Maglev: the history
Case Study: Japan’s SCMaglev
Japan’s world -leading SC (Superconducting)Maglev system, a pioneer in the EDS system that currently holds the current speed record of 603km/h by a L0 series train, is planned to enter commercial use by 2027 between Tokyo and Nagoya, with an extension to Osaka planned by 2037. It is estimated to cover the 438km distance in just 67 minutes, which is faster than a commercial plane. 14 To power the electricity within the carriage, the SCMaglev invented an inductive power collection system that uses magnetic induction and wireless power transmission between the coils on the ground and the carriage. It doesn’t need a power supply to levitate, as it will continue to float if its speed is over 150km/h due to the increased strength of the induced current and the magnetic force.
Within its system, coils are used for both propulsion and levitation, effectively acting as a linear motor as the alternating current in the coils generates a varying magnetic field that moves along the track (see figure 9). This is because the polarity of the magnets is swapped every time the train reaches the next electromagnet to continue producing a net forward force to propel the train. Therefore, the frequency of this alternation directly determines how fast the train passes along these
Figure 9: Propulsion via the alternating magnetic field in propulsion coils
magnets; hence, the frequency needs to be synced with the speed.
For levitation, 8-shaped coils are arranged next to the propulsion coils outside the train. The alternating flux will induce EMF on both loops of the coil as the train’s superconducting magnets move across the track, according to Faraday’s law. If the magnet is moving along the centre of the coil, no current will flow through the loops. There is no net EMF if we unwind the ‘8’ shape into a rectangle, with the upper and bottom sections having their induced EMF in the opposite direction (see figure 10). However, if we now repeat the scenario, but with the superconducting magnets slightly below the centre, the EMF induced in the bottom loop will be higher than in the upper loop. A net current will now flow through the coil, and a resultant upward force is produced. This process continues until the magnet reaches the centre of the coil, where the upward force is equal to the gravitational pull, achieving levitation of around 3.9 inches (see figure 11). 15
Figure 10: unwinding the '8' shaped coils, green arrows show the direction of the induced EMF (Lesics, YouTube)
Figure 11: Force analysis of the coil and the superconducting magnet at the centre position (Lesics, YouTube)
For its guidance system, the 8-shaped coils from opposite sides of the train become interconnected, with no current flowing between them if the train is in the centre.
14 https://www.youtube.com/watch?v=-MmcQKE12Hg; consulted: 30/7/2023; see also ‘I rode the world’s fastest train’ (2023) at https://www.youtube.com/watch?v=4ZX9T0kWb4Y, Consulted: 29/7/2023. 15 https://www.youtube.com/watch?v=XjwF-STGtfE; consulted: 30/7/2023.
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