Fundamentals of Electrical Machines.pdf

7/29/2019 Fundamentals of Electrical Machines.pdf

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Houssem Rafik El-Hana BOUCHEKARA2009/2010 1430/1431

KINGDOM OF SAUDI ARABIAMinistry Of High Education

Umm Al-Qura UniversityCollege of Engineering & Islamic Architecture

Department Of Electrical Engineering

Fundamentals of Electrical

Engineering5. Fundamentals of

Electrical Machines


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5 FUNDAMENTALS OF ELECTRICAL MACHINES ................................................................. 3

5.1 INTRODUCTION............................................................................................................... 3

5.2 INTRODUCTION TO MACHINERY PRINCIPLES......................................................... ................ 3

5.2.1 Introduction ........................................................................................................... 3

5.2.2 Rotational Motion, Newtons Law and Power Relationship .................................. 4

Angular position, ....................................................................................................... 4

5.2.2.2 Angular Velocity, ...................................................................................................... 4

5.2.2.3 Angular acceleration, ................................................................................................ 4

5.2.2.4 Torque, ...................................................................................................................... 5

5.2.2.5 Work, W ....................................................................................................................... 5

5.2.2.6 Power, P ....................................................................................................................... 5

5.2.2.7 Newtons Law of Rotation ............................................................................................ 6

5.2.3 1.2 The Magnetic Field ........................................................................................ 6

5.2.3.1 Production of a Magnetic Field .................................................................................... 6

5.2.4 Magnetics Circuits ................................................................................................. 8

5.2.5 Production of Induced Force on a Wire. .............................................................. 14

5.3 TRANSFORMERS............................................................................................................ 155.3.1 Construction of Transformers .............................................................................. 15

5.3.2 Types of transformers: ........................................................................................ 17

5.3.3 The Ideal Transformer ......................................................................................... 18

5.3.4 Power in an Ideal Transformer ............................................................................ 19

5.4 INTRODUCTION TO POWER ELECTRONICS ............................................................. .............. 20

5.4.1 Diodes .................................................................................................................. 20

5.4.2 Silicon Controlled Rectifiers ................................................................................. 21

5.4.3 Triacs ................................................................................................................... 21

5.4.4 Transistors ........................................................................................................... 21

5.5 BASIC PRINCIPLES OF OPERATION............................................................ ......................... 22

5.5.1 Classification Of Electric Machines ...................................................................... 23

5.5.2 Basic Features Of Electric Machines .................................................................... 25

5.5.3 Electric Machines Applications ............................................................................ 25

5.5.3.1 Asynchronous Machines ............................................................................................ 25

5.5.3.2 Synchronous Machines .............................................................................................. 25

5.5.3.3 D.C. Machines ............................................................................................................ 26


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5 FUNDAMENTALS OF ELECTRICAL MACHINES

5.1 INTRODUCTION

The objective of this Module is to introduce the basic operation of rotating electricmachines. The operation of the three major classes of electric machines is described. The

emphasis of this module will be on explaining the properties of each type of machine, with

its advantages and disadvantages with regard to other types; and on classifying these

machines in terms of their performance characteristics and preferred field of application.

5.2 INTRODUCTION TO MACHINERY PRINCIPLES

This section will develop some basic tools for the analysis of magnetic field systems.

These results will then be applied to the analysis of transformers. In later sections they will

be used in the analysis of rotating machinery.

5.2.1 INTRODUCTION

1. Electric Machinesmechanical energy to electric energy or vice versa.Mechanical energy Electric energy : GENERATOR

Electric energymechanical energy : MOTOR.

2. Almost all practical motors and generators convert energy from one form toanother through the action of a magnetic field.

3. Only machines using magnetic fields to perform such conversions will beconsidered in this course.

4. When we talk about machines, another related device is the transformer. Atransformer is a device that converts ac electric energy at one voltage level to ac

electric energy at another voltage level.

5. Transformers are usually studied together with generators and motors becausethey operate on the same principle, the difference is just in the action of a

magnetic field to accomplish the change in voltage level.

6. Why are electric motors and generators so common?6.1 Electric power is a clean and efficient energy source that is very easy to

transmit over long distances and easy to control.

6.2 Does not require constant ventilation and fuel (compare to internal-combustion engine), free from pollutant associated with combustion.


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5.2.2 ROTATIONAL MOTION, NEWTONS LAW AND POWER

RELATIONSHIP

Almost all electric machines rotate about an axis, called the shaft of the machines. It

is important to have a basic understanding of rotational motion.

Angular position, Is the angle at which it is oriented, measured from some arbitrary reference point.

Its measurement units are in radians (rad) or in degrees. It is similar to the linear concept of

distance along a line.

Conventional notation: + value for anticlockwise rotation

- value for clockwise rotation

5.2.2.2 Angular Velocity, Defined as the velocity at which the measured point is moving. Similar to the

concept of standard velocity where:

= (5. 1)where:

r distance traverse by the body

t time taken to travel the distance r

For a rotating body, angular velocity is formulated as:

= (rad/s) (5. 2)where:

- Angular position/ angular distance traversed by the rotating body

t time taken for the rotating body to traverse the specified distance, .

5.2.2.3 Angular acceleration, is defined as the rate of change in angular velocity with respect to time. Its

formulation is as shown:

= (rad/s2) (5. 3)


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5.2.2.4 Torque, In linear motion, a force applied to an object causes its velocity to change. In the

absence of a net force on the object, its velocity is constant. The greater the force applied to

the object, the more rapidly its velocity changes. Similarly in the concept of rotation, when

an object is rotating, its angular velocity is constant unless a torque is present on it. Greater

the torque, more rapid the angular velocity changes.

Torque is known as a rotational force applied to a rotating body giving angular

acceleration, a.k.a. twisting force.

Definition of Torque: Product of force applied to the object and the smallest

distance between the line of action of the force and the objects axis of rotation.

= Force perpondicular distance = sin (5. 4)

5.2.2.5 Work, W

Is defined as the application of Force through a distance. Therefore, work may be

defined as:

= (5. 5)Assuming that the direction of F is collinear (in the same direction) with the direction

of motion and constant in magnitude, hence,

= (5. 6)Applying the same concept for rotating bodies,

= (5. 7)Assuming that is constant,

= (Joules) (5. 8)

5.2.2.6 Power, P

Is defined as rate of doing work. Hence,

= (watts) (5. 9)Applying this for rotating bodies,

=

=

=

(5. 10)


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This equation can describe the mechanical power on the shaft of a motor or

generator.

5.2.2.7 Newtons Law of Rotation

Newtons law for objects moving in a straight line gives a relationship between theforce applied to the object and the acceleration experience by the object as the result of

force applied to it. In general,

= (5. 11)where:

F Force applied

m mass of object

a resultant acceleration of object

Applying these concept for rotating bodies,

= (Nm) (5. 12)where:

- Torque

J moment of inertia

- angular acceleration

5.2.3 THE MAGNETIC FIELD

Magnetic fields are the fundamental mechanism by which energy is converted from

one form to another in motors, generators and transformers.

First, we are going to look at the basic principle A current-carrying wire produces a

magnetic field in the area around it.

5.2.3.1 Production of a Magnetic Field

Amperes Law the basic law governing the production of a magnetic field by a

current:

= (5. 13)where H is the magnetic field intensity produced by the current Inet and dl is a

differential element of length along the path of integration. H is measured in Ampere-turnsper meter.


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Figure 5. 1: Simple Magnetic Circuit.

Consider a current currying conductor is wrapped around a ferromagnetic core;

applying Amperes law, the total amount of magnetic field induced will be proportional to

the amount of current flowing through the conductor wound with N turns around the

ferromagnetic material as shown. Since the core is made of ferromagnetic material, it is

assume that a majority of the magnetic field will be confined to the core.

The path of integration in Amperes law is the mean path length of the core, l c. The

current passing within the path of integration Inet is then Ni, since the coil of wires cuts the

path of integration N times while carrying the current i. Hence Amperes Law becomes,

= = (5. 14)In this sense, H (Ampere turns per meter) is known as the effort required to induce a

magnetic field. The strength of the magnetic field flux produced in the core also depends on

the material of the core. Thus,

= (5. 15)B = magnetic flux density (webers per square meter, Tesla (T))

= magnetic permeability of material (Henrys per meter)

H = magnetic field intensity (ampere-turns per meter)

The constant may be further expanded to include relative permeabilitywhich can

be defined as below:

= 0 (5. 16)where: o permeability of free space (a.k.a. air)

Hence the permeability value is a combination of the relative permeability and the

permeability of free space. The value of relative permeability is dependent upon the type of

material used. The higher the amount permeability, the higher the amount of flux induced in

the core. Relative permeability is a convenient way to compare the magnetizability of

materials.


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Also, because the permeability of iron is so much higher than that of air, the majority

of the flux in an iron core remains inside the core instead of travelling through the

surrounding air, which has lower permeability. The small leakage flux that does leave the

iron core is important in determining the flux linkages between coils and the self-

inductances of coils in transformers and motors.

In a core such as in the figure 5.1,

= (5. 17)Now, to measure the total flux flowing in the ferromagnetic core, consideration has

to be made in terms of its cross sectional area (CSA). Therefore,

=

(5. 18)

Where: A cross sectional area throughout the core

Assuming that the flux density in the ferromagnetic core is constant throughout

hence constant A, the equation simplifies to be:

= (5. 19)Taking into account past derivation of B,

=

(5. 20)

5.2.4 MAGNETICS CIRCUITS

The flow of magnetic flux induced in the ferromagnetic core can be made analogous

to an electrical circuit hence the name magnetic circuit.

The analogy is as follows:

+

-

A

RV+

-

Reluctance, RF=Ni

(mmf)

Electric Circuit Analogy Magnetic Circuit Analogy

Figure 5. 2: Analogy between Electric and Magnetic circuits.


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Referring to the magnetic circuit analogy, F is denoted as magnetomotive force

(mmf) which is similar to Electromotive force in an electrical circuit (emf). Therefore, we can

safely say that F is the prime mover or force which pushes magnetic flux around a

ferromagnetic core at a value ofNi (refer to amperes law). Hence F is measured in ampere

turns. Hence the magnetic circuit equivalent equation is as shown:

= Similar to = (5. 21)The polarity of the mmf will determine the direction of flux. To easily determine the

direction of flux, the right hand curl rule is utilized:

a) The direction of the curled fingers determines the current flow.b) The resulting thumb direction will show the magnetic flux flow.The element of R in the magnetic circuit analogy is similar in concept to the electrical

resistance. It is basically the measure of material resistance to the flow of magnetic flux.

Reluctance in this analogy obeys the rule of electrical resistance (Series and Parallel Rules).

Reluctance is measured in Ampere-turns per Weber.

Series Reluctance,

= 1 + 2 + 3 + (5. 22)Parallel Reluctance

1

=

1

1+

1

2+

1

3+

(5. 23)

The inverse of electrical resistance is conductance which is a measure of conductivity

of a material. Hence the inverse of reluctance is known as permeance, P where it represents

the degree at which the material permits the flow of magnetic flux.

= 1 (5. 24)Since

= (5. 25)Thus,

= (5. 26)Also,

= = =

(5. 27)

Thus


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= (5. 28)And

= (5. 29)By using the magnetic circuit approach, it simplifies calculations related to the

magnetic field in a ferromagnetic material; however, this approach has inaccuracy

embedded into it due to assumptions made in creating this approach (within 5% of the real

answer). Possible reason of inaccuracy is due to:

a) The magnetic circuit assumes that all flux are confined within the core, but in realitya small fraction of the flux escapes from the core into the surrounding low-

permeability air, and this flux is called leakage flux.

b) The reluctance calculation assumes a certain mean path length and cross sectionalarea (csa) of the core. This is alright if the core is just one block of ferromagnetic

material with no corners, for practical ferromagnetic cores which have corners due

to its design, this assumption is not accurate.

c) In ferromagnetic materials, the permeability varies with the amount of flux alreadyin the material. The material permeability is not constant hence there is an

existence of non-linearity of permeability.

d) For ferromagnetic core which has air gaps, there are fringing effects that should betaken into account as shown:

Figure 5. 3: Air gap.

Example 5. 1:

A ferromagnetic core is shown. Three sides of this core are of uniform width, whilethe fourth side is somewhat thinner. The depth of the core (into the page) is 10cm, and the

other dimensions are shown in the figure. There is a 200 turn coil wrapped around the left

side of the core. Assuming relative permeability r of 2500, how much flux will be produced

by a 1A input current?


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Figure 5. 4: For this example.

Solution:

3 sides of the core have the same csa, while the 4th

side has a different area. Thus

the core can be divided into 2 regions:

(1) the single thinner side

(2) the other 3 sides taken together

The magnetic circuit corresponding to this core:


Example 5. 2:


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Figure shows a ferromagnetic core whose mean path length is 40cm. There is a

small gap of 0.05cm in the structure of the otherwise whole core. The csa of the core is

12cm2, the relative permeability of the core is 4000, and the coil of wire on the core has 400

turns. Assume that fringing in the air gap increases the effective csa of the gap by 5%. Given

this information, find

(a) the total reluctance of the flux path (iron plus air gap)(b) the current required to produce a flux density of 0.5T in the air gap.

Solution:

The magnetic circuit corresponding to this core is shown below:


Example 5. 3:

A ferromagnetic core is shown in Figure 5.4. The depth of the core is 5 cm. The other

dimensions of the core are as shown in the figure. Find the value of the current that will

produce a flux of 0.005 Wb. With this current, what is the flux density at the top of the core?What is the flux density at the right side of the core?


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Assume that the relative permeability of the core is 1000.


Solution:

There are three regions in this core. The top and bottom form one region, the left

side forms a second region, and the right side forms a third region. If we assume that the

mean path length of the flux is in the center of each leg of the core, and if we ignorespreading at the corners of the core, then the path lengths are 1 = 2(27.5 ) = 55 ,2 = 30 , and 3 = 30 . The reluctances of these regions are:

The total reluctance is thus

and the magnetomotive force required to produce a flux of 0.003 Wb is

and the required current is


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The flux density on the top of the core is

The flux density on the right side of the core is

5.2.5 PRODUCTION OF INDUCED FORCE ON A WIRE.

A current carrying conductor present in a uniform magnetic field of flux density B,

would produce a force to the conductor/wire. Dependent upon the direction of the

surrounding magnetic field, the force induced is given by:

= ( ) (5. 30)where:

i represents the current flow in the conductor

l length of wire, with direction of ldefined to be in the direction of current

flow.

B magnetic field density

The direction of the force is given by the right-hand rule. Direction of the force

depends on the direction of current flow and the direction of the surrounding magnetic

field. A rule of thumb to determine the direction can be found using the right-hand rule as

shown below:

Figure 5. 9: Right-hand rule for determining the direction magnetic-field component of the Lorentz force.


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5.3 TRANSFORMERS

Before we proceed with a study of electric machinery, it is desirable to discuss

certain aspects of the theory of magnetically-coupled circuits, with emphasis on transformer

action.

Although the static transformer is not an energy conversion device, it is an

indispensable component in many energy conversion systems. A significant component of ac

power systems, it makes possible electric generation at the most economical generator

voltage, power transfer at the most economical transmission voltage, and power utilization

at the most suitable voltage for the particular utilization device.

The transformer is also widely used in low-power, low-current electronic and control

circuits for performing such functions as matching the impedances of a source and its load

for maximum power transfer, isolating one circuit from another, or isolating direct current

while maintaining ac continuity between two circuits.

The transformer is one of the simpler devices comprising two or more electric

circuits coupled by a common magnetic circuit. Its analysis involves many of the principles

essential to the study of electric machinery. Thus, our study of the transformer will serve as

a bridge between the introduction to magnetic-circuit analysis and the study of electric

machinery to follow.

5.3.1 CONSTRUCTION OF TRANSFORMERS

Essentially, a transformer consists of two or more windings coupled by mutual

magnetic flux. If one of these windings, the primary, is connected to an alternating-voltage

source, an alternating flux will be produced whose amplitude will depend on the primary

voltage, the frequency of the applied voltage, and the number of turns. The mutual flux will

link the other winding, the secondary, and will induce a voltage in it whose value will depend

on the number of secondary turns as well as the magnitude of the mutual flux and the

frequency. By properly proportioning the number of primary and secondary turns, almost

any desired voltage ratio, or ratio of transformation, can be obtained.

The essence of transformer action requires only the existence of time-varying

mutual flux linking two windings. Such action can occur for two windings coupled through

air, but coupling between the windings can be made much more effectively using a core of

iron or other ferromagnetic material, because most of the flux is then confined to a definite,

high-permeability path linking the windings. Such a transformer is commonly called an iron-

core transformer. Most transformers are of this type. The following discussion is concerned

almost wholly with iron-core transformers.

Types of cores for power transformer (both types are constructed from thin

laminations electrically isolated from each other minimize eddy currents)


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Core Form: a simple rectangular laminated piece of steel with the transformer windings

wrapped around two sides of the rectangle.

Shell Form: a three legged laminated core with the windings wrapped around the centre

leg.

Figure 5. 10: Transformers construction.

The primary and secondary windings are wrapped one on top of the other with the

low-voltage winding innermost, due to 2 purposes:

1. It simplifies the problem of insulating the high-voltage winding from the core.2. It results in much less leakage flux


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5.3.2 TYPES OF TRANSFORMERS:

1. Distribution transformers are generally used in power distribution andtransmission systems.

2. Power transformers are used in electronic circuits and come in many differenttypes and applications.

3. Control transformers are generally used in circuits that require constant voltageor constant current with a low power or volt-amp rating.

4. Auto transformers are generally used in low power applications where a variablevoltage is required.

5. Isolation transformers are normally low power transformers used to isolatenoise from or to ground electronic circuits.

6. Instrument potential and instrument current transformers are used foroperation of instruments such as ammeters, voltmeters, watt meters, and relays

used for various protective purposes.

Figure 5. 11: Examples of Transformers.


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5.3.3 THE IDEAL TRANSFORMER

Definition a lossless device with an input winding and an output winding. Figures

below show an ideal transformer and schematic symbols of a transformer.

Figure 5. 12: Ideal transformer and schematic symbols of a transformer.

The transformer has Np turns of wire on its primary side and Ns turns of wire on its

secondary sides. The relationship between the primary and secondary voltage is as follows:

=

= (5. 31)

where a is the turns ratio of the transformer.


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The relationship between primary and secondary current is:

=

1

(5. 32)

Note that since both types of relations give a constant ratio, hence the transformeronly changes ONLY the magnitude value of current and voltage. Phase angles are not

affected.

5.3.4 POWER IN AN IDEAL TRANSFORMER

The power supplied to the transformer by the primary circuit:

= cos (5. 33)Where p = the angle between the primary voltage and the primary current. The

power supplied by the transformer secondary circuit to its loads is given by:

= cos (5. 34)Where s = the angle between the secondary voltage and the secondary current.

The primary and secondary windings of an ideal transformer have the SAME power

factor because voltage and current angles are unaffected = = How does power going into the primary circuit compare to the power coming out?

= cos (5. 35)Also,

= = (5. 36)

= cos (5. 37)So,

= cos = (5. 38)The same idea can be applied for reactive power Q and apparent power S.

= (5. 39)


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5.4 INTRODUCTION TO POWER ELECTRONICS

Until the last few decades of the twentieth century, ac machines tended to be

employed primarily as single-speed devices. Typically they were operated from fixed-

frequency sources (in most cases this was the 50- or 60-Hz power grid). In the case of

motors, control of motor speed requires a variable-frequency source, and such sources were

not readily available. Thus, applications requiring variable speed were serviced by dc

machines, which can provide highly flexible speed control, although at some cost since they

are more complex, more expensive, and require more maintenance than their ac

counterparts.

The availability of solid-state power switches changed this picture immensely. It is

now possible to build power electronics capable of supplying the variable voltage/ current,

variable-frequency drive required to achieve variable-speed performance from ac machines.

Ac machines have now replaced dc machines in many traditional applications, and a wide

range of new applications have been developed.

Power electronics is a discipline which can be mastered only through significant

study. Many books have been written on this subject. It is clear that a single lesson cannot

begin to do justice to this topic. Thus our objectives here are limited. Our goal is to provide

an overview of power electronics.

5.4.1 DIODES

Diodes constitute the simplest of power switches. The essential features of a diode

are captured in the idealized v-i characteristic of Figure 5.14.a. The symbol used to representa diode is shown in Figure 5.14.b.

Figure 5. 13: (a) v-icharacteristic of an ideal diode.(b) Diode symbol.

We can see that the ideal diode blocks current flow when the voltage is negative (i =

0 for v < 0) and passes positive current without voltage drop (v - 0 for i > 0). We will refer to

the negative-voltage region as the diode's OFF state and the positive current region as the

diode's ON state.

The diode is the simplest power switch in that it cannot be controlled; it simply turns

ON when positive current begins to flow and turns OFF when the current attempts to

reverse. In spite of this simple behavior, it is used in a wide variety of applications, the most

common of which is as a rectifier to convert ac to dc.


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Example 5. 4:

Consider the half-wave rectifiercircuit of Figure 5.15 in which a resistor R is supplied

by a voltage source () = 0 sin through a diode. Assume the diode to be ideal.Find the resistor voltage

()and current

().

Figure 5. 14: Half-wave rectifier circuit for this Example

Solution :

Figure 5. 15: Resistor Voltage.

() = 0 sin 00 < 0

The current has the same form of the voltage and is found simply as =

.

The terminology half-wave rectification is applied to this system because voltage is

applied to the resistor during only the half cycle for which the supply voltage waveform is

positive.

5.4.2 SILICON CONTROLLED RECTIFIERS

5.4.3 TRIACS

5.4.4 TRANSISTORS


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5.5 TERMINOLOGY

The parts of an alternator or related equipment can be expressed in either

mechanical terms or electrical terms. Although distinctly separate, these two sets of

terminology are frequently used interchangeably or in combinations that include one

mechanical term and one electrical term. This may cause confusion when working with

compound machines such as brushless alternators, or in conversation among people who

are accustomed to work with differently configured machinery.

In alternating current machines, the armature is usually stationary, and is known as

the stator winding. In DC rotating machines other than brushless DC machines, it is usually

rotating, and is known as the rotor. The pole piece of a permanent magnet or electromagnet

and the moving, iron part of a solenoid, especially if the latter acts as a switch or relay, may

also be referred to as armatures.

MechanicalRotor: The rotating part of an alternator, generator, dynamo or motor.

Stator: The stationary part of an alternator, generator, dynamo or motor

Electrical

Armature: The power-producing component of an alternator, generator, dynamo or motor.

The armature can be on either the rotor or the stator.

Field: The magnetic field component of an alternator, generator, dynamo or motor. The field

can be on either the rotor or the stator and can be either an electromagnet or a permanent

magnet.

5.6 BASIC PRINCIPLES OF OPERATION OF ELECTRICAL MACHINES

Electric motors and generators are a group of devices used to convert mechanical

energy into electrical energy or electrical energy into mechanical energy, by electromagnetic

means. A machine that converts mechanical energy into electrical energy is called a

generator, alternator or dynamo, and a machine that converts electrical energy into

mechanical energy is called a motor.

Two related physical principles underline the operation of generators and motors.

The first is the principle of electromagnetic induction discovered by Michael Faraday in

1831. If a conductor is moved through a magnetic field, or if the strength of a stationary

conducting loop is made to vary, a current is set up or induced in the conductor. The

converse of this principle of the electromagnetic reaction, first discovered by Andr Ampere

in 1820. If a current is passed through a conductor located in a magnetic field, the field

exerts a mechanical force on it.

Both motors and generators consist of two basic units, the field, which is the

electromagnets with its coils, and the armature (the structure that supports the conductors

which cut the magnetic field and carry the induced current in a motor). The armature is

usually a laminated soft-iron core around which conducting wires are wound in coils.


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Figure 5. 16: Functional block diagram of electromechanical energy conversion devices as (A) motor, and (B)

generator.

5.7 CLASSIFICATION OF ELECTRIC MACHINES

There are several methods of classifying electric machines:

Electric power supply - Electric machines are classified as D.C. and A.C. machines as

well as according to their stator and rotor constructions as shown in Figure

5.18.


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Figure 5. 17: Classification of Electric Machines.

It is also useful to classify electric machines in terms of their energy conversion

characteristics. A machine acts as a generator if it converts mechanical

energy from a prime movere.g., an internal combustion enginetoelectrical form.

Examples of generators are the large machines used in power-generating plants, or

the common automotive alternator.

A machine is classified as a motor if it converts electrical energy to mechanical form.

The latter class of machines is probably of more direct interest to you,

because of its widespread application in engineering practice.

Electric motors are used to provide forces and torques to generate motion in

countless industrial applications. Machine tools, robots, punches, presses,

mills, and propulsion systems for electric vehicles are but a few examples of

the application of electric machines in engineering.

AC Machines

Universal Machines

Single phase

Synchrounous Induction

Singlecage

Woundrotor

Polyphase

Synchrounous

SalientPermanent

Magnet

Induction

Singlecage

Woundrotor

DC Machines

Permanentmagnet

Series Wound Shunt Wound Compound Wound


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Figure 5. 18: Stator and rotor fields and the force acting on a rotating machine.

In most industrial applications, the induction machine is the preferred choice,

because of the simplicity of its construction. However, the analysis of the performance of an

induction machine is rather complex. On the other hand, DC machines are quite complex in

their construction but can be analyzed relatively simply with the analytical tools we have

already acquired.

5.8 BASIC FEATURES OF ELECTRIC MACHINES

5.9 ELECTRIC MACHINES APPLICATIONS

5.9.1.1 Asynchronous Machines

Petroleum and chemical pumps.. Cooling towers. Air-handling equipment. Compressors. Process machinery. Blowers and fans. Drilling machines. Grinders. Lathes. Conveyors. Crushers, etc.

5.9.1.2 Synchronous Machines

Power generation Wind energy turbines Power factor correction


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Voltage regulation improvement of transmission lines. Electric clock drives. Servo drives. Compressors.

5.9.1.3 D.C. Machines

Rolling mills Elevators Conveyors Electric locomotives Rapid transit systems Cranes and hoists Lathes Machines tools Blowers and fans, etc.

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