Hyperloop
2.1 EMS
EMS is a type of active magnetic suspension that relies on the attraction forces between permanent magnets (normally in the vehicle) and
electromagnets in the track. EMS maglevs have been in operation since early 80s, and are so far the most common around the globe. A maglev using EMS, like Transrapid, constantly levitates over the track and, therefore, doesn’t
Permanent magnets levitate over passive coils
Figure 8
require any support/secondary propulsion systems. This, however, can be regarded as a drawback, since in case of system failure magnetic levitation would not be sustained. Transrapid engineers included heavy backup batteries in the construction of the vehicle, so that the train can switch instantaneously to the alternative energy source, although this increased the total weight significantly.
Stable magnetic levitation is only achievable by constantly altering the currents passing through electromagnets, since, according to Earnshaw's theorem, it is impossible to maintain stationary levitation using any combination of permanent magnets and electric charges. This requires a very accurate feedback algorithm for adjusting the magnetic fields and leaves no space for calculation error. The issue has been solved in trains like Transrapid, but the predicted operation speeds of Hyperloop are beyond 1000 km/h, while Transrapid reaches only 440 km/h, so a very high-
performance response system would be necessary for Musk’s vacuum train. Another disadvantage of using EMS is that electromagnets are used both for levitation and propulsion, which results in high energy consumption and, therefore, reduces the energy-efficiency advantage of maglevs. Figure 9
2.2 EDS
The second type of magnetic suspension is EDS, which is by its nature a passive system. So far, the most reliable EDS has been the Null-Flux system, which is basically an array of pairs of interconnected 8- shaped coils that are put on opposite sides of the track (figs. 7 & 12). When interacting with superconducting magnets in the vehicle, this setup provides both levitation and guidance and has a stable equilibri um position. The working principle relies on Faraday’s Law and Lenz’s Law, according to which, when a closed loop experiences a change in magnetic flux through it, an EMF is generated in it, which in turn creates a magnetic field that opposes the change in flux.
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