问答题

Practice 5　　Maglev is a system in which the vehicle runs levitated from the guide way (corresponding to the rail tracks of conventional railways) by using electromagnetic forces between superconducting magnets on board the vehicle and coils on the ground.　　Different from conventional wheel-on-rail system, the Trans rapid accomplishes the functions of support, guidance, acceleration and braking by using non-contact electromagnetic instead of mechanical force. Because there is almost no mechanical contact Trans rapid can run with lower noise, but relatively higher speed up to 500 km/h.　　The magnetic levitation system is based on the power of attraction between the electromagnets in the vehicle and the ferromagnetic stator packs in the guide way. In contrast to the conventional trains, the propulsion system for the Trans rapid is not mounted in the vehicle but in the guide way. The long-stator linear motor in the guide way is divided into segments which are individually switched on and off, with power only being supplied to the given segment as the train passes.　　Electronically controlled support magnets located on both sides along the entire length of the vehicle pull the vehicle up to the ferromagnetic stator packs mounted to the underside of the guideway.　　Guidance magnets located on both sides along the entire length of the vehicle keep the vehicle laterally on the track. Electronic systems guarantee that the clearance remains constant (nominally10 mm). To hover, the maglev requires less power than its air conditioning equipment. The levitation system is supplied from on-b0ard batteries and thus independent of the propulsion system. The vehicle is capable of hovering up to 30 minutes without external energy. While travelling, the on-board batteries are recharged by linear generators integrated into the support magnets.　　The maglev hovers over a single or double track guide way. It can be mounted either at-grade or elevated on slim columns and consists of individual steel or concrete beams up to 62 meters in length.　　To change tracks, bendable switches are used which consist of a continuous steel beam which is elastically bent by means of electro-mechanical setting drives. Low speed switches, approx.78 meters long, are used to change tracks near stations and can be passed over in the turnout direction at 100 km/h (in the straight direction at full operating speed). High speed switches, approx.150 meters long, are used where higher turnout speeds are required (200 km/h turnout speed and in the straight direction at full operating speed).　　The maglev is propelled by a non-contact, long-stator linear motor which is installed in the guide way and functions like a rotating electric motor with the stator cut open and stretched out below the guide way.