How a Maglev Train Works (EMS and EDS)?

  

                                 
    Maglev trains are one of the greatest inventions in man-made history. These trains float over the track using magnetic power. The name Maglev is an abbreviation of Magnetic Levitation. As there is no contact between the train and the track, these type of trains moves faster with minimum energy loss. These trains are also well known for their eco-friendly operation, as it does not use any petroleum products like petrol, diesel, etc. From the year 1902, magnetic levitation has begun to rule the world. In 1984, the first commercial maglev train was introduced in Birmingham, the UK, with levitation of 15mm and a track length of 600m. From the past to the present, there were several breakthroughs made in maglev technology. These breakthroughs were successfully implemented at present in three countries; namely China, South Korea, and Japan. All these three countries had developed their own maglev model, among which Japan’s SC maglev stands at the topmost, with a speed recording break of 375 mph. Even though each country follows a different physical model, they all fall under two main categories of working principles, namely,

·        EMS (Electromagnetic Suspension)

·        EDS (Electrodynamic Suspension)

Most maglev trains use the EMS principle, while the SC maglev in Japan uses the EDS principle. Let’s look into each type of principle.

 

EMS (Electromagnetic Suspension)

Credit (Transrapid):By Jklamo - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=62481147

    Electromagnetic Suspension mainly relies on the support of electromagnets for working. Some of the commercial maglev trains that use the EMS principle are Shanghai Maglev (Transrapid) in China, Linimo in Japan, Incheon maglev in Korea, etc., Among all these trains, the transrapid maglev quite went successful in the EMS working principle. It was first proposed as a German technology which went later unsuccessful, after the Lathen accident in 2006. This technology was later then got by china and its own maglev system was opened for commercial purposes in 2003. This principle was also then proposed by Korea and Japan as different models. Now let’s see the working principle of the Transrapid system.

 

Construction of Electromagnetic Suspension

    First and foremost, if a train should be moved by magnetic levitation (either EMS or EDS), three things are necessary; namely propulsion, levitation, and guidance. The propulsion is done for moving the vehicle along a particular direction, and the levitation is done to lift the train by a few inches and the guidance is done for making the train to stay at a particular path without moving to any other angles.

 

Requirements of a Maglev Train

    In transrapid, the levitation is done by placing permanent magnets over the tracks and electromagnets over the train (undercarriage). When the electromagnets are charged, it exhibits a magnetic property, which is then attracted to the ferromagnetic material on the track. By this attraction, the train is lifted up by a few centimeters. Another set of electromagnets was also attached to the undercarriage of the train, to maintain the train at a particular position without moving over sideways.

Levitation

Levitation

Guidance

The propulsion part in the transrapid is done by a linear induction motor. As we think, the motor’s output is not given as a rotational part here; rather it is produced linearly. Therefore this motor is called a linear induction motor. It is a simple induction motor which does consists of a stator and rotor. But unlike a rotating part, the stator and rotor are present in a flat position. In the transrapid system, the track acts as the stator and the train acts as the rotor, as it will be moving. Let’s see the propulsion part in detail by understanding the operation of the linear induction motor.

   As the stator part acts as the field, it is given a 3 phase supply. When it is given, the stator acts as an electromagnet and produces its own magnetic field. But as we are providing a variable supply, which changes its intensity with respect to time, the field produced by it also changes. So the poles (North Pole & South Pole) present on the electromagnets also changes, which you can observe from the below figure.  By the interaction between the electromagnet on the train and the permanent magnet on the guideway, the train is made to move forward. By simple mechanism, through the supply given to the rotor, each rotor is classified as North and South Pole at different time instances. These poles are attracted and repulsed by the permanent magnet on the track. As the train moves, the polarity over the electromagnets changes, and the next attraction and repulsion forces take place. Such that the train is made to move continuously by the 3phase supply. By changing the frequency of the supply given to the rotor, the speed of the train is also controlled.

PROPULSION of EMS

EDS (Electrodynamic Suspension)

    

Credit: By Maryland GovPics - SC Maglev Test Ride, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=41059020

     EDS (Electrodynamic Suspension) is a Japanese technology. This technology was currently used in the Japanese SC Maglev train. The letter SC denotes the word Super Conductor which is the primary object in the operation. This train is considered one of the fastest trains in the world which attains a maximum speed of 375mph. Let’s look into the technology for this blazing speed.

Construction of ElectroDynamic Suspension

Like EMS, this type of train also floats and propels, but unlike EMS train it completely uses a different method for floating and propulsion. For levitation, a special material called a superconductor is used. A superconductor is a type of conductor which has no energy loss when electrical energy is given across it. When passing electrical energy to normal conductors, some amount of energy is wasted as heat due to the irregular movement of electrons. But in the case of superconductors, the electrons move in a straight way, which makes no waste of energy. So if the superconductor is once energized, it does not need to be recharged once again. This property belongs to only certain materials when it is cooled below its critical temperature. This cooling is basically done by liquid helium in maglev trains. This cooling has to be maintained below its critical temperature to maintain the superconducting property of the material. 

Superconductor with a radiation Shield

SC Maglev incorporates an ingenious design principle in placing the operation. As the liquid helium is passed through the superconductor, it gets evaporated by the heat of the material. Thus it is converted back to its original stage by a compression and refrigeration cycle. So by keeping this cooling temperature around the magnet we can able to retain its electrical energy. Also, a radiation shield cooled with liquid nitrogen is used to protect the superconductor magnets from external radiation and the formation of eddy currents in the radiation shield. Four such magnets are placed in a setup on both sides of the train with opposite polarity, which you can observe from the below figure.

Now by using these superconducting magnets we can achieve the property of propulsion, levitation, and guidance. First, for the propulsion part, normal electromagnets are used in the guideway with opposite polarity. By changing the polarity of the electromagnets, the attraction and repulsion action will be taken place between the superconducting magnets and the electromagnets on the guideway. The operation of the propulsion part can be observed in the below figure.

 

PROPULSION

Levitation of SC Maglev

    The levitation part also includes the same superconducting magnets which makes the support for levitation with another set of twisted metal on the guideway. The operation is very simpler which lies in the generation of the potential energy across the twisted coil. Let’s consider a simple demonstration, in which the superconducting magnets on both sides of the train can be pretended as a bar magnet exerting a single main electric field. Now when the train is moving, the magnetic field from the bar magnet interacts with the twisted coil. Now due to faraday’s law of electromagnetic induction, the voltage generated over the coil will be in an opposite manner as shown in the below figure. So the net output voltage will be zero. 

                           

    If the bar magnet is slightly down to the twisted coil, then the interaction on the bottom coil will be more than the interaction over the upper coil. So the EMF generated will be more on the bottom part, leading to a flow of current on the coil. Now the bottom loop will act as the North Pole and the upper loop will act as the South Pole. Now the attraction and repulsion force between the superconducting magnet and the twisted coil takes place, which pulls the magnet upwards. If the pulling force is greater than the gravitational pull, then the train begins to float. Now when the train moves up, the magnetic interaction on the South Pole decreases, and when the pulling force is equal to the gravitational pull, the train will perfectly achieve the levitation state. So the levitation can be achieved only during the movement of the train and not during a standstill. For this purpose, the SC Maglev uses wheels at the starting purpose. After the magnetic levitation property was attained the wheels are pulled back and the train is made to float.

When moving into the guidance part, nothing more than the connection of the two twisted coils on the guideway is made. As shown in the below figure, the generated electric voltage across the pair of twisted coils manages the guidance of the train. Now let’s consider an instance, in which the train slips to the left side of the guideway. Such that, the magnetic interaction on the left side of the twisted coil is more than on the right side of the coil. This makes a current flow over the interconnecting loop which increases and decreases the pole strength of the bottom loop. So in this case, the left side of the twisted loop will have more magnetic strength than the right side twisted loop. This creates a repulsion force and the train guidance is maintained. If the train is moving to the left side the opposite happens. This is how a maglev train works.

TWISTED COILS ON THE GUIDEWAY