Wagon Tippler
5. Locomotive trains and High Power applications.
VI. CONCLUSION:
This paper presents an approach for the design of five phase induction motor. It describes the design of stator i.e. determining the shape of stator slots, no of stator slots, and the other aspects and special attention to the designing the stator winding. The slot distribution and winding distribution for 5 phases is presented. Also the various applications of the 5 phase machine are listed.

Design”,

Dhanpatrai