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SINGLE PHASING OF THREE PHASE INDUCTION MOTOR

A project based lab report Submitted in partial fulfilment of the

Requirements for the award of degree of

BACHELOR OF TECHNOLOGY

In

ELECTRICAL AND ELECTRONICS ENGINEERING

By

U.CHENCHU LAKSHMI (13006043)

N.SARANKUMAR (13006050)

K.JAHNAVI (13006051)

Under the esteemed guidance of

Mr.B.LOVESWARA RAO

(Assoct.Prof)

EEE Department

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERIN

K L UNIVERSITY

Green Fields, Vaddeswaram, Tadepalli,

Guntur - 522 502, Andhra Pradesh.

2014-2015

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K L UNIVERSITY

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

CERTIFICATE

This is certified that the project based lab entitled “SINGLE PHASING OF THREE PHASE INDUCTION

MOTOR” which is an experimental work carried out by U.CHENCHU LAKSHMI (13006043), N.SARANKUMAR

(13006050), and K.JAHNAVI (13006051) in partial fulfilment for the award of degree of BACHELOR IN

TECHNOLOGY in Department ELECTRICAL AND ELECTRONICS ENGINEERING, during the year 2014-2015.

The lab based project has been approved as it satisfies the academic requirements.

Project Guide & Lab Incharge Head of the Department

Mr.B.LOVESWARA RAO (Dr.M.Venugopalarao)

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ACKNOWLEDGEMENT

I express my sincere thanks and gratitude to Head of the Department, Dr.M.Venugopalarao, Course

coordinator Mr.B.LOVESWARA RAO and Lab In charge Mr.B.LOVESWARA RAO for their

supervision and guidance.

I wish to express deep sense of gratitude to our guide Mr.B.LOVESWARA RAO for his/her co-operation,

encouragement and timely suggestions.

Project Associates

U.CHENCHU LAKSHMI-(13006043)

N.SARANKUMAR-(13006050)

K.JAHNAVI-(13006051)

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INDEX OR CONTENTS

ABSTRACT

1. INTRODUCTION PAGE NO

1.1. Induction Motor 7

1.2. Working Principle of Induction Motor 7

1.3. Types of Induction Motor 8

2. THREE PHASE INDUCTION MOTOR

2.1. Three Phase Induction Motor 9

2.2. Working of Three Phase Induction Motor 10

2.3. Why is Three Phase Induction Motor Self-Starting? 10

2.4. Construction of Three Phase Induction Motor 11

2.5. Stator of Three Phase Induction Motor 12

2.6. Types of Three Phase Induction Motor 14

2.7 .Difference of slip ring and squirrel cage induction motor 16

2.8. Efficiency of Three Phase Induction Motor 18

3. SINGLE PHASE INDUCTION MOTOR

3.1. Single Phase Induction Motor 25

3.2. Construction of Single phase Induction Motor 25

3.3. Stator of Single Phase Induction Motor 25

3.4. Rotor of Single Phase Induction Motor 26

3.5. Working Principle of Single Phase Induction Motor 26

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3.6. Why Single Phase Induction Motor is not self –Starting 27

4. EXPERIMENTAL SETUP

1. Aim 28

2. Name Plate Details 28

3. Apparatus Required 28

4. Theory 28

5. Circuit Diagram 29

6. Procedure 30

7. Observations 30

8. Formula Used 31

9. Effects 32

10. Causes 32

11. Precautions 32

12. Model Graph 33

13. Conclusion 33

14. REFERENCES 33

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ABSTRACT

SINGILE PHASING OF THREEE PHASE INDUCTION MOTOR

One of the most common electrical motor used in most applications which is known as

induction motor. This motor is also called as asynchronous motor because it runs at a speed

less than synchronous speed. Types of Three Phase Induction Motor are Squirrel cage

induction motor and Slip ring induction motor.

Analysis of the induction motor failures show, that a significant number of motors are

damaged due to single phasing. At such conditions the current increases rapidly and the

motor is subjected to burnouts and consequently to long downfalls in the corresponding

industry. Normally all motors are protected against thermal overloading by bimetal relays,

but they are not always capable to ensure protection at single phasing. A secure protection is

needed to trip the motor off in any case of single phasing especially for high power motors.

In this project study the behaviour of three phase induction motor under normal working and

single phasing condition experimentally.

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INTRODUCTION

1.1INDUCTION MOTOR

One of the most common electrical motor used in most applications is known as

Induction motor. This motor is also called as asynchronous motor because it runs at a speed

less than synchronous speed. Synchronous speed is the speed of rotation of the magnetic

field in a rotary machine and it depends upon the frequency and number poles of the

machine. An induction motor always runs at a speed less than synchronous speed because the

rotating magnetic field which is produced in the stator will generate flux in the rotor which

will make the rotor to rotate, but due to the lagging of flux current in the rotor with flux

current in the stator, the rotor will never reach to its rotating magnetic field speed i.e. the

synchronous speed. There are basically two types of induction motor that depend upon the

input supply. They are:

1. Single phase induction motor and

2. Three phase induction motor.

Single phase induction motor is not a self-starting motor and three phase induction

motor is a self-starting motor. In general we need to give two supply i.e. double excitation to

make a machine to rotate. For example if we consider a DC motor, we will give one supply

to the stator and another to the rotor through brush arrangement.

1.2Working Principle of Induction Motor

In induction motor we give only one supply, so it is really interesting to know that

how it works. It is very simple, from the name itself we can understand that there is induction

process occurred. Actually when we are giving the supply to the stator winding, flux will

generate in the coil due to flow of current in the coil. Now the rotor winding is arranged in

such a way that it becomes short circuited in the rotor itself. The flux from the stator will cut

the coil in the rotor and since the rotor coils are short circuited, according to Faraday’s law of

electromagnetic induction, current will start flowing in the coil of the rotor. When the current

will flow, another flux will get generated in the rotor. Now there will be two fluxes, one is

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stator flux and another is rotor flux and the rotor flux will be lagging to the stator flux. Due

to this, the rotor will feel a torque which will make the rotor to rotate in the direction of

rotating magnetic flux. So the speed of the rotor will be depending upon the ac supply and

the speed can be controlled by varying the input supply. This is the working principle of an

induction motor of either type.

1.3Types of induction motor

Single Phase Induction Motor:

Single phase induction motor was classified into four types

1. Split phase induction motor

2. Capacitor start induction motor

3. Capacitor start capacitor runs induction motor

4. Shaded pole induction motor

Three Phase Induction Motor:

Three phase induction motor was classified into two types

1. Squirrel cage induction motor

2. Slip ring induction motor

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2. THREE PHASE INDUCTION MOTOR

2.1. Three phase Induction motor

An electrical motor is such an electromechanical device which converts electrical energy into

a mechanical energy. In case of three phase AC operation, most widely used motor is three

phase induction motor as this type of motor does not require any starting device or we can

say they are self-starting induction motor.

For better understanding the principle of three phase induction motor, the basic

constructional feature of this motor must be known to us. This Motor consists of two major

parts:

Stator:

Stator of three phase induction motor is made up of numbers of slots to construct a 3 phase

winding circuit which is connected to 3 phase AC source. The three phase winding are

arranged in such a manner in the slots that they produce a rotating magnetic field after AC is

given to them.

Rotor:

Rotor of three phase induction motor consists of cylindrical laminated core with parallel

slots that can carry conductors. Conductors are heavy copper or aluminum bars which fits in

each slots & they are short circuited by the end rings. The slots are not exactly made parallel

to the axis of the shaft but are slotted a little skewed because this arrangement reduces

magnetic humming noise & can avoid stalling of motor.

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2.2. Working of Three Phase Induction Motor

Production of Rotating Magnetic Field:

The stator of the motor consists of overlapping winding offset by an electrical angle of 120°.

When the primary winding or the stator is connected to a 3 phase AC source, it establishes a

rotating magnetic field which rotates at the synchronous speed.

Secrets behind the rotation:

According to Faraday’s law an emf induced in any circuit is due to the rate of change of

magnetic flux linkage through the circuit. As the rotor winding in an induction motor are

either closed through an external resistance or directly shorted by end ring, and cut the stator

rotating magnetic field, an emf is induced in the rotor copper bar and due to this emf a

current flows through the rotor conductor.

Here the relative velocity between the rotating flux and static rotor conductor is the cause of

current generation; hence as per Lenz’s law the rotor will rotate in the same direction to

reduce the cause i.e. the relative velocity.

Thus from the working principle of three phase induction motor it may observed that the

rotor speed should not reach the synchronous speed produced by the stator. If the speeds

equals, there would be no such relative velocity, so no emf induction in the rotor& no current

would be flowing, and therefore no torque would be generated. Consequently the rotor

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cannot reach at the synchronous speed. The difference between the stator (synchronous

speed) and rotor speeds is called the slip. The rotation of the magnetic field in an induction

motor has the advantage that no electrical connections need to be made to the rotor.

Thus the three phase induction motor is:

1. Self-starting.

2. Less armature reaction and brush sparking because of the absence of commutators and

brushes that may cause sparks.

3. Robust in construction.

4. Economical.

5. Easier to maintain.

2.3. Why is Three Phase Induction Motor Self Starting?

In three phase system, there are three single phase line with 120° phase difference. So the

rotating magnetic field is having the same phase difference which will make the rotor to

move. If we consider three phases a, b and c, when phase a is magnetized, the rotor will

move towards the phase a winding, in the next moment phase b will get magnetized and it

will attract the rotor and then phase c. So the rotor will continue to rotate.

2.4. CONSTRUCTION OF THREE PHASE IM

The three phase induction motor is the most widely used electrical motor. Almost 80% of the

mechanical power used by industries is provided by three phase induction motors because of

its simple and rugged construction, low cost, good operating characteristics, absence of

commutator and good speed regulation. In three phase induction motor the power is

transferred from stator to rotor winding through induction. The Induction motor is also called

asynchronous motor as it runs at a speed other than the synchronous speed.

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Like any other electrical motor induction motor also have two main parts namely rotor and

stator. The rotor of the three phase induction motor are further classified as

1. Squirrel cage rotor,

2. Slip ring rotor or wound rotor or phase wound rotor.

Depending upon the type of rotor construction used the three phase induction motor are

classified as:

1. Squirrel cage induction motor,

2. Slip ring induction motor or wound induction motor or phase wound induction motor.

The construction of stator for both the kind of three phase induction motor remains the same.

The other parts, which are required to complete the induction motor, are:

1. Shaft for transmitting the torque to the load. This shaft is made up of steel.

2. Bearings for supporting the rotating shaft.

One of the problems with electrical motor is the production of heat during its rotation. In

order to overcome this problem we need fan for cooling.

1. For receiving external electrical connection Terminal box is needed.

2. There is a small distance between rotor and stator which usually varies from 0.4 mm to 4

mm. Such a distance is called air gap.

2.5 Stator of Three Phase Induction Motor

The stator of the three phase induction motor consists of three main parts:

1. Stator frame

2. Stator core

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3. Stator winding or field winding

1. Stator frame:

It is the outer most part of the three phase induction motor. Its main function is to support

the stator core and the field winding. It acts as a covering and provides protection and

mechanical strength to all the inner parts of the machine. The frame is either made up of die

cast or fabricated steel. The frame of three phase induction motor should be very strong and

rigid as the air gap length of three phase induction motor is very small, otherwise rotor will

not remain concentric with stator which will give rise to unbalanced magnetic pull.

2. Stator core:

The main function of the stator core is to carry alternating flux. In order to reduce the eddy

current losses the stator core is laminated. This laminated type of structure is made up of

stamping which is about 0.4 to 0.5 mm thick. All the stamping are stamped together to form

stator core, which is then housed in stator frame. The stamping is generally made up of

silicon steel, which reduces the hysteresis loss.

3. Stator winding or field winding:

The slots on the periphery of stator core of the three phase induction motor carries three

phase windings. This three phase winding is supplied by three phase ac supply. The three

phases of the winding are connected either in star or delta depending upon which type of

starting method is used. The squirrel cage motor is mostly started by star – delta starter and

hence the stator of squirrel cage motor is delta connected. The slip ring three phase induction

motor are started by inserting resistances so, the stator winding can be connected either in

star or delta. The winding wound on the stator of three phase induction motor is also called

field winding and when this winding is excited by three phase ac supply it produces rotating

magnetic field.

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2.6. Types of Three Phase Induction Motor

1. Squirrel cage three phase induction motor:

The rotor of the squirrel cage three phase inductions motor is cylindrical in shape and have

slots on its periphery. The slots are not made parallel to each other but are bit skewed

(skewing is not shown in the figure of squirrel cadge rotor beside) as the skewing prevents

magnetic locking of stator and rotor teeth and makes the working of motor more smooth and

quieter. The squirrel cage rotor consists of aluminium, brass or copper bars (copper bras rotor

is shown in the figure beside). This aluminium, brass or copper bars are called rotor

conductors and are placed in the slots on the periphery of the rotor. The rotor conductors are

permanently shorted by the copper or aluminium rings called the end rings. In order to

provide mechanical strength these rotor conductor are braced to the end ring and hence form

a complete closed circuit resembling like a cage and hence got its name as “squirrel cage

induction motor”. The squirrel cage rotor winding is made symmetrical. As the bars are

permanently shorted by end rings, the rotor resistance is very small and it is not possible to

add external resistance as the bars are permanently shorted. The absence of slip ring and

brushes make the construction of Squirrel cage three phase induction motor very simple and

robust and hence widely used three phase induction motor. These motors have the advantage

of adapting any number of pole pairs. The below diagram shows squirrel cage induction rotor

having aluminium bars short circuit by aluminium end rings.

Advantages of squirrel cage induction rotor

1. Its construction is very simple and rugged.

2. As there are no brushes and slip ring, these motors requires less maintenance.

Applications:

Squirrel cage induction motor is used in lathes, drilling machine, fan, blower printing

machines etc.

2. Slip ring or wound three phase induction motor :

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In this type of three phase induction motor the rotor is wound for the same number of poles

as that of stator but it has less number of slots and has less turns per phase of a heavier

conductor. The rotor also carries star or delta winding similar to that of stator winding. The

rotor consists of numbers of slots and rotor winding are placed inside these slots. The three

end terminals are connected together to form star connection. As its name indicates three

phase slip ring induction motor consists of slip rings connected on same shaft as that of rotor.

The three ends of three phase windings are permanently connected to these slip rings. The

external resistance can be easily connected through the brushes and slip rings and hence used

for speed control and improving the starting torque of three phase induction motor. The

brushes are used to carry current to and from the rotor winding. These brushes are further

connected to three phase star connected resistances. At starting, the resistance are connected

in rotor circuit and is gradually cut out as the rotor pick up its speed. When the motor is

running the slip ring is shorted by connecting a metal collar, which connect all slip ring

together and the brushes are also removed. This reduces wear and tear of the brushes. Due to

presence of slip rings and brushes the rotor construction becomes somewhat complicated

therefore it is less used as compare to squirrel cage induction motor.

Advantages of slip ring induction motor

1. It has high starting torque and low starting current.

2. Possibility of adding additional resistance to control speed.

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Application:

Slip ring induction motor is used where high starting torque is required i.e. in hoists, cranes,

elevator etc.

2.7. Difference between Slip Ring and Squirrel Cage Induction Motor

SLIP RING OR PHASE WOUND

INDUCTION MOTOR

SQUIRREL CAGE INDUCTION

MOTOR

Construction is complicated due to

Presence of slip ring and brushes

Construction is very simple

The rotor winding is similar to the

stator winding

The rotor consists of rotor bars which are

permanently shorted with the help of end

rings

We can easily add rotor resistance

by using slip ring and brushes

Since the rotor bars are permanently

shorted, it’s not possible to add external

resistance

Due to presence of external resistance

high starting torque can be obtained

Staring torque is low and cannot be

improved

Slip ring and brushes are present Slip ring and brushes are absent

Frequent maintenance is required due

to presence of brushes

Less maintenance is required

This motor is rarely used only 10 % Due to its simple construction and low cost.

The squirrel cage induction motor is widely

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industry uses slip ring induction motor used

Rotor copper losses are high and hence

less efficiency

Less rotor copper losses and hence high

efficiency

Speed control by rotor resistance method

is possible

Speed control by rotor resistance method is

not possible

Slip ring induction motor are used where high

starting torque is required i.e. in hoists, cranes,

elevator etc.

Squirrel cage induction motor is used in

lathes, drilling machine, fan, blower printing

machines etc.

2.8. Efficiency of Three Phase Induction Motor

Efficiency is defined as the ratio of the output to that of input,

Rotor efficiency of the three phase induction motor ,

= Gross mechanical power developed / rotor input

Three phase induction motor efficiency,

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Three phase induction motor efficiency

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3. SINGLE PHASE INDUCTION MOTOR

3.1. SINGLE PHASE INDUCTION MOTOR

For lightning and general purposes in homes, offices, shops, small factories single phase

system is widely used as compared to three phase system as the single phase system is more

economical and the power requirement in most of the houses, shops, offices are small, which

can be easily met by single phase system. The single phase motors are simple in

construction, cheap in cost, reliable and easy to repair and maintain. Due to all these

advantages the single phase motor finds its application in vacuum cleaner, fans, washing

machine, centrifugal pump, blowers, washing machine, small toys etc.

The single phase ac motors are further classified as:

1. Single phase induction motors or asynchronous motors.

2. Single phase synchronous motors.

3. Commutator motors.

3.2. Construction of Single Phase Induction Motor

Like any other electrical motor asynchronous motor also have two main parts namely rotor

and stator.

Stator:

As its name indicates stator is a stationary part of induction motor. A single phase ac supply

is given to the stator of single phase induction motor.

Rotor:

The rotor is a rotating part of induction motor. The rotor is connected to the mechanical load

through the shaft. The rotor in single phase induction motor is of squirrel cage rotor type.

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The construction of single phase induction motor is almost similar to the squirrel cage three

phase motor except that in case of asynchronous motor the stator have two windings instead

of one as compare to the single stator winding in three phase induction motor.

3.3. Stator of Single Phase Induction Motor

The stator of the single phase induction motor has laminated stamping to reduce eddy current

losses on its periphery. The slots are provided on its stamping to carry stator or main

winding. In order to reduce the hysteresis losses, stamping are made up of silicon steel.

When the stator winding is given a single phase ac supply, the magnetic field is produced

and the motor rotates at a speed slightly less than the synchronous speed Ns which is given

by

The construction of the stator of asynchronous motor is similar to that of three phase

induction motor except there are two dissimilarity in the winding part of the single phase

induction motor.

1. Firstly the single phase induction motors are mostly provided with concentric coils. As the

number of turns per coil can be easily adjusted with the help of concentric coils, the mmf

distribution is almost sinusoidal.

2. Except for shaded pole motor, the asynchronous motor has two stator windings namely the

main winding and the auxiliary winding. These two windings are placed in space quadrature

with respect to each other.

3.4. Rotor of Single Phase Induction Motor

The construction of the rotor of the single phase induction motor is similar to the squirrel

cage three phase induction motor. The rotor is cylindrical in shape and has slots all over its

periphery. The slots are not made parallel to each other but are bit skewed as the skewing

prevents magnetic locking of stator and rotor teeth and makes the working of induction

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motor more smooth and quieter. The squirrel cage rotor consists of aluminum, brass or

copper bars. These aluminium or copper bars are called rotor conductors and are placed in

the slots on the periphery of the rotor. The rotor conductors are permanently shorted by the

copper or aluminium rings called the end rings. In order to provide mechanical strength these

rotor conductor are braced to the end ring and hence form a complete closed circuit

resembling like a cage and hence got its name as “squirrel cage induction motor”. As the bars

are permanently shorted by end rings, the rotor electrical resistance is very small and it is not

possible to add external resistance as the bars are permanently shorted. The absence of slip

ring and brushes make the construction of single phase induction motor very simple and

robust.

3.5. Working Principle of Single Phase Induction Motor

When single phase ac supply is given to the stator winding of single phase induction motor,

the alternating current starts flowing through the stator or main winding. This alternating

current produces an alternating flux called main flux. This main flux also links with the rotor

conductors and hence cut the rotor conductors. According to the Faraday’s law of

electromagnetic induction, emf gets induced in the rotor. As the rotor circuit is closed one so,

the current starts flowing in the rotor. This current is called the rotor current. This rotor

current produces its own flux called rotor flux. Since this flux is produced due to induction

principle so, the motor working on this principle got its name as induction motor. Now there

are two fluxes one is main flux and another is called rotor flux. These two fluxes produce the

desired torque which is required by the motor to rotate.

3.6. Why Single Phase Induction Motor is not Self Starting?

According to double field revolving theory, any alternating quantity can be resolved into two

components, each component have magnitude equal to the half of the maximum magnitude

of the alternating quantity and both these component rotates in opposite direction to each

other. For example – a flux, φ can be resolved into two components

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Each of these components rotates in opposite direction i.e. If one φm /2 is rotating in

clockwise direction then the other φm / 2 rotates in anticlockwise direction.

When a single phase ac supply is given to the stator winding of single phase induction motor,

it produces its flux of magnitude, φm. According to the double field revolving theory, this

alternating flux, φm is divided into two components of magnitude φm /2. Each of these

components will rotate in opposite direction, with the synchronous speed, Ns. Let us call

these two components of flux as forward component of flux, φf and backward component of

flux, φb. The resultant of these two component of flux at any instant of time, gives the value

of instantaneous stator flux at that particular instant.

Now at starting, both the forward and backward components of flux are exactly opposite to

each other. Also both of these components of flux are equal in magnitude. So, they cancel

each other and hence the net torque experienced by the rotor at starting is zero. So, the single

phase induction motors are not self-starting motors.

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4. EXPERIMENTAL SETUP

AIM: To determine experimentally single phasing of three phase induction motor.

Name plate Details:

3 Phase Squirrel Cage 3 Phase Auto Transformer

Induction Motor (3 Phase Variac)

Horse power: 7.5/5.5KW Input: 415V

Voltage: 415V output: 0-470V

Current: 10.5A : 15A

RPM: 1400rpm

APPARATUS REQUIRED:

S.NO APPARATUS RANGE TYPE QUANTITY

1 VOLTMETER (0-600)V 1 NO

2 AMMETER (0-20)A 1 NO

3 WATTMETER (600V/20A) 1 NO

4 VOLTMETER (0-150)V 1 NO

5 AMMETER (0-10)A 1 NO

6 WATTMETER (150V/10A) 1 NO

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THEORY

For proper working of any 3 phase induction motor it must be connected to a 3 phase

alternating current (ac) power supply of rated voltage and load. Once these three phase

motors are started they will continue to run even if one of the three phase supply lines gets

disconnected. The loss of current through one of these phase supply is described as single

phasing.

CIRCUIT DIAGRAM

THREE PHASE

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SINGLE PHASE

PROCEDURE

1. Connections are made as per the circuit diagram.

2. By varying the autotransformer slowly rated voltage is given to the motor and

run at rated speed.

3. At no-load the speed, current, voltage and power are noted.

4. By applying the load for various values of current the above mentioned

readings are noted.

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5. After taking the readings release the load completely and switch OFF the

supply to the motor.

6. Then remove one phase by connecting a switch to make it single phase as

shown in the circuit.

7. Repeat the procedure and note down the readings.

8. Performance curves are drawn for the tabulated values.

OBSERVATIONS

THREE PHASE

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SINGLE PHASE

FORMULA USED

1. Torque = (S1~ S2) (R + t/2) x 9.81 N-m

Where S1, S2 - Spring Balance readings in Kg

R - Radius of the brake drum in ‘m’

t - Thickness of the belt in ‘m’

2. Output Power = 2πNT/60 Watts

Where, N - Rotor Speed in RPM

T - Torque in N-m

3. Input power = W Watts (W - Wattmeter Readings)

4. Percentage efficiency=Output power/Input power X 100 .

5. Percentage Slip = Ns – Nr X 100

Ns

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Where, Ns – Synchronous Speed

Nr - Rotor Speed

6. Power Factor = W / VL x IL

7. R =

8. t =

CALCULATED VALUES

THREE PHASE

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SINGLE PHASE

EFFECTS

1. Due to single phasing the current in the remaining two phases increases and it is

approximately 2.4 times the normal current value.

2. Single phasing reduces the speed of the motor.

3. The motor becomes noisy and starts vibrating due to uneven torque produced in the motor.

4. If the motor is arranged for standby and automatic starting then the motor will not start,

and if the overload relay provided fails to function then the motor may burn.

5. The windings will melt due to overheating and can give a fatal shock to the personnel.

6. It may cause overloading of the generator.

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CAUSES

1. One of the three back up fuses blows (or fuse wire melts).

2. One of the contactor for motor is open circuited.

3. Single phasing might also be caused due to wrong setting of the protection devices

provided on the motor.

4. Contactors are coated due to oxidation hence not conducting.

5. Relay contacts may be damage or broken.

PRECAUTIONS

1. The motor should be started without any load.

2. The load should not exceed rated value.

3. Initially the autotransformer should be in minimum voltage position .

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MODEL GRAPH

The graph drawn for

1. Output Power Vs Speed

2. Output Power Vs Line Current

3. Output Power Vs Torque

4. Output Power Vs Efficiency

5. Output Power Vs Slip

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CONCLUSION

1. Even though one phase is removed machine does not stop running.

2. Single phasing could lead to burnouts and costly fall downs.

3. Single phase induction motor draws very high current at starting when compared to three

phase induction motor.

PROOF

REFERENCES

WWW.WIKIPEDIA.ORG

WWW.ELECTRONICS4U.COM

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