CHAPTER-1

INTRODUCTION

This project is basically about designing model using matlab in which a synchronous motor

starting on induction principle by means of damper winding is called a synduction motor. The

damper winding act like the squirrel cage rotor producing the starting torque. In the starting

operation of a synduction motor the field is kept shorted while the stator is switched on to three

phase ac supply. As the motor reaches close to synchronous speed the field is energized from dc

supply. The rotor now get synchronized automatically because coupling of rotor with stator

magnetic field. It is essential to keep the field shorted at start otherwise in the initial part of the

starting time when the slip is close to unity high voltage would be induced in the field winding it

has normally large number of turns which can damage it. In fact to avoid high starting current in

the field resistance, it is shorted through resistance several times the field resistance adds to

motor starting torque. This method is employed for no load or low load starting. The machine is

loaded after it has synchronized. A high starting torque synchronous motor is combination of

synchronous and slip ring induction motor into one machine.

1.1 BASICS OF SYNCHRONOUS MOTOR

A synchronous electric motor is an AC motor in which, at steady state, the rotation of the shaft

the motor that create a magnetic field which rotates in time with the oscillations of the line

current. The rotor turns in step with this field, at the same rate is synchronized with

the frequency of the supply current; the rotation period is exactly equal to an integral number

of AC cycles.

The synchronous motor and induction motor are the most widely used types of AC motor. The

difference between the two types is that the synchronous motor rotates in exact synchronism with

the line frequency. In contrast the induction motor requires "slip" the rotor must rotate slightly

slower than the AC current alternations, to develop torque. Therefore small synchronous motors

are used in timing applications such as in synchronous clocks, timers in appliances, tape

recorders and precision servomechanisms in which the motor must operate at a precise speed.

1

Synchronous motors are available in sub-fractional self-excited sizes to high-horsepower

industrial sizes. In the fractional horsepower range, most synchronous motors are used where

precise constant speed is required. In high-horsepower industrial sizes, the synchronous motor

provides two important functions. First, it is a highly efficient means of converting AC energy to

work. Second, it can operate at leading or unity power factor and thereby provide power-factor

correction. These machines are commonly used in analog electric clocks, timers and other

devices where correct time is required. The brushless wound-rotor doubly-fed synchronous

motor system as only provided by the Synchro-Sym electric machine system with an

independently excited rotor multiphase AC winding set that does not depend on slip-induction of

current can produce torque about synchronous speed where induction is irrelevant or ceases to

exist and as a result, is another type of synchronous motor with at least all the attractive attributes

of a synchronous motor, such as leading to lagging power factor adjustment, but also has startup

capability, which differs from the classic synchronous motor with the rotor shaft always in

synchronism with the AC excitation.

1.2 CONSTRUCTION

The principal components of a synchronous motor are the stator and the rotor. The stator of

synchronous motor and stator of induction motor are similar in construction. With the wound-

rotor synchronous doubly-fed electric machine as the exception, the stator frame

contains wrapper plate. Circumferential ribs and key-bars are attached to the wrapper plate. To

carry the weight of the machine, frame mounts and footings are required. When the field winding

is excited by DC excitation, brushes and slip rings are required to connect to the excitation

supply. The field winding can also be excited by a brushless exciter. Cylindrical, round rotors,

(also known as non salient pole rotor) are used for up to six poles. In some machines or when a

large number of poles are needed, a salient pole rotor is used.

1.3 OPERATION

The rotating magnetic field is formed from the sum of the magnetic field vectors of the three

phases of the stator windings. The operation of a synchronous motor is due to the interaction of

the magnetic fields of the stator and the rotor. With the wound-rotor synchronous doubly-fed

electric machine, which is a doubly-fed or double armature electric machine, and the permanent

2

magnet electric machine with two electrical ports as exceptions, synchronous motor is a doubly

excited machine i.e. two electrical inputs are provided to it. Its stator winding which consists of a

3 phase winding is provided with 3 phase supply and rotor is provided with DC supply.

Fig. no. 1.1 Working of synchronous motor

The 3 phase stator winding carrying 3 phase currents produces 3 phase rotating magnetic flux

(and therefore rotating magnetic field).The rotor locks in with the rotating magnetic field and

rotates along with it. Once the rotor locks in with the rotating magnetic field, the motor is said to

be in synchronization. A single-phase (or two-phase derived from single phase) stator winding is

possible, but in this case the direction of rotation is not defined and the machine may start in

either direction unless prevented from doing so by the starting arrangements.

Once the motor is in operation, the speed of the motor is dependent only on the supply

frequency. When the motor load is increased beyond the breakdown load, the motor falls out of

synchronization and the field winding no longer follows the rotating magnetic field. Since the

motor cannot produce (synchronous) torque if it falls out of synchronization, practical

synchronous motors have a partial or complete squirrel-cage damper winding to stabilize

operation and facilitate starting. Because this winding is smaller than that of an equivalent

induction motor and can overheat on long operation, and because large slip-frequency voltages

are induced in the rotor excitation winding, synchronous motor protection devices sense this

condition and interrupt the power supply (out of step protection). The rotor locks in with the

rotating magnetic field and rotates along with it. Once the rotor locks in with the rotating

magnetic field, the motor is said to be in synchronization.

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1.4 STARTING OF SYNCHRONOUS MOTOR

It cannot be started from a standstill by applying three-phase ac power to the stator. When ac is

applied to the stator, a high-speed rotating magnetic field appears immediately. This rotating

field rushes past the rotor poles so quickly that the rotor does not have a chance to get started. In

effect, the rotor is repelled first in one direction and then the other. Asynchronous motor in its

purest form has no starting torque. It has torque only when it is running at synchronous speed.

Fig.no.1.2 Starting of Synchronous Motor as a induction motor

A squirrel-cage type of winding is added to the rotor of a synchronous motor to cause it to start

are called damper winding. It is so named because it is shaped and looks something like a turn

able squirrel cage. Simply, the windings are heavy copper bars shorted together by copper rings.

A low voltage is induced in these shorted windings by the rotating three-phase stator field.

Because of the short circuit, a relatively large current flows in the squirrel cage. This causes a

magnetic field that interacts with the rotating field of the stator. Because of the interaction, the

rotor begins to turn, following the stator field; the motor starts. To start a practical synchronous

motor, the stator is energized, but the dc supply to the rotor field is not energized. The squirrel-

cage windings bring the rotor to near synchronous speed. At that point, the dc field is energized.

This locks the rotor in step with the rotating stator field. Full torque is developed, and the load is

driven.

The purpose of auxiliary motor is to bring the synchronous motor near to synchronous speed.

The auxiliary motor may be an induction motor or dc motor. If three phase induction motor is

used as an auxiliary motor then it is mechanically coupled with synchronous motor both the

motors have same number of pole are energied from same three phase supply.The auxiliary three

phase induction motor bring the main motor speed almost equal to synchronous speed at this

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time the armature winding of synchronous motor is also energized from three phase

supply .Now when the field winding of the main motor is connected to dc source the field pole

get locked with those produce by armature winding as a result of this main motor start running as

a synchronous motor at synchronous speed. The auxiliary motor can be disconnected from supp

Fig. no. 1.3 Starting of Synchronous Motor with an auxiliary motor

1.5 APPLICATION OF SYNCHRONOUS MOTOR

Use as synchronous condenser

Fig. no. 1.4 V curves of synchronous motor

By varying the excitation of a synchronous motor, it can be made to operate at lagging, leading

and unity power factor. Excitation at which the power factor is unity is termed normal excitation

voltage. The magnitude of current at this excitation is minimum. Excitation voltage more than

normal excitation is called over excitation voltage, excitation voltage less than normal excitation

is called under excitation. When the motor is over excited, the back emf will be greater than the

motor terminal voltage. This causes a demagnetizing effect due to armature reaction.

5

The V curve of a synchronous machine shows armature current as a function of field current.

With increasing field current armature current at first decreases, then reaches a minimum, then

increases. The minimum point is also the point at which power factor is unity.

This ability to selectively control power factor can be exploited for power factor correction of the

power system to which the motor is connected. Since most power systems of any significant size

have a net lagging power factor, the presence of overexcited synchronous motors moves the

system's net power factor closer to unity, improving efficiency. Such power-factor correction is

usually a side effect of motors already present in the system to provide mechanical work,

although motors can be run without mechanical load simply to provide power-factor correction.

In large industrial plants such as factories the interaction between synchronous motors and other,

lagging, loads may be an explicit consideration in the plant's electrical design.

Steady state stability limit

where,

 is the torque

 is the torque angle

 is the maximum torque

here,

When load is applied, torque angle   increases. When   = 90° the torque will be maximum. If

load is applied further then the motor will lose its synchronism, since motor torque will be less

than load torque. The maximum load torque that can be applied to a motor without losing its

synchronism is called steady state stability limit of a synchronous motor.

Synchronous motors are three phase AC motors which run at synchronous speed, without slip.

Synchronous motors have the following characteristics . A three-phase stator similar to that of an

induction motor. Medium voltage stators are often used. - A wound rotor-rotating field which has

the same number of poles as the stator, and is supplied by an external source of direct current

(DC). Both brush-type and brushless exciters are used to supply the DC field current to the rotor.

With the rotor at standstill and a three-phase voltage applied to the armature winding, the

resultant rotating armature MMF moves past the rotor at synchronous velocity, producing an

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alternating torque with an average value of zero. The plain synchronous motor thus has no

inherent starting torque. To start the motor, the following methods may be employed Pony motor

starting: Earlier machines were started using this method. A small directly coupled induction

motor is used to drive the synchronous machine close to synchronous speed, and synchronizing

is carried out by means of a synchroscope.

1.6 PROBLEM STATEMENT

When 3 phase supply is given to the motor there is a rotating flux generated, which rotates at

the synchronous speed. Now the rotor which is a magnet which is not rotated automatically, or it

can be said that the synchronous motor is not self starting. The reason behind that the rotating

flux rotates at very high speed. So, the poles of the rotor can not get locked with the stator poles

and the motor does not works. Above a certain size, synchronous motors are not self-starting

motors. This property is due to the inertia of the rotor; it cannot instantly follow the rotation of

the magnetic field of the stator. Since a synchronous motor produces no inherent average torque

at standstill, it cannot accelerate to synchronous speed without some supplemental mechanism.

1.7 OBJECTIVE

The objective of project are:

illustrates the starting procedure of a 60-kVA 400-V 50Hz synchronous motor. The

motor is started at no load.

Synchronous motor is started in induction machine mode with currents induced in the

damper and field windings.

1.8 PROJECT SCOPE

The scope of project are:

To develop MATLAB model to start synchronous motor as induction machine .

To develop computer simulation for starting purpose of synchronous motor.

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CHAPTER 2

LITERATURE REVIEW

2.1 INTRODUCTION

This project is basically about designing model using MATLAB in which a SYNCHRONOUS

MOTOR starting on induction principle by means of damper winding is called a synduction

motor. A synchronous electric motor is an AC motor in which, at steady state, the rotation of the

shaft is synchronized with the frequency of the supply current; the rotation period is exactly

equal to an integral number of AC cycles. Synchronous motors contain electromagnets on

the stator of the motor that create a magnetic field which rotates in time with the oscillations of

the line current. The rotor turns in step with this field, at the same rate.

The synchronous motor and induction motor are the most widely used types of AC motor. The

difference between the two types is that the synchronous motor rotates in exact synchronism with

the line frequency. In contrast the induction motor requires "slip", the rotor must rotate slightly

slower than the AC current alternations, to develop torque. Therefore small synchronous motors

are used in timing applications such as in synchronous clocks, timers in appliances, tape

recorders and precision servomechanisms in which the motor must operate at a precise speed.

Synchronous motors are available in sub-fractional self-excited sizes to high-horsepower

industrial sizes. In the fractional horsepower range, most synchronous motors are used where

precise constant speed is required. In high-horsepower industrial sizes, the synchronous motor

provides two important functions. First, it is a highly efficient means of converting AC energy to

work. Second, it can operate at leading or unity power factor and thereby provide power-factor

correction. These machines are commonly used in analog electric clocks, timers and other

devices where correct time is required.

Irving L. Kosow[11]: It is evident that synchronous motor must be brought up to a speed

sufficiently close to synchronous speed in order to lock into synchronism with the rotating field.

The means by which it brought up to speed are :-

1. A dc motor coupled to synchronous motor shaft.

2. Using the field exciter generator as dc motor.

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3. A small induction motor of at least one pair of pole less than synchronous motor.

4. Using the damper winding as squirrel cage induction motor.

Dr. P.S. Bimbhra[10]: The purpose of auxiliary motor is to bring the synchronous motor

near to synchronous speed. The auxiliary motor may be an induction motor or dc motor. If three

phase induction motor is used as an auxiliary motor then it is mechanically coupled with

synchronous motor both the motors have same number of pole are energized from same three

phase supply. The auxiliary three phase induction motor bring the main motor speed almost

equal to synchronous speed at this time the armature winding of synchronous motor is also

energized from three phase supply .Now when the field winding of the main motor is connected

to dc source the field pole get locked with those produce by armature winding as a result of this

main motor start running as a synchronous motor at synchronous speed. The auxiliary motor can

be disconnected from supply.

M.G. Say[13]: Starting a synchronous motor by utilizing a induction torque require a rotor to

have either solid pole or laminated shoe carrying a cage type of damper winding. Three phase

supply at full or reduce voltages is switch on to the stator and rotating field interact with current

induced in pole shoe to raise speed of rotor close to synchronous speed. It is now connected to

exciter or dc supply and rotor pull into step on account of slow pulsation of synchronizing torque

produced as rotor pole slip past stator pole.

D P KOTHARI and I J NAGRATH[12]: A ‘SYNCHRONOUS MOTOR’ starting on

induction principle by means of damper winding is called a synduction motor. The damper

winding act like the squirrel cage rotor producing the starting torque. In the starting operation of

a synduction motor the field is kept shorted while the stator is switched on to three phase ac

supply. As the motor reaches close to synchronous speed the field is energized from dc supply.

The rotor now get synchronized automatically because coupling of rotor with stator magnetic

field. It is essential to keep the field shorted at start otherwise in the initial part of the starting

time when the slip is close to unity high voltage would be induced in the field winding it has

normally large number of turns which can damage it. In fact to avoid high starting current in the

9

field resistance, it is shorted through resistance several times the field resistance adds to motor

starting torque. This method is employed for no load or low load starting. The machine is loaded

after it has synchronized. A high starting torque synchronous motor is combination of

synchronous and slips ring induction motor into one machine.

2.2 SYNCHRONOUS MOTOR ANALYSIS

In developing the basic equation of a synchronous motor, the following assumption are made.the

stator winding are symmetrical and have a perfect sinusoidal distribution along the air gap. The

performance of magnetic paths on rotor is dependent on rotor position. Saturation synchronous

motor studies, the two axis equivalent circuit with two or three damping winding is usually

assumed at the proper structure. In this paper, and using park transformation, the synchronous

method is supposed to be modeled with one damper winding for the d-axis and a one damper

winding for the q-axis.

In this chapter we have covered the brief view of the starting of synchronous motor, briefly we

can say literature review. This project is basically about designing model using matlab in which a

synchronous motor starting on induction principle by means of damper winding is called a

synduction motor. The damper winding act like the squirrel cage rotor producing the starting

torque.In the starting operation of a synduction motor the field is kept shorted while the stator is

switched on to three phase ac supply. As the motor reaches close to synchronous speed the field

is energized from dc supply. The rotor now get synchronized automatically because coupling of

rotor with stator magnetic field. It is essential to keep the field shorted at start otherwise in the

initial part of the starting time when the slip is close to unity high voltage would be induced in

the field winding it has normally large number of turns which can damage it. In fact to avoid

high starting current in the field resistance, it is shorted through resistance several times the field

resistance adds to motor starting torque. This method is employed for no load or low load

starting. Other basic issues also have been covered in next chapter for further study.

Starting a synchronous motor by utilizing a induction torque require a rotor to have either solid

pole or laminated shoe carrying a cage type of damper winding. Three phase supply at full or

reduce voltages is switch on to the stator and rotating field interact with current induced in pole

shoe to raise speed of rotor close to synchronous speed. It is now connected to exciter or dc

10

supply and rotor pull into step on account of slow pulsation of synchronizing torque produced as

rotor pole slip past stator pole.

Before discuss further about the job that the starting a synchronous a motor, it is time to explain

about the software needed to develop the model for starting a synchronous motor using

MATLAB.

2.3 MATLAB

2.3.1 INTRODUCTION:

MATLAB (matrix laboratory) is a numerical computing environment and fourth-generation

programming language. Developed by Math Works, MATLAB allows matrix manipulations,

plotting of functions and data, implementation of algorithms, creation of user interfaces, and

interfacing with programs written in other languages, including C, C++, Java, and Fortran.

Although MATLAB is intended primarily for numerical computing, an optional toolbox uses

the Mu PAD symbolic engine, allowing access to symbolic computing capabilities. An additional

package, Simulink, adds graphical multi-domain simulation and Model-Based Design for

dynamic and embedded systems.

Figure 2.1 MATLAB

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2.3.2 HISTORY:

Cleve Moler, the chairman of the computer-science department at the University of New

Mexico, started developing MATLAB in the late 1970s. He designed it to give his student’s

access to LINPACK and EISPACK without them having to learn FORTRAN. Jack Little, an

engineer, was exposed to it during a visit Moler made to Stanford University in 1983.

Recognizing its commercial potential, he joined with Moler and Steve Bangert. They rewrote

MATLAB in C and founded Math Works in 1984 to continue its development. These rewritten

libraries were known as JACKPAC. In 2000, MATLAB was rewritten to use a newer set of

libraries for matrix manipulation, LAPACK.

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Figure 2.2 MATLAB help page2.3.3 MATLAB/SIMULINK

ENVIRONMENT:

MATLAB (short for Matrix Laboratory) is a special-purpose computer program optimized to

perform engineering and scientific calculations. It is a high-performance language for technical

computing. It integrates computation, visualization, and programming in an easy-to-use

environment where problems and solutions are expressed in familiar mathematical notation.

Typical uses include:

Scientific and engineering graphics

Math and computation

Algorithm development

Modeling, simulation and prototyping

Data analysis, exploration and visualization

Application development, including

Graphical User Interface (GUI) building.

MATLAB is a world-wide recognized software package, for modeling, simulating, and

analyzing dynamic systems. MATLAB comes along with SIMULINK, which is MATLAB’s

time domain solver. SIMULINK supports linear and nonlinear systems modeled in continuous

time, sampled time and a combination of both. Different parts of a system can be also sampled at

different rates.

SIMULINK has a powerful graphical user interface, which allows rapid development with great

visualization capabilities. SIMULINK is a toolbox extension of the MATLAB program. It is a

program for simulating dynamic systems. Student editions of MATLAB 5 and SIMULINK 2 are

currently available through Prentice Hall.

The SIMULINK simulations given in CD-ROM accompanying this text were originally

developed on MATLAB version 4.2c and SIMULINK version 1.3c.To accommodate the newly

released MATLAB version 5 and SIMULINK version 2, files for these versions are also

provided on CD-ROM.

Briefly, the steps of using SIMULINK involve first defining a model or mathematical

representation and the parameters of your system, picking a suitable integration method, and

setting up the run conditions, such as run time and initial conditions. In SIMULINK, model

13

definition is facilitated by the graphical interface and the library of templates or function blocks

that are commonly used in mathematical descriptions of dynamic systems.

Briefly, the steps of using SIMULINK involve first defining a model or mathematical

representation and the parameters of your system, picking a suitable integration method, and

setting up the run conditions, such as run time and initial conditions.

Figure 2.3: MATLAB home page

2.3.4 ADVANTAGES OF MATLAB

MATLAB has many advantages compared to conventional computer languages for technical

problem solving. Among them are:

Ease of Use. MATLAB is an interpreted language. Program may be easily written and modified

with the built-in integrated development environment and debugged with the MATLAB

debugger. Because the language is so easy to use, it is ideal for the rapid prototyping of new

programs.

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Platform Independence. MATLAB is supported on many different computer systems,

providing a large measure of platform independence. At the time of this writing, the language is

supported on Windows NT/2000/XP, Linux, several versions of UNIX and the Macintosh.

Predefined Function: MATLAB comes complete with an extensive library of predefined

functions that provide tested and pre-packaged solutions to many basic technical tasks. For

examples, the arithmetic mean, standard deviation, median, etc. these and hundreds of other

functions are built right into the MATLAB language, making your job much easier. In addition

to the large library of function built into the basic MATLAB language, there are many special-

purpose toolboxes available to help solve complex problems in specific areas. There is also an

extensive collection of free user-contributed MATLAB programs that are shared through the

MATLAB Web site.

2.3.5 LIMITATIONS OF MATLAB

MATLAB has two principal disadvantages. The first is that it is an interpreted language and

therefore can execute more slowly than compiled languages. This problem can be mitigated by

properly structuring the MATLAB program, and by the use of the MATLAB compiler to

compile the final MATLAB program before distribution and general use.

The second disadvantage is cost: a full copy of MATLAB is five to ten times more expensive

than a conventional C or Fortran compiler. This relatively high cost is more than offset by then

reduced time required for an engineer or scientist to create a working program, so MATLAB is

cost-effective for businesses. However, it is too expensive for most individuals to consider

purchasing. Fortunately, there is also an inexpensive Student Edition of MATLAB, which is a

great tool for students wishing to learn the language. The Student Edition of MATLAB is

essentially identical to the full edition.

15

CHAPTER 3

PRESENT WORK

3.1 Starting of Synchronous Motor

16

This example shows the starting procedure for a synchronous motor.

Fig no. 3.1 Simulation Model For Starting A Synchronous Motor

17

3.2 Working

When a synchronous motor is started, the excitation DC voltage is not applied to the field

winding. The motor is started in induction machine mode with currents induced in the damper

and field windings. A resistor is connected across the field winding in order to produce an

acceptable field current and to limit voltage induced across the field winding. Then when speed

reaches a preset value near synchronous speed, the field winding is connected to the DC voltage

source and the motor synchronizes on the system frequency.

In the synchronous machine model, the field winding terminals are not available. Instead, a

Simulink signal representing the field voltage must be applied at the Vf input of the machine.

Therefore if the Vf input is left unconnected, a zero field voltage is applied on the rotor. In other

words, the field winding is short-circuited. In this example, the field current (idf) and a gain

block (R_start) are used to implement the resistance connected across the field winding.

This model illustrates the starting procedure of a 60-kVA 400-V 50Hz synchronous motor. The

motor is started at no load by closing the circuit breaker at t=0.1s . A 2 pu resistor is initially

connected across the field winding. When the rotor speed reaches 0.99 pu, the "R_start" resistor

is disconnected from the field terminals and it is replaced by the "Vf source" (1 pu). At the same

time, the mechanical power is ramped from zero to 50% of the nominal mechanical power (Pm =

-0.5 pu) in one second. The motor locks into step at synchronous speed (1 pu) at approximately t

= 1.3 s.

Today Synchronous motors are widely used in modern societies: industrial, commercial,

agricultural, and domestic applications as constant-speed motors or as compensators for reactive

power control in large power systems. Also understanding the machine’s behaviour and

determining its equivalent network and performance characteristics are of prime importance to a

power engineer. Synchronous motors are three phase AC motors which run at synchronous

speed, without slip. Synchronous motors have the following characteristics . A three-phase stator

similar to that of an induction motor. Medium voltage stators are often used. - A wound rotor-

rotating field which has the same number of poles as the stator, and is supplied by an external

source of direct current (DC). Both brush-type and brushless exciters are used to supply the DC

field current to the rotor. With the rotor at standstill and a three-phase voltage applied to the

armature winding, the resultant rotating armature MMF moves past the rotor at synchronous

velocity, producing an alternating torque with an average value of zero. The plain synchronous

18

motor thus has no inherent starting torque. To start the motor, the following methods may be

employed Pony motor starting: Earlier machines were started using this method. A small directly

coupled induction motor is used to drive the synchronous machine close to synchronous speed,

and synchronizing is carried out by means of a synchroscope. The induction motor usually has

two poles fewer than the synchronous motor, and so is capable of raising the speed of the main

motor to synchronous speed. This method is not convenient for industry applications. - Starting

as an induction motor: Modern machines are usually of self synchronizing type and are arranged

to start as induction motors. The pole faces of the synchronous motor are fitted with a damper

winding (similar to a partial squirrel cage winding). With the field winding open-circuited, the

armature winding is connected to a reduced voltage provided by an autotransformer. The rotor

accelerates by induction motor action and runs up to a speed slightly less than the synchronous

speed. Excitation is then applied and synchronizing torque produced. Provided that the slip is not

too large, the rotor will pull into synchronism. Synchronous motors will run at synchronous

speed in according to well known equation below Synchronous-RPM=(120 f/N)

3.3 Phasor diagram

(1) Where, f is Frequency & N is Number of Poles When studying the effect of field excitation

on motor performance, it is often assumed that the motor is loaded such that it draws a constant

power from the supply. Since both the power and the voltage are constant, it follows that I.cosΦ

= Ia = constant

(2) Where Ia is the active component of armature current, and I .Z = constant Figure 1 shows the

effect of change in field excitation on the operation of the synchronous motor. As the field

current is changed, the tip of armature current phasor I will flow the locus XX (a line

perpendicular to V), while the tip of the back EMF. Phasor Ef will flow the locus YY (a line

perpendicular I2Zs ), where I2 is the in-phase component of armature current . When the

synchronous motor is initially overexcited and is operating at point 1 the corresponding armature

current I1 is leading V, and hence the input power factor is leading. Reduction of field current

causes the tip of Ef phasor to move towards point 2: the armature current decreases to a

minimum (I2) and the motor input power factor increases to unity. Further reduction of field

current causes Ef to move to point 3: the armature current increases to I3, and the input power

19

factor becomes lagging. In general, over-excitation will cause the synchronous motor to operate

at a leading power factor, while underexcitation will cause the motor to operate at a lagging

power factor. The synchronous thus posses variable power factor characteristic [6]. The equation

of the cylindrical rotor motor becomes: Va = Ea + (Ra + jXs)Ia ... (3) Figure 2 illustrate the

relation between Ea and supply voltage Va for three types of loads.

Fig no. 3.2 Phasor diagram for synchronous motor at unity power factor

Fig no.3.3 Phasor diagram for synchronous motor at leading power factor

The relation between the stator current and the field current of a synchronous motor at a constant

terminal voltage and with a constant shaft load is known to be a V -curve. V-Curve Analysis.

The analysis of the V-curves for a given power delivered, the excitation will control the power

20

factor. Hence the synchronous motor can be set to operate at any desired power factor. Usually

powers factor it to be at unity since it giving the less current magnitude, hence less Joules losses.

A special application of synchronous motor running at no-load by varying the excitation to

control a leading/lagging power factor

Fig no.3.4 Phasor diagram for synchronous motor at lagging power factor

hence this becomes either “capacitor”, a “small resistor”, or a “reactor”. this can be controlled

continuously with the excitation current and called “synchronous compensator” that can

compensate for reactive power.

3.4 Equivalent circuit diagram of synchronous motor

The equivalent circuit of the synchronous motor When the rotor field current is just enough to

produce the required magnetic flux, a unit power factor is obtained. If the rotor field current is

more than required the spurious reactive power is to be exported to the power lines of the power

supply. This state is known as over excitation. In practice, because of this feature, synchronous

motors are often run at no active load as synchronous condensers for the purpose of power factor

correction. Figure 3.6 explain the power factor compensation for an inductive load, which is

common for factories using large induction motor drives, and a synchronous condenser.

By controlling the rotor excitation current such that the synchronous condenser draws a line

current of leading phase angle, whose imaginary component cancels that of the load current, the

total line current would have a minimum imaginary component.

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Therefore, the overall power factor of the inductive load and the synchronous condenser would

be close to one and the magnitude of the overall line current would be the minimum. Also

understanding the machine’s behavior and determining its equivalent network and performance

characteristics are of prime importance to a power engineer. Synchronous motors are three phase

AC motors which run at synchronous speed, without slip. Synchronous motors have the

following characteristics.

Figure 3.5 The Equivalent Circuit Of The Synchronous Motor.

A three-phase stator similar to that of an induction motor. Medium voltage stators are often used.

A wound rotor-rotating field which has the same number of poles as the stator, and is supplied by

an external source of direct current.

Figure 3.6 Power factor compensation using synchronous condenser.

When the rotor field current is just enough to produce the required magnetic flux, a unit power

factor is obtained. If the rotor field current is more than required the spurious reactive power is to

be exported to the power lines of the power supply. This state is known as over excitation. In

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practice, because of this feature, synchronous motors are often run at no active load as

synchronous condensers for the purpose of power factor correction. Figure 3.6 explain the phasor

diagram of the power factor compensation for an inductive load, which is common for factories

using large induction motor drives, and a synchronous condenser. By controlling the rotor

excitation current such that the synchronous condenser draws a line current of leading phase

angle, whose imaginary component cancels that of the load current, the total line current would

have a minimum imaginary component. Therefore, the overall power factor of the inductive load

and the synchronous condenser would be close to one and the magnitude of the overall line

current would be the minimum. Also understanding the machine’s behaviour and determining its

equivalent network and performance characteristics are of prime importance to a power engineer.

This paper explains the constructional features and operating principles of the synchronous

motor performance, the effects of load and field excitation on the synchronous motor are

investigated. Synchronous motors are three phase AC motors which run at synchronous speed,

without slip. Synchronous motor is motor in which power factor can be controlled by adjusting

the excitation of the rotating DC field.

3.5 V curves

Unlike AC induction motors which always run at a lagging power factor, synchronous motors

can run at unity or even at a leading power factor. This will improve the over-all electrical

system power factor and voltage drop and also improve the voltage drop at the terminals of the

motor.

As load on the motor increases, the armature (stator) current Ia increases regardless of excitation.

For under and over excited motor, the power factor (p.f.) tends to approach unity with increase in

load. Both with under and over excitation, change in p.f. is greater than in Ia with increase in

load. With normal excitation, when load is increased, change in Ia is greater than in p.f. which

tends to become increasingly lagging. The magnitude of armature current varies with excitation.

The current has large value both for low and high values of excitation (though it is lagging for

low excitation and leading for higher excitation). In between, it has minimum value

corresponding to a certain excitation. For the same input, the armature current varies over a wide

range and so causes the power factor also to vary accordingly.

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When over-excited, motor runs with leading power factor and with lagging power factor when

under-excited. In between, the power factor is unity.The curve for power factor looks like

inverted V curve. Also, the minimum armature current corresponds to unity power factor. As per

the first point, an over-excited motor can be run with leading power factor.

This property renders it extremely useful for phase advancing (and so power factor correction)

purposes in the case of industrial loads driven by induction motors and lighting and heating rods

supplied through transformers.

Figure 3.7 The V-curves of synchronous motor

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Both transformers and induction motors draw lagging currents from the line. Especially on light

loads, the power drawn by them has a large reactive component and the power factor has a very

low value. This reactive component, though essential for operating the electrical machinery,

entails appreciable losses in many ways. By using synchronous motors in conjunction with

induction motors and transformers, the lagging reactive power required by the latter is supplied

locally by the leading reactive component taken by the former, thereby relieving the line and

generators of much of the reactive component.

Hence, they now supply only the active component of the load current. Synchronous motors are

more expensive than the lower horsepower motors that currently applicable in industrial

environment. Conclusion Synchronous motors have the unique ability to run at different power

factors.

As load on the motor increases, the armature (stator) current Ia increases regardless of excitation.

For under and over excited motor, the power factor (p.f.) tends to approach unity with increase in

load. Both with under and over excitation, change in p.f. is greater than in Ia with increase in

load. With normal excitation, when load is increased, change in Ia is greater than in p.f. which

tends to become increasingly lagging.

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CHAPTER-4

SIMULATION RESULT

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Fig no.4.1 Output of synchronous motor

SIMULATION RESULT

Run the model and observe signal on the synchronous motor block. Hence the Synchronous

Motor is self-started on basis of induction principle. During starting there should be no load or

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light load. We observed the different parameter of synchronous motor from standstill position to

synchronous speed for example stator current, electromagnetic torque etc.

STATOR CURRENT

During staring, there is large starting current is as large as five times the full load current, the

starting torque just equals full load torque. With such a large starting current, the motor must

accelerate and reach normaly speed quickly, otherewise overheating may damage the motor. The

load on the motor at the time of starting must be light or preferably there must be no load.

ROTOR SPEED

At standstill rotor speed is zero but as motor is started as a induction motor, As the motor

reaches close to synchronous speed the field is energized from dc supply. The rotor now get

synchronized automatically because coupling of rotor with stator magnetic field. Synchronous

motor get constant speed.

ns = 120 f / Pwhere ,

ns is synchronous speed,

f is frequency,

P is number of poles.

Electromagnetic torque:

At starting there is high torque because large amount of torque is required to overcome large

amount of inertia. As the motor acquire synchronous speed electromagnetic torque is also

reduced.

Field current:

When rotor is standstill and ac voltage is applied on stator, due to this in damper winding

alternating current will produce. At synchronous speed there is no current will produce in

damper winding. As the motor achieve near about synchronous speed, the field voltage is

applied. The field voltage is applied constant during all its operation. It can also be varied.

Therefore field current also remain constant during all its operation.

Applied voltage:

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On stator ac voltage is applied that is 230 volt of 60 hertz frequency. It can be varied according

to our requirement and rating of motor. On rotor dc voltage is applied when rotor attain near

about synchronous speed called field voltage.

From above we have concluded that synchronous motor started on induction principle . The

damper winding act like the squirrel cage rotor producing the starting torque. In the starting

operation of a synduction motor the field is kept shorted while the stator is switched on to three

phase ac supply. As the motor reaches close to synchronous speed the field is energized from dc

supply. The rotor now get synchronized automatically because coupling of rotor with stator

magnetic field. It is essential to keep the field shorted at start otherwise in the initial part of the

starting time when the slip is close to unity high voltage would be induced in the field winding it

has normally large number of turn which can damage it. Starting a synchronous motor by

utilizing a induction torque require a rotor to have either solid pole or laminated shoe carrying a

cage type of damper winding. Three phase supply at full or reduce voltages is switch on to the

stator and rotating field interact with current induced in pole shoe to raise speed of rotor close to

synchronous speed. It is now connected to exciter or dc supply and rotor pull into step on

account of slow pulsation of synchronizing torque produced as rotor pole slip past stator pole.

CHAPTER-5

CONCLUSION AND FUTURE SCOPE

5.1 CONCLUSION

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From above we have concluded that synchronous motor started on induction principle . The

damper winding act like the squirrel cage rotor producing the starting torque. In the starting

operation of a synduction motor the field is kept shorted while the stator is switched on to three

phase ac supply. As the motor reaches close to synchronous speed the field is energized from dc

supply. The rotor now get synchronized automatically because coupling of rotor with stator

magnetic field. It is essential to keep the field shorted at start otherwise in the initial part of the

starting time when the slip is close to unity high voltage would be induced in the field winding it

has normally large number of turn which can damage it. . In fact to avoid high starting current in

the field resistance, it is shorted through resistance several times the field resistance adds to

motor starting torque. This method is employed for no load or low load starting. The machine is

loaded after it has synchronized. A high starting torque synchronous motor is combination of

synchronous and slip ring induction motor into one machine.Synchronous motors have the

unique ability to run at different power factors.

5.2 FUTURE SCOPE

This project has demonstrated the starting of Synchronous Motor in MATLAB /SIMULINK,

both in basic and extended mode. This is easy to implement and requires a small amount of time.

This technique does not require any auxiliary motor. So, starting a Synchronous Motor by the

use of advance soft computing technique like genetic algorithm and meme tic algorithm attracts

the researchers always. A Synchronous Motor is perhaps more often used in all industrial

processes including electrical, mechanical, construction, petroleum industry, power sectors,

development sites, paper industry, beverage industry, etc. where constant speed of operation is

required. Another advantage of the synchronous motor is that power factor can be controlled

simply by variation of its field current. This is the reason why in most large industrial

installations a part of the load is usually handled by synchronous motors which are operated at a

leading power factor so as to yield an overall high power factor for the complete installation.

REFERENCES

[1] S. Yamamura, “Saliency torque and V-curve of permanent-magnet-excited synchronous

motor”, international conference on Unconventional Electromechanical and Electrical Systems,

Russia, June, 2000.

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[2] L.Shi-Dong, L.Jian-Zhao, “Analytic calculation of V-curve for salient-pole synchronous

electric machine”, Proceedings of the Chinese Society of Electrical Engineering, Vol. 28, no. 18,

pp. 110-113, 15 June 2008.

[3] Say M.G. (1983), “ Alternating Current Machines”, 5th edn., pp632, London: Pitman.

[4] Enrique L. Carrillo Arroyo, “Modelling and simulation of permanent magnet synchronous

motor drive system”, M. Sc. Thesis, University of Puerto Rico, 2006.

[5] H. Macbahi, A. Ba-razzouk, J. Xu, A. Cheriti, and V. Rajagopalan, “A unified method for

modeling and simulation of three phase induction motor drives," 2000.

[6] Matlab-Works-Support, “PM Synchronous Motor”,

http://www.mathworks.com/access/helpdesk/hel, p/toolbox/physmod/powersys/powersys.html.

[7] S. Onoda and A. Emadi, “PSIM-based modelling of automotive power systems:

conventional, electric, and hybrid electric vehicles”, Vehicular Technology, IEEE Transactions

on, vol. 53, pp. 390-400, 2004.

[8] C. D. French, J. W. Finch, and P. P. Acarnley, “Rapid prototyping of a real time DSP based

motor drive controller using Simulink”, 1998.

[9] Mostafa.A. Fellani, and Dawo.E. Abaid, “Sliding Mode Control of Synchronous Reluctance

Motor”, International Journal of Electronics, Circuits and Systems Vol.3, No.2, 2009.

[10] DR. P.S. Bimbrha, “Electrical Machinery” Khanna Publisher seventh edition Pp676-680

2009.

[11] Irving L. Kosow , “Electric machinery and Transformer”,PHI Learning private ltd. second

edition, Pp218-225, 2008.

[12] D P Kothari and I J Nagrath, “ Electric machine”, TMH Publishers second edition, Pp 250-

260, 1998.

[13] M. G. Say, “Performance and design of ac machine”, CBS Publishers third edition, Pp250-

260, 2002.

[14] P.K. Mukherjee and S. Chakraverti , “Electrical machine”, Dhanpat Rai Publishers fifteenth

edition,Pp635-640, 2004.

[15] R.H. Park, "Two-Reaction theory of synchronous machines - generalized method of analysis

- part I, part II", AIEE Trans., vol. 48, 1929, pp. 716-727; . 

[16] E.C. Bortoni, J.A. Jardini, "A Standstill Frequency Response Method for Large Salient Pole

Synchronous Machines," IEEE Trans on E.C, Vol. 19, No. 4, December 2004, pp. 687-691. 

31

[17] IEEE 115, IEEE Guide, “ Test Procedures for Synchronous Machines Part I - Acceptance

and Performance Testing Part II-Test Procedures and Parameter Determination for Dynamic

Analysis”, 1995. 

[18] IEEE 1110, “Guide for Synchronous Generator Modeling Practices and Applications in

Power System Stability Analyses”, 2002. 

[19] IEEE Trans, “ Power Apparatus and Systems”, vol. 96, July/Aug 1977, pp. 1211-1218. 

[20] IEC, “Recommendations for Rotating Electrical Machinery”, Part.4: Methods for

Determining Synchronous Machine Quantities, 34-4A, 1985. 

[21] IEEE 115, “Guide for Test Procedures for Synchronous Machines Part I - Acceptance and

Performance Testing Part II-Test Procedures and Parameter Determination for Dynamic

Analysis”, 2009. 

[22] J.C. Peqquena, E. Ruppert and M.T. Mendoza, "On the Synchronous Generator Parameters

Determination Using Dynamic Simulations Based on IEEE Standards," in Proc. Industrial

Technology (ICIT), IEEE International Conference on, Vina del Mar, Chile, 2010, pp. 386-391. 

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