Propulsion
The Transrapid is both propelled and braked using
a synchronous longstator linear motor. Ferromagnetic stator
packs and three phase stator windings are mounted on both
sides along the underside of the guideway. The operation of
this equally non-contact, propulsion and brake system is analogous
to a rotating electric motor whose stator is cut open and
stretched along the underside of the guideway and whose rotor
(excitation) function is assumed by the levitation magnets
in the vehicle. In contrast to the rotating field in a conventional
motor, the longstator linear motor produces an electromagnetic
traveling field which propels the vehicle along the guideway.
With the help of converters in substations along the route,
the thrust can be regulated by changing the amplitude and
frequency of the alternating current to allow the vehicle
to accelerate smoothly from standstill to full speed. By slowing
down the traveling field, the motor becomes a generator and
the vehicle is braked, without contact, to a smooth, controlled,
and safe stop (regenerative braking). In the event of public
power or propulsion system failure, independent backup brakes
in each vehicle section provide safe and accurate braking
to the next available stopping area.
Propulsion System Layout
The substations receive 23kV power from the energy supply
system and convert it into the proper format to propel the
train. The propulsion control system both controls and monitors
the position of the train at all times comparing these real-time
inputs to the set-points given by the OCS which result from
the pre-programmed speed/time/location profile developed for
the route.
The number and location of the substations depend on a number
of factors which are applied both to the entire route and
locally:
Through the spacing of the substations along the route, the
route is divided into propulsion segments. Each propulsion
segment is divided into smaller motor sections, usually between
0.5 km and 2km in length. The longstator windings on the right
and left sides of the guideway are fed independently and physically
offset with respect to each other. This helps to smooth the
transition between motor sections and even if one side fails,
the other has sufficient reserves to propel the train through
the segment. Only one motor section is energized at any one
time in each propulsion segment. Wayside switch stations switch
the propulsion power from one section to the next as the Transrapid
train proceeds. A propulsion segment can be fed redundantly
from two substations.
The propulsion power is supplied by independent by converters
in the substation. If an individual converter fails, the train
can still continue to proceed at a slower speed. Even if an
entire substation fails, the next substation can provide power
in its place, thereby allowing the vehicle to reach its destination.
Substations
The primary purpose of substations is the conversion and control
of 23 kV input power into variable frequency, amplitude and
phase power to propel the maglev vehicles along the guideway.
Substations supply power to propulsion segments that represent
the total route between substations. A substation, depending
on the track layout, will be fitted with up to four propulsion
blocks (one per track per direction).
The propulsion blocks which power each propulsion/track segment
contain the following general components:
Input and output inverters
Motor regulation/control system
Switchgear
Input and output transformers
Decentral diagnostics system
Data transmission system (fiber optic)
Two methods are available for switching of the motor sections
on/off as the train passes through:
Alternating step switching is normally used for low acceleration/braking
and/or constant speed portions of the route and requires less
installed propulsion power and therefore fewer components.
Three step switching is the better choice for increased propulsion
performance. It is normally used for high acceleration/braking
and/or high load (climbing hills) portions of the route. It
provides high ride comfort under all conditions and requires
more components (and more space) both in the substations and
along the route.
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