electromagnetic piston engine car
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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
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