MAGNETIC LEVITATION SECAB I.E.T. VIJAYPUR DEPT. OF EEE Page 1 CHAPTER 1: INTRODUCTION Magnetic levitation (maglev) systems are electromechanical device that suspend ferromagnetic material using electromagnetism. Magnetic levitation technology is used in high speed trains, in which the train is lifted from the guideway by a magnetic field. Propulsion is by means of a moving magnetic field. Magnetic levitation systems have received much attention as a mean of eliminating Coulomb friction due to mechanical contact. They are becoming popular in two different kinds of realization: high-speed motion and precision engineering industry. Levitation bearing has been used from the beginning in rotating machinery to support rotors without friction low energy consumption, high rotational speed, no lubrication and greater reliability. It also allows a simpler and safer mechanical design as in the case of pumps used in nuclear installations where fluid leakage avoidance is of primary importance. The most famous application is high speed ground transportation systems: Japanese “Maglev” and German “Transrapid”, shown in Fig. 1, are very fast trains with linear motor. Fig.1: German “Transrapid”
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MAGNETIC LEVITATION
SECAB I.E.T. VIJAYPUR DEPT. OF EEE Page 1
CHAPTER 1: INTRODUCTION
Magnetic levitation (maglev) systems are electromechanical device that suspend
ferromagnetic material using electromagnetism. Magnetic levitation technology is used in
high speed trains, in which the train is lifted from the guideway by a magnetic field.
Propulsion is by means of a moving magnetic field. Magnetic levitation systems have
received much attention as a mean of eliminating Coulomb friction due to mechanical
contact. They are becoming popular in two different kinds of realization: high-speed
motion and precision engineering industry.
Levitation bearing has been used from the beginning in rotating machinery to
support rotors without friction low energy consumption, high rotational speed, no
lubrication and greater reliability. It also allows a simpler and safer mechanical design as
in the case of pumps used in nuclear installations where fluid leakage avoidance is of
primary importance. The most famous application is high speed ground transportation
systems: Japanese “Maglev” and German “Transrapid”, shown in Fig. 1, are very fast
trains with linear motor.
Fig.1: German “Transrapid”
MAGNETIC LEVITATION
SECAB I.E.T. VIJAYPUR DEPT. OF EEE Page 2
There are different categories of magnetic levitation in which research and
development efforts are being made. Based on the basic principle, magnetic levitation
may broadly be classified into two types, electrodynamics levitation and electromagnetic
levitation. The electrodynamics system actuates through repulsive forces. Most of such
systems utilize superconducting magnets to generate the forces. One of the main
constraints of the superconducting repulsion principle is that it cannot provide suspension
force below some critical speed. The electrodynamics levitation system (EDLS) is
inherently stable, but at high speed it possess stability problem due to negative damping.
So some kind of passive damper is required in electro-dynamically levitated vehicle to
maintain stability at high speed.
In electromagnetic levitation system (EMLS), the levitation is produced due to the
attractive force between electromagnets and ferromagnetic object. In electromagnetic
levitation (attraction system), the electromagnets are driven either by AC or DC source.
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CHAPTER 2: MAGNETIC LEVITATION TRAIN
Magnetic levitation is method by which an object is suspended in air with no support
other than magnetic field. Maglev can create frictionless, efficient, far-out sounding
technology. If a Maglev wants to use this force to levitate, it needs a strong magnetic field
in its wagons. We could use normal magnets, but their magnetic power is limited. The
most efficient way to produce the most powerful magnetic field we know of today, with a
reasonable energy cost, is the use superconducting coil. For efficiency reasons, the
superconducting coils are placed on the sides of the wagons (four on each side), these
coils are made with conventional superconductors that require very low temperatures, a
few kelvins above absolute zero: they are hence always surrounded with liquid helium.
Magnetically levitated train is a highly modern vehicle. Maglev vehicles use noncontact
magnetic levitation, guidance, and propulsion systems and have no wheels, axles, and
transmission. Contrary to traditional railroad vehicles, there is no direct physical contact
between maglev vehicle and its guide-way. These vehicles move along magnetic fields
that are established between the vehicle and its guide-way. Conditions of no mechanical
contact and no friction provided by such technology make it feasible to reach higher
speeds of travel attributed to such train.
Maglev trains can be conveniently considered as a solution for transportation
needs of the current time as well as future needs of the world. . The levitation coils are
installed on the sidewalls of the guide-way. When the on-board superconducting magnets
pass at a high speed about several centimeters below the center of these coils, an electric
current is induced within the coils, which then act as electromagnets temporarily. As a
result, there are forces which push the superconducting magnet upwards and ones which
pull them upwards simultaneously, thereby levitating the maglev vehicle. The levitation
coils facing each other are connected under the guidway, constituting a loop.
When a running maglev vehicle, that is a superconducting magnet, displaces
laterally, an electric current is induced in the loop, resulting in a repulsive force acting on
the levitation coils of the side near the car and an attractive force acting on the levitation
coils of the side farther apart from the car. Thus, a running car is always located at the
center of the guideway. A repulsive force and an attractive force induced between the
magnets are used to propel the vehicle (superconducting magnet). The propulsion coils
located on the sidewalls on both sides of the guideway are energized by a three-phase
alternating current from a substation, creating a shifting magnetic field on the guideway.
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The on-board superconducting magnets are attracted and pushed by the shifting field,
propelling the maglev vehicle. There are two types of magnetic levitation as follows,
2.1 TYPES OF MAGNETIC LEVITATION TRAIN
Magnetic levitation Train can be based on several types follows as
2.1.1 Electromagnetic suspension
2.1.2 Electrodynamics suspension
2.1.1 Electromagnetic suspension
Electromagnetic suspension works like an active magnetic bearing. This
principle is sometimes called a servo-stabilization. Sensors measure the air-gap between
an electromagnet and guideway. Control system tries to keep it constant.
Servo-stabilization is able to hold the body in the required position, even if the
train standstill. Therefore no wheels are required for assuring of the main levitation
function. However some retainer wheels for safety purposes are usually employed. In
EMS system, the vehicle is levitated about 1 to 2 cm above the guideway using attractive
forces, the electromagnets on the vehicle interact with and are attracted to levitation rails
on the guideway. Electromagnets attached to the vehicle are directed up toward the
guideway, which levitates the vehicle above the guideway and keeps the vehicle levitated.
Control of allowed air gaps between the guideway and vehicle is achieved by using
highly advanced control systems. The electromagnet use feedback control to maintain
train at a constant distance from the track.
Fig. 2.1: Electromagnetic suspension
In EMS train levitate due to the attraction between the opposite poles of magnets one in
the guideway & the other in the undercarriage. The distance between the train & the
undercarriage must maintained 15mm. The train also remains suspended in air when it is
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not moving, Minor changing between the magnets and the train produces a varying force
and this force is very unstable do complex electronic Feedback system is Necessary to
maintain the accurate distance. The system varies the current in electromagnets & control
the magnetic force of attraction.
2.1.2 Electrodynamics Suspension
In Electrodynamics suspension the train is levitated by the repulsive force
between these magnetic fields. The magnetic field in the train is produced by either
electromagnets or by an array of permanent magnets. The repulsive force in the track is
created by an induced magnetic field in wires or other conducting strips in the track. In
EDS system, the vehicle is levitated about above the track using repulsive forces.
Fig 2.2 Electrodynamics suspension
In EDS both the track & the train exert a magnetic field & the train is levitate by
the repulsive force between these magnetic field
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CHAPTER 3: BASIC PRINPLES OF THE MAGNETIC
LEVITATION TRAIN & BLOCK DIAGRAM
Maglev trains have to perform the following functions to operate in high speed
1. Levitation
2. Propulsion
3. Lateral guidance
3.1 Levitation
The levitation coils are installed on the sidewalls of the guideway. When the on-
board superconducting magnets pass at a high speed about several centimeters below the
center of these coils, an electric current is induced within the coils, which then act as
electromagnets temporarily. As a result, there are forces which push the superconducting
magnet upwards and ones which pull them upwards simultaneously, thereby levitating the
maglev vehicle. The levitation coils facing each other are connected under the guideway,
constituting a loop.
When a running maglev vehicle, that is a superconducting magnet, displaces
laterally, an electric current is induced in the loop, resulting in a repulsive force acting on
the levitation coils of the side near the car and an attractive force acting on the levitation
coils of the side farther apart from the car. Thus, a running car is always located at the
center of the guideway. A repulsive force and an attractive force induced between the
magnets are used to propel the vehicle (superconducting magnet). The propulsion coils
located on the sidewalls on both sides of the guideway are energized by a three-phase
alternating current from a substation, creating a shifting magnetic field on the guideway.
The on-board superconducting magnets are attracted and pushed by the shifting field,
propelling the maglev vehicle.
Fig 3.1 shows principle of levitation
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3.2 Propulsion
The propulsion coils are active, which means they are supplied by a source of
energy: this makes sense; the train must accelerate and defeat air resistance. Since these
coils are made of metal, they consume energy. Nevertheless, they can be totally
controlled: when the direction and the intensity of the currents going through them are
controlled, the sign and the intensity of the created magnetic field are also controlled. To
make the Maglev accelerate, you only need to send an electric current in the propulsion
coils located in the beams upstream from the Maglev in order to attract it; and to send an
electric current in the coils downstream in order to push it. Attracted in the front and
pushed in the back, the Maglev accelerates. The engine of the Maglev is hence located in
the tracks! To slow down, we only need to invert the current, pushing the front of the
Maglev and attracting its back.
Furthermore, the wagons are equipped with air brakes in order to slow down
without consuming any energy. The propulsion coils located on the sidewalls on both
sides of the guideway are energized by a three-phase alternating current from a
substation, creating a shifting magnetic field on the guideway. The on-board
superconducting magnets are attracted and pushed by the shifting field, propelling the
maglev vehicle.
Fig 3.2 shows of principle propulsion
3.3 Lateral Guidance
The track along which the train moves is called the guide way. Both the guide way
as well as the train’s undercarriage also have magnets which repel each other. Thus the
train is said to levitate about 0.39 inches on top of the guide way. After the levitat ion is
complete, enough power has to be produced so as to move the train through the guide
MAGNETIC LEVITATION
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way. This power is given to the coils within the guide way, which in turn produces
magnetic fields, which pulls and pushes the train through the guide way.
Fig 3.3 shows principle of lateral guidance
The current that is given to the electric coils of the guide way will be alternating in
nature. Thus the polarity of the coils will be changing in period. Thus the change causes a
pull force for the train in the front and to add to this force, the magnetic field behind the
train adds more forward thrust.
3.4 BLOCK DIAGRAM OF MAGNETIC LEVITATION TRAIN
Fig. 3.4: Block diagram of maglev train
Fig.3.1 shows the block diagram of maglev train. Here the 3ø AC Power (variable) is
being fed to a controller (variable frequency). The frequency will decide the speed of the
train. The overall MAGLEV system is made up of two subsystems: propulsion and