different type of first generation maglev system, termed Transrapid,
is presently operating in Germany. Instead of using superconducting
magnets on the maglev vehicle, the German system uses conventional,
room temperature electromagnets. The electromagnets are located
on each side of the vehicle, and run along its entire length. These
electromagnets are magnetically attracted upwards to iron rails
positioned under the edges of the guideway structure. The magnetic
lift force then levitates the vehicle.
Since the attractive force between the vehicle electromagnets and
the iron rails on the guideway increases as the gap between them
decreases, the Transrapid Levitation system maintains stability
by servo control of the current that energizes the magnets. Upwards
movements of the vehicle are countered by decreasing the magnet
current, while downwards movements from the rails are increasing
the magnet current.
Rather than relying on the passive stability inherent in the superconducting
maglev system, where any small displacement from the equilibrium
suspension point is automatically countered by an induced magnetic
force in the guideway, the Transrapid system thus relies on active
stabilization to maintain levitation of the maglev vehicles. The
gap between the vehicle and the guideway is continuously monitored,
and the current in the electromagnets continuously adjusted on a
fast time scale of thousandths of a second, so as to maintain a
constant value for the vehicle guideway gap. The magnitude of the
gap is small, about 3/8ths of an inch. In comparison, superconducting
maglev operates with a larger vehicle/guideway gap, typically on
the order of 4 to 6 inches. The large gap allows the tolerances
for construction of superconducting maglev guideways to be greater.
Greater tolerances enable lower guideway cost and reduce sensitivity
to earth settling, thermal expansion effects and earthquake movements.
Transrapid has demonstrated safe and reliable operation of its
Maglev vehicles at speeds up to 280 mph on its 35 kilometer test
track in Emsland, Germany, on which it has carried hundreds of thousands
of passengers. Transrapid has been certified as ready for commercial
service. China has indicated that it plans to build a system for
the Shanghai Airport.