MagLev –Magnetic LeviationDriving without wheels, Flying without wings

BY – Debasis Ray, BS-10-224

Magnetic Leviation 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 Diamagnetisim object can be leviated.

A superconductor is perfectly diamagnetic and electromagnets can exhibit varying levels of ferromagnetism

Most imoportant application of Magnetic Leviation is Transrapid magnetic lift trains.

Basic Principle of Maglev TrainsMaglev trains have to perform the following functions to

operate in high speeds

1.Leviation

2.Propulsion

3.Lateral Guidance

Types of Maglev TrainsBased on the technique used for Leviation the are two types of

Maglev trains

1. Electromagnetic Suspension -Attractive

2. Electrodynamic Suspension -repulsive

Electromagnetic Suspension(EMS) Electromagnetic Suspension uses electromagnets to leviate

the train

Principle of Magnetic Leviation 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.

The rail, which is in the shape of an inverted T, is a ferromagnetic rail.

When a current is passed through it, and the electromagnet switched on, there is attraction, and the levitation electromagnets, which are below the rail, raise up to meet the rail. The car levitates.

EMS Levitation Principle:

Principle of Propulsion

A linear electric motor (LEM) is a mechanism which converts electrical energy directly into linear motion without employing any intervening rotary components

Linear Induction Motor (LIM) is basically a rotating squirrel cage induction motor opened out flat

Instead of producing rotary torque from a cylindrical machine it produces linear force from a flat one.

LIM thrusts vary from just a few to thousands of Newtons , depending mainly on the size and rating

Speeds vary from zero to many meters per second and are determined by design and supply frequency

EMS Propulsion Principle

Gap Sensor The attractive force is controlled by a gap sensor that measures the

distance between the rails and electromagnets.

Principle of Lateral Guidance

The levitation magnets and rail are both

U shaped(with rail being an inverted U).

The mouths of U face one another.

This configuration ensures that when ever a levitational force is exerted, a lateral guidance force occurs as well.

If the electromagnet starts to shift laterally from the center of the rail, the lateral guidance force is exerted in proportion to the extent of the shift, bringing the electromagnet back into alignment.

Electrodynamic Suspension Electrodynamics Suspension uses Superconductors for

levitation, propulsion and lateral guidance

Superconductivity Superconductivity occurs in certain materials at very low

temperatures. When superconductive, a material has an electrical resistance

of exactly zero. It is also characterized by a phenomenon called the Miessner

effect. This is the ejection of any sufficiently weak magnetic field from the interior of the superconductor as it transitions into the superconducting state.

•The passing of the superconducting magnets by figure eight levitation coils on the side of the tract induces a current in the coils and creates a magnetic field. This pushes the train upward so that it can levitate 10 cm above the track.

•The train does not levitate until it reaches 50 mph, so it is equipped with retractable wheels.

PRINCIPLE OF MAGNET LEVITATION

•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.

PRINCIPLE OF PROPULSION

•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.

PRINCIPLE OF LATERAL GUIDANCE

The SCM (Super Conducting Magnet) Each SCM contains 4 SC coils. The SCM features high

reliability and high durability. The cylindrical unit at the top is a tank holding liquefied helium

and nitrogen. The bottom unit is an SC coil alternately generating N poles

and S poles.

An EDS system can provide both levitation and propulsion using an onboard linear motor.

EMS systems can only levitate the train using the magnets onboard, not propel it forward.

EDS Mechanism:

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.

TECHNOLOGY PROS CONS

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 superconductors in its onboard magnets, cooled with inexpensive liquid nitrogen

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; limitations on guideway inductivity limit the maximum speed of the vehicle; vehicle must be wheeled for travel at low speeds.

Advantages of Magnetic Levitated Transportation System

Maglev uses 30% less energy than a high-speed train traveling at the same speed (1/3 more power for the same amount of energy).

The operating costs of a maglev system are approximately half that of conventional long-distance railroads.

Research has shown that the maglev is about 20 times safer than

airplanes, 250 times safer than conventional railroads, and 700 times safer than automobile travel.

Maglev vehicle carries no fuel to increase fire hazard

The materials used to construct maglev vehicles are non-combustible, poor penetration transmitters of heat, and able to withstand fire.

Current Projects

Currently operational systems include Transrapid (Germany ) and High Speed Surface Transport (Japan ). There are several other projects under scrutiny such as the Swiss Metro, Seraphim and Inductrack. All have to do with personal rapid transit

Germany and Japan have been the pioneering countries in Maglev research

Other Applications NASA plans to use magnetic levitation for launching of space

vehicles into low earth orbit.

Boeing is pursuing research in MagLev to provide a Hypersonic Ground Test Facility for the Air Force.

The mining industry will also benefit from MagLev.

There are probably many more undiscovered applications!

Conclusion The MagLev Train: Research on this ‘dream train' has been

going on for the last 30 odd years in various parts of the world.

The chief advantages of this type of train are:

Non-contact and non-wearing propulsion, independent of friction, no mechanical components like wheel, axle.

Maintenance costs decrease

The MagLev offers a cheap, efficient alternative to the current rail system. A country like India could benefit very much if this were implemented here. Further possible applications need to be explored.

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