Maglev Trains


1. INTRODUCTION
1.1 History
First generation Maglev systems have been developed in Japan and Germany.
Hermann Kemper began research on Maglev system in Germany and conducted successfully tests in the 1930’s (receiving a patent in 1934).
In the late 1960’s the German government began a study of traffic and modes which led to the development of very high speed maglev system by the German ministry of research and technology. The development included short stator, EDS and EMS technology and system was selected for null scale development based on performance cost and magnetic fields considerations.
In 1979 TRO5, the first Maglev system licensed to carry passengers was demonstrated at the international traffic and transport exhibition in Hamburg.
In 1988 TRO6 set a speed record of 257 mph (412 Km/hr) and participated in a month long high speed public demonstration at the Emsland test facility with 8 to 10 min. transits of the 25 mile (40 Km) circuit at speed up to 250 mph (400 Km/hr).
TRO7, the prototype revenue services vehicle, began testing in 1989
1.2 Need for speedy transportation:
The main function of any transportation system is to carry people and goods from one place to other. To satisfy this various systems have been developed like cars, buses, trains, boats, airplanes etc.
In the world we are living in various, industries and businesses are continuously developing. Time has become important in every bodies life. Today time lost is counted in turn of money lost. It is desired that minimum time should be wasted in moving from one place to other so that more time can be devoted for other important activities. Hence many efforts are being made to save time as much as possible. One of the ways to save time is to provide a faster transportation system.
1.3 Motive behind the development of Maglev:
Existing ground transportation systems are road transportation and railways. road transportation has maneuverability limitation at high speeds and so higher speeds can not be achieved. Railways are running on a rail or rails and at quite high speeds. But further improvement in the speeds is difficult due to the typical relation between its Dead Weight and Friction.
Both systems have one common limiting factor i.e. Friction. But it cannot be eliminated completely unless the physical contact with the ground is avoided while vehicle is in motion.
For these and many other reasons effort was made to develop Maglev which avoids contact with guide ways thereby completely eliminating friction.
1.4 What is a Magnetic Levitation Train?
A magnetic levitation train is a train that runs levitated or lifted above the guide ways by using magnetic forces either of attraction or of repulsion resulting due to current flow in coils placed in guide ways and in the train itself.
Magnetic Levitation Train is sometimes abbreviated as Maglev. The train runs levitated or lifted above the guide ways with very high of about 150 m/s or 540 km/hr or 336 miles/hr.
The train has no physical contact with the guide ways. As a result the friction is totally avoided, which is the main reason for such a high speed of Maglev.
2. BASIC PRINCIPLE
2.1 Basic principle of magnetism
Force Due to current flowing in two Parallel Conductors:
Suppose two parallel conductors carry current through then. Because of this current both conductors generate their own magnetic fields. Depending on the direction of magnetic field they attract or repel each other. This results in forces acting on the two conductors.
 If both the conductors carry current in same directing then the conductors attract each other.
 But if both of them carry current in opposite direction then they repel each other.
 These forces are used to levitate the train above guide ways as discussed in following sections.
2.2 Types of Maglev
There are basically two types of Magnetic Levitation train depending on the types of magnetic force for levitation of train.
2.2 a) Electrodynamics Magnetic Levitation Train.
2.2 b) Electromagnetic Magnetic Levitation Train.
2.2 a) Electrodynamics Magnetic Levitation Train.
Principle of operation:To understand the principle of operation let us assume that there are two coils one above the other. One coil is in guideway and other is in train. The coil in the guideway is directly below the coil in the train. Arrangement is made such that the directions of currents in both coils are opposite to each other. This results in upward force experienced by coil in the train. As the coil in guideway is fixed the train is levitated upwards. Principle of EDS is explained in fig. 1.

Actual arrangement:The actual arrangement in the train is somewhat different. Here the coils in the guideway are placed in sidewall. The guideway coils are not supplied with any current. The coils located in train are supplied with on board DC source, which produces magnetic field. The train is moved up to some distance initially by external means. The method of moving the train initially is explained ahead in detail. As coils in guideway encounter moving magnetic field, currents are developed in the coils in guideway which are opposite in direction to that in coils in the train. As a result on production of sufficient upward force the train gets levitated.
This type of magnetic levitation system is capable of lifting the train by about four inches maximum. Generally superconducting magnets are used in this train.
2.2 b) Electromagnetic Magnetic Levitation Train.
Principle of operation of this train can be seen from the fig 2. In this type also there are two coils. But only difference is that the coil in the train is placed directly below the coil in the guideway in part of train that envelopes the guideway.
In this type the direction of current in the two coils is same. As we know that whenever the direction of current in the two coils carrying currents is same the two coils will experience the force of attraction.
Same case happens here also. As the coil in the train is placed directly below the coil in guideway the coil in the train experiences force of attraction in upward direction thus lifting the train up.
This train uses conventional electromagnets on train instead of superconducting magnets, which are capable of lifting the train by about 3/8th of an inch or 10mm.
Scientists have succeeded in using superconducting magnets for the same purpose, which is capable of levitating the train by about two inches.
This type of system is generally not preferred because of its lack of capacity to lift the train by same amounts as that of Electrodynamic Levitation System.
2.3. Propulsion method
A repulsive force and attractive forces induced between the magnets are used to propel the vehicle. The propulsion coils located on sidewalls on both sides of the guide way are energized by a three-phase alternating current from a substation creating a shifting magnetic field on the guide way. The on board magnets are attached and pushed by the shifting field propelling the maglev vehicle. For propulsion system, utility substations are located at about 20 to 30 km intervals. Normally these are located in the vicinity of high voltage power transmission lines.
At each substation AC power is transformed and rectified to produce low voltage DC. This DC power is fed to underground transmission lines, which run along entire length of guide way.
Invertors are placed at about 2 to 4 km intervals. These tap the power from DC transmission lines which generate variable frequency, variable voltage AC power for exciting Linear Electric Motor (LEM).
Linear electric motors: Linear Electric Motor is an electric motor that generates a motion in a straight line.We can generate straight-line motion with conventional ways also i.e. we can use a conventional electric motor which produces a rotary motion. This rotary motion can be converted into linear motion by suitable mechanism like crank mechanism. But Linear Electric Motor can generate straight-line motion more efficiently than any other conventional ways. Also conventional drives cannot be used here because of the fact that there is no physical contact between the Maglev and the guide ways.
Theoretically a Linear Electric Motor is obtained if we cut any conventional motor and develop it.
There are two types of Linear Electric Motors used viz.
a) Linear Synchronous Motor
b) Linear Induction Motor
a) Linear Synchronous Motor:
The principle of operation of Linear Synchronous Motor is same as that of a Synchronous Motor which the rotary counterpart of Linear Synchronous Motor.
In a conventional synchronous motor the stator winding is supplied with a 3-phase AC supply. The stator coils corresponding to each phase are separated by 120 0. As a result whenever the supply to stator is switched on a rotating magnetic field is produced this rotates with the supply frequency.
The rotor is supplied with DC, which as a result will act as a permanent magnet. The rotor is rotated with same speed add that of rotating field by some external means. As rotor picks up the speed it gets locked with the rotating field and keeps on rotating in same direction. This speed is called as asynchronous speed and is dependent on supply frequency. Thus speed of rotor can be varied by simply changing frequency of current. Fig 3 shows magnetic locking of stator and rotor fields.
Same is the case with Linear Synchronous Motor. Here stator consists of propulsion coils, which are located in the sidewalls of guide way. Stator is provided with variable frequency variable voltage current. This induces a traveling field in straight line instead of a rotating magnetic field.
The rotor is nothing but the electromagnet or superconducting magnet on train. It acts as a permanent magnet and is driven with the traveling magnetic field. Here rotor gets locked with the stator fielld.Varying the frequency can control the speed of train. Fig 4 shows the principle of working of LSM.
b) Linear Induction Motor:
As in the case of Linear Synchronous motor the working principle of Linear Induction Motor is exactly similar with its rotary counterpart i.e. Induction Motor.
In a conventional induction motor stator is supplied with 3-phase AC supply which produces a rotating magnetic field. This rotating magnetic field is cut by rotor windings in which currents are generated which produce their own field. These two fields get locked with each other, which rotate the rotor.
In a Linear Induction Motor stator windings are nothing but propulsion coils which are supplied with variable frequency variable voltage AC supply. This produces traveling magnetic field in straight line.
Rotor here is located in the train which gets locked with traveling magnetic field produced by stator or propulsion coils and thus is propelled in one direction.