2013 10th International Multi-Conference on Systems, Signals & Devices (SSD) Hammamet, Tunisia, March 18-21, 2013

SSOl13 1569708495

Performance Analysis of a Five Phase Induction Motor under Unbalanced Voltage Supply

Abdellah KoUZOU1,2, Payami. Saifullah3, Atif Iqbae,3, Haitham Abu-Rub2 IDepartment of Science & Technology, Faculty of Science & Technology, Djelfa University , Algeria

2Department of Electrical & Computer Engineering, Texas A&M University at Qatar, Doha, Qatar 30epartment of Electrical Engineering, Aligarh Muslim University, India

kouzouabdellah@ieee.org

Abstract- Multi-phase (more than three-phase) systems have

attracted much attention in the recent past both for power

transmission and electric drives applications. The supply from

the grid is prone to unbalance and also the winding structure

may have some inherent unbalance. Multi-phase systems are more sensitive to such unbalance supply conditions. Little effort has been put towards the study on the unbalance in the multi­

phase systems. This paper first proposes the different definitions

possible of unbalance factor in five phase system to carry out the unbalance studies. Then among these definitions two suitable

definitions has been selected to be used for further analysis. Where, The effect of these unbalance factors on the parameters like efficiency, power factor, and stator copper loss of a five

phase induction motor has been investigated and.

I. INTRODUCTION

Multi-phase (more than three phases) systems are shown to offer a number of advantages over their three-phase counterpart both in power transmission and electric drives. The feasibility study of multi-phase power transmission systems are investigated at length and few important references are [1-3]. Load balancing and power factor correction methodology is proposed in [4] for a twelve-phase power system. Specifically in variable speed electric drives the interface between the grid supply and the electric motor is the inverter. As such addition of the number of legs in an inverter is not constrained technically, and thus any of phases can be obtained from an inverter. This has led to the development of multi-phase drive systems. Detailed reviews on the state of the art in the multi-phase drives are reported in [5-9]. The most common phase numbers investigated in the literature are five and six. Unbalancing in three-phase supply system and its impact on the behavior of a three-phase induction machine is extensively studied in the literature [10-15], however, the same is not true for multi-phase systems, where some studies have been reported that the multi-phase machine does have some inherent structural unbalance[16-17]. O n the other side, the unbalance due to a loss of phase is investigated clearly in [18-19].

978-1-4673-6457-7/13/$31.00 ©2013 IEEE

To study the effect of unbalance in the supply voltage of a five phase system firstly the symmetrical components have to be defined and clarified, this has been thoroughly dealt in a previous work [20]. Based on the symmetrical components of five phase system various definitions have been proposed in this paper in concurrence with the three phase system, where the main aim is to clarifY the degree and nature of different unbalances and their effects on the operational behaviors of the machine.

n. SYMETRICAL COMPONENTS OF FIVE PHASE

UNBALANCED SYSTEM

It was proved by Fortescue that an unbalanced n-phase system can be formed of "n" balanced system called the symmetrical components of the original n-phase system. It is obvious that all these balanced systems have each, a set of "n" vectors corresponding to the "n" phases with the same magnitude and the angles between each two adjacent vectors

are eq ual to 27r / n. In this paper the discussion is confined to

a five-phase system. In a five-phase system there are two system of line voltage namely; adjacent line voltages and non-adjacent line voltage. Therefore, the symmetrical components for a 5-phase system can be defined as follows:

1. Adjacent Positive-sequence vA+ : these components have equal magnitude and each two adjacent components are displaced from each other by 72°, on the other side, they have the same phase sequence as the original unbalanced five-phase system, i.e. same as a-b-c-d-e if a-b-c-d-e is the original phase sequence.

2. Adjacent Negative-sequence VA- : these components have equal magnitude and each two adjacent components are displaced from each other by 72°, But they have an opposite phase sequence to the original unbalanced five-phase system, i.e a-e-d-c-b, if a-b-c-d-e is the original phase sequence.

3. Non-adjacent Positive-sequence VNA+ : they have equal magnitude and each two adjacent components are displaced from each other by 72°, on the other side, they have the same phase sequence as the non­adjacent original unbalanced five-phase system. i.e. a-c-e-b-d if a-b-c-d-e is the original phase

4. Non-adjacent Negative-sequence VNA-: they have equal magnitude and each two adjacent components are displaced from each other by 72°, on the other side, they have the opposite phase sequence as the non-adjacent original unbalanced five-phase system, i.e. a-d-b-e-c if a-b-c-d-e is the original phase sequence.

5. Zero-sequence vo: they have equal magnitude and are displaced from each other by 0°.

If the original components are considered as voltages, they may be designated Va, VI, Vc, Vd and Ve. The five sets of symmetrical components of component a, Val, Va2, Va3, Va4 and VaO can be obtained as follows [20]:

VO a va

vA+ I /3 /32 /33 /34 Vh a =.!. I VA- /34 /33 /32 /3 Vc (1) a 5

VNA+ /33 /3 /34 /32 Vd a VNA-a /32 /34 /3 /33 Ve

Where � is the operator which causes a rotation of 72° in the counterclockwise direction. This operator is a complex number of unit magnitude with an angle of 72° and is defined by :

f3 = IL'no = ej27f/5 = 0.3090+ )0.90511 (2)

TIT. TIT UNBALNCE FACTORS IN FIVE PHASE VOLTAGE

SYSTEM

Depending upon the different standards unbalance in the five phase system can be defined as it has been defined in the three phase system. Although no such definition is available in the literature, the definitions proposed in this paper are the logical extension of the existing ones of three phase systems.

1. Phase Voltage Unbalance Factor (PVUF): This definition is based on the IEEE definition for three phase system which is presented in IEEE standard (141), it is presenting the ratio of maximum voltage deviation from the average phase voltage magnitude to the average phase voltage magnitude. Similarly this factor can be defined for the five phase voltage system as follows:

Where:

max�Vavg - VallVavg - VhllVavg - VcllVavg - VdllVavg - ve il (3) PVUR=--�--�L---�----�--�----� Vavg

[va+Vh+Vc+Vd+V e] Vavg =

5 (4)

2

2. Line Voltage Unbalance Rate (LVUR): In three phase system it is defmed by National Electrical Manufactures Association (NEMA), the ratio of maximum voltage deviation from the average line voltage magnitude to the average line voltage magnitude. But in five phase system two types of line voltages are available. First is adjacent line voltage and second is non adjacent line voltage [21]. Depending upon the type of line voltages we can defme the unbalance in the NEMA pattern as Adjacent Line Voltage Unbalance Rate (ALVUR) and Non­Adjacent Line Voltage Unbalance Rate (NALVUR).

2.a. Adjacent Line Voltage Unbalance Rate (AL VURE): It is defined as the ratio of maximum voltage deviation from the average adjacent line voltage magnitude to the average adjacent line voltage magnitude.

where, Vavg

(5)

V = vah + vhc + vcd + vde + vea (6) avg 5

2.b. Non-Adjacent Line Voltage Unbalance Rate (NAL VUR): It is defined as the ratio of maximum voltage deviation from the average non-adjacent line voltage magnitude to the average non-adjacent line voltage magnitude.

NALVUR= max {Vavg - Vacl· IVavg - Vbdl· IVavg - Vcel, IVal'g - Vdal, IVmx - vehl} (7) Vavg

v: = /!;,c + Vhd + Vce + Vda + /!;,,, avg 5

(8)

3. Voltage Unbalance Factor (VUF): This is the lEe or Symmetrical Component Definition. For three phase system it is defined as the ratio of the magnitude of the negative sequence component of voltage to that of positive sequence component of voltage. In five phase system we have five symmetrical components out of which we have two positive sequence components, two negative sequence components and a zero sequence component. Adjacent positive sequence component has the largest magnitude, whereas the other sequence component has lower value so we can define the unbalancing in the above pattern as Adjacent Voltage Unbalance Factor and N on-Adjacent Voltage Unbalance Factor 3.a Adjacent Voltage Unbalance Factor (A VUF): It is defined as the ratio of the magnitude of the adjacent negative sequence component of voltage to that of adjacent positive sequence component of voltage. It is given by

Where:

AVUF = !:::.:..XIOO (9) VI

V]= Adjacent positive sequence component. V2= Adjacent negative sequence component

3.b. Non-Adjacent Voltage Unbalance Factor (NAVUF): It is defmed as the ratio of the magnitude of the non-adjacent negative sequence component of voltage to that of adjacent positive sequence component of voltage. It is given by

Where

NAVUF = V4 XI00 (10) VI

V 1= Adjacent positive sequence component. V 4=Non-adjacent negative sequence component.

4. Complex Voltage Unbalance Factor (CVUF): In three phase system this definition is similar to that of VUF; the difference is that the angles in addition to the amplitudes of VI and V2 have been included. In five phase system we can also define in the similar way as we have define the A VUF and N A VUF but instead of taking only magnitudes of symmetrical component we can consider their angle also. And based on this we can define the unbalancing as Complex Adjacent Voltage Unbalance Factor and Complex Non-Adjacent Voltage Unbalance Factor. 4.a. Complex Adjacent Voltage Unbalance Factor (CA VUF): It is defined as the ratio of the adjacent negative sequence component of voltage to that of adjacent positive sequence component of voltage. It is given by

Where,

CAVUF = V2 X100 VI

(11 )

VI= Adjacent positive sequence component with amplitude and angle. V2= Adjacent negative sequence component with amplitude and angle 4.b. Complex Non-Adjacent Voltage Unbalance Factor (CNA VUF): It is defined as the ratio of the non-adjacent negative sequence component of voltage to that of adjacent positive sequence component of voltage. It is given by

Where,

CA VU F = V 4 X100 VI

(12)

VI= Adjacent positive sequence component with amplitude and angle V 4= Non-adjacent negative sequence component with amplitude and angle To select the suitable definition for the determination of the degree of unbalances and their impact on five phase induction machine, unbalances in the different phases were created and then the different unbalance factors were calculated. It was observed that if the unbalance is created in only one phase, all the definition give a particular value among which PVUR gives the highest value for the same level of unbalance. Now when an unbalance is created in two phases, the PVUR gives the same value, even if these two phases are adjacent or non­adjacent, whereas ALVUR, NALVUR, AVUF and NAVUF give different values. O n the other side, it is well observed that if the two phases are adjacent, ALVUR and NA VUF are greater than NALVUR and AVUF. Contrary if the two phases are non-adjacent, N AL VUR and A VUF are greater than ALVUR and NA VUF respectively. When an unbalance

3

in three phases is occurred then two cases are possible. Firstly, all the three phases are adjacent to each other. Secondly the two phases are adjacent and one phase in non­adjacent to the two phases for example A,B and D or B, C and E. For these two cases PVUR gives the same value, whereas the other factors give different value. If the unbalance is occurred in four phases then only one case is possible and that is four phases are in sequence like, ABCD, BCDE etc. In this case, all the factors depend upon the degree of the voltage unbalance through the different phases in case. It is important to clarify that with angle unbalance only the PVUR is nil, while the other factors have different values. From the above discussions, it can be concluded that the degree of unbalance in the five phase system can be evaluated using the definition of ALVUR, NALVUR, AVUF and NAVUF, where the two factors AVUF and NAVUF are more accurate for presenting the degree of unbalance in the different cases. For the analysis of the impact of the five phase unbalance over the five phase induction machine presented in this paper, the definition of AVUF and NA VUF are used to clarify quantitatively the presence of the positive sequence components and the negative sequence components.

IV. PEFORMANCE OF A FIVE PHASE INDUCTION MOTOR

UNDER UNBALANCE VOLTAGE SUPPLY

The performances of a five phase induction motor under unbalanced supply are carried out with simulation, this is based on the evaluation of the parameters such as : the efficiency, the power factor, the stator copper loss and the rotor copper loss that are observed under the variation of the load torque. The five phase voltage system unbalance can occur following to several cases, at least 14 cases possible can be presented, and even the combination of these 14 cases can be occurred. The simulations presented in this paper are based on the values of the selected factors AVUF and NA VUF. O n the other side, the balanced cases are simulated following the level of the voltage magnitude such as:

i. Five phase balanced ii. 10% balanced overvoltage

ii i. 10% balanced undervoltage

Each parameter is observed first for balanced, 10% balanced over-voltage and 10% balanced under-voltage. Then the same parameters are observed for unbalance cases. The unbalance cases are first observed for the Adjacent voltage unbalance factor (A VUF) =2% where the value of N on-adjacent voltage unbalance factor (NA VUF) is considered randomly. Then the same analysis is carried out for the NA VUF = 2% where the value of A VUF is kept constant. This is done to check out which of the two factors A VUF and NAVUF is having more prominent effect on the different parameters and so on the behaviors of the motors.

IV.1 The Voltage Magnitude Variation Effect of balanced Voltage system on the Motor Efficiency

0.94 0,92

>- 0,9

Eficiency vs load

+---�p!!��t...M::"'"---------:_ balanced

Efficiency vs load

0

,

92 J:�������;:===�=balanced

- lphUV 0,88 -2phUV

v <: .� 0.88 :t:

is. 0,84 +--#;1'1------------- h +-...... �-----"I._-----"�--------=�lO% bal 0\ -;: -- 3p UV � 0,8 --4phUV ClJ UJ 0.86

-lO%baIUV:g 0,76 -5phUV +-�--------��---- � 0.84

0.82 o 20 40 60 80 100 120 140

%load Fig, I, Efficiency vs load graph under balanced condition

Under balance conditions we can observe from figurel that for 10% balanced undervoltage supply, efficiency is more than the other two cases up to the maximum efficiency loading condition, After maximum efficiency loading condition, efficiency is the highest for the 10% balanced overvoltage condition. This is interesting results as the situation reverses with the change in the loading conditions. For low load conditions the undervoltage case offer better efficiency compared to nominal value of voltage or over voltage. It is well known that a three-phase induction motor under partial load condition offer better efficiency if reduced voltage is applied [22-23], the same applies to the five-phase induction motor as well.

[V.l The effect of Voltage unbalance on the Motor Efficiency

Figures 2,3 and 4 present the efficiency vs load for overvoltage, undervoltage and angle unbalancing cases for A VUF = 2% , where N A VUF is not fixed rather it is taken randomly. It is obvious that the efficiency has the highest values for the balanced cases, on the other side; the efficiency is highest for the unbalance cases that are having the lowest value of NAVUF, whereas the efficiency is lowest for the cases that are having the highest value of NA VUF,

0,94 Efficiency vs Load -balanced

0,9 :::I Q. 0,86 >-u 0,82 c:: ClJ 'u 0,78 � ..... 0,74

0,7

°

./ /R/- -

- lph OV

� I J

V - 2phOV

-3phOV

-4phOV

-5phOV

20 40 60 80 100 120 %Ioad

Fig,2, Efficiency vs load for overvoltage unbalance cases for AVUF=2%

4

0,72

+---------,-----,------------, ° 50 %Ioad 100 150

Figure3: Efficiency vs load for undervoltage unbalancing cases for AVUF=2%

0,96

0,92 _0,88 :::I Q.

-;:0,84 u

� 0,8 'u !E 076 ..... '

Efficiency vs load

--balanced -lphA -- 2phA --3phA --4phA

° 20 40 60 80 100 120 %Ioad

Figure4: Efficiency vs load for angle unbalancing cases for AVUF=2%

To clarify the effect of NA VUF the motor is simulated for the value of NA VUF=2%, while the value of A VUF is kept constant. From figure 11, 12 and 13 it is obviously shown that as the unbalancing factor is increased under NA VUF= 2%, there is a decrease in the efficiency for the unbalanced cases, Also it is observed that the efficiency is almost equal for all the unbalancing cases. This is because the value of N A VUF and A VUF is kept constant for each unbalancing cases,

:::I Q.

"> u c:: ClJ 'u ::E .....

0,96

0,92

0,88

0,84

0,8

0,76

Efficiency vs load -balanced r-7.:;;i:II�:------ lphOV

+-��----��---- -2 phOV

+-�-----------3 phOV

+-.----------- --4phOV

+----,----,----,-5phOV

° 50 % load 100 150

Figure II: Efficiency vs load for overvoltage unbalancing cases for NAVUF=2%

Efficiency vs load 0.95 - l p hU V

:I 0.9 - 2phUV

Q. -3phUV >-�0.S5 III -4phUV

'w � O.S --5phUV LU

0.75 -- bala nced

0 50 % load 100 150

Figure 12: Efficiency vs load for undervoltage unbalance cases for NAVUF=2%

0.95

:::s 0.9 Q. >-� 0.S5 III 'w :t O.S LU

0.75

0

Efficiency vs load

50 ol d 100 % oa

- balanced

-- lA -- 2A

-3A

- 4A

150

Figure 6. 13: Efficiency vs load for angle unbalance cases for NAVUF=2%

IV,3 The Voltage Magnitude Variation Effect of balanced Voltage system on the Power Factor The power factor is presented for the balanced case and unbalanced cases with a constant value of AVUF = 2% and a random value of NAVUF.

1

O.S ... 0 .... � 0.6 ..... ... III �Oo4 0

a.. 0.2

0

Power factor vs load

-l---------::;7�::;s:::=;��--- ba la nced

+---���------- - 10% b a I OV

+-----.fh�--------- -- lO% b a I UV

0 20 40 60 SO 100 120 % load

Fig.14. Power factor vs load for balanced cases

From Fig.14 it is obvious that the power factor of the motor improves for the 10% balanced undervoltage condition as compared to the balanced case while it becomes poorer for the 10% balanced overvoltage case.

5

IVA The effect of Voltage unbalance on the Factor

1 o O.S .... � 0.6 ..... ... � Oo4 0 a.. 0.2

0

Power factor vs load

- balanced +-------::::;;;;ji-...... ��- I ph OV

-2phOV +---��-----------------.-3phOV +-�-------------------------4phOV

�--�--�--�--�--�--�-5phOV

0 20 40 60 SO 100 120 % load

Fig.lS. Power factor vs load for overvoltage unbalance cases for AVUF=2%

1

... O.S 0 .... �0.6 ... � 0.4 0 0..0.2

0 0

Power factor vs load

- balanced - lphUV

- 2phUV

-- 3phUV -4phUV

-5phUV 20 40 60 SO 100 120

% load

Fig.16. Power factor vs load for under voltage unbalance cases for AVUF=2%

1

... O.S o

� 0.6 ..... ... � 004 o

a.. 0.2

o

Power factor vs load

+---------=�::iiii;iiiiiiilll!!l!!�'------- bala nced

+-____ -.��------------- - l p hA

+-__ ��------------------ -2 p hA

-3phA +-�----------------------

-- 4phA +---,--,--,---,--,---. o 20 40 60 SO 100 120

%Ioad Fig.17. Power factor vs load for angle unbalance cases for AVUF=2%

From Fig. 15, 16 and 17 it is clear that the power factor is the better for the balanced case as compared to the unbalanced cases. For the overvoltage unbalance cases the power factor is almost same under A VUF=2%. For the undervoltage cases it is observed that the power factor is poorer for 2phUV case as it has the highest value of NA VUF. It must be noted that the same effect is also seen on the efficiency of the motor. For the angle unbalance case it is observed that the power factor is poorer for the 3phA case as it has the highest N A VUF. Thus it can be said that the for the unbalance cases with highest NA VUF, the poorest power factor is obtained.

In this case to observe the effect of increasing the value NAVUF on the power factor of the motor, the motor is simulated for the value of NAVUF=2%, while the value of A VUF kept constant.

1

0°·8 ....

�0.6 I.J.. ...

3°.4 0 c..O.2

°

Power Factor vs load

- balanced +--------:::::;;;..,III!!!!IIIII'!'��- lPhOV

-2phOV +---��----------------�-- 3phOV +-� ____________________ �- 4phOV +-__ � __ � __ � __ � __ � __ -,- 5ph OV

° 20 40 60 80 100 120 % load

Fig.24. Power factor vs load for overvoltage unbalance cases for

NAVUF=2%

1

... 0.8 o .... � 0.6

..... ...

3°.4 o

c.. 0.2

°

Power Factor vs load --,-------------------O- b a lanced

-lphUV +-----��------------�- 2phUV

+---��----------------.- 3phUV

+.�-------------------.- 4ph UV

° 20 40 60 % load

80 100 120 5phUV

Fig.25. Power factor vs load for undervoltage unbalance cases for

NAVUF=2%

Power Factor vs Load 1

... 0.8 +-______ ��::;;;;;:;��� - balanced 0 .... �0.6 +-___ ��--------- lA

I.J.. ...

3° · 4 +-__ ��----------------- - 2A

0

c..O.2 -3A

-4A °

° 20 40 60 80 100 120 %Ioad

Fig.26. Power factor vs load for angle unbalance cases for NAVUF=2%

From Fig. 24, 25 and 26 it is observed that by keeping the value of the unbalance factor N A VUF=2% the power factor of the motor is almost equal in all the unbalanced cases. It is also clear as the unbalance is increased the power factor becomes poorer.

6

IV.5 The Voltage Magnitude Variation Effect of balanced Voltage system on the Stator Copper Loss

Stator copper loss is firstly presented for the balanced case and for 10% balanced overvoltage and 10% balanced undervoltage case for different loading cases. Then the stator copper loss is presented for the unbalanced cases.

200 �

i 150 �

� :;; 100 a. a. 3 � 50 ......

o o

Stator Copper loss vs load

-- balanced --10%baIOV --10%baIUV

20 40 60 80 100 120 % load

Fig.27. Stator copper loss vs load at balanced cases.

From Fig.27 it is observed that stator copper loss is lower than the balanced case for 10% balanced undervoltage case depending on the loading condition at which the maximum efficiency is obtained. Hence, the effect of this can be related to the efficiency. The efficiency is higher for undervoltage for partial load and then it decreases. After the maximum efficiency loading condition, the stator copper loss for the 10% balanced undervoltage case is greater than the balanced case. For 10% balanced overvoltage case the stator copper loss is greater than that of balanced case up to the maximum efficiency loading condition then after that it is lower than the balanced case.

IV,6 The effect of Voltage unbalance on the Stator copper loss Stator copper loss is observed for the unbalance condition for different loading cases. Firstly it is observed for the A VUF=2% without fixing any value for the NAVUF. Then it is observed for the NA VUF= 2%, keeping the value of A VUF nearly to constant.

200 V> :t: '" � 150 V> V>

.2 :;; 100 a. a. o u

B 50 � V'I

o

Stator copper loss vs load

-- balanced --lphOV

+-________________ ���-------- 2phOV -- 3phOV

���������--------------4PhOV

o

-- 5phOV

20 40 60 80 100 120 % load

Fig.28. Stator copper loss vs load for overvoltage unbalance cases for

AVUF=2%.

200 -;:;;-:::: '" Z-150 <II <II o -;: 100 ., 0. 0. 8 50 o ....

a a

Stator copper loss vs Load ,----------------------------- ----- ba l a n ced +-__________________ ��L- ----- 1ph UV

----- 2phUV -- 3phUV

i�siii iiiI��=------------ -- 4ph UV +-__ �---.---,--_,--_,--_, ----- 5 p h U V

a 20 40 60 80 100 120 %Load

Fig.29. Stator copper loss vs load for undervoltage unbalance cases for

200 .,

... �150 ., ., o

-;: 100 or a. a.

3 50 B IV

on a o 20

AVUF=2%

40 60 80 100 120 %Ioad

----- balanced ----- lphA ----- 2phA -- 3phA -----4phA

Fig.30. Stator copper loss vs load for angle unbalance cases for A VUF=2%

From Fig. 28, 29 and 30 it is observed that the stator copper loss is minimum for the balanced case. For overvoltage unbalance case it is clear that for fixed value of AVUF, the stator copper loss is maximum for the increased value of NAVUF. It is well shown that for 2phOV, the stator copper loss is maximum as it has highest value of NAVUF. For undervoltage unbalance case it is observed that for a constant value of A VUF, the stator copper loss is maximum for the highest value of NA VUF. It is well shown that for 2phUV, stator copper loss is maximum as it has highest value of NAVUF. For angle unbalance case it is observed that for constant value of A VUF, the stator copper loss is maximum for the highest value of NA VUF. It is shown that for 3phA, the stator copper loss is maximum as it has highest value of N A VUF. From above observation it is deduced that the unbalance factor NA VUF has prominent effect on the stator copper loss. From the above figures it is deduced that the stator copper loss is highest for the cases which are having the highest value ofNA VUF

V. CONCLUSION

In this paper it is proved that the five phase induction machine is more susceptible to the unbalance on the five phase voltage system compared to the traditional three-phase induction machine. Where several factors are proposed to characterize the unbalanced of the five phase voltage system based on the existent definitions which were used in three phase voltage system. The study presented in this paper has

7

led to the use of two factors among the proposed factors; the adjacent voltage unbalance factor AVUF and the non­adjacent voltage unbalance factor NAVUF. Indeed these two factors are more reflecting the degree of unbalance in five phase voltage system, therefore their impact on the efficiency, the power factor and stator copper loss are analyzed. It is observed for the five phase induction machine that as the adjacent voltage unbalance factor is increased A VUF, the efficiency reduces, the power factor becomes more poor and the stator copper loss and the rotor copper loss increase. O n the other side the unbalance case which is having the highest value of NAVUF has the lowest efficiency, the highest stator copper loss and the lowest power factor. Whereas for the values of N A VUF <= 1 % A VUF=<= 0.6% the effect of unbalance on the above parameters of the five phase induction motor are not so pronounced, hence, in five phase induction motor the effect of unbalance is less, it can be tolerated that the effect of unbalanced has sense for NAVUF above 1 % .

ACKNOWLEDGMENT

This publication was made possible by an NPRP grant No. 4-152-02-53 from the Qatar National Research Fund (a member of The Qatar Foundation). The statements made herein are solely the responsibility of the authors.

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