Maglevs Train

 MagLev Trains:

P.K.Ghatak,MD

No: 56

The common properties of magnets – similar poles of magnets repel, and opposite poles attract each other are utilized very ingeniously in superfast trains - Maglev Trains. The train is lifted up from the tract (Levitation), movement forwards and backwards (Linear Acceleration) and keep the train steady on the tract (Guidance). These three properties are achieved in Maglev Trains by cleverly employing permanent magnets and electromagnets.

Levitation:

The human quest for levitation is mentioned in a story of Buddha. Buddha came upon a group of ascetics, while he was waiting for the boatmen to ferry him across the river, he saw the ascetics were meditating. One of the ascetics recognized Buddha and invited him for some religious discourses. Buddha asked him what he was trying to achieve by meditation. The ascetic said, “to walk across the river on water”. To that Buddha invited them to join him on the boat in crossing the river and advised him to give up attempts to walk on water.

Here, we are not discussing the spiritual levitation, but levitation generated by magnets.

The Train:

The train as a whole is one part of the magnet bearing part of this system. The undersurface of the board of the train carries a powerful permanent magnet made with superconductive rare metals. To keep the superconductive state, liquid Helium pump and condenser are used to reuse it. To eliminate magnetic eddy generated in this magnet and to control heat coming from outside, the liquid Nitrogen is pumped in.

The Rail:

The upper surface of the rail contains a strong Electromagnet. The same magnetic pole of both the rail and train face each other and repel and lift up the train about 10mm off the rail.

Effects of Levitation is to eliminate metal to metal friction and resistance. However, because of such high speed of the train, very strong air resistance the train has to overcome to gain speed, The energy saved from elimination of friction is partly used up against wind resistance.

Two different suspensions are in operation in Maglev trains.

1. EMS (electromagnetic suspension).

The bottom of the train wraps around the rail on the ground. When power flows through the rail, it attracts electromagnets embedded in the train button.

2. EDS (electrodynamic suspension).

The powerful superconductive magnets on the bottom of the moving train create a magnetic field in the nearby metallic conductors and results in a push and keep the train in suspension – just above the rail.

Propulsion:

When the system is energized the train is levitating and remaining stable in one place. When itis time to start, a separate electric motor is switched on, the rubber wheels descend on the tract and the train begins to move forward, After the train attains certain speed the Maglev propulsion system is automatically becomes operate, rubber wheels are retracted and electric motor is turned off. As the train moves, the diagram on the right shows how Pull and Push forward of the train is obtained by the magnet placed along the length of the train. The N pole of the train magnet finds the S pole of the magnet on the Guide wall first and the opposite poles of the magnets attract each other and pull the train forward; the next moment the N pole of the train magnet finds N pole on the wall and gives a push and increases the forward speed.

In the electric engineering term, the guide wall acts as a Stator and the train as the Rotor of a Linear Electromotor.

This forward motion is unopposed by any friction and because the train is floating above the tract is able to gain such high speed, usually 300 miles per hour, the record is 605 miles in an experimental tunnel where air resistance is minimized.

When it is time to go backwards the polarity of electric current is reversed of the electromagnets of the sidewalls.

Guidance:

The underbelly of the train is U shaped, and a slot runs all the way from the front to the rear of the train. In addition to sets of magnets shown in the diagram, the slot also houses rubber wheels. Just like airplanes, the train rests on these wheels and runs forwards and backwards in slow speed. Like a plane, the train runs on the rubber wheels to reach the Maglev speed, and the wheels are retracted back into the belly, then the wheels reappear when the train slows down and comes to a stop.

When the train moves to any side, away from the midline, the guidance electromagnet adjusts the current flow and voltage to match the force of pull of the other side, and the train takes again the central position.

The train ride is noiseless and is so smooth and except for the display of speed overhead and announcement of an approaching stop or terminus, it would not register any forward motion.

Elevated Tract:

To avoid delays and accidents, the tract and intermediate stations are on the elevated platform. The terminus is generally underground, and it takes the passengers right into the passenger boarding area.

Unlike the rattles and shakes made in earlier days by the L-trains, the Maglev trains make no noise. Inside the passenger compartment one can drink a cup of hot coffee without spilling a drop on the floor.

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Footnote:

If this is the bare minimum description of the Maglev system interests, you - you will have a better understanding of this science subject by watching this short clip. (the material is in the public domain).

https://www.youtube.com/watch?v=XjwF-STGtfE

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