Our discussions should be as to which maglev technology (or perhaps multiple maglev technologies) we should use for updating our Post Roads of the near future.
Several commercial maglev systems are currently in operation around the world. In Aichi, Japan, near Nagoya, a system built for the 2005 World’s Fair is still in operation. It is about 9 km (5.6 miles) long, with nine station stops over that distance, and reaches speeds of about 100 km (62 miles) per hour. The Korean Rotem Maglev runs in the city of Taejeŏn between the Taejeŏn Expo Park and the National Science Museum, a distance of 1 km (0.6 mile). The longest commercial maglev system is in Shanghai; it covers about 30 km (18.6 miles) and runs from downtown Shanghai to Pudong International Airport. However, Japan has plans to create a long-distance system by the middle of the 21st century that connects Osaka to Tokyo, a distance of 514 km (319 miles). The United States has no commercial maglev trains, but several prototype systems exist or are under construction.
Each implementation of the magnetic levitation principle for train-type travel involves advantages and disadvantages.
|EMS (Electromagnetic suspension)||Magnetic fields inside and outside the vehicle are less than EDS; proven, commercially available technology that can attain very high speeds (500 km/h (310 mph)); no wheels or secondary propulsion system needed.||The separation between the vehicle and the guideway must be constantly monitored and corrected by computer systems to avoid collision due to the unstable nature of electromagnetic attraction; due to the system's inherent instability and the required constant corrections by outside systems, vibration issues may occur.|
|Onboard magnets and large margin between rail and train enable highest recorded train speeds (581 km/h (361 mph)) and heavy load capacity; has demonstrated (December 2005) successful operations using high-temperature superconductors in its onboard magnets, cooled with inexpensive liquid nitrogen.||Strong magnetic fields on board the train would make the train inaccessible to passengers with pacemakers or magnetic data storage media such as hard drives and credit cards, necessitating the use of magnetic shielding; limitations on guideway inductivity limit the maximum speed of the vehicle; vehicle must be wheeledfor travel at low speeds.|
|Inductrack System (Permanent Magnet Passive Suspension)||Failsafe Suspension—no power required to activate magnets; Magnetic field is localized below the car; can generate enough force at low speeds (around 5 km/h (3.1 mph)) to levitate maglev train; in case of power failure cars slow down on their own safely; Halbach arrays of permanent magnets may prove more cost-effective than electromagnets.||Requires either wheels or track segments that move for when the vehicle is stopped. New technology that is still under development (as of 2008) and as yet has no commercial version or full scale system prototype.|
Neither Inductrack nor the Superconducting EDS are able to levitate vehicles at a standstill, although Inductrack provides levitation down to a much lower speed; wheels are required for these systems. EMS systems are wheel-less.
The German Transrapid, Japanese HSST (Linimo), and Korean Rotem EMS maglevs levitate at a standstill, with electricity extracted from guideway using power rails for the latter two, and wirelessly for Transrapid. If guideway power is lost on the move, the Transrapid is still able to generate levitation down to 10 km/h (6.2 mph) speed, using the power from onboard batteries. This is not the case with the HSST and Rotem systems.
Some EMS systems such as HSST/Linimo can provide both levitation and propulsion using an onboard linear motor. But EDS systems and some EMS systems such as Transrapid can only levitate the train using the magnets on board, not propel it forward. As such, vehicles need some other technology for propulsion. A linear motor (propulsion coils) mounted in the track is one solution. Over long distances the cost of propulsion coils could be prohibitive.
Earnshaw's theorem shows that any combination of static magnets cannot be in a stable equilibrium. However, the various levitation systems achieve stable levitation by violating the assumptions of Earnshaw's theorem. Earnshaw's theorem assumes that the magnets are static and unchanging in field strength and that the relative permeability is constant and greater than unity everywhere. EMS systems rely on active electronic stabilization. Such systems constantly measure the bearing distance and adjust the electromagnet current accordingly. All EDS systems are moving systems (no EDS system can levitate the train unless it is in motion).
Because maglev vehicles essentially fly, stabilisation of pitch, roll and yaw is required by magnetic technology. In addition to rotation, surge (forward and backward motions), sway (sideways motion) or heave (up and down motions) can be problematic with some technologies.
If superconducting magnets are used on a train above a track made out of a permanent magnet, then the train would be locked in to its lateral position on the track. It can move linearly along the track, but not off the track. This is due to the Meissner effect.
Some systems use Null Current systems (also sometimes called Null Flux systems); these use a coil which is wound so that it enters two opposing, alternating fields, so that the average flux in the loop is zero. When the vehicle is in the straight ahead position, no current flows, but if it moves off-line this creates a changing flux that generates a field that pushes and pulls it back into line. However, some systems use coils that try to remain as much as possible in the null flux point between repulsive magnets, as this reduces eddy current losses.
Some systems (notably the Swissmetro system) propose the use of vactrains—maglev train technology used in evacuated (airless) tubes, which removes air drag. This has the potential to increase speed and efficiency greatly, as most of the energy for conventional maglev trains is lost in air drag.
One potential risk for passengers of trains operating in evacuated tubes is that they could be exposed to the risk of cabin depressurization unless tunnel safety monitoring systems can re-pressurize the tube in the event of a train malfunction or accident. The RAND Corporation has depicted a vacuum tube train that could, in theory, cross the Atlantic or the USA in ~21 minutes.
Energy for maglev trains is used to accelerate the train, and may be regained when the train slows down ("regenerative braking"). It is also used to make the train levitate and to stabilise the movement of the train. The main part of the energy is needed to force the train through the air ("air drag"). Also some energy is used for air conditioning, heating, lighting and other miscellaneous systems.
At low speeds the percentage of power (energy per time) used for levitation can be significant consuming up to 15% more power than a subway or light rail service. Also for very short distances the energy used for acceleration might be considerable. But the power used to overcome air drag increases with the cube of the velocity, and hence dominates at high speed (note: the energy needed per mile increases by the square of the velocity and the time decreases linearly.).