A PROJECT REPORT

ON

“ELECTROMAGNETIC

PISTON ENGINE CAR” BY

ALANKRIT SHUKLA (0807040001)

AVADHESH KUMAR (0807040006)

ANKUSH KUMAR (0807040402)

UPENDRA KUMAR (0807040038)

PUSHKAR SINGH GAUNIYA (0807040025)

Submitted to

Department of “Mechanical Engineering”

College of Engineering & Rural Technology (Affiliated to Gautam Buddha Technical University, Lucknow)

Partapur Bye-pass Road, Meerut (U.P) – 250103

(Session 2011-12)

DECLARATION

We hereby declare that this submission is our own work and that, to the

best of our knowledge and belief, it contains no material previously

published or written by another person nor material which to a substantial

extent has been accepted for the award of any other degree or diploma of

the university or other institute of higher learning, except where due

acknowledgement has been made in the text

Signature: Signature:

Name: Alankrit Shukla Name: Avadhesh Kumar

Roll No: 0807040001 Roll No: 0807040006

Date: Date :

Signature: Signature:

Name: Ankush Kumar Name: Upendra kumar

Roll No: 0807040402 Roll No: 0807040038

Date: Date:

Signature:

Name: Pushkar Singh Gauniya

Roll No: 0807040025

Date:

COLLEGE OF ENGINEERING & RURAL T8ECHNOLOGY Approved By A.I.C.T.E., New Delhi Affiliated to G.B. Technical University, Lucknow Partapur Bye-Pass Road, Meerut-250103

Ph.: 0121-2440262, 2440263, 2440821, 3243537 Fax: 0121-2440257

Web site: www.certmeerut.org •E-mail: cert_9@rediffmaill.com

CERTIFICATE

This is to certify that Project Report entitled “ELECTROMAGNETIC PISTON

ENGINE CAR” which is submitted by Alankrit Shukla,Avadhesh Kumar,Ankush

Kumar,Upendra Kumar,Pushkar Singh Gauniyain partial fulfillment of the

requirement for the award of degree B. Tech. in Department of Mechanical Engineering

of U. P. Technical University, is a record of the candidate own work carried out by him

under my supervision. The matter embodied in this thesis is original and has not been

submitted for the award of any other degree.

Mr. D.P. Singh

Date: Sr. Lecturer

Department of Mechanical Engineering

ACKNOWLEDGEMENT Sincierity, thoroughness and preserverance have been a constant source of

inspiration for us. It is only his cognizant efforts that our endeavors have seen

ligh of the day.

We also take the opportunity to acknowledge the contribution of Mr. B.K.

SINGH, Head of Department, Mechanical Engineering, College of Engineering &

Rural Technology, Meerut for his full suport and assistance during the

development of the project. It gives us a great sense of pleasure to present the

report of the B.Tech project undertaken during B.Tech. Final Year. We owe

special debt of gratitude to Mr. S.K. Pal (department of Mechanical Engineering)

at College of Engineering & Rural Technology, Meerut, for his constant support

and guidance throughout the course of our work. His

We also do not like to miss the opportunity to acknowledge the

contribution of all faculty members of the department for their kind assistance

and cooperation during the development of our project. Last but not least, we

acknowledge our friends for their contributionin the comptition in the project.

Signature: Signature:

Name: Alankrit Shukla Name: Avadhesh Kumar

Roll No: 0807040001 Roll No: 0807040006

Date: Date:

Signature: Signature:

Name: Ankush Kumar Name: Upendra Kumar

Roll No: 0807040402 Roll No: 0807040038

Signature:

Name: Pushksr singh Gauniya

Roll No: 0807040025

MEANING OF PROJECT

The project gives the significance of the following field of engineering-

P- signifies the phenomenon of planning which deals with symbolic nation

and proper arrangement of sense and suggestion receptivity accordingly to

the needs.

R- It is associate with the word resources which guides to promote

planning.

OJ-This letters signifies the overhead expenses in un estimated expenses

that may occur in the manufacture design or layout of the project.

E- signifies the word engineering.

C- signifies the convey about phenomenon of construction low cost.

T-The word T stands for the word technique unless there is technique; it is

impossible to complete the project.

CONTENTS

CHAPTER PAGE

INTRODUCTION 1-13

Electromagnet …..1

Working of Iron Core …..2

History …..3

Uses of Electromagnets ……4

Analysis of ferromagnetic electromagnets ……5

Force between electromagnets ……8

Electromagnetic Piston Engine 14-17

Working principle ….14

POWER SUPPLY 18-22

Need of power supply ….18

TRANSFORMER 23-43

Basic principle ….24

Induction law ….24

Energy losses ….28

Core construction ….37

RECTIFIERS 44-54

Half wave rectifier ….44

Full wave rectifier …..45

Rectifier technologies …..51

D C MOTOR 55-61

Basic motor action …..55

Rules for motor action …..57

Torque and rotory motion …..57

Production of continuous rotation …..59

Elementary d c motor …..61

Cost of components 65

INTRODUCTION

ELECTROMAGNETS

An electromagnet is a type of magnet in which the magnetic field is produced by the flow of electric

current. The magnetic field disappears when the current is turned off. Electromagnets are widely

used as components of other electrical devices, such

as motors, generators, relays, loudspeakers, hard disks, MRI machines, scientific instruments,

and magnetic separation equipment, as well as being employed as industrial lifting electromagnets

for picking up and moving heavy iron objects like scrap iron.

A simple electromagnet consisting of a coil of insulated wire wrapped around an iron core. The

strength of magnetic field generated is proportional to the amount of current.

Current (I) through a wire produces a magnetic field (B). The field is oriented according to the right-

hand rule.

An electric current flowing in a wire creates a magnetic field around the wire (see drawing below).

To concentrate the magnetic field, in an electromagnet the wire is wound into a coil with many

turns of wire lying side by side. The magnetic field of all the turns of wire passes through the center

of the coil, creating a strong magnetic field there. A coil forming the shape of a straight tube

(a helix) is called a solenoid; a solenoid that is bent into a donut shape so that the ends meet is

called a toroid. Much stronger magnetic fields can be produced if a "core"

of ferromagnetic material, such as soft iron, is placed inside the coil. The ferromagnetic core

increases the magnetic field to thousands of times the strength of the field of the coil alone, due to

the high magnetic permeability μ of the ferromagnetic material. This is called a ferromagnetic-core

or iron-core electromagnet.

Magnetic field produced by a solenoid(coil of wire). This drawing shows a cross section through the

center of the coil. The crosses are wires in which current is moving into the page; the dots are wires

in which current is moving up out of the page.

The direction of the magnetic field through a coil of wire can be found from a form of the right-

hand rule. If the fingers of the right hand are curled around the coil in the direction of current flow

(conventional current, flow of positive charge) through the windings, the thumb points in the

direction of the field inside the coil. The side of the magnet that the field lines emerge from is

defined to be the north pole.

The main advantage of an electromagnet over a permanent magnet is that the magnetic field can

be rapidly manipulated over a wide range by controlling the amount of electric current. However, a

continuous supply of electrical energy is required to maintain the field.

Working of Iron Core

The material of the core of the magnet (usually iron) is composed of small regions called magnetic

domains that act like tiny magnets (see ferromagnetism). Before the current in the electromagnet is

turned on, the domains in the iron core point in random directions, so their tiny magnetic fields

cancel each other out, and the iron has no large scale magnetic field. When a current is passed

through the wire wrapped around the iron, its magnetic field penetrates the iron, and causes the

domains to turn, aligning parallel to the magnetic field, so their tiny magnetic fields add to the

wire's field, creating a large magnetic field that extends into the space around the magnet. The

larger the current passed through the wire coil, the more the domains align, and the stronger the

magnetic field is. Finally all the domains are lined up, and further increases in current only cause

slight increases in the magnetic field: this phenomenon is called saturation.

When the current in the coil is turned off, most of the domains lose alignment and return to a

random state and the field disappears. However some of the alignment persists, because the

domains have difficulty turning their direction of magnetization, leaving the core a weak permanent

magnet. This phenomenon is called hysteresis and the remaining magnetic field is called remanent

magnetism. The residual magnetization of the core can be removed by degaussing.

Fig:Electromagnet used in the Tevatron particle accelerator, Fermilab, USA

History

Fig:Sturgeon's electromagnet, 1824

Danish scientist Hans Christianorsted discovered in 1820 that electric currents create magnetic

fields. British scientist William Sturgeon invented the electromagnet in 1824.His first electromagnet

was a horseshoe-shaped piece of iron that was wrapped with about 18 turns of bare copper wire

(insulated wire didn't exist yet). The iron was varnished to insulate it from the windings. When a

current was passed through the coil, the iron became magnetized and attracted other pieces of

iron; when the current was stopped, it lost magnetization. Sturgeon displayed its power by showing

that although it only weighed seven ounces (roughly 200 grams), it could lift nine pounds (roughly 4

kilos) when the current of a single-cell battery was applied. However, Sturgeon's magnets were

weak because the uninsulated wire he used could only be wrapped in a single spaced out layer

around the core, limiting the number of turns. Beginning in 1827, US scientist Joseph

Henry systematically improved and popularized the electromagnet. By using wire insulated by silk

thread he was able to wind multiple layers of wire on cores, creating powerful magnets with

thousands of turns of wire, including one that could support 2,063 lb (936 kg). The first major use

for electromagnets was in telegraph sounders.

The magnetic domain theory of how ferromagnetic cores work was first proposed in 1906 by

French physicist Pierre-Ernest Weiss, and the detailed modern quantum mechanical theory of

ferromagnetism was worked out in the 1920s by Werner Heisenberg, Lev Landau, Felix Bloch and

others.

USES OF ELECTROMAGNETS

Fig: Industrial electromagnet lifting scrap iron, 1914

Electromagnets are very widely used in electric and electromechanical devices, including:

Motors and generators

Transformers

Relays, including reed relays originally used in telephone exchanges

Electric bells

Loudspeakers

Magnetic recording and data storage equipment: tape recorders, VCRs, hard disks

Scientific instruments such as MRI machines and mass spectrometers

Particle accelerators

Magnetic locks

Magnetic separation of material

Industrial lifting magnets

Electromagnetic suspension used for MAGLEV trains

Analysis of ferromagnetic electromagnets

For definitions of the variables below, see box at end of article.

The magnetic field of electromagnets in the general case is given by Ampere's Law:

which says that the integral of the magnetizing field H around any closed loop of the field is equal

to the sum of the current flowing through the loop. Another equation used, that gives the magnetic

field due to each small segment of current, is the Biot-Savart law. Computing the magnetic field and

force exerted by ferromagnetic materials is difficult for two reasons. First, because the strength of

the field varies from point to point in a complicated way, particularly outside the core and in air

gaps, where fringing fields and leakage flux must be considered. Second, because the magnetic field

B and force are nonlinear functions of the current, depending on the nonlinear relation between B

and H for the particular core material used. For precise calculations, computer programs that can

produce a model of the magnetic field using the finite element method are employed.

Magnetic circuit – The constant B field approximation

Magnetic field (green) of a typical electromagnet, with the iron coreC forming a closed loop with

two air gaps G in it. Most of the magnetic field B is concentrated in the core. However some of the

field lines BL, called the "leakage flux", do not follow the full core circuit and so do not contribute to

the force exerted by the electromagnet. In the gapsG the field lines spread out beyond the

boundaries of the core in "fringing fields" BF. This increases the "resistance" (reluctance) of the

magnetic circuit, decreasing the total magnetic flux in the core. Both the leakage flux and the

fringing fields get larger as the gaps are increased, reducing the force exerted by the magnet.

Line L shows the average length of the magnetic circuit, used in equation (1) below. It is the sum of

the length Lcore in the iron core and the length Lgap in the air gaps

In many practical applications of electromagnets, such as motors, generators, transformers, lifting

magnets, and loudspeakers, the iron core is in the form of a loop or magnetic circuit, possibly

broken by a few narrow air gaps. This is because iron presents much less "resistance" (reluctance)

to the magnetic field than air, so a stronger field can be obtained if most of the magnetic field's

path is within the core.

Since most of the magnetic field is confined within the outlines of the core loop, this allows a

simplification of the mathematical analysis. See the drawing at right. A common simplifying

assumption satisfied by many electromagnets, which will be used in this section, is that the

magnetic field strength B is constant around the magnetic circuit and zero outside it. Most of the

magnetic field will be concentrated in the core material (C). Within the core the magnetic

field (B) will be approximately uniform across any cross section, so if in addition the core has

roughly constant area throughout its length, the field in the core will be constant. This just leaves

the air gaps (G), if any, between core sections. In the gaps the magnetic field lines are no longer

confined by the core, so they 'bulge' out beyond the outlines of the core before curving back to

enter the next piece of core material, reducing the field strength in the gap. The bulges (BF) are

called fringing fields. However, as long as the length of the gap is smaller than the cross section

dimensions of the core, the field in the gap will be approximately the same as in the core. In

addition, some of the magnetic field lines (BL) will take 'short cuts' and not pass through the entire

core circuit, and thus will not contribute to the force exerted by the magnet. This also includes field

lines that encircle the wire windings but do not enter the core. This is called leakage flux. Therefore

the equations in this section are valid for electromagnets for which:

1. The magnetic circuit is a single loop of core material, possibly broken by a few air gaps

2. The core has roughly the same cross sectional area throughout its length.

3. Any air gaps between sections of core material are not large compared with the cross

sectional dimensions of the core.

4. There is negligible leakage flux

The main nonlinear feature of ferromagnetic materials is that the B field saturates at a certain

value, which is around 1.6 teslas (T) for most high permeability core steels. The B field increases

quickly with increasing current up to that value, but above that value the field levels off and

becomes almost constant, regardless of how much current is sent through the windings.

Magnetic field created by a current

The magnetic field created by an electromagnet is proportional to both the number of turns in the

winding, N, and the current in the wire, I, hence this product, NI, in ampere-turns, is given the

name magnetomotive force. For an electromagnet with a single magnetic circuit, of which

lengthLcore is in the core material and length Lgap is in air gaps, Ampere's Law reduces to:

where

is the permeability of free space (or air) . A is amperes.

This is a nonlinear equation, because the permeability of the core, μ, varies with the magnetic

field B. For an exact solution, the value of μ at the B value used must be obtained from the core

material hysteresis curve. If B is unknown, the equation must be solved by numerical methods.

However, if the magnetomotive force is well above saturation, so the core material is in saturation,

the magnetic field will be approximately the saturation value Bsat for the material, and won't vary

much with changes in NI. For a closed magnetic circuit (no air gap) most core materials saturate at a

magnetomotive force of roughly 800 ampere-turns per meter of flux path.

For most core materials, . So in equation (1) above, the second

term dominates. Therefore, in magnetic circuits with an air gap, the strength of the magnetic

field B depends strongly on the length of the air gap, and the length of the flux path in the core

doesn't matter much.

Force exerted by magnetic field

The force exerted by an electromagnet on a section of core material is:

The 1.6 T limit on the field mentioned above sets a limit on the maximum force per unit core area,

or pressure, an iron-core electromagnet can exert; roughly:

In more intuitive units it's useful to remember that at 1T the magnetic pressure is approximately 4

atmospheres, or kg/cm2.

Given a core geometry, the B field needed for a given force can be calculated from (2); if it comes

out to much more than 1.6 T, a larger core must be used.

Closed magnetic circuit

Fig:Cross section of lifting electromagnet

Fig showing cylindrical construction. The windings (C)are flat copper strips to withstand the Lorentz

force of the magnetic field. The core is formed by the thick iron housing(D) that wraps around the

windings.

For a closed magnetic circuit (no air gap), such as would be found in an electromagnet lifting a piece

of iron bridged across its poles, equation (1) becomes:

Substituting into (2), the force is:

It can be seen that to maximize the force, a core with a short flux path L and a wide cross sectional

area A is preferred. To achieve this, in applications like lifting magnets (see photo above)

and loudspeakers a flat cylindrical design is often used. The winding is wrapped around a short wide

cylindrical core that forms one pole, and a thick metal housing that wraps around the outside of the

windings forms the other part of the magnetic circuit, bringing the magnetic field to the front to

form the other pole.

Force between electromagnets

The above methods are inapplicable when most of the magnetic field path is outside the core. For

electromagnets (or permanent magnets) with well defined 'poles' where the field lines emerge

from the core, the force between two electromagnets can be found using the 'Gilbert model' which

assumes the magnetic field is produced by fictitious 'magnetic charges' on the surface of the poles,

with pole strength m and units of Ampere-turn meter. Magnetic pole strength of electromagnets

can be found from:

The force between two poles is:

This model doesn't give the correct magnetic field inside the core, and thus gives incorrect results if

the pole of one magnet gets too close to another magnet.

Side effects in large electromagnets

There are several side effects which become important in large electromagnets and must be

provided for in their design:

Ohmic heating

Large aluminumbusbars carrying current into the electromagnets at the LNCMI (Laboratoire

National des Champs MagnétiquesIntenses) high field laboratory.

The only power consumed in a DC electromagnet is due to the resistance of the windings, and is

dissipated as heat. Some large electromagnets require cooling water circulating through pipes in

the windings to carry off the waste heat.

Since the magnetic field is proportional to the product NI, the number of turns in the

windings N and the current I can be chosen to minimize heat losses, as long as their product is

constant. Since the power dissipation, P = I2R, increases with the square of the current but only

increases approximately linearly with the number of windings, the power lost in the windings can

be minimized by reducing I and increasing the number of turns N proportionally. For example

halving I and doubling N halves the power loss. This is one reason most electromagnets have

windings with many turns of wire.

However, the limit to increasing N is that the larger number of windings takes up more room

between the magnet's core pieces. If the area available for the windings is filled up, more turns

require going to a smaller diameter of wire, which has higher resistance, which cancels the

advantage of using more turns. So in large magnets there is a minimum amount of heat loss that

can't be reduced. This increases with the square of the magnetic flux B2.

Inductive voltage spikes

An electromagnet is a large inductor, and resists changes in the current through its windings. Any

sudden changes in the winding current cause large voltage spikes across the windings. This is

because when the current through the magnet is increased, such as when it is turned on, energy

from the circuit must be stored in the magnetic field. When it is turned off the energy in the field is

returned to the circuit.

If an ordinary switch is used to control the winding current, this can cause sparks at the terminals of

the switch. This doesn't occur when the magnet is switched on, because the voltage is limited to

the power supply voltage. But when it is switched off, the energy in the magnetic field is suddenly

returned to the circuit, causing a large voltage spike and an arc across the switch contacts, which

can damage them. With small electromagnets a capacitor is often used across the contacts, which

reduces arcing by temporarily storing the current. More often a diode is used to prevent voltage

spikes by providing a path for the current to recirculate through the winding until the energy is

dissipated as heat. The diode is connected across the winding, oriented so it is reverse-biased

during steady state operation and doesn't conduct. When the supply voltage is removed, the

voltage spike forward-biases the diode and the reactive current continues to flow through the

winding, through the diode and back into the winding. A diode used in this way is often called

a flyback diode.

Large electromagnets are usually powered by variable current electronic power supplies, controlled

by a microprocessor, which prevent voltage spikes by accomplishing current changes slowly, in

gentle ramps. It may take several minutes to energize or deenergize a large magnet.

Lorentz forces

In powerful electromagnets, the magnetic field exerts a force on each turn of the windings, due to

the Lorentz force acting on the moving charges within the wire. The Lorentz force is

perpendicular to both the axis of the wire and the magnetic field. It can be visualized as a pressure

between the magnetic field lines, pushing them apart. It has two effects on an electromagnet's

windings:

The field lines within the axis of the coil exert a radial force on each turn of the windings,

tending to push them outward in all directions. This causes a tensile stress in the wire.

The leakage field lines between each turn of the coil exert a repulsive force between

adjacent turns, tending to push them apart.

The Lorentz forces increase with B2. In large electromagnets the windings must be firmly clamped in

place, to prevent motion on power-up and power-down from causing metal fatigue in the windings.

In the Bitter design, below, used in very high field research magnets, the windings are constructed

as flat disks to resist the radial forces, and clamped in an axial direction to resist the axial ones.

Core losses

In alternating current (AC) electromagnets, used in transformers, inductors, and AC

motors and generators, the magnetic field is constantly changing. This causes energy losses in

their magnetic cores that are dissipated as heat in the core. The losses stem from two processes:

Eddy currents: From Faraday's law of induction, the changing magnetic field induces

circulating electric currents inside nearby conductors, called eddy currents. The energy in

these currents is dissipated as heat in the electrical resistance of the conductor, so they are

a cause of energy loss. Since the magnet's iron core is conductive, and most of the magnetic

field is concentrated there, eddy currents in the core are the major problem. Eddy currents

are closed loops of current that flow in planes perpendicular to the magnetic field. The

energy dissipated is proportional to the area enclosed by the loop. To prevent them, the

cores of AC electromagnets are made of stacks of thin steel sheets, or laminations, oriented

parallel to the magnetic field, with an insulating coating on the surface. The insulation layers

prevent eddy current from flowing between the sheets. Any remaining eddy currents must

flow within the cross section of each individual lamination, which reduces losses greatly.

Another alternative is to use a ferrite core, which is a nonconductor.

Hysteresis losses: Reversing the direction of magnetization of the magnetic domains in the

core material each cycle causes energy loss, because of the coercivity of the material. These

losses are called hysteresis. The energy lost per cycle is proportional to the area of

the hysteresis loop in the BH graph. To minimize this loss, magnetic cores used in

transformers and other AC electromagnets are made of "soft" low coercivity materials, such

as silicon steel or soft ferrite.

The energy loss per cycle of the AC current is constant for each of these processes, so the power

loss increases linearly with frequency.

High field electromagnets

Superconducting electromagnets

When a magnetic field higher than the ferromagnetic limit of 1.6 T is needed, superconducting

electromagnets can be used. Instead of using ferromagnetic materials, these

use superconducting windings cooled with liquid helium, which conduct current without electrical

resistance. These allow enormous currents to flow, which generate intense magnetic fields.

Superconducting magnets are limited by the field strength at which the winding material ceases to

be superconducting. Current designs are limited to 10–20 T, with the current (2009) record of 33.8

T. The necessary refrigeration equipment and cryostat make them much more expensive than

ordinary electromagnets. However, in high power applications this can be offset by lower operating

costs, since after startup no power is required for the windings, since no energy is lost to ohmic

heating. They are used in particle accelerators, MRI machines, and research.

Bitter electromagnets

Both iron-core and superconducting electromagnets have limits to the field they can produce.

Therefore the most powerful man-made magnetic fields have been generated by air-

core nonsuperconducting electromagnets of a design invented by Francis Bitter in 1933,

called Bitter electromagnets. Instead of wire windings, a Bitter magnet consists of a solenoid made

of a stack of conducting disks, arranged so that the current moves in a helical path through them.

This design has the mechanical strength to withstand the extreme Lorentz forces of the field, which

increase with B2. The disks are pierced with holes through which cooling water passes to carry away

the heat caused by the high current. The strongest continuous field achieved with a resistive

magnet is currently (2008) 35 T, produced by a Bitter electromagnet. The strongest continuous

magnetic field, 45 T, was achieved with a hybrid device consisting of a Bitter magnet inside a

superconducting magnet.

Definition of terms

square meter cross sectional area of core

Tesla Magnetic field (Magnetic flux density)

Newton Force exerted by magnetic field

ampere per meter Magnetizing field

Ampere Current in the winding wire

Meter Total length of the magnetic field

path

Meter Length of the magnetic field path in

the core material

Meter Length of the magnetic field path in air

gaps

ampere meter Pole strength of the electromagnet

newton per square ampere Permeability of the electromagnet

core material

newton per square ampere Permeability of free space (or air) =

4π(10−7)

- Relative permeability of the

electromagnet core material

- Number of turns of wire on the

electromagnet

Meter Distance between the poles of two

electromagnets

Electromagnetic Piston Engine

Working principle

The electromagnetic piston engine according to the present invention in one aspect comprises a

cylinder and a piston, each made of a magnetic material, a cylinder electromagnet having an inner

wall of the cylinder magnetisable to a one magnetic pole, and a piston magnetization unit for

magnetizing a portion of the piston engage able with the cylinder to a single magnetic pole in a

fixed manner, in which the piston is transferred in a one direction by creating a magnetic attraction

force between the cylinder and the piston by exciting the cylinder electromagnet; and the piston is

then transferred in the opposite direction by creating a magnetic repellent force there between,

followed by repeating this series of the actions of alternately creating the magnetic attraction force

and the magnetic repellent force to allow the piston to perform a reciprocal movement.

The electromagnetic piston engine according to the present invention in a still further aspect is

constructed by arranging a combination of the cylinder with the piston in -the aspects described

above as a one assembly, arranging the one assembly in plural numbers and operating the plural

assemblies in a parallel way, and converting a reciprocal movement of the piston in each of the

plural assemblies into a rotary movement of a single crank shaft by a crank mechanism so that

more can be produce for propelling any heavy vehicle.

Proposed model of Electromagnetic Piston Engine

Single cylinder engine

Fig.shows an appearance of the cylinder and piston portion of the electromagnetic piston engine. In

FIG., reference numeral 1 stands for a piston, reference numeral 2 for a cylinder, reference numeral

3 for an outer cylinder, and reference numerals 4 and 9 each for a connecting portion, each made

of a silicon steel plate. The cylinder 2 and the outer cylinder 3 are each of a shape having its top

portion closed. An outer wall at the top portion of the cylinder 2 is formed integrally with a

connecting portion 4. The cylinder 2 is disposed in the interior of the outer cylinder 3 with the

connecting portion 4 arranged so as to come into abutment with an inner wall at the top portion of

the outer cylinder 3. The connecting portion 4 is fixed to the top portion of the outer cylinder 3 with

a mounting screw 16. An exciting coil 5 is wound about the connecting portion 4. On an outer side

of the top portion of the outer cylinder 3 are mounted two electrodes 6 which in turn pass over the

entire length to the inner wall side of the outer cylinder 3 and are connected to lead wires at the

both ends of the exciting coil 5, respectively, to excite the exciting coil 5 throughelectrode

To the surface of the N pole side of the permanent magnet 7 is fixed a connecting portion 9. An

axial hole 9a of the connecting portion 9 is supported axially with a crank shaft of a connecting rod

10 which in turn is axially supported at an axial hole 10a on its other end with a crank mechanism

(not shown). The connecting portion 9 is wound with an exciting coil 8 for a booster (herein

referred to as "booster coil"). The lead wires on the both sides of the booster coil 8 are connected

each to a copper plate electrode 12 embedded extending in the axial direction on the outerwall.

The piston 1 is supported in the interior of the cylinder 2 with a bearing 15 to enable a smooth

reciprocal movement (vertical movement) in the axial direction of the cylinder. The piston 1 is

arranged to reciprocally move in the distance indicated by "L" in the drawing. The bearing 15 is

disposed each in the upper and lower positions along a circumferential direction of the inner wall of

the cylinder 2 (i.e. the outer wall of the piston 1) and is made of ceramics so as for the piston 1 to

fail to be connected magnetically to the cylinder 2. The bearing 15 may be replaced with as

called roller.

The cylinder 2 has a brush electrode 14 (hereinafter referred to simply as "a brush") pass

therethrough over its whole length from its outer wall side to its inner wall side and a topside end

of the brush 14 is disposed to come slidably into contact with the copper plate electrode 12. The

other topside end of the brush 14 is further disposed to pass all the way through the outer cylinder

3 so as to permit a flow of current from the outside. The brush 14 may be made of carbon and the

topside end portion of the brush 14 may be formed in the shape of a so-called roller to reduce wear

by the sliding movement. FIG. 3 shows an example of the brush 14 formed at its topside end

portion in the shape of such a so-called roller. As shown in the drawing, the brush 14 is mounted at

its topside end portion with a cylinder-shaped electrode 14a so as to be rotatable and the cylinder-

shaped electrode 14a is disposed to come into contact with the surface of the copper plate

electrode12whilebeingrotated.

It is to be understood that a contact mechanism for feeding electricity to the booster coil 8 in

accordance with the present invention is not restricted to a contact mechanism with the copper

plate electrode 12 and the brush 14 and a variety of contact mechanisms may include, for example,

such as a slidable contact mechanism in which the connecting rod 10 is made hollow, the lead wire

of the booster coil 8 passes through the hollow portion of the connecting rod 10, a ring electrode is

mounted on the crank shaft side so as to make a turn in the circumferential direction of a crank

shaft, and a brush is disposed to slide together with the ring electrode.

Now, the actions of the electromagnetic piston engine will be described hereinafter.

In operation of the electromagnetic piston engine, a current is fed through the booster coil 8 in the

direction in which the magnitude of the magnetic pole of the permanent magnet 7 is increased.

Although the piston 1 moves reciprocally in the cylinder 2 in a manner as will be described

hereinafter, the feeding of electricity to the booster coil 8 can be performed by supplying a current

to the copper plate electrode 12 through the sliding copper plate electrode 14. This feeding can

excite the whole area of the piston 1 to the S pole by the magnetic forces of the permanent magnet

7andboostercoil.8.The excitation of the exciting coil 5 can be performed in a manner as will be

described hereinafter. A current is fed in the direction of exciting the cylinder 2 to the S pole and

the outer cylinder 3 to the N pole during a period of time during which the piston 1 moves from the

top dead center to the bottom dead center (in the direction from bottom to top in the drawing). On

the other hand, the current is fed in the direction of magnetizing the cylinder 2 to the N pole and

the outer cylinder 3 to the S pole during a period of time during which the piston is being directed

to the top dead center from the bottom dead center (from to the top from the bottom in the

drawing). The feeding of the exciting current is performed repeatedly in a periodical way.

By exciting the exciting coil 5 in the manner as described hereinabove, the S pole of the piston 1

and the N pole of the cylinder 2 become attracting each other during the time during which the

piston 1 moves toward the top dead center from the bottom dead center, thereby raising the

piston 1 toward the top dead center by the attracting force. As the piston 1 has reached the top

dead center, the exciting current of the exciting coil 5 is inverted. The inversion of the exciting

current then excites the cylinder 2 to the S pole to repel the S pole of the piston 1 and the S pole of

the cylinder 2 from each other and the repellent force pushes down the piston 1 downwardly

toward the bottom dead center. As the piston 1 has reached the bottom dead center, the exciting

current of the exciting coil 5 is inverted again. This repetitive actions create a reciprocal movement

of the piston 1 in the cylinder 2 and the reciprocal movement is then converted into a rotary

movement of a crank shaft 11 through the connecting rod 10.

POWER SUPPLY In alternating current the electron flow is alternate, i.e. the electron flow increases to maximum in one direction, decreases back to zero. It then increases in the other direction and then decreases to zero again. Direct current flows in one direction only. Rectifier converts alternating current to flow in one direction only. When the anode of the diode is positive with respect to its cathode, it is forward biased, allowing current to flow. But when its anode is negative with respect to the cathode, it is reverse biased and does not allow current to flow. This unidirectional property of the diode is useful for rectification. A single diode arranged back-to-back might allow the electrons to flow during positive half cycles only and suppress the negative half cycles. Double diodes arranged back-to-back might act as full wave rectifiers as they may allow the electron flow during both positive and negative half cycles. Four diodes can be arranged to make a full wave bridge rectifier. Different types of filter circuits are used to smooth out the pulsations in amplitude of the output voltage from a rectifier. The property of capacitor to oppose any change in the voltage applied across them by storing energy in the electric field of the capacitor and of inductors to oppose any change in the current flowing through them by storing energy in the magnetic field of coil may be utilized. To remove pulsation of the direct current obtained from the rectifier, different types of combination of capacitor, inductors and resistors may be also be used to increase to action of filtering. NEED OF POWER SUPPLY Perhaps all of you are aware that a ‘power supply’ is a primary requirement for the ‘Test Bench’ of a home experimenter’s mini lab. A battery eliminator can eliminate or replace the batteries of solid-state electronic equipment and the equipment thus can be operated by 230v A.C. mains instead of the batteries or dry cells. Nowadays, the use of commercial battery eliminator or power supply unit has become increasingly popular as power source for household appliances like transreceivers, record player, cassette players, digital clock etc. THEORY USE OF DIODES IN RECTIFIERS: Electric energy is available in homes and industries in India, in the form of alternating voltage. The supply has a voltage of 220V (rms) at a frequency of 50 Hz. In the USA, it is 110V at 60 Hz. For the operation of most of the devices in electronic equipment, a dc voltage is needed. For instance, a transistor radio requires a dc supply for its operation. Usually, this supply is provided by dry cells. But sometime we use a battery eliminator in place of dry cells. The battery eliminator converts the ac voltage into dc voltage and thus eliminates the need for dry cells. Nowadays, almost all-electronic equipment includes a circuit that converts ac voltage of mains supply into dc voltage. This part of the equipment is called Power Supply. In general, at the input of the power supply, there is a power transformer. It is followed by a diode circuit called Rectifier. The output of the rectifier goes to a smoothing filter, and then to a voltage regulator circuit. The rectifier circuit is the heart of a power supply.

RECTIFICATION Rectification is a process of rendering an alternating current or voltage into a unidirectional one. The component used for rectification is called ‘Rectifier’. A rectifier permits current to flow only during the positive half cycles of the applied AC voltage by eliminating the negative half cycles or alternations of the applied AC voltage. Thus pulsating DC is obtained. To obtain smooth DC power, additional filter circuits are required. A diode can be used as rectifier. There are various types of diodes. But, semiconductor diodes are very popularly used as rectifiers. A semiconductor diode is a solid-state device consisting of two elements is being an electron emitter or cathode, the other an electron collector or anode. Since electrons in a semiconductor diode can flow in one direction only-from emitter to collector- the diode provides the unilateral conduction necessary for rectification. Out of the semiconductor diodes, copper oxide and selenium rectifier are also commonly used. FULL WAVE RECTIFIER It is possible to rectify both alternations of the input voltage by using two diodes in the circuit arrangement. Assume 6.3 V rms (18 V p-p) is applied to the circuit. Assume further that two equal-valued series-connected resistors R are placed in parallel with the ac source. The 18 V p-p appears across the two resistors connected between points AC and CB, and point C is the electrical midpoint between A and B. Hence 9 V p-p appears across each resistor. At any moment during a cycle of vin, if point A is positive relative to C, point B is negative relative to C. When A is negative to

C, point B is positive relative to C. The effective voltage in proper time phase which each diode "sees" is in Fig. The voltage applied to the anode of each diode is equal but opposite in polarity at any given instant. When A is positive relative to C, the anode of D1 is positive with respect to its cathode.

Hence D1 will conduct but D2 will not. During the second alternation, B is positive relative to C. The

anode of D2 is therefore positive with respect to its cathode, and D2 conducts while D1 is cut off.

There is conduction then by either D1 or D2 during the entire input-voltage cycle.

Since the two diodes have a common-cathode load resistor RL, the output voltage across RL

will result from the alternate conduction of D1 and D2. The output waveform vout across RL,

therefore has no gaps as in the case of the half-wave rectifier. The output of a full-wave rectifier is also pulsating direct current. In the diagram, the two equal resistors R across the input voltage are necessary to provide a voltage midpoint C for circuit connection and zero reference. Note that the load resistor RL is connected from the cathodes to

this center reference point C. An interesting fact about the output waveform vout is that its peak amplitude is not 9 V as

in the case of the half-wave rectifier using the same power source, but is less than 4½ V. The reason, of course, is that the peak positive voltage of A relative to C is 4½ V, not 9 V, and part of the 4½ V is lost across R.

Though the full wave rectifier fills in the conduction gaps, it delivers less than half the peak output voltage that results from half-wave rectification. BRIDGE RECTIFIER A more widely used full-wave rectifier circuit is the bridge rectifier. It requires four diodes instead of two, but avoids the need for a centre-tapped transformer. During the positive half-cycle of the secondary voltage, diodes D2 and D4 are conducting and diodes D1 and D3 are non-conducting. Therefore, current flows through the secondary winding, diode D2, load resistor RL and diode D4. During negative half-cycles of the secondary voltage, diodes D1 and D3 conduct, and the diodes D2 and D4 do not conduct. The current therefore flows through the secondary winding, diode D1, load resistor RL and diode D3. In both cases, the current passes through the load resistor in the same direction. Therefore, a fluctuating, unidirectional voltage is developed across the load. FILTRATION The rectifier circuits we have discussed above deliver an output voltage that always has the same polarity: but however, this output is not suitable as DC power supply for solid-state circuits. This is due to the pulsation or ripples of the output voltage. This should be removed out before the output voltage can be supplied to any circuit. This smoothing is done by incorporating filter networks. The filter network consists of inductors and capacitors. The inductors or choke coils are generally connected in series with the rectifier output and the load. The inductors oppose any change in the magnitude of a current flowing through them by storing up energy in a magnetic field. An inductor offers very low resistance for DC whereas; it offers very high resistance to AC. Thus, a series connected choke coil in a rectifier circuit helps to reduce the pulsations or ripples to a great extent in the output voltage. The fitter capacitors are usually connected in parallel with the rectifier output and the load. As, AC can pass through a capacitor but DC cannot, the ripples are thus limited and the output becomes smoothed. When the voltage across its plates tends to rise, it stores up energy back into voltage and current. Thus, the fluctuations in the output voltage are reduced considerable. Filter network circuits may be of two types in general: CHOKE INPUT FILTER If a choke coil or an inductor is used as the ‘first- components’ in the filter network, the filter is called ‘choke input filter’. The D.C. along with AC pulsation from the rectifier circuit at first passes through the choke (L). It opposes the AC pulsations but allows the DC to pass through it freely. Thus AC pulsations are largely reduced. The further ripples are by passed through the parallel capacitor C. But, however, a little nipple remains unaffected, which are considered negligible. This little ripple may be reduced by incorporating a series a choke input filters. CAPACITOR INPUT FILTER If a capacitor is placed before the inductors of a choke-input filter network, the filter is called capacitor input filter. The D.C. along with AC ripples from the rectifier circuit starts charging the capacitor C. to about peak value. The AC ripples are then diminished slightly. Now the capacitor C, discharges through the inductor or choke coil, which opposes the AC ripples, except the DC. The second capacitor C by passes the further AC ripples. A small ripple is still present in the output of DC, which may be reduced by adding additional filter network in series.

CIRCUIT DIAGRAM

TRANSFORMER

A transformer is a device that transfers electrical energy from one circuit to another

through inductively coupled conductors—the transformer's coils. A varying current in the first

or primary winding creates a varying magnetic flux in the transformer's core and thus a

varying magnetic field through the secondary winding. This varying magnetic field induces a

varying electromotive force (EMF), or "voltage", in the secondary winding. This effect is

called inductive coupling.

If a load is connected to the secondary, current will flow in the secondary winding, and electrical

energy will be transferred from the primary circuit through the transformer to the load. In an ideal

transformer, the induced voltage in the secondary winding (Vs) is in proportion to the primary

voltage (Vp) and is given by the ratio of the number of turns in the secondary (Ns) to the number of

turns in the primary (Np) as follows:

By appropriate selection of the ratio of turns, a transformer thus enables an alternating

current (AC) voltage to be "stepped up" by making Ns greater than Np, or "stepped down" by

making Ns less than Np. The windings are coils wound around a ferromagnetic core, air-

core transformers being a notable exception.

Transformers range in size from a thumbnail-sized coupling transformer hidden inside a

stage microphone to huge units weighing hundreds of tons used to interconnect portions of power

grids. All operate on the same basic principles, although the range of designs is wide. While new

technologies have eliminated the need for transformers in some electronic circuits, transformers

are still found in nearly all electronic devices designed for household ("mains") voltage.

Transformers are essential for high-voltage electric power transmission, which makes long-distance

transmission economically practical.

Basic principle

Fig:An ideal transformer

The secondary current arises from the action of the secondary EMF on the (not shown) load

impedance.The transformer is based on two principles: first, that an electric current can produce

a magnetic field(electromagnetism) and second that a changing magnetic field within a coil of wire

induces a voltage across the ends of the coil (electromagnetic induction). Changing the current in

the primary coil changes the magnetic flux that is developed. The changing magnetic flux induces a

voltage in the secondary coil.

An ideal transformer is shown in the adjacent figure. Current passing through the primary coil

creates a magnetic field. The primary and secondary coils are wrapped around a core of very

high magnetic permeability, such as iron, so that most of the magnetic flux passes through both the

primary and secondary coils. If a load is connected to the secondary winding, the load current and

voltage will be in the directions indicated, given the primary current and voltage in the directions

indicated (each will be alternating current in practice).

Induction law

The voltage induced across the secondary coil may be calculated from Faraday's law of induction,

which states that:

where Vs is the instantaneous voltage, Ns is the number of turns in the secondary coil and Φ is

the magnetic flux through one turn of the coil. If the turns of the coil are oriented perpendicularly

to the magnetic field lines, the flux is the product of the magnetic flux density B and the

area A through which it cuts. The area is constant, being equal to the cross-sectional area of the

transformer core, whereas the magnetic field varies with time according to the excitation of the

primary. Since the same magnetic flux passes through both the primary and secondary coils in an

ideal transformer, the instantaneous voltage across the primary winding equals

Taking the ratio of the two equations for Vs and Vp gives the basic equation for stepping up or

stepping down the voltage

Np/Ns is known as the turns ratio, and is the primary functional characteristic of any transformer. In

the case of step-up transformers, this may sometimes be stated as the reciprocal, Ns/Np. Turns

ratio is commonly expressed as an irreducible fraction or ratio: for example, a transformer with

primary and secondary windings of, respectively, 100 and 150 turns is said to have a turns ratio of

2:3 rather than 0.667 or 100:150.

Ideal power equation

Fig:The ideal transformer as a circuit element

If the secondary coil is attached to a load that allows current to flow, electrical power is transmitted

from the primary circuit to the secondary circuit. Ideally, the transformer is perfectly efficient. All

the incoming energy is transformed from the primary circuit to the magnetic field and into the

secondary circuit. If this condition is met, the input electric power must equal the output power:

This formula is a reasonable approximation for most commercial built transformers today.

If the voltage is increased, then the current is decreased by the same factor. The impedance in one

circuit is transformed by the square of the turns ratio. For example, if an impedance Zs is attached

across the terminals of the secondary coil, it appears to the primary circuit to have an impedance of

(Np/Ns)2Zs. This relationship is reciprocal, so that the impedance Zp of the primary circuit appears to

the secondary to be (Ns/Np)2Zp.

Detailed operation

The simplified description above neglects several practical factors, in particular, the primary current

required to establish a magnetic field in the core, and the contribution to the field due to current in

the secondary circuit.

Models of an ideal transformer typically assume a core of negligible reluctance with two windings

of zero resistance. When a voltage is applied to the primary winding, a small current flows,

driving flux around the magnetic circuit of the core. The current required to create the flux is

termed the magnetizing current. Since the ideal core has been assumed to have near-zero

reluctance, the magnetizing current is negligible, although still required, to create the magnetic

field.

The changing magnetic field induces an electromotive force (EMF) across each winding. Since the

ideal windings have no impedance, they have no associated voltage drop, and so the voltages

VP and VSmeasured at the terminals of the transformer, are equal to the corresponding EMFs. The

primary EMF, acting as it does in opposition to the primary voltage, is sometimes termed the "back

EMF". This is in accordance with Lenz's law, which states that induction of EMF always opposes

development of any such change in magnetic field.

Practical considerations

Leakage flux

Fig:Leakage flux of a transformer

The ideal transformer model assumes that all flux generated by the primary winding links all the

turns of every winding, including itself. In practice, some flux traverses paths that take it outside the

windings. Such flux is termed leakage flux, and results in leakage inductance in series with the

mutually coupled transformer windings. Leakage results in energy being alternately stored in and

discharged from the magnetic fields with each cycle of the power supply. It is not directly a power

loss (see "Stray losses" below), but results in inferior voltage regulation, causing the secondary

voltage to not be directly proportional to the primary voltage, particularly under heavy

load. Transformers are therefore normally designed to have very low leakage inductance.

Nevertheless, it is impossible to eliminate all leakage flux because it plays an essential part in the

operation of the transformer. The combined effect of the leakage flux and the electric field around

the windings is what transfers energy from the primary to the secondary.

In some applications increased leakage is desired, and long magnetic paths, air gaps, or magnetic

bypass shunts may deliberately be introduced in a transformer design to limit the short-

circuit current it will supply. Leaky transformers may be used to supply loads that exhibit negative

resistance, such as electric arcs, mercury vapor lamps, and neon signs or for safely handling loads

that become periodically short-circuited such as electric arc welders.

Air gaps are also used to keep a transformer from saturating, especially audio-frequency

transformers in circuits that have a direct current component flowing through the windings.

Leakage inductance is also helpful when transformers are operated in parallel. It can be shown that

if the "per-unit" inductance of two transformers is the same (a typical value is 5%), they will

automatically split power "correctly" (e.g. 500 kVA unit in parallel with 1,000 kVA unit, the larger

one will carry twice the current).

Effect of frequency

Transformer universal EMF equation

If the flux in the core is purely sinusoidal, the relationship for either winding between

its rmsvoltage Erms of the winding, and the supply frequency f, number of turns N, core cross-

sectional area a and peak magnetic flux density Bis given by the universal EMF equation:

If the flux does not contain even harmonics the following equation can be used for half-

cycleaverage voltage Eavg of any waveshape:

The time-derivative term in Faraday's Law shows that the flux in the core is the integral with

respect to time of the applied voltage. Hypothetically an ideal transformer would work with direct-

current excitation, with the core flux increasing linearly with time. In practice, the flux rises to the

point where magnetic saturation of the core occurs, causing a large increase in the magnetizing

current and overheating the transformer. All practical transformers must therefore operate with

alternating (or pulsed direct) current.

The EMF of a transformer at a given flux density increases with frequency. By operating at higher

frequencies, transformers can be physically more compact because a given core is able to transfer

more power without reaching saturation and fewer turns are needed to achieve the same

impedance. However, properties such as core loss and conductor skin effect also increase with

frequency. Aircraft and military equipment employ 400 Hz power supplies which reduce core and

winding weight. Conversely, frequencies used for some railway electrification systems were much

lower (e.g. 16.7 Hz and 25 Hz) than normal utility frequencies (50 – 60 Hz) for historical reasons

concerned mainly with the limitations of early electric traction motors. As such, the transformers

used to step down the high over-head line voltages (e.g. 15 kV) were much heavier for the same

power rating than those designed only for the higher frequencies.

Operation of a transformer at its designed voltage but at a higher frequency than intended will lead

to reduced magnetizing current. At a lower frequency, the magnetizing current will increase.

Operation of a transformer at other than its design frequency may require assessment of voltages,

losses, and cooling to establish if safe operation is practical. For example, transformers may need to

be equipped with "volts per hertz" over-excitation relays to protect the transformer from

overvoltage at higher than rated frequency.

One example of state-of-the-art design is transformers used for electric multiple unit high speed

trains, particularly those required to operate across the borders of countries using different

electrical standards. The position of such transformers is restricted to being hung below the

passenger compartment. They have to function at different frequencies (down to 16.7 Hz) and

voltages (up to 25 kV) whilst handling the enhanced power requirements needed for operating the

trains at high speed.

Knowledge of natural frequencies of transformer windings is necessary for the determination of

winding transient response and switching surge voltages.

Energy losses

An ideal transformer would have no energy losses, and would be 100% efficient. In practical

transformers, energy is dissipated in the windings, core, and surrounding structures. Larger

transformers are generally more efficient, and those rated for electricity distribution usually

perform better than 98%.

Experimental transformers using superconducting windings achieve efficiencies of 99.85%. The

increase in efficiency can save considerable energy, and hence money, in a large heavily loaded

transformer; the trade-off is in the additional initial and running cost of the superconducting

design.

Losses in transformers (excluding associated circuitry) vary with load current, and may be expressed

as "no-load" or "full-load" loss. Winding resistance dominates load losses,

whereas hysteresis and eddy currents losses contribute to over 99% of the no-load loss. The no-

load loss can be significant, so that even an idle transformer constitutes a drain on the electrical

supply and a running cost. Designing transformers for lower loss requires a larger core, good-

quality silicon steel, or even amorphous steel for the core and thicker wire, increasing initial cost so

that there is a trade-off between initial cost and running cost (also see energy efficient

transformer).

Transformer losses are divided into losses in the windings, termed copper loss, and those in the

magnetic circuit, termed iron loss. Losses in the transformer arise from:

Winding resistance

Current flowing through the windings causes resistive heating of the conductors. At higher

frequencies, skin effect and proximity effect create additional winding resistance and losses.

Hysteresis losses

Each time the magnetic field is reversed, a small amount of energy is lost due to hysteresis within

the core. For a given core material, the loss is proportional to the frequency, and is a function of the

peak flux density to which it is subjected.

Eddy currents

Ferromagnetic materials are also good conductors and a core made from such a material also

constitutes a single short-circuited turn throughout its entire length. Eddy currents therefore

circulate within the core in a plane normal to the flux, and are responsible for resistive heating of

the core material. The eddy current loss is a complex function of the square of supply frequency

and inverse square of the material thickness.Eddy current losses can be reduced by making the core

of a stack of plates electrically insulated from each other, rather than a solid block; all transformers

operating at low frequencies use laminated or similar cores.

Magnetostriction

Magnetic flux in a ferromagnetic material, such as the core, causes it to physically expand and

contract slightly with each cycle of the magnetic field, an effect known as magnetostriction. This

produces the buzzing sound commonly associated with transformers that can cause losses due to

frictional heating. This buzzing is particularly familiar from low-frequency (50 Hz or 60 Hz) mains

hum, and high-frequency (15,734 Hz (NTSC) or 15,625 Hz (PAL)) CRT noise.

Mechanical losses

In addition to magnetostriction, the alternating magnetic field causes fluctuating forces between

the primary and secondary windings. These incite vibrations within nearby metalwork, adding to

the buzzing noise and consuming a small amount of power.

Stray losses

Leakage inductance is by itself largely lossless, since energy supplied to its magnetic fields is

returned to the supply with the next half-cycle. However, any leakage flux that intercepts nearby

conductive materials such as the transformer's support structure will give rise to eddy currents and

be converted to heat. There are also radiative losses due to the oscillating magnetic field but these

are usually small.

Dot convention

It is common in transformer schematic symbols for there to be a dot at the end of each coil within a

transformer, particularly for transformers with multiple primary and secondary windings. The dots

indicate the direction of each winding relative to the others. Voltages at the dot end of each

winding are in phase; current flowing into the dot end of a primary coil will result in current flowing

out of the dot end of a secondary coil.

Core form and shell form transformers

Fig:core and shell form transformer

As first mentioned in regard to earliest ZBD closed-core transformers, transformers are generally

considered to be either core form or shell form in design depending on the type of magnetic circuit

used in winding construction (see image). That is, when winding coils are wound around the core,

transformers are termed as being of core form design; when winding coils are surrounded by the

core, transformers are termed as being of shell form design. Shell form design may be more

prevalent than core form design for distribution transformer applications due to the relative ease in

stacking the core around winding coils. Core form design tends to, as a general rule, be more

economical, and therefore more prevalent, than shell form design for high voltage power

transformer applications at the lower end of their voltage and power rating ranges (less than or

equal to, nominally, 230 kV or 75 MVA). At higher voltage and power ratings, shell form

transformers tend to be more prevalent.Shell form design tends to be preferred for extra high

voltage and higher MVA applications because, though more labor intensive to manufacture, shell

form transformers are characterized as having inherently better kVA-to-weight ratio, better short-

circuit strength characteristics and higher immunity to transit damage.

Equivalent circuit

The physical limitations of the practical transformer may be brought together as an equivalent

circuit model (shown below) built around an ideal lossless transformer.Power loss in the windings is

current-dependent and is represented as in-series resistances Rp and Rs. Flux leakage results in a

fraction of the applied voltage dropped without contributing to the mutual coupling, and thus can

be modeled as reactances of each leakage inductance Xp and Xs in series with the perfectly coupled

region.

Iron losses are caused mostly by hysteresis and eddy current effects in the core, and are

proportional to the square of the core flux for operation at a given frequency. Since the core flux is

proportional to the applied voltage, the iron loss can be represented by a resistance RC in parallel

with the ideal transformer.

A core with finite permeability requires a magnetizing current Im to maintain the mutual flux in the

core. The magnetizing current is in phase with the flux. Saturation effects cause the relationship

between the two to be non-linear, but for simplicity this effect tends to be ignored in most circuit

equivalents. With a sinusoidal supply, the core flux lags the induced EMF by 90° and this effect can

be modeled as a magnetizing reactance (reactance of an effective inductance) Xm in parallel with

the core loss component, Rc. Rc and Xm are sometimes together termed the magnetizing branch of

the model. If the secondary winding is made open-circuit, the current I0 taken by the magnetizing

branch represents the transformer's no-load current.

The secondary impedance Rs and Xs is frequently moved (or "referred") to the primary side after

multiplying the components by the impedance scaling factor (Np/Ns)2.

Fig:Transformer equivalent circuit, with secondary impedances referred to the primary side

The resulting model is sometimes termed the "exact equivalent circuit", though it retains a number

of approximations, such as an assumption of linearity. Analysis may be simplified by moving the

magnetizing branch to the left of the primary impedance, an implicit assumption that the

magnetizing current is low, and then summing primary and referred secondary impedances,

resulting in so-called equivalent impedance.

The parameters of equivalent circuit of a transformer can be calculated from the results of two

transformer tests: open-circuit test and short-circuit test.

TYPES OF TRANSFORMER

A wide variety of transformer designs are used for different applications, though they share several

common features. Important common transformer types are described below.

Autotransformer

Fig:A variable autotransformer

In an autotransformer portions of the same winding act as both the primary and secondary. The

winding has at least three taps where electrical connections are made. An autotransformer can be

smaller, lighter and cheaper than a standard dual-winding transformer however the

autotransformer does not provide electrical isolation.

As an example of the material saving an autotransformer can provide, consider a double wound

2 kVA transformer designed to convert 240 volts to 120 volts. Such a transformer would require

8 amp wire for the 240 volt primary and 16 amp wire for the secondary. If constructed as an

autotransformer, the output is a simple tap at the centre of the 240 volt winding. Even though the

whole winding can be wound with 8 amp wire, 16 amps can nevertheless be drawn from the

120 volt tap. This comes about because the 8 amp 'primary' current is of opposite phase to the

16 amp 'secondary' current and thus it is the difference current that flows in the common part of

the winding (8 amps). There is also considerable potential for savings on the core material as the

apertures required to hold the windings are smaller. The advantage is at its greatest with a 2:1 ratio

transformer and becomes smaller as the ratio is greater or smaller.

Autotransformers are often used to step up or down between voltages in the 110-117-120 volt

range and voltages in the 220-230-240 volt range, e.g., to output either 110 or 120V (with taps)

from 230V input, allowing equipment from a 100 or 120V region to be used in a 230V region.

A variable autotransformer is made by exposing part of the winding coils and making the secondary

connection through a sliding brush, giving a variable turns ratio.Such a device is often referred to by

the trademark name Variac.

Fig:Screenshot of a FEM simulation of the magnetic flux inside a three-phase power transformer

Polyphase transformers

For three-phase supplies, a bank of three individual single-phase transformers can be used, or all

three phases can be incorporated as a single three-phase transformer. In this case, the magnetic

circuits are connected together, the core thus containing a three-phase flow of flux. A number of

winding configurations are possible, giving rise to different attributes and phase shifts. One

particular polyphase configuration is the zigzag transformer, used for grounding and in the

suppression of harmonic currents.

Leakage transformers

Fig:Leakage transformer

A leakage transformer, also called a stray-field transformer, has a significantly higher leakage

inductance than other transformers, sometimes increased by a magnetic bypass or shunt in its core

between primary and secondary, which is sometimes adjustable with a set screw. This provides a

transformer with an inherent current limitation due to the loose coupling between its primary and

the secondary windings. The output and input currents are low enough to prevent thermal overload

under all load conditions—even if the secondary is shorted.

Uses

Leakage transformers are used for arc welding and high voltage discharge lamps (neon

lights and cold cathode fluorescent lamps, which are series-connected up to 7.5 kV AC). It acts then

both as a voltage transformer and as a magnetic ballast.

Other applications are short-circuit-proof extra-low voltage transformers for toys

or doorbell installations.

Resonant transformers

A resonant transformer is a kind of leakage transformer. It uses the leakage inductance of its

secondary windings in combination with external capacitors, to create one or more resonant

circuits. Resonant transformers such as the Tesla coil can generate very high voltages, and are able

to provide much higher current than electrostatic high-voltage generation machines such as

the Van de Graaff generator. One of the applications of the resonant transformer is for the CCFL

inverter. Another application of the resonant transformer is to couple between stages of

a superheterodyne receiver, where the selectivity of the receiver is provided by tuned

transformers in the intermediate-frequency amplifiers.

Audio transformers

Audio transformers are those specifically designed for use in audio circuits. They can be used to

block radio frequency interference or the DC component of an audio signal, to split or combine

audio signals, or to provide impedance matching between high and low impedance circuits, such as

between a high impedance tube (valve) amplifier output and a low impedance loudspeaker, or

between a high impedance instrument output and the low impedance input of a mixing console.

Such transformers were originally designed to connect different telephone systems to one another

while keeping their respective power supplies isolated, and are still commonly used to interconnect

professional audio systems or system components.

Being magnetic devices, audio transformers are susceptible to external magnetic fields such as

those generated by AC current-carrying conductors. "Hum" is a term commonly used to describe

unwanted signals originating from the "mains" power supply (typically 50 or 60 Hz). Audio

transformers used for low-level signals, such as those from microphones, often include magnetic

shielding to protect against extraneous magnetically-coupled signals.

Output transformer

Early audio amplifiers used transformers for coupling between stages, i.e., for transferring signal

without connecting different operating voltages together. It was realised that transformers

introduced distortion; furthermore they produced significant frequency-dependent phase shifts,

particularly at higher frequencies. The phase shift was not problematical in itself, but made it

difficult to introduce distortion-cancelling negative feedback, either over a transformer-coupled

stage or the whole amplifier. Where they were used as a convenient way to isolate stages while

coupling signals, transformers could be eliminated by using capacitor coupling. The transformer

coupling the output of the amplifier to the loudspeaker, however, had the important requirement

to couple the high impedance of the output valves with the low impedance of the loudspeakers.

With the 1940s Williamson amplifier as a much-quoted early example, audio amplifiers with

hitherto unprecedentedly low distortion were produced, using designs with only one transformer,

the output transformer, and large overall negative feedback. Some attempts to design

transformerless amplifiers were made, for example using very-low-impedance power triodes (such

as the 6080, originally designed for power regulation), but were not widely used. The design of

output transformers became a critical requirement for achieving low distortion, and carefully-

designed, expensive components were produced with minimal inherent distortion and phase

shift. Bluefin's Ultra-Linear transformer design was used in conjunction with Williamson's principles,

allowing pentode output devices to produce the higher power of a pentode than a triode, and

lower distortion than either type.

Some early junction transistor amplifiers used transformers in the signal path, both interstage and

output, but solid-state designs were rapidly produced with suitably low impedance to drive

loudspeakers without using transformers, allowing very large amounts of feedback to be applied

without instability.

Since the replacement of thermionic by solid-state electronics, signal transformers, including

output transformers, are rarely or never used in modern audio designs. A few very expensive valve

audio amplifiers are produced for vacuum-tube audio enthusiasts, and they require well-designed

output transformers.

Instrument transformers

Instrument transformers are used for measuring voltage and current in electrical power systems,

and for power system protection and control. Where a voltage or current is too large to be

conveniently used by an instrument, it can be scaled down to a standardized low value. Instrument

transformers isolate measurement, protection and control circuitry from the high currents or

voltages present on the circuits being measured or controlled.

Fig:Current transformers

A current transformer is a transformer designed to provide a current in its secondary coil

proportional to the current flowing in its primary coil.

Voltage transformers (VTs), also referred to as "potential transformers" (PTs), are designed to have

an accurately known transformation ratio in both magnitude and phase, over a range of measuring

circuit impedances. A voltage transformer is intended to present a negligible load to the supply

being measured. The low secondary voltage allows protective relay equipment and measuring

instruments to be operated at a lower voltages.

Both current and voltage instrument transformers are designed to have predictable characteristics

on overloads. Proper operation of over-current protective relays requires that current transformers

provide a predictable transformation ratio even during a short-circuit.

Electrical machines are generally understand to include not only rotating and linear electro-

mechanical machines but transformers as well. Transformers can be further classified according to

such key parameters as follow:

Power capacity: from a fraction of a volt-ampere (VA) to over a thousand MVA;

Duty of a transformer: continuous, short-time, intermittent, periodic, varying;

Frequency range: power-, audio-, or radio frequency;

Voltage class: from a few volts to hundreds of kilovolts;

Cooling type: (dry and liquid-immersed) self-cooled, forced air-cooled; (liquid-immersed)

forced oil-cooled, water-cooled;

Application: such as power supply, impedance matching, output voltage and current

stabilizer or circuit isolation;

Purpose: distribution, rectifier, arc furnace, amplifier output, etc.;

Basic magnetic form: core form, shell form;

Constant-potential transformer descriptor: power, step-up, step-down, isolation, high-

voltage, low voltage;

Three phase winding configuration: autotransformer, delta, wye, zigzag;

System characteristics: ungrounded, solidly grounded, high or low resistance grounded,

reactance grounded;

Efficiency, losses and regulation: excitation, impedance & total losses, resistance, reactance

& impedance drop, regulation.

Cores construction

Laminated steel cores

Laminated core transformer showing edge of laminations at top of above showing figure

Transformers for use at power or audio frequencies typically have cores made of

high permeability silicon steel. The steel has a permeability many times that of free space and the

core thus serves to greatly reduce the magnetizing current and confine the flux to a path which

closely couples the windings. Early transformer developers soon realized that cores constructed

from solid iron resulted in prohibitive eddy-current losses, and their designs mitigated this effect

with cores consisting of bundles of insulated iron wires. Later designs constructed the core by

stacking layers of thin steel laminations, a principle that has remained in use. Each lamination is

insulated from its neighbors by a thin non-conducting layer of insulation. The universal transformer

equation indicates a minimum cross-sectional area for the core to avoid saturation.

The effect of laminations is to confine eddy currents to highly elliptical paths that enclose little flux,

and so reduce their magnitude. Thinner laminations reduce losses,but are more laborious and

expensive to construct. Thin laminations are generally used on high frequency transformers, with

some types of very thin steel laminations able to operate up to 10 kHz.

Fig:reducing eddy-current losses

One common design of laminated core is made from interleaved stacks of E-shaped steel sheets

capped with I-shaped pieces, leading to its name of "E-I transformer". Such a design tends to exhibit

more losses, but is very economical to manufacture. The cut-core or C-core type is made by winding

a steel strip around a rectangular form and then bonding the layers together. It is then cut in two,

forming two C shapes, and the core assembled by binding the two C halves together with a steel

strap. They have the advantage that the flux is always oriented parallel to the metal grains,

reducing reluctance.

A steel core's remanence means that it retains a static magnetic field when power is removed.

When power is then reapplied, the residual field will cause a high inrush current until the effect of

the remaining magnetism is reduced, usually after a few cycles of the applied alternating

current. Overcurrent protection devices such as fuses must be selected to allow this harmless

inrush to pass. On transformers connected to long, overhead power transmission lines, induced

currents due to geomagnetic disturbances during solar storms can cause saturation of the core and

operation of transformer protection devices.

Distribution transformers can achieve low no-load losses by using cores made with low-loss high-

permeability silicon steel or amorphous (non-crystalline) metal alloy. The higher initial cost of the

core material is offset over the life of the transformer by its lower losses at light load.

Solid cores

Powdered iron cores are used in circuits such as switch-mode power supplies that operate above

mains frequencies and up to a few tens of kilohertz. These materials combine high

magnetic permeability with high bulk electrical resistivity. For frequencies extending beyond

the VHF band, cores made from non-conductive magnetic ceramic materials called ferrites are

common. Some radio-frequency transformers also have movable cores (sometimes called 'slugs')

which allow adjustment of the coupling coefficient (and bandwidth) of tuned radio-frequency

circuits.

Toroidal cores

Fig:Smalltoroidal core transformer

Toroidal transformers are built around a ring-shaped core, which, depending on operating

frequency, is made from a long strip of silicon steel or permalloy wound into a coil, powdered iron,

or ferrite. A strip construction ensures that the grain boundaries are optimally aligned, improving

the transformer's efficiency by reducing the core's reluctance. The closed ring shape eliminates air

gaps inherent in the construction of an E-I core. The cross-section of the ring is usually square or

rectangular, but more expensive cores with circular cross-sections are also available. The primary

and secondary coils are often wound concentrically to cover the entire surface of the core. This

minimizes the length of wire needed, and also provides screening to minimize the core's magnetic

field from generating electromagnetic interference.

Toroidal transformers are more efficient than the cheaper laminated E-I types for a similar power

level. Other advantages compared to E-I types, include smaller size (about half), lower weight

(about half), less mechanical hum (making them superior in audio amplifiers), lower exterior

magnetic field (about one tenth), low off-load losses (making them more efficient in standby

circuits), single-bolt mounting, and greater choice of shapes. The main disadvantages are higher

cost and limited power capacity (see "Classification" above). Because of the lack of a residual gap in

the magnetic path, toroidal transformers also tend to exhibit higher inrush current, compared to

laminated E-I types.

Ferrite toroidal cores are used at higher frequencies, typically between a few tens of kilohertz to

hundreds of megahertz, to reduce losses, physical size, and weight of a switched-mode power

supply. A drawback of toroidal transformer construction is the higher labor cost of winding. This is

because it is necessary to pass the entire length of a coil winding through the core aperture each

time a single turn is added to the coil. As a consequence, toroidal transformers are uncommon

above ratings of a few kVA. Small distribution transformers may achieve some of the benefits of a

toroidal core by splitting it and forcing it open, then inserting a bobbin containing primary and

secondary windings.

Air cores

A physical core is not an absolute requisite and a functioning transformer can be produced simply

by placing the windings near each other, an arrangement termed an "air-core" transformer. The air

which comprises the magnetic circuit is essentially lossless, and so an air-core transformer

eliminates loss due to hysteresis in the core material. The leakage inductance is inevitably high,

resulting in very poor regulation, and so such designs are unsuitable for use in power

distribution. They have however very high bandwidth, and are frequently employed in radio-

frequency applications, for which a satisfactory coupling coefficient is maintained by carefully

overlapping the primary and secondary windings. They're also used for resonant transformers such

as Tesla coils where they can achieve reasonably low loss in spite of the high leakage inductance.

Windings

Fig:Typical windings arrangement

Windings are usually arranged concentrically to minimize flux leakage.

The conducting material used for the windings depends upon the application, but in all cases the

individual turns must be electrically insulated from each other to ensure that the current travels

throughout every turn. For small power and signal transformers, in which currents are low and the

potential difference between adjacent turns is small, the coils are often wound from enamelled

magnet wire, such as Formvar wire. Larger power transformers operating at high voltages may be

wound with copper rectangular strip conductors insulated by oil-impregnated paper and blocks

of pressboard.

Cut view through transformer windings. White: insulator. Green spiral: Grain oriented silicon steel.

Black: Primary winding made of oxygen-free copper. Red: Secondary winding. Top left: Toroidal

transformer. Right: C-core, but E-core would be similar. The black windings are made of film. Top:

Equally low capacitance between all ends of both windings. Since most cores are at least

moderately conductive they also need insulation. Bottom: Lowest capacitance for one end of the

secondary winding needed for low-power high-voltage transformers. Bottom left: Reduction

of leakage inductance would lead to increase of capacitance.

High-frequency transformers operating in the tens to hundreds of kilohertz often have windings

made of braided Litz wire to minimize the skin-effect and proximity effect losses. Large power

transformers use multiple-stranded conductors as well, since even at low power frequencies non-

uniform distribution of current would otherwise exist in high-current windings. Each strand is

individually insulated, and the strands are arranged so that at certain points in the winding, or

throughout the whole winding, each portion occupies different relative positions in the complete

conductor. The transposition equalizes the current flowing in each strand of the conductor, and

reduces eddy current losses in the winding itself. The stranded conductor is also more flexible than

a solid conductor of similar size, aiding manufacture.

For signal transformers, the windings may be arranged in a way to minimize leakage inductance and

stray capacitance to improve high-frequency response. This can be done by splitting up each coil

into sections, and those sections placed in layers between the sections of the other winding. This is

known as a stacked type or interleaved winding.

Power transformers often have internal connections or taps at intermediate points on the winding,

usually on the higher voltage winding side, for voltage regulation control purposes. Such taps are

normally manually operated, automatic on-load tap changers being reserved, for cost and reliability

considerations, to higher power rated or specialized transformers supplying transmission or

distribution circuits or certain utilization loads such as furnace transformers. Audio-frequency

transformers, used for the distribution of audio to public address loudspeakers, have taps to allow

adjustment of impedance to each speaker. A center-tapped transformer is often used in the output

stage of an audio power amplifier in a push-pull circuit. Modulation transformers

in AM transmitters are very similar.

Certain transformers have the windings protected by epoxy resin. By impregnating the transformer

with epoxy under a vacuum, one can replace air spaces within the windings with epoxy, thus sealing

the windings and helping to prevent the possible formation of corona and absorption of dirt or

water. This produces transformers more suited to damp or dirty environments, but at increased

manufacturing cost.

Cooling

Fig:Cutaway view of oil-filled power transformer

The conservator (reservoir) at top provides oil-to-atmosphere isolation. Tank walls' cooling fins

provide required heat dissipation balance.

Though it is not uncommon for oil-filled transformers to have today been in operation for over fifty

years high temperature damages winding insulation, the accepted rule of thumb being that

transformer life expectancy is halved for every 8 degree C increase in operating temperature. At the

lower end of the power rating range, dry and liquid-immersed transformers are often self-cooled by

natural convection and radiation heat dissipation. As power ratings increase, transformers are often

cooled by such other means as forced-air cooling, force-oil cooling, water-cooling, or a

combinations of these. The dielectic coolant used in many outdoor utility and industrial service

transformers is transformer oil that both cools and insulates the windings. Transformer oil is a

highly refined mineral oil that inherently helps thermally stabilize winding conductor insulation,

typically paper, within acceptable insulation temperature rating limitations. However, the heat

removal problem is central to all electrical apparatus such that in the case of high value transfomer

assets, this often translates in a need to monitor, model, forecast and manage oil and winding

conductor insulation temperature conditions under varying, possibly difficult, power loading

conditions. Indoor liquid-filled transformers are required by building regulations in many

jurisdictions to either use a non-flammable liquid or to be located in fire-resistant rooms. Air-cooled

dry transformers are preferred for indoor applications even at capacity ratings where oil-cooled

construction would be more economical, because their cost is offset by the reduced building

construction cost.

The oil-filled tank often has radiators through which the oil circulates by natural convection. Some

large transformers employ electric-operated fans or pumps for forced-air or forced-oil cooling

or heat exchanger-based water-cooling.Oil-filled transformers undergo prolonged drying processes

to ensure that the transformer is completely free of water vapor before the cooling oil is

introduced. This helps prevent electrical breakdown under load. Oil-filled transformers may be

equipped with Buchholz relays, which detect gas evolved during internal arcing and rapidly de-

energize the transformer to avert catastrophic failure. Oil-filled transformers may fail, rupture, and

burn, causing power outages and losses. Installations of oil-filled transformers usually includes fire

protection measures such as walls, oil containment, and fire-suppression sprinkler systems.

Polychlorinated biphenyls have properties that once favored their use as a dielectic coolant, though

concerns over their environmental persistence led to a widespread ban on their use. Today, non-

toxic, stable silicone-based oils, or fluorinated hydrocarbons may be used where the expense of a

fire-resistant liquid offsets additional building cost for a transformer vault. Before 1977, even

transformers that were nominally filled only with mineral oils may also have been contaminated

with polychlorinated biphenyls at 10-20 ppm. Since mineral oil and PCB fluid mix, maintenance

equipment used for both PCB and oil-filled transformers could carry over small amounts of PCB,

contaminating oil-filled transformers.

Some "dry" transformers (containing no liquid) are enclosed in sealed, pressurized tanks and cooled

by nitrogen or sulfur hexafluoride gas.

Experimental power transformers in the 2 MVA range have been built

with superconducting windings which eliminates the copper losses, but not the core steel loss.

These are cooled by liquid nitrogen or helium.

Insulation drying

Construction of oil-filled transformers requires that the insulation covering the windings be

thoroughly dried before the oil is introduced. There are several different methods of drying.

Common for all is that they are carried out in vacuum environment. The vacuum makes it difficult

to transfer energy (heat) to the insulation. For this there are several different methods. The

traditional drying is done by circulating hot air over the active part and cycle this with periods of

hot-air vacuum (HAV) drying. More common for larger transformers is to use evaporated solvent

which condenses on the colder active part. The benefit is that the entire process can be carried out

at lower pressure and without influence of added oxygen. This process is commonly called vapour-

phase drying (VPD).

For distribution transformers, which are smaller and have a smaller insulation weight, resistance

heating can be used. This is a method where current is injected in the windings to heat the

insulation. The benefit is that the heating can be controlled very well and it is energy efficient. The

method is called low-frequency heating (LFH) since the current is injected at a much lower

frequency than the nominal of the grid, which is normally 50 or 60 Hz. A lower frequency reduces

the effect of the inductance in the transformer, so the voltage needed to induce the current can be

reduced. The LFH drying method is also used for service of older transformers.

RECTIFIER

A rectifier is an electrical device that converts alternating current (AC), which periodically reverses

direction, to direct current (DC), which flows in only one direction. The process is known

as rectification. Physically, rectifiers take a number of forms, including vacuum

tube diodes, mercury-arc valves, solid-state diodes, silicon-controlled rectifiers and other silicon-

based semiconductor switches. Historically, even synchronous electromechanical switches and

motors have been used. Early radio receivers, called crystal radios, used a "cat's whisker" of fine

wire pressing on a crystal of galena (lead sulfide) to serve as a point-contact rectifier or "crystal

detector".

Rectifiers have many uses, but are often found serving as components of DC power

supplies and high-voltage direct current power transmission systems. Rectification may serve in

roles other than to generate direct current for use as a source of power. As

noted, detectors of radio signals serve as rectifiers. In gas heating systems flame rectification is

used to detect presence of flame.

The simple process of rectification produces a type of DC characterized by pulsating voltages and

currents (although still unidirectional). Depending upon the type of end-use, this type of DC current

may then be further modified into the type of relatively constant voltage DC characteristically

produced by such sources as batteries and solar cells.

A device which performs the opposite function (converting DC to AC) is known as an inverter.

Rectifier devices

Before the development of silicon semiconductor rectifiers, vacuum tube diodes and copper(I)

oxide or selenium rectifier stacks were used. With the introduction of semiconductor electronics,

vacuum tube rectifiers became obsolete, except for some enthusiasts of vacuum tube audio

equipment. For power rectification from very low to very high current, semiconductor diodes of

various types (junction diodes, Schottky diodes, etc.) are widely used. Other devices which have

control electrodes as well as acting as unidirectional current valves are used where more than

simple rectification is required, e.g., where variable output voltage is needed. High power rectifiers,

such as are used in high-voltage direct current power transmission, employ silicon semiconductor

devices of various types. These are thyristors or other controlled switching solid-state switches

which effectively function as diodes to pass current in only one direction.

Half-wave rectifier

In half wave rectification of a single-phase supply, either the positive or negative half of the AC

wave is passed, while the other half is blocked. Because only one half of the input waveform

reaches the output, mean voltage is lower. Half-wave rectification requires a single diode in

a single-phase supply, or three in a three-phase supply. Rectifiers yield a unidirectional but

pulsating direct current; half-wave rectifiers produce far more ripple than full-wave rectifiers, and

much more filtering is needed to eliminate harmonics of the AC frequency from the output.

Fig:half wave rectifier

The output DC voltage of an ideal half wave rectifier is:

A real rectifier will have a characteristic which drops part of the input voltage (a voltage drop, for

silicon devices, of typically 0.7 volts plus an equivalent resistance, in general non-linear), and at high

frequencies will distort waveforms in other ways; unlike an ideal rectifier, it will dissipate power.

Full-wave rectifier

A full-wave rectifier converts the whole of the input waveform to one of constant polarity (positive

or negative) at its output. Full-wave rectification converts both polarities of the input waveform to

DC (direct current), and yields a higher mean output voltage. Two diodes and a center

tapped transformer, or four diodes in a bridge configuration and any AC source (including a

transformer without center tap), are needed. Single semiconductor diodes, double diodes with

common cathode or common anode, and four-diode bridges, are manufactured as single

components.

Fig: A full-wave rectifier using 4 diodes.

For single-phase AC, if the transformer is center-tapped, then two diodes back-to-back (cathode-to-

cathode or anode-to-anode, depending upon output polarity required) can form a full-wave

rectifier. Twice as many turns are required on the transformer secondary to obtain the same output

voltage than for a bridge rectifier, but the power rating is unchanged.

Fig:AFull wave rectifier with two diodes

Fig: Full wave rectifier, with vacuum tube having two anodes.

A very common double-diode rectifier tube contained a single common cathode and

two anodes inside a single envelope, achieving full-wave rectification with positive output. The 5U4

and 5Y3 were popular examples of this configuration.

Fig:3-phase AC input, half & full-wave rectified DC output waveforms

For three-phase AC, six diodes are used. Double diodes in series, with the anode of the first diode

connected to the cathode of the second, are manufactured as a single component for this purpose.

Some commercially available double diodes have all four terminals available so the user can

configure them for single-phase split supply use, half a bridge, or three-phase rectifier.

Fig:Three-phase bridge

rectifier

Fig:Disassembledautomobilealternator, showing the six diodes that

comprise a full-wave three-phase bridge rectifier.

Many devices that generate alternating current (some such devices are called alternators) generate

three-phase AC. For example, an automobile alternator has six diodes inside it to function as a full-

wave rectifier for battery charging applications.

The average and root-mean-square output voltages of an ideal single-phase full-wave rectifier are:

For a three-phase full-wave rectifier with ideal thyristors, the average output voltage is

Where:

Vdc, Vav - the DC or average output voltage,

Vpeak - the peak value of half wave,

Vrms - the root-mean-square value of output voltage.

π = ~ 3.14159

α = firing angle of the thyristor (0 if diodes are used to perform rectification)

Peak loss

An aspect of most rectification is a loss from the peak input voltage to the peak output voltage,

caused by the built-in voltage drop across the diodes (around 0.7 V for ordinary silicon p–n

junction diodes and 0.3 V for Schottky diodes). Half-wave rectification and full-wave rectification

using a center-tapped secondary will have a peak voltage loss of one diode drop. Bridge

rectification will have a loss of two diode drops. This reduces output voltage, and limits the

available output voltage if a very low alternating voltage must be rectified. As the diodes do not

conduct below this voltage, the circuit only passes current through for a portion of each half-cycle,

causing short segments of zero voltage (where instantaneous input voltage is below one or two

diode drops) to appear between each "hump".

Rectifier output smoothing

While half-wave and full-wave rectification can deliver unidirectional current, neither produces a

constant voltage. In order to produce steady DC from a rectified AC supply, a smoothing circuit

or filter is required. In its simplest form this can be just a reservoir capacitor or smoothing

capacitor, placed at the DC output of the rectifier. There will still be an AC ripple voltage

component at the power supply frequency for a half-wave rectifier, twice that for full-wave, where

the voltage is not completely smoothed.

Fig: RC-Filter Rectifier

This circuit was designed and simulated using Multisim 8 software.Sizing of the capacitor

represents a tradeoff. For a given load, a larger capacitor will reduce ripple but will cost more and

will create higher peak currents in the transformer secondary and in the supply feeding it. The peak

current is set in principle by the rate of rise of the supply voltage on the rising edge of the incoming

sine-wave, but in practice it is reduced by the resistance of the transformer windings. In extreme

cases where many rectifiers are loaded onto a power distribution circuit, peak currents may cause

difficulty in maintaining a correctly shaped sinusoidal voltage on the ac supply.

To limit ripple to a specified value the required capacitor size is proportional to the load current and

inversely proportional to the supply frequency and the number of output peaks of the rectifier per

input cycle. The load current and the supply frequency are generally outside the control of the

designer of the rectifier system but the number of peaks per input cycle can be affected by the

choice of rectifier design.

A half-wave rectifier will only give one peak per cycle and for this and other reasons is only used in

very small power supplies. A full wave rectifier achieves two peaks per cycle, the best possible with

a single-phase input. For three-phase inputs a three-phase bridge will give six peaks per cycle;

higher numbers of peaks can be achieved by using transformer networks placed before the rectifier

to convert to a higher phase order.

To further reduce ripple, a capacitor-input filter can be used. This complements the reservoir

capacitor with a choke (inductor) and a secondfilter capacitor, so that a steadier DC output can be

obtained across the terminals of the filter capacitor. The choke presents a highimpedance to the

ripple current.For use at power-line frequencies inductors require cores of iron or other magnetic

materials, and add weight and size. Their use in power supplies for electronic equipment has

therefore dwindled in favour of semiconductor circuits such as voltage regulators.

A more usual alternative to a filter, and essential if the DC load requires very low ripple voltage, is

to follow the reservoir capacitor with an active voltage regulator circuit. The reservoir capacitor

needs to be large enough to prevent the troughs of the ripple dropping below the minimum voltage

required by the regulator to produce the required output voltage. The regulator serves both to

significantly reduce the ripple and to deal with variations in supply and load characteristics. It would

be possible to use a smaller reservoir capacitor (these can be large on high-current power supplies)

and then apply some filtering as well as the regulator, but this is not a common strategy. The

extreme of this approach is to dispense with the reservoir capacitor altogether and put the rectified

waveform straight into a choke-input filter. The advantage of this circuit is that the current

waveform is smoother and consequently the rectifier no longer has to deal with the current as a

large current pulse, but instead the current delivery is spread over the entire cycle. The

disadvantage, apart from extra size and weight, is that the voltage output is much lower –

approximately the average of an AC half-cycle rather than the peak.

Voltage-multiplying rectifiers

The simple half wave rectifier can be built in two electrical configurations with the diode pointing in

opposite directions, one version connects the negative terminal of the output direct to the AC

supply and the other connects the positive terminal of the output direct to the AC supply. By

combining both of these with separate output smoothing it is possible to get an output voltage of

nearly double the peak AC input voltage. This also provides a tap in the middle, which allows use of

such a circuit as a split rail supply.

Fig:Switchable full bridge / Voltage doubler.

A variant of this is to use two capacitors in series for the output smoothing on a bridge rectifier

then place a switch between the midpoint of those capacitors and one of the AC input terminals.

With the switch open this circuit will act like a normal bridge rectifier: with it closed it will act like a

voltage doubling rectifier. In other words this makes it easy to derive a voltage of roughly 320V (+/-

around 15%) DC from any mains supply in the world, this can then be fed into a relatively

simple switched-mode power supply.

Fig:Voltage multiplier

Cascaded diode and capacitor stages can be added to make a voltage multiplier (Cockroft-Walton

circuit). These circuits are capable of producing a DC output voltage potential tens of times that of

the peak AC input voltage, but are limited in current capacity and regulation. Diode voltage

multipliers, frequently used as a trailing boost stage or primary high voltage (HV) source, are used

in HV laser power supplies, powering devices such as cathode ray tubes (CRT) (like those used in

CRT based television, radar and sonar displays), photon amplifying devices found in image

intensifying and photo multiplier tubes (PMT), and magnetron based radio frequency (RF) devices

used in radar transmitters and microwave ovens. Before the introduction of semiconductor

electronics, transformerless vacuum tube equipment powered directly from AC power sometimes

used voltage doublers to generate about 170VDC from a 100-120V power line.

Applications

The primary application of rectifiers is to derive DC power from an AC supply. Virtually all electronic

devices require DC, so rectifiers are used inside the power supplies of virtually all electronic

equipment.

Converting DC power from one voltage to another is much more complicated. One method of DC-

to-DC conversion first converts power to AC (using a device called an inverter), then use a

transformer to change the voltage, and finally rectifies power back to DC. A frequency of typically

several tens of kilohertz is used, as this requires much smaller inductance than at lower frequencies

and obviates the use of heavy, bulky, and expensive iron-cored units.

Fig:Output voltage of a full-wave rectifier with controlled thyristors

Rectifiers are also used for detection of amplitude modulated radio signals. The signal may be

amplified before detection. If not, a very low voltage drop diode or a diode biased with a fixed

voltage must be used. When using a rectifier for demodulation the capacitor and load resistance

must be carefully matched: too low a capacitance will result in the high frequency carrier passing to

the output, and too high will result in the capacitor just charging and staying charged.

Rectifiers are used to supply polarised voltage for welding. In such circuits control of the output

current is required; this is sometimes achieved by replacing some of the diodes in a bridge rectifier

with thyristors, effectively diodes whose voltage output can be regulated by switching on and off

with phase fired controllers.

Thyristors are used in various classes of railway rolling stock systems so that fine control of the

traction motors can be achieved. Gate turn-off thyristors are used to produce alternating current

from a DC supply, for example on the Eurostar Trains to power the three-phase traction motors.

Rectification technologies

Electromechanical

Early power conversion systems were purely electro-mechanical in design, since electronic devices

were not available to handle significant power. Mechanical rectification systems usually use some

form of rotation or resonant vibration (e.g. vibrators) in order to move quickly enough to follow the

frequency of the input power source, and cannot operate beyond several thousand cycles per

second.

Due to reliance on fast-moving parts of mechanical systems, they needed a high level of

maintenance to keep operating correctly. Moving parts will have friction, which requires lubrication

and replacement due to wear. Opening mechanical contacts under load results in electrical arcs and

sparks that heat and erode the contacts.

Synchronous rectifier

To convert alternating into direct current in electric locomotives, a synchronous rectifier may be

uses It consists of a synchronous motor driving a set of heavy-duty electrical contacts. The motor

spins in time with the AC frequency and periodically reverses the connections to the load at an

instant when the sinusoidal current goes through a zero-crossing. The contacts do not have

to switch a large current, but they need to be able to carry a large current to supply the

locomotive's DC traction motors.

Vibrator

Vibrators used to generate AC from DC in pre-semiconductor battery-to-high-voltage-DC power

supplies often contained a second set of contacts that performed synchronous mechanical

rectification of the stepped-up voltage.

Motor-generator set

A motor-generator set, or the similar rotary converter, is not strictly a rectifier as it does not

actually rectify current, but rather generates DC from an AC source. In an "M-G set", the shaft of an

AC motor is mechanically coupled to that of a DC generator. The DC generator produces multiphase

alternating currents in its armature windings, which a commutator on the armature shaft converts

into a direct current output; or a homopolar generator produces a direct current without the need

for a commutator. M-G sets are useful for producing DC for railway traction motors, industrial

motors and other high-current applications, and were common in many high power D.C. uses (for

example, carbon-arc lamp projectors for outdoor theaters) before high-power semiconductors

became widely available.

Electrolytic

The electrolytic rectifier was a device from the early twentieth century that is no longer used. A

home-made version is illustrated in the 1913 book The Boy Mechanic [5] but it would only be

suitable for use at very low voltages because of the low breakdown voltage and the risk of electric

shock. A more complex device of this kind was patented by G. W. Carpenter in 1928 (US Patent

1671970).

When two different metals are suspended in an electrolyte solution, direct current flowing one way

through the solution sees less resistance than in the other direction. Electrolytic rectifiers most

commonly used an aluminum anode and a lead or steel cathode, suspended in a solution of tri-

ammonium ortho-phosphate.

The rectification action is due to a thin coating of aluminum hydroxide on the aluminum electrode,

formed by first applying a strong current to the cell to build up the coating. The rectification process

is temperature-sensitive, and for best efficiency should not operate above 86 °F (30 °C). There is

also a breakdown voltage where the coating is penetrated and the cell is short-circuited.

Electrochemical methods are often more fragile than mechanical methods, and can be sensitive to

usage variations which can drastically change or completely disrupt the rectification processes.

Similar electrolytic devices were used as lightning arresters around the same era by suspending

many aluminium cones in a tank of tri-ammomiumortho-phosphate solution. Unlike the rectifier

above, only aluminium electrodes were used, and used on A.C., there was no polarization and thus

no rectifier action, but the chemistry was similar.

The modern electrolytic capacitor, an essential component of most rectifier circuit configurations

was also developed from the electrolytic rectifier.

Plasma type

Mercury arc

A rectifier used in high-voltage direct current (HVDC) power transmission systems and industrial

processing between about 1909 to 1975 is a mercury arc rectifier or mercury arc valve. The device is

enclosed in a bulbous glass vessel or large metal tub. One electrode, the cathode, is submerged in a

pool of liquid mercury at the bottom of the vessel and one or more high purity graphite electrodes,

called anodes, are suspended above the pool. There may be several auxiliary electrodes to aid in

starting and maintaining the arc. When an electric arc is established between the cathode pool and

suspended anodes, a stream of electrons flows from the cathode to the anodes through the ionized

mercury, but not the other way (in principle, this is a higher-power counterpart to flame

rectification, which uses the same one-way current transmission properties of the plasma naturally

present in a flame).

These devices can be used at power levels of hundreds of kilowatts, and may be built to handle one

to six phases of AC current. Mercury arc rectifiers have been replaced by silicon semiconductor

rectifiers and high power thyristor circuits in the mid 1970s. The most powerful mercury arc

rectifiers ever built were installed in the Manitoba HydroNelson River Bipole HVDC project, with a

combined rating of more than 1 GW and 450 kV

Argon gas electron tube

The General Electric Tungar rectifier was an argon gas-filled electron tube device with a tungsten

filament cathode and a carbon button anode. It was used for battery chargers and similar

applications from the 1920s until lower-cost metal rectifiers, and later semiconductor diodes,

supplanted it. These were made up to a few hundred volts and a few amperes rating, and in some

sizes strongly resembled an incandescent lamp with an additional electrode.

The 0Z4 was a gas-filled rectifier tube commonly used in vacuum tube car radios in the 1940s and

1950s. It was a conventional full-wave rectifier tube with two anodes and one cathode, but was

unique in that it had no filament (thus the "0" in its type number). The electrodes were shaped such

that the reverse breakdown voltage was much higher than the forward breakdown voltage. Once

the breakdown voltage was exceeded, the 0Z4 switched to a low-resistance state with a forward

voltage drop of about 24 V.

Vacuum tube (valve)

Since the discovery of the Edison effect or thermionic emission, various vacuum tube devices were

developed to rectify alternating currents. The simplest is the simple vacuum diode (the term "valve"

came into use for vacuum tubes in general due to this unidirectional property, by analogy with a

unidirectional fluid flow valve). Low-current devices were used as signal detectors, first used in

radio by Fleming in 1904. Many vacuum-tube devices also used vacuum diode rectifiers in their

power supplies, for example the All American Five radio receiver. Vacuum rectifiers were made for

very high voltages, such as the high voltage power supply for the cathode ray

tube of television receivers, and the kenotron used for power supply in X-ray equipment. However,

vacuum rectifiers generally had current capacity rarely exceeding 250 mA owing to the maximum

current density that could be obtained by electrodes heated to temperatures compatible with long

life. Another limitation of the vacuum tube rectifier was that the heater power supply often

required special arrangements to insulate it from the high voltages of the rectifier circuit.

Solid state

Crystal detector

The cat's-whisker detector, typically using a crystal of galena, was the earliest type of

semiconductor diode, though not recognised as such at the time.

Selenium and copper oxide rectifiers

Once common until replaced by more compact and less costly silicon solid-state rectifiers, these

units used stacks of metal plates and took advantage of the semiconductor properties

of selenium or copper oxide. While selenium rectifiers were lighter in weight and used less power

than comparable vacuum tube rectifiers, they had the disadvantage of finite life expectancy,

increasing resistance with age, and were only suitable to use at low frequencies. Both selenium and

copper oxide rectifiers have somewhat better tolerance of momentary voltage transients than

silicon rectifiers.

Typically these rectifiers were made up of stacks of metal plates or washers, held together by a

central bolt, with the number of stacks determined by voltage; each cell was rated for about 20 V.

An automotive battery charger rectifier might have only one cell: the high-voltage power supply for

a vacuum tube might have dozens of stacked plates. Current density in an air-cooled selenium stack

was about 600 mA per square inch of active area (about 90 mA per square centimeter).

Silicon and germanium diodes

In the modern world, silicon diodes are the most widely used rectifiers for lower voltages and

powers, and have largely replaced earlier germanium diodes. For very high voltages and powers,

the added need for controllability has in practice caused simple silicon diodes to be replaced by

high-power thyristors (see below) and their newer actively-gate-controlled cousins.

High power: thyristors (SCRs) and newer silicon-based voltage sourced converters

In high power applications, from 1975–2000, most mercury valve arc-rectifiers were replaced by

stacks of very high power thyristors, silicon devices with two extra layers of semiconductor, in

comparison to a simple diode.

In medium power-transmission applications, even more complex and sophisticated voltage sourced

converter (VSC) silicon semiconductor rectifier systems, such asinsulated gate bipolar transistors

(IGBT) and gate turn-off thyristors (GTO), have made smaller high voltage DC power transmission

systems economical. All of these devices function as rectifiers.

As of 2009 it was expected that these high-power silicon "self-commutating switches," in particular

IGBTs and a variant thyristor (related to the GTO) called the integrated gate-commutated

thyristor (IGCT), would be scaled-up in power rating to the point that they would eventually replace

simple thyristor-based AC rectification systems for the highest power-transmission DC applications.

Early 21st century developments

High-speed rectifiers

Researchers at Idaho National Laboratory (INL) have proposed high-speed rectifiers that would sit

at the center of spiral nanoantennas and convert infrared frequency electricity from AC to

DC Infrared frequencies range from 0.3 to 400 terahertz.

Unimolecular rectifiersA Unimolecular rectifier is a single organic molecule which functions as a

rectifier, in the experimental stage as of 2012.

DC Motor

Faradays used oersteds discovered, that electricity could be used to produce motion, to build the

world first electric motor in 1821. Ten years later, using the same logic in reverse, faraday was

interested in getting the motion produced by oersteds experiment to be continuous, rather then

just a rotatory shift in position. In his experiments, faraday thought in terms of magnetic lines of

force. He visualized how flux lines existing around a current carrying wire and a bar magnet. He was

then able to produce a device in which the different lines of force could interact a produce

continues rotation. The basic faradays motor uses a free-swinging wire that circles around the end

of a bar magnet. The bottom end of the wire is in a pool of mercury. Which allows the wire to

rotate while keeping a complete electric circuit.

BASIC MOTOR ACTION

Although Faraday's motor was ingenious. It could not be used to do any practical work. This is

because its drive shaft was enclosed and it could only produce an internal orbital motion. It could

not transfer its mechanical energy to the outside for deriving an external load. However it did show

how the magnetic fields of a conductor and a magnet could be made to interact to produce

continuous motion. Faradays motor orbited its wire rotor must pass through the magnet’s lines of

force.

When a current is passes through the wire ,circular lines of force are produced around the wire. Those flux lines go in a direction described by the left-hand rule. The lines of force of the magnet go from the N pole to the S pole You can see that on one side of the wire, the magnetic lines of force are going in the opposite direction as a result the wire, s flux lines oppose the magnet’s flux line since flux lines takes the path of least resistance, more lines concentrate on the other side of the wire conductor, the lines are bent and are very closely spaced. The lines tend to straighten and be wider spaced. Because of this the denser, curved field pushes the wire in the opposite direction.

The direction in which the wire is moved is determined by the right hand rule. If the current in the

wire went in the opposite direction. The direction of its flux lines would reverse, and the wire would

be pushed the other way.

RULES FOR MOTOR ACTION

The left hand rule shows the direction of the flux lines around a wire that is carrying current. When the thumb points in the direction of the magnetic lines of force. The right hand rule for motors shows the direction that a current carrying wire will be moved in a magnetic field. When the forefinger is pointed in the direction of the magnetic field lines, and the centre finger is pointed in the direction of the current in the wire the thumb will point in the direction that the wire will be moved.

Fig:left and right hand rule

TORQUE AND ROTATORY MOTION

In the basic action you just studied the wire only moves in a straight line and stops moving once out

of the field even though the current is still on. A practical motor must develop a basic twisting force

called torque loop. We can see how torque is produced. If the loop is connected to a battery.

Current flows in one direction one side of the loop, and in the opposite direction on the other.

Therefore the concentric direction on the two sides.

If we mount the loop in a fixed magnetic field and supply the current the flux lines of the field and

both sides of the loop will interact, causing the loop to act like a lever with a force pushing on its

two sides in opposite directions. The combined forces result in turning force, or torque because the

loop is arranged to piot on its axis. In a motor the loop that moves in the field is called an armature

or rotor. The overall turning force on the armature depends upon several factors including field

strength armature current strength and the physical construction of the armature especially the

distance from the loop sides to the axis lines. Because of the lever action the force on the sides are

further from the axis; thus large armature will produce greater torques.

In the practical motor the torque determines the energy available for doing useful work. The greater the torque the greater the energy. If a motor does not develop enough torque to pull its load it stalls. PRODUCTION OF CONTINUOUS ROTATION

The armature turns when torque is produced and torque is produced as long as the fields of the

magnet and armature interact. When the loop reaches a position perpendicular to the field, the

interaction of the magnetic field stops. This position is known as the neutral plane. In the neutral

plane, no torque is produced and the rotation of the armature should stop; however inertia tends

to keep a moving object in the motion even after the prime moving force is removed and thus the

armature tends to rotate past the neutral plane. But when the armature continues o the sides of

the loop start to swing back in to the flux lines, and apply a force to push the sides of the loop back

and a torque is developed in the opposite direction. Instead of a continuous rotation an oscillating

motion is produced until the armature stops in the neutral plane.

To get continuous rotation we must keep the armature turning in the same direction as it passes through the neutral plane .We could do this by reversing either the direction of the current flow through the armature at the instant the armature goes through the neutral pole. Current reversals of this type are normally the job of circuit switching devices. Since the switch would have to be synchronized with the armature, it is more logical to build it into the armature then in to the field. The practical switching device, which can change the direction of current flow through an armature to maintain continuous rotation, is called a commutator.

THE ELEMANTARY DC MOTOR

At this point, you have been introduced to the four principal parts that make up the elementary D.C

motor. These parts are the same as those you met in your study of the basic D.C generator .a

magnetic field, a movable conductor, a commutator and brushes. In practice, the magnetic field can

be supplied by a permanent magnet or by an electromagnet. For most discussions covering various

motor operating principles, we will assume that a permanent magnet is used at other times when it

is important for you to understand that the field of the motor is develop electrically, we will show

that an electromagnet is used. In either case, the magnetic field itself consists of magnetic flux lines

that form a closed magnetic circuit. The flux lines leave the north pole of the magnet, extend across

the air gap between the poles of the magnet, enter the South Pole and then travel through the

magnet itself back to the north pole. The movable conductor, usually a loop, called armature,

therefore is in the magnetic field.

When D.C motor is supplied to the armature through the brushes and commutator, magnetic flux is

also build up around the armature. It is this armature flux that interacts with the magnetic field in

which the armature is suspended to develop the torque that makes the motor operate.

THE COMMUTATOR

For the single-loop armature, the commutator is simple. It is a conducting ring that is split into two

segment with each segment connected to an end of the armature loop. Power for the armature

from an external power source such as a battery is brought to the commutator segments by means

of brushes. The arrangement is almost identical to that for the basic dc generator.

The logic behind the operation of the commutator is easy to see in the figures. You can see in figure

A that current flows into the side of the armature closest to the South Pole of the field and out of

the side closest to the North Pole. The interaction of the two fields produces a torque in the

direction indicated, and the armature rotates in that direction.

No torque is produced but the armature continues to rotate past the neutral plane due to inertia.

Notice that at the neutral position the commutator disconnects from the brushes sides of the loop

reverse positions. But the switching action of the commutator keeps the direction of current flow

through the armature the same as it was in the figure. A. Current still flows into the armature side

that is now closest to the South Pole.

Since the magnet’s field direction remains the same throughout the interaction of fields after

commutation keeps the torque going in the original direction; thus the same direction of rotation is

maintained.

As you can see in figure D, Inertia again carries the armature past neutral to the position shown in the fig. A while communication keeps the current flowing in the direction that continues to maintain rotation. In this way, the commutator keeps switching the current through the loop, so that the field it produces always interacts with the pole field to develop a continuous torque in the same direction.

Cost of component used

Components Amount(in Rupees)

Electromagnetic piston 450 each

DC motor 375

Transformer 680

Speed regulator 105

Special purpose Switch 165

Rectifier 100

Others(approx) 250