The movement of a train along a route is
influenced by many forces, including traction
effort, train resistance, braking forces, and
equivalent mass.
Tractive effort, Te, provides the propulsion
to overcome resistances and to accelerate
the train. Train resistance, Re, is the result of
train characteristics and alignment geometries.
Braking force, Be, is used to decelerate the train
and bring it to full stop. During the movement
of the train, the wheels, shafts, axles may store
kinetic energy. As a result, the net force available
for accelerating/decelerating the train includes
not only its static mass, but also the rotating
mass. Their sum is called equivalent mass of the
train, Me.
Thus, traction simulation is all about
simulating the movement of trains along specified
route and is governed by Newton’s Second Law
of Motion.
The train movement simulation calculates
the interaction between trains and the track
alignment. The speed limits determine how fast
the train can travel. The vehicle characteristics
determine how fast the train can accelerate and
decelerate. These in turn will determine how much
power the train will demand from the traction
power system or how much power it can make
available by returning to the traction power system
(regenerative braking power is treated as negative
power demand).
The electrical network simulation determines
the voltage and current in the traction power
system. Based on the train operations schedules
and/or headways, the train movement simulator
calculates the locations of all the trains at any
given time instant and their power demands
across the system route. This data is then fed
into the electrical network simulator to perform
the load flow simulation for the given time instant.
The load flow simulation is basically of single-end
source radial feeds sectionalized lengths of 25kV
distribution system with moving electrical loads
(moving trains) across the system route.
The train movement simulation and the
electrical network calculation are carried out in
discrete time steps of one second. For a given
instant of time, the locations and power demand
(or back feeding power) of trains on the route
are known from the train movement simulation
Figure A9: Modelling and Simulation Process for Traction Power Simulation.
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