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l Introduction
High-speed rail is a type of rail transport that operates significantly faster than traditional rail traffic, using an

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integrated system of specialized rolling stock and dedicated tracks. (Wikipedia). Electrical engineering plays a really
important role in the high-speed rail. In this report, we will discuss how to satisfy the needs of the high-speed rail in an
EE view.
l What is needed?

a)
i.

ii.
b)

i.
ii.

The main difference between the electrical supply system AC and DC is not only the existence of a frequency
or the levels of voltage, but it is mostly about the infrastructure. DC systems require the installation of a DC Substation
(DCS) and for the AC systems an AC Substation (ACS). The conjunction of these two types of systems makes
necessary the installation of a combined system. In the sections between the electrical supplies, we might install so-
called Traction Sectioning Point (TSP).

n DC
Early electric systems used low-voltage DC. Electric motors were fed directly from the traction supply and

were controlled using a combination of resistors and relays that connected the motors in parallel or series. The DC
system is quite simple but it requires thick cables and short distances between feeder stations because of the high
currents required.

n AC
Alternating current can be transformed to lower voltages inside the locomotive. This allows much higher

voltages and therefore smaller currents along the line, which means smaller energy losses along long railways.This

How to get power
Electric wires

Pantograph or other connectors between the trains and the wires
How to use power

Use power for driving

Use power for passengers
l DC vs AC in power supply

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system is quite economical and have a higher power-to-weight ratio, but it has its drawbacks: the phases of the external

power system are loaded unequally and there is significant electromagnetic interference generated as well as significant
acoustic noise.
l Overhead line systems

Overhead lines or overhead wires are used to transmit electrical energy to trains at a distance from the energy
supply point.

n Tensioning
For medium and high speeds, the wires are generally tensioned by means

of weights or occasionally by hydraulic tensioners. Either method is known as
auto-tensioning (AT), or constant tension and ensures that the tension in the
equipment is virtually independent of temperature. Tensions are typically between
9 and 20 kN (2,000 and 4,500 lbf) per wire. Where weights are used, they slide up
and down on a rod or tube attached to the mast, to stop the weights from swaying.

n Crossings
There are usually situations that 2 different railways come to a crossing. Sometimes the voltage supply is

different, suppose Line 1 has a higher voltage than Line 2 This is usually solved by Line 2 wires running continuously
through the crossing, with the Line 1 conductors a few centimeters lower. Close to the junction on each side, the wire
merges into a solid bar running parallel to Line 1 for about half a meter. Another bar similarly angled at its ends is hung
between the Line 2. This is electrically connected above to the Line 1. The Line 1 train’s pantograph bridges the gap
between the different conductors, providing it with a

continuous pickup.
l Pantograph

The pantograph is operated by compressed
air from the braking system. This system pushes the
pallets that can be seen in Figure, most of them made
of metal-carbon strip, which reaches the contact wire
so the vehicle can draw electricity for running. The material used for this part of the pantograph and its geometrical
dimensions are also really important parameters considered for interoperability standards.

l Traction
n Dependent traction (DT)

This is the most important type of electric traction. In this type of traction system the train needs to be
connected directly and constantly to a substation for its power supply, firstly it is connected through the overhead line
which is in contact with the current collector, or most commonly called pantograph collector, a graphical description is
shown in Figure.

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From: F3-DP-2016-Servin Marson-Dalva Leonor-Dalva Leonor Servin Marson – Master Thesis

n AC Locomotives with DC Drives
The 25 kV AC is collected by the pantograph and passed to the transformer. The transformer is needed to step

down the voltage to a level which can be managed by the traction motors. The level of current applied to the motors is
controlled by a “tap changer”, which switches in more sections of the transformer to increase the voltage passing
through to the motors. Before being passed to the motors, the AC has to be changed to DC by passing it through a
rectifier. For the last 30 years, rectifiers have used diodes and their derivatives, the continuing development of which
has led to the present, state-of-the-art AC

traction systems.
n The DC Traction Motor

The motor consists of two parts, a
rotating armature, and a fixed field (Figure 1).
The fixed field consists of tightly wound coils
of wire fitted inside the motor case. The
armature is another set of coils wound round a central shaft. It is connected to the field through “brushes” which are
spring loaded contacts pressing against an extension of the armature called the commutator. The commutator collects

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all the terminations of the armature coils and distributes them in a circular pattern to allow the correct sequence of

current flow.
From http://www.railway-technical.com/_Media/motor-basic-2_med_hr_med_hr.png

l Forward and Reverse
To ensure the correct direction is

achieved by a second locomotive (Unit 2) that
is coupled to the first, the forward and reverse
wires are crossed over in the jumper cable. If
the second locomotive faces in the opposite
direction to the first, its reverse wire (shown
in black here) will be energised to make the
loco run in the same direction as its partner.
To make sure this always happens, all multiple unit control jumpers have their forward and reverse wires crossed.

From: http://www.railway-technical.com/_Media/for-rev_med_hr.png
l Dynamic Braking

Trains equipped with thyristor (a development of the diode) control can readily use dynamic braking, where the
motors become generators and feed the resulting current into an on-board resistance (rheostatic braking) or back into
the supply system (regenerative braking). The circuits are reconfigured, usually by a “motor/brake switch” operated by
a command from the driver, to allow the thyristors to control the current flow as the motors slow down. An advantage
of the thyristor control circuitry is its ability to choose either regenerative or rheostatic braking simply by automatically
detecting the state of receptivity of the line. So, when the regenerated voltage across the supply connection filter circuit
reaches a preset upper limit, a thyristor fires to divert the current to the on-board resistor.
l Multiple Unit Control

In a multiple unit system, sets of equipment along the train are controlled from one location. In the figure, all
the lighting contactors on the train are connected to train wires, in this case one for “lights on” (in black) and one for

“lights off” (in blue). The ON and
OFF buttons are in the driving cabs
at each end of the train so, the
lighting can be switched on or off
from either end of the train. (From:
http://www.railway-
technical.com/_Media/light-
mu_med_hr.png)

l A detailed design: Electric
Driven Door System

n FCPM driven type (1 drive unit / 1 doorway) Features
Accurate and sensitive operation in obstruction detection;High reliability and safety design;Built-in fault

diagnosis function;Highly efficient maintenance and service works;Simplified structure for easy installation and
adjustment;Low-friction mechanism for easy manual door operation in emergency and maintenance

Linear type FCPM driven type
n Linear motor driven type (1 drive unit / 1 doorway) Features

Accurate and sensitive operation in obstruction detection;High reliability and safety design;Built-in fault

diagnosis function;Highly efficient maintenance and service works;Low-friction mechanism for easy manual door

operation in emergency and maintenance
n Linear motor driven type (2 drive units / 1 doorway)

Direct drive with Linear motor;System redundancy with independent drive for each door panel;Accurate
and sensitive operation in obstruction detection;High reliability and safety design;Built-in fault diagnosis
function;Highly efficient maintenance and service works;Low-friction mechanism for easy manual door operation
in emergency and maintenance

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