Magnetic Levitation

A

Seminar Report

Submitted in Partial Fulfillment of the Requirements for the Degree

of

Bachelor of Technology

in

Electrical Engineering

Submitted By:

Vasav Shethna (13bee110)

Tushar Shingala (13bee111)

Under Guidance of:

Prof. Hormaz Amrolia

Department of Electrical Engineering

Institute of Technology, Nirma University

Ahmedabad – 382481

April 2015

ACKNOWLEDGEMENT

We have immense pleasure in successful completion of the work titled: ‘MAGNETIC

LEVITATION’. The special environment at Nirma University, Institute of Technology,

Ahmedabad that always supports educational activities, facilitated our work on this presentation.

We greatly appreciate the motivation and understanding extended for the presentation, by Prof. H.

Z. Amrolia and Prof. A. N. Patel, who responded promptly and enthusiastically to our requests for

expertise, despite their congested schedules. We are indebted to all of them, who did their best to

bring improvements through their suggestions.

We thank our Dearest Parents, who encouraged us to extend our reach. With their help and support,

we have been able to complete this work.

ABSTRACT

Magnetic levitation is the use of magnetic fields to levitate a (usually) metallic object.

Manipulating magnetic fields and controlling their forces can levitate an object. Using either

Ferromagnetism or Diamagnetism object can be levitated. A superconductor is perfectly

diamagnetic and electromagnets can exhibit varying levels of ferromagnetism.

Most important application of Magnetic Levitation is Trans-rapid magnetic lift trains and Magnetic

Bearing in order to reduce friction.

Here in this report a detail study of magnetic bearing and maglev trains is given. And also we have

included their advantages disadvantages and future scopes.

LIST OF FIGURES

Figure 1.1 Diamagnetic levitation

Figure 1.2 Magnetic Levitation

Figure 1.3 Magnetic Suspension

Figure 1.4 Maglev Trains

Figure 1.5 Contactless Melting

Figure 1.6 Magnetic Bearing

Figure 1.7 Product Display Purpose

Figure 3.1 Mechanical Constraint

Figure 3.2 Direct Diamagnetic levitation

Figure 3.3 Superconductor Levitation

Figure 3.4 Diamagnetically Stabilized Levitation

Figure 3.5 Rotational Stabilization

Figure 4.1 Plain Bearing

Figure 4.2 Rolling Bearing

Figure 4.3 Operation Diagram

Figure 4.4 Turbo Blower

Figure 4.5 Gas Turbine

Figure 4.6 Prototype Figure

Figure 4.7 Ferrofluid

Figure 4.8 PMB

Figure 5.1 Maglev Train

Figure 5.2 Eric Laithwaite

Figure 5.3 Three functions of maglev trains

Figure 5.4 Types of Trains

Figure 5.5 EMS Technique

Figure 5.6 Gap Sensor

Figure 5.7 EDS Technique

Figure 5.8 Lateral Guidance

Figure 5.9 Vertical Guidance

LIST OF TABLES

Table 5.1 Pros and Cons of Different Technologies

NOMENCLATURE/ABBREVIATIONS

AMB – Active Magnetic Bearing

PMB – Passive Magnetic Bearing

EMS – ElectroMagnetic Suspension

EDS – ElecroDynamic Suspension

LSM – Linear Synchronous Motor

LIM – Linear Induction Motor

TABLE OF CONTENTS

ACKNOWLEDGEMENT III

ABSTRACT IV

LIST OF FIGURES V

LIST OF TABLES VI

NOMENCLATURE/ABBREVIATIONS VII

TABLE OF CONTENTS VIII

CHAPTER 1: Introduction 1

1.1 Definition of Magnetic Levitation 1

1.1.1 Magnetic Levitation

1.1.2 Magnetic Suspension

1

1

1.2 Area of Attraction

1.3 Uses

1.4 Issues

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2

4

CHAPTER 2: Earnshaw’s Theorem

4

2.1 Statement

2.2 Stability

4

4

CHAPTER 3: Methods For Magnetic Levitation

3.1 Mechanical Constraint

3.2 Direct Diamagnetic Levitation

3.3 Superconductors

3.4 Diamagnetically Stabilized Levitation

3.5 Rotational Stabilization

3.6 Servo Stabilization

3.7 Rotating conductors beneath magnets

3.8 High-Frequency Oscillating Electromagnetic fields

CHAPTER 4: Applications of Magnetic Levitation

4.1 Magnetic Bearing

4.1.1 Meaning of Bearing

4.1.2 Types of Bearing

4.1.3 Magnetic Bearing

4.1.4 Classification of Magnetic Bearing

4.1.5 Active Magnetic Bearing

4.1.6 Application of Active Magnetic Bearing

4.1.7 Advantages and Disadvantages of AMB

4.1.8 PMB

4.1.9 Application of PMB

4.2 Application of Magnetic Bearing

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CHAPTER 5: Maglev Train

5.1 History of Maglev Trains

5.2 basic Principle of Maglev Trains

5.3 How does it work?

5.4 Types of maglev train

5.4.1 EMS Technique

5.4.2 Gap Sensor

5.4.3 EDS Technique

5.5 Pros and Cons of Different Techniques

5.6 Propulsion

5.6.1 Propulsion Force

5.6.2 Techniques of Propulsion

5.7 Principle of Guidance

5.7.1 Principle of Lateral Guidance

5.7.2 Principle of Vertical Guidance

5.8 Advantages

5.9 Economic Aspect

5.10 Current Projects

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REFERENCES 24

APPENDIX 25

.

CHAPTER 1: Introduction

Figure 1.1 Diamagnetic levitation

1.1 Definition of Magnetic Levitation

Magnetic levitation, maglev or magnetic suspension is a method by which an object is suspended

with no support other than magnetic fields. Magnetic force is used to counteract the effect of

gravitational force.

The Difference between levitation and suspension

1.1.1 Magnetic Levitation: If an object is kept in air using the force of repulsion given from the

bottom of the object then it is known as magnetic levitation.

1.1.2 Magnetic Suspension:

If an object is suspended using the force of attraction applied from top of the object then it is known

as magnetic suspension.

1.2 Area of Attraction:

The main area of attraction in the field of magnetic levitation is as a means of eliminating friction

or physical contact.

As a means of eliminating friction magnetic levitation gives its use in magnetic bearing.

As a means of eliminating physical contact magnetic levitation gives its use in magnetic levitated

trains.

1.3 Uses:

Magnetic levitation finds its application in following applications:

Figure 1.2 Magnetic Levitation

Figure 1.3 Magnetic Suspension

1. Maglev trains: For high speed ground transportation maglev trains are designed to take

advantage of magnetic levitation.

2. Contactless Melting: Metal having high resistance can be levitated and melt in magnetic

field.

3. Magnetic Bearing: For rotating machines to stabilize shaft without friction and contact

magnetic bearing are used.

4. Product Display Purpose: For displaying the product by levitating it in air.

Figure 1.4 Maglev Trains

Figure 1.5 Contactless Melting

Figure 1.6 Magnetic Bearing

1.4 Issues:

Primary issues involved in magnetic levitation are stability and lifting force. Lifting force should

be sufficient to provide upward force to counteract gravity. Stability to ensure that the system does

not slide or flip into a configuration when lift is neutralized.

CHAPTER 2: Earnshaw’s Theorem:

2.1 Statement:

It is impossible for a pole placed in a static field of force to have a position of stable equilibrium

when an inverse square law operates and this fundamental calculation is known as ‘Earnshaw’s

theorem’.

2.2 Stability:

Static Stability:

Static stability means that any small displacement away from a stable equilibrium causes a net

force to push it back to the equilibrium point.

Dynamic Stability:

Dynamic stability occurs when the levitation system is able to damp out any vibration-like motion

that may occur.

CHAPTER 3: Methods for Magnetic Levitation:

For Stable and successful levitation and control of all 6 axes by combination of permanent

magnets, diamagnets, electromagnets and superconductors by using force of attraction or repulsion

can be used. From Earnshaw’s theorem at least one stable axe should be present to levitate an

object.

Figure 1.7 Product Display

Purpose

3.1 Mechanical Constraint:

Mechanical constraint deals with levitation using two permanent magnets. Both magnets are

permanent therefore by Earnshaw’s theorem it can’t be made stable without any external support.

Figure 3.1 Mechanical Constraint

3.2 Direct Diamagnetic Levitation

Direct diamagnetic levitation is done by a diamagnetic material and permanent magnet. It is

because of the property of diamagnetic material to repel magnet.

Figure 3.2 Direct Diamagnetic levitation

3.3 Superconductors:

Superconductors levitates when it kept on magnetic track made using strong magnets and

combination of force of repulsion and attraction.

Figure 3.3 Superconductor Levitation

3.4 Diamagnetically Stabilized levitation:

In this method permanent magnet is levitated using various configuration of diamagnetic materials.

Figure 3.4 Diamagnetically Stabilized Levitation

3.5 Rotational Stabilization:

It is also known as spin stabilized magnetic levitation. Happens when the forces acting on the

levitating object- gravitational, magnetic, and gyroscopic- are in equilibrium. Earnshaw’s theorem

says it is impossible.

Figure 3.5 Rotational Stabilization

3.6 Servo Stabilization:

The attraction from a fixed strength magnet decreases with increased distance, and increases at

closer distances. This is unstable. For a stable system, the opposite is needed, variations from a

stable position should push it back to the target position. Stable magnetic levitation can be achieved

by measuring the position and speed of the object being levitated, and using a feedback loop which

continuously adjusts one or more electromagnets to correct the object's motion, thus forming

a servomechanism.

Maglev Trains uses servo mechanism.

3.7 Rotating conductors beneath magnets:

In this type of method conductors are rotated and because of their rotation it cuts the magnetic flux

and emf induced which opposes main field and hence it levitates.

3.8 High-frequency oscillating electromagnetic fields:

High frequency oscillating electromagnetic fields which are created by ac current, induces eddy

currents in conducting material and levitates it.

CHAPTER 4: Applications of Magnetic Levitation

Magnetic Bearing

Maglev Train

Maglev wind turbine

Maglev Fan

StartRam

Flying Car

Flywheels

4.1 Magnetic Bearing

4.1.1 Meaning of Bearing

A device which is used to enable linear or rotational motion of the shaft while reducing

friction is called bearing. It provides stability to the rotating shaft and frictionless rotation

of the same. The contacting surfaces in a bearing may be partially or completely separated

by a film of oil or any other liquid in order to reduce friction.

4.1.2 Types of Bearing

(a) Plain or Slider Bearing

In which the rotating shaft has a sliding contact with the bearing which is held stationary.

Due to large contact area friction between mating parts is high requiring greater lubrication.

Figure 4.1 Plain Bearing

(b) Rolling or Antifriction Bearing

Due to less contact area rolling friction is much lesser than the sliding friction, hence these

bearings are also known as antifriction bearing.

Figure 4.2 Rolling Bearing

4.1.3 Magnetic Bearing.

A magnetic bearing system supports a rotating shaft, without any physical contact by

suspending the rotor in the air, with an electrically controlled magnetic force. It works on

the basic principle of Magnetic Levitation and Electromagnetism. We can call it as the

future for upcoming generation of motors.

Hence we can say Magnetic bearings are designed to support rotating and linear moving

machinery elements without contact with rotor, this is accomplished by Electro-magnet

(bearing) which attracts a Ferromagnetic material (rotor) , using this principle rotor can be

suspended in magnetic field which is generated by bearing.

Main components of magnetic bearing are Actuators, Sensors and Control Mechanism.

4.1.4 Classification of Magnetic Bearing

a) Based on control action

b) Based on Forcing Action:

c) Based on load supported:

d) Based on magnetic effect:

Based on magnetic effect it can be classified in attractive type and repulsive type of

bearings.

4.1.5 Active Magnetic Bearing:

Because of Earnshaw’s Theorem it is not possible to use permanent magnets in magnetic

bearing. Even techniques that deal with diamagnets are under-developed. Hence

electromagnets are used for magnetic bearing. Hence magnetic bearing requires a

continuous power input & control system to stable the load. Even back-up powering is

required in case of power failure.

4.1.5.1 Operation

An Active Magnetic Bearing (AMB) consists of an electromagnet assembly, a set of power

amplifiers which supply current to the electromagnets, a controller, and gap sensors with

associated electronics to provide the feedback required to control the position of the rotor

within the gap. The power amplifiers supply equal bias current to two pairs of

electromagnets on opposite sides of a rotor.

The controller offsets the required bias current by equal but opposite perturbations of

current as the rotor deviates by a small amount from its center position. The gap sensors

are usually inductive in nature and continuously sensing the gap between rotor and the

bearing. The sensor measures the position of the body. The control electronics then

calculates the right current to suspend the ball.

This current is set by the amplifier. The resulting force is within limits proportional to the

square of the current and inversely proportional to the square of the position.

F = (I/X)^2

Controller uses Microprocessor to allow the whole system function in a stable manner.

Figure 4.3 Operation Diagram

4.1.5.2 Digital control System:

A-D converter Control Algorithm Processor D-A Converter

E.g. The position, is sampled. The data serves as input of the control algorithm, which runs

on the processor. Then the calculated desired value is converted into an analog form.

According to the application the data width lies between 10 and 64 bits.

4.1.6 Application of Active Magnetic Bearing

Turbo-blower: cooling gas compressor (CO2) for a power laser, cutting metal sheets up to

25 mm. The laser needs uncontaminated gas.

The speed is 54000 rpm, the rotor mass 3.6 kg, the motor power 12 kW.

Figure 4.4 Turbo Blower

Gas-turbine/Generator for power generation: 4 radial bearings and 1 thrust bearing, 6010

rpm, 9000 kW, bearing diameter 400 mm.

Figure 4.5 Gas Turbine

4.1.7 Advantages and Disadvantages of AMB:

Advantages:

o Magnetic Bearings are free of contact and can be utilized in vacuum techniques,

clean and sterile rooms and transportation of aggressive media or pure media.

o Highest speeds are possible even till the ultimate strength of the rotor.

o Absence of lubrication seals allows the larger and stiffer rotor shafts.

o Absence of mechanical wear results in lower maintenance costs and longer life of

the system.

Disadvantages:

High cost and larger in size.

4.1.8 Passive Magnetic Bearing (PMB):

Passive Magnetic Bearing differs from AMB in terms of magnets and electronic system.

The rotor is stabilized only by permanent uncontrolled magnetic fields. Because of this

PMB are less expensive than AMB.

Background:

PMB can be constructed using:

Permanent magnets.

Ferrofuilds(A liquid that gets strongly energized under magnetic field).

Diamagnetic materials eg copper, gold, quartz, mercury, water, alcohol.

Shown Prototype is built at GLENN RESEARCH CENTER.

Figure 4.6 Prototype Figure

Figure 4.7 Ferrofluid

Figure 4.8 PMB

4.1.9 Application of PMB

As far as the application is concerned it is limited as the diamagnetic or the permanent

magnets can be damaged easily.

It can only be used in application of flywheels.

First PMB bearing was prepared at GLENN RESEARCH CENTER at the speed of

5500rpm.

Disadvantage of PMB is Permanent Magnets are used hence they can be easily damaged

due to hammering or overheating. Therefore they are not economical.

4.2 Application of Magnetic Bearing:

• Used in industrial machines like compressors, turbines, pumps, motors and generators.

• Can be used in watt-hour meter to measure home power consumption.

• Useful in high precision equipment & to support equipment in a vacuum.

• To support maglev trains for smooth & noise free ride.

• Useful in artificial heart.

• Anywhere where rotating part is used

CHAPTER 5: Maglev Train

MAGLEV=MAGnetic+LEVitation

Figure 5.1 Maglev Train

5.1 History of Maglev trains:

In the 1960s in Britain Eric Laithwaite developed a functional maglev train. His maglev had 1.6

km of track and was in detail tested. His research was stopped in 1973 because lack of money and

his progress was not enough. In the 1970s, Germany and Japan also began research and after some

failures both nations developed mature technologies in the 1990’s.

Figure 5.2 Eric Laithwaite

5.2 Basic Principle Maglev Trains:

Maglev trains have to perform the following function to operate in high speed.

1. Levitation

2. Propulsion

3. Guidance

Figure 5.3 Three functions of maglev trains

5.3 How does it work?

A maglev train floats about 10mm above the guide way on a magnetic field.

It is propelled by the guideway itself rather than an onboard engine by changing magnetic fields.

Once the train is pulled into the next section the magnetism switches so that the train is pulled on

again. The Electro-magnets run the length of the guideway.

5.4 Types of Maglev Trains:

Based on the technique used for Levitation the are two types of Maglev trains

1. Electromagnetic Suspension - Attractive

2. Electrodynamic Suspension – Repulsive

Figure 5.4 Types of Trains

5.4.1 EMS Technique

In the EMS-attractive system, the electromagnets which do the work of levitation are attached on

the top side of a casing that extends below and then curves back up to the rail that is in the center

of the track.

Figure 5.5 EMS Technique

5.4.2 Gap Sensor

This attractive force is controlled by a gap sensor that measures the distance between the rails

and electromagnets.

Figure 5.6 Gap Sensor

5.4.3 EDS Technique

Electrodynamic Suspension uses Superconductors for levitation, propulsion and lateral guidance.

Figure 5.7 EDS Technique

5.5 Pros and Cons of Different Technologies

Table 5.1 Pros and Cons of Different Technologies

Technology Pros Cons

EMS

(Electromagnetic suspension)

Magnetic fields inside and

outside the vehicle are less

than EDS; proven,

commercially available

technology that can attain

very high speeds (500 km/h);

no wheels or secondary

propulsion system needed

The separation between the

vehicle and the guideway

must be constantly monitored

and corrected by computer

systems to avoid collision due

to the unstable nature of

electromagnetic attraction;

due to the system's inherent

instability and the required

constant corrections by

outside systems, vibration

issues may occur.

EDS

(Electrodynamic suspension)

Onboard magnets and large

margin between rail and train

enable highest recorded train

speeds (581 km/h) and heavy

load capacity; has recently

demonstrated (December

2005) successful operations

using high temperature

Strong magnetic fields

onboard the train would make

the train inaccessible to

passengers with pacemakers

or magnetic data storage

media such as hard drives and

credit cards, necessitating the

use of magnetic shielding;

superconductors in its

onboard magnets, cooled with

inexpensive liquid nitrogen

limitations on guideway

inductivity limit the maximum

speed of the vehicle; vehicle

must be wheeled for travel at

low speeds.

5.6 Propulsion:

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.

Braking is accomplished by sending an alternating current in the reverse direction so that it is

slowed by attractive and repulsive forces.

5.6.1 Propulsion Force:

This is a horizontal force which causes the movement of train. It requires 3 parameters.

i. Large electric power supply

ii. Metal coil lining, a guide way or track.

iii. Large magnet attached under the vehicle.

5.6.2 Techniques of propulsion:

Maglev vehicles are propelled primarily by one of the following three options:

a. Linear synchronous motor (LSM) in which coils in the guide way are excited by a

three phase winding to produce a traveling wave at the speed desired; Trans Rapid in

Germany employs such a system.

b. Linear Induction Motor (LIM) in which an electromagnet underneath the vehicle

induces current in an aluminium sheet on the guide way.

c. Reluctance motor is employed in which active coils on the vehicle are pulsed at the

proper time to realize thrust.

5.7 Principle of Guidance:

5.7.1 Principle of Lateral Guidance:

When one side of the train nears the side of the guideway, the super conducting magnet on the

train induces a repulsive force from the levitation coils on the side closer to the train and an

attractive force from the coils on the farther side.

This keeps the train in the center.

Figure 5.8 Lateral Guidance

5.7.2 Principle of Vertical Guidance:

The electromagnets on the underside of the train pull it up to the ferromagnetic stators on the track

and levitate the train.

The magnets on the side keep the train from moving from side to side.

Figure 5.9 Vertical Guidance

5.8 Advantages:

• The train is earthquake proof because the greater space (10 cm) between the track and the

train leaves more room for track deformation.

• Only the part of the track that is used will be electrified so no energy is wasted.

• Its top speed with people aboard is 350 mph.

• Since there is no friction these trains can reach high speeds.

• It is a safe and efficient way to travel.

5.9 Economic Aspect:

• The initial investment is similar to other high speed rail roads.

• Operating expenses are half of that of other railroads.

• A train is composed of sections that each contain 100 seats, and a train can have between

2 and 10 sections.

• The linear generators produce electricity for the cabin of the train, Thus it also consumes

the energy.

5.10 Current Projects:

• Currently operational systems include Transrapid (Germany) and High Speed Surface

Transport (Japan). There are several other projects under scrutiny such as the SwissMetro,

Seraphim and Inductrack. All have to do with personal rapid transit.

• Germany and Japan have been the pioneering countries in MagLev research.

References:

• Introduction to magnetic bearing by JAGU SRINIVASA RAO (Pdf)

• Magnetic Bearings by HILLYARD (Pdf)

• Design and Control of Active Magnetic Bearing Systems for High Speed Rotation by

RENE LARSONNEUR (Pdf)

• PMB by Gerhard Schweitzer (PDF)

• Optimization of Repulsive Passive Magnetic Bearings Roland Moser, Jan Sandtner, and

Hannes Bleule1.

• http://en.wikipedia.org/wiki/MAGLEV_TRAIN

• J. Powell, G. Maise, and J. Paniagua, “MAGLEV: A new concept for very low cost

transportation using technique of magnetic levitation,” paper IAF-01-S.6.04, 52nd

International Astronautical Congress, Toulouse, France, Oct. 1-5, 2001.