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TABLE OF CONTENTS
Acknowledgement
Preface
Introduction To Indian Railways.
Module 1: Microwave Communication.
Module 2: Railway Signalling And Signal
Workshop.
Conclusion
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Acknowledgement
Behind the completion of any successful work there lies the
contribution of not one but many individuals who may have directly or
indirectly contributed to it.
First and foremost I am grateful to the management of NORTH
EASTERN RAILWAY,GORAKHPUR for providing me the opportunity
to undertake my Summer Industrial Training in the organization.I
specially convey my thanks to all the staff members for their precious
guidance during our training and in completion of this project. I feel
priviledged to express my deep regards and gratitude to all the Engineers
and staffs of MICROWAVE CENTRE,N.E RLY,GORAKHPUR and
SIGNAL WORKSHOP,N.E RLY,GORAKHPUR.
I am thankful to all my teachers who have best owed upon me their
knowledge and have been guiding light through out my course. They have
cast an indelible impression on my existence.
I am much indent to my friends whose moral support alwaysinspired me to come out with the best.Its great pleasure to extend my
heartfelt thanks to everybody who helped me through the successful
completion of my training.
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The acknowledgement would be incomplete if I fail to express deep
sense of my obligation and reverence to my parents without whom this
work would not have seen the light of the day.
Akhilesh kumar
singh
Preface
Engineering students gain theoretical knowledge only through books.
Only theoretical knowledge is not sufficient for absolute mastery in any
field. Theoretical knowledge in our books is not of much use without
knowing its practical implementation. It has been experienced thattheoretical knowledge is volatile in nature; however practical knowledge
imparts solid foundation in our mind.
The practical industrial training is a part of four year degree
course.Practical industrial training mainly aims at making one aware of
industrial environment which means that one gets to know the
limitations,constraints and freedom under which an engineer works.
To accomplish this aspect Gautam Buddh Technical University
(GBTU), Lucknow(U.P.) has included 4 weeks summer training for
B.Tech 3rd Year students in our curriculm.
This report is infact a summary of, what I have learnt and seen during my
training in N.E Railways. It simply summarizes the Microwave
communication, signaling and signal workshop as carried out in Indian
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railways.The training mainly involves industrial and complete knowledge
about designing,assembling and manufacturing of equipments.Thus it is
very necessary before becoming a professional engineer.
INDIAN RAILWAYS
FOUNDED - 16TH APRIL,1853
HEADQUARTER - New Delhi,India
AREA SERVED - India
INDUSTRY - Railway and Locomotives
SERVICES - Rail Transport
REVENUE - Rs. 107.66 billion
EMPLOYEES - 1,406,430
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INDIAN RAILWAYS(BHARTIYA RAIL) abbreviated as IR,is a state
owned railway company of India,which owns and operate most of the
countrys rail transport.It is overseen by Ministry of Railways and
Government of India.
Indian Railways has one of the largest and busiest rail networks
in the world,transporting over 18 million passengers and more than two
million tones of freight daily.It is the worlds largest commercial or utility
employer,with more than 1.4 million employees.The railways traverse the
length and breadth of the country,covering 6,909 stations over a total route
length of more than 63,327 kms (39,350 miles).As to rolling stock,IR owns
over 20,000 freight wagons, 50,000 coaches and 8,000
locomotives.Railways were first introduced to India in 1853.By 1947,the
year of Indias independence,there were 42 rail systems.In 1951,the
systems were nationalized as one unit,becoming one of the largest networks
in the world.IR operates both long distance and sub-urban rail systems on a
multi-gauge network of broad,meter and narrow gauges.It also owns
locomotives and coach production facilities.
As the economy of India improved,almost all railway production
units were Indigenized(produced in India).By 1985,steam locomotives
were phased out in favour of Diesel and Electric locomotive.The entire
railway reservation system was streamlined with computerization between
1987 and 1995.
In 2003,the Indian Railways celebrated 150 years of its
existence.Various zones of the railways celebrated the event by running
Heritage trains on routes similar to the ones on which the first trains on the
zones ran.The Ministry of Railway commemorated the event by launching a
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special logo celebrating the completion of 150 years of service.Also
launched was a new mascot for the 150 th year celebrations,named
Bholu,the Guard Elephant.
Snapshots:-
It encompasses 6,909 stations over a total route length of
more than
63,028 kilometres of route length and a track length of 111,600
km .
It is one of the world's largest commercial or utility
employers, with more than 1.6 million employees.
It grossed a revenue of ` 88,355 cr and bagging a netincome of ` 951 cr in
the financial year 2009-10 .
It moves 2 million tons of freight & 20 million people daily
across the
county with the help of 200,000 (freight) wagons.
7,000 passenger trains across the country services 20
million people to
their destinations .
Vivek Sahai is the current Chairman of Railway Board .
Organizational Structure-:
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Indian Railways is a department owned and controlled by the Government
of India, the Ministry of Railways . IR is administered by the Railway
Board, which has a financial commissioner, five members and a chairman.
Railway zones:-
IR is divided into zones, which are further sub-divided into divisions. The
number
of zones in Indian Railways increased from six to eight in 1951, nine in
1952, and finally 16 in 2003. Each zonal railway is made up of a certain
number of divisions, each having a divisional headquarters. There are a
total of 67 divisions under 16 zones , presently operating in the country .
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Each of the 16 zones, is headed by a General Manager (GM) who reports
directly to the Railway Board. The zones are further divided into divisions
under the control of Divisional Railway Managers (DRM). The divisional
officers of engineering, mechanical, electrical, signal and
telecommunication, accounts, personnel, operating, commercial and
safety branches report to the respective Divisional Manager and are in
charge of operation and maintenance of assets.
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Further down the hierarchy tree are the Station Masters who control
individual stations and the train movement through the track territory under
their stations' administration.
Practical Training under NER:-
We've received the scheduled Summer Practical Training, as a part of our
curriculum, from June 22, 2010 July 12, 2010 under Divisional Railway
Manager,NER,Gorakhpur.
.
We've studied about the following operational technologies in the IR-
1. Microwave Communication & Links.
2. Railway Signalling.
3. Signal Workshop(Automatic track changer,Electronic point machines
and relays)
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MODULE I
MICROWAVE COMMUNICATION
Microwaves are electromagnetic waves whose frequencies range from 1
GHz to 1000 GHz. Microwaves are so called since they are defined in
terms of their wave -length.There are large number of bands in microwave
region. Microwaves are used for controlling of trains.It is necessary to give
correct running and stopping of the trains and there should be a single train
on a single track.
Microwaves help the railway staff to communicate for this purpose.Stations
on average of 40km can communicate with each other by microwave.there
are large number of bands in microwave region.Before the advent of fiber
optics, these microwaves formed the heart of the long distance telephone
transmission system.
In its simplest form the microwave link can be one hop,
consisting of one pair of antennas spaced as little as one or two
kilometers apart, or can be a backbone, including multiple hops,
spanning several thousand kilometers.
A single hop is typically 30 to 60 km in relatively flat regions
for frequencies in the 2 to 8 GHz bands. When antennas areplaced between mountain peaks, a very long hop length can be
achieved. Hop distances in excess of 200 km are in
existence.
The "line-of-sight" nature of microwaves has some very
attractive advantages over cable systems. Line of sight is a term
which is only partially correct when describing microwave paths.
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Microwave Transmitter and Receiver-:
Below figure shows block diagram of microwave link transmitter andreceiver section --
The voice, video, or data channels are combined by a technique known
as
multiplexing to produce a BB signal. This signal is frequency modulated to
an IF
and then up converted (heterodyned) to the RF for transmission through the
atmosphere.
The reverse process occurs at the receiver. The microwave transmission
frequencies are within the approximate range 2 to 24 GHz.
The frequency bands used for digital microwave radio are recommended
by the
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CCIR. Each recommendation clearly defines the frequency range, the
number of
channels that can be used within that range, the channel spacing the bit rate
and
the polarization possibilities.
Microwave Transmitter and Receiver.
Application Of Microwave In Indian Railways -:
Microwaves are used for controlling of trains.
It is necessary to give correct running and stopping of the trains and
there should be a single train on a single track.
Microwave communication help the railway staff to communicate for
this purpose.
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Stations on average of 40 km can communicate with each other by
microwave.
Frequency Range In Microwave Region-:
BANDS FREQUENCY(GHZ)
L 1.1-1.7
LS 1.7-2.6
S 2.6-3.9
C 3.9-8.0
X 8.0-12.5
Ku 12.5-18.0
K 18.0-26.0Ka 26.0-40.0
How Terrestrial Microwave Transfer And Receive Data :
Terrestrial microwaves communication employs earth based
transmitters and receivers to transfer and receive data.
The frequencies used are in the low giga-hertz range,which limits all
communication to line of sight.
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Examples of terrestrial microwave equipment-Telephone relay
towers,which are placed every few miles to relay telephone signals
across country.
Antennas Are Used To Transfer Data -:
Microwave transmissions typically use a parabolic antenna that
produces a narrow,highly directional signals.
A similar antenna at the receiving site is sensitive to signals only
within a narrow focus.
Because the transmitter and receiver are highly focused,they must be
adjusted carefully so that the transmitted signal is aligned with the
receiver.
Role Of Microwaves In Passenger Reservation System -:
In PRS,the Gorakhpur Zone is connected to the main server
through communication lines and there is the need of non stop
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working of PRS in Indian Railways otherwise there will be
big loss to Indian Railways.
So to increase the reliability of PRS,the main server is also
connected to the zones through microwave links.In case if
there is a failure in the physical mediathen the PRS can be
operated by microwave.
Microwave Systems -:
There are two types of Microwave Systems.In first schematic processing is
in analog form and in second schematic processing is in digital form.
According to this there are two types of microwave systems as follows-:
1. Analog system.
2. Digital system.
The analog system is old system and digital system is new one.
Analog Systems -:
The analog system is simple and this system consists of
Transmitter,Receiver and communication media which is Microwave here.
Transmitter:
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The role of Transmitter is to send the signals and it consists of following
parts:-
Multiplexer(MUX):-
This is used to transmit various signals simultaneously.Here
there is many Input and there is only one output.The output of the
multiplexer is given to the Radio Equipment.
Radio Equipment:-
It receives the output of the multiplexer and then processes thesignals.This is the most important part of the transmitter and the
antenna is connected to the radio equipment directly.
Transmitting Antenna:-
This is a metallic object and this is used to transmit the signals in
free space.The antenna transmit the signals at 7 GHz in the
space.Here the antenna consists of a parabolic reflector and a Horn
antenna.The antenna is directional and directive.
Tower:-
The tower is a metallic and this is used only to give height to the
antenna.
Receiver:-
The role of receiver is to receive the signals.The receiver consists of
following parts:
Receiving Antenna:
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The receiving antenna receives the incoming signal and then it gives
the signals to the mixer.
Mixer:
Here in the mixer the frequency mixing takes place and now the
output frequency is different.And the output of the mixer is given to
the Discriminator.
Discriminator:
The Discriminator seperates the signals and the demodulationprocess is done here.This means that the carrier signal is removed
and only the
Message signals are taken.
Demultiplexer:
The demultiplexer has only one input and here the separation process
is done and the sent signals are recovered back.
Digital Systems :
This system has a large number of advantages over analog
system.This system is a new system and uses digital
technology.Digital system is more reliable and efficient.
Digital system consists of following parts:
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Transmitter-:
The transmitter of digital system is different from analog system.In
this transmitter two types of multiplexers are used which are as
follows:
Primary multiplexer:
This is the first multiplexer at the transmitter side.It multiplexes 30
voice signals and in the digital system sixteen multiplexers are used
of this type.The output of every primary multiplexer is 2.04 Mbps.
Higher order multiplexers:
This multiplexer is big and multiplexes the signal coming from the
primary multiplexers.The output of this multiplexer is 34.368 Mbps.
Radio Equipment:-
The output of the higher order multiplexer is given to the radio
equipment.Radio equipment process these signals and make them
able to be transmitted by antenna.
Antenna-:
The antenna is same as we are using in analog system.Here also we
use horn antenna and parabolc reflector.Horn antenna is at the focus
and it send the signals to the parabolic reflector surface.After striking
from the surface,the signals are parallel and it is transmitted in such
form.
Tower-:
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Here also the role of tower is to give height to antenna.In Microwave
station (Gorakhpur) of Indian railways,there are two towers ,one is
for analog and the other one is for digital communication.
Receiving Antenna-:
The receiving antenna is at the receiving side,receives the signals and
sends it to radio equipment.There is line of sight communication of
microwave in between transmitting and receiving antenna.
Radio Equipment-:
The radio receiver receives the signal coming from the antenna.Here
the signals are processed and then these signals are sent to higher
order demultiplexers.
Higher Order Demultiplexers-:
In this demultiplexer the signals are separated.And the output of this
multiplexer is given to the low level multiplexer.There is sixteen
outputs and every output has a bit rate of 2.048 Mbps.
Low level multiplexer-:
This multiplexer receives the output from the higher order
multiplexer.It has one input and thirty outputs.The output frequency
rate is 0-4 KHZ.This is the frequency range of human voice.Here the
original voice signals are obtained.
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Power Reqirement-:
Both systems require power for their operation.A dc current
is required for both systems.This dc current is provided by a
set of batteries.An extra set of battery is also kept for
emergency.
Analog System-:Analog system requires a dc voltage of -24v for its
operation.
Digital communication-:Digital system requires a voltage of 48 v
for its operation.
Essential Environment For Analog And Digital Systems-:
There are some requirements for these systems for there proper
functioning.Following are some of the requirements:-
1. Air Conditioning.
2.Dust Free Environment.
3.Uninterrupted Power supply.
4.Proper trained staff.
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Use Of Repeaters-:
After travelling some distance the microvave gets distorted.
The Repeater is a device which is used to obtain distortion free
microwave and this clean and distortion free microwave is
transmitted again in forward direction.
Repeaters are used at the average distance of 40 km.
Fault Control Procedure-:
In a typical Railway Telecom network Scenario,following types of
Telecom Network coexists:
Transmission-:
1.Microwave/UHF Network.
2.Optical Fibre Cable Network.
3.RE Telecom Cable Control Network.
4.Railways Overhead Wire Control Network.
5.DOT owned Overhead wire control Network.
Switching-:
1.Electronic Telephone Exchanges.
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2.Electromechanical Telephone Exchanges.
Others-:
1.Single Channel Duplex UHF/VHF Radio Systems.
2.Multiple Access Radio Relay.
3.Pair Gain System.
4.VHF/UHF Simplex Trans-receivers.
5.Talk Back systems for Major yards.
It is indeed very necessary to established well defined Fault Control
procedures for satisfactory maintenance of such diverse Railway
Telecommunication Networks so as to meet the demanding requirements
of Indian Railways in 21st century.
Typical Telecom Fault Control Setup-:
Typical telecom fault control setupon railway shall consist of
following-:
1. Zonal Telecom Fault Control Setup.
2. Divisional Telecom Fault Control Setup.
The Zonal Telecom Fault Control Setup shall be one for entire zonal
railway.
The Divisional Telecom Fault control setup shall be established in each
Division of the zonal railway.
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1.Zonal Telecom Fault control setup-:
It shall be manned by Section Engineer(Telecom) in a general
shift.Three section engineers(Telecom) shall be earmarked and should man
the zonal fault control setup round the clock in case of
emergencies.Following Telecom Network shall be monitored by zonal
Telecom fault control Room.
Microwave/UHF Network on the entire zonal Railway-:
The Zonal Telecom Fault Control room shall also function as an
emergency telecom control room in case of emergencies requiring
immediate telecom facilities/restoration.The emergencies may
consist of the following-:
Major rail accidents.
Cyclones.
Breaches.
When the Zonal Telecom Fault control room function as the Emergency
Telecom Control room,the divisional Telecom fault control rooms of theaffected Division(s)shall report their positions to the Zonal Telecom Fault
control room which in turn shall advice the Telecom officials at HQs of the
latest developments.
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The zonal Telecom Fault Control Room shall function under the direct
control of Dy. Chief Signal & Telecom Engineer(Microwave) or any other
officer designated by communication engineer of railway.
2.Divisional Telecom Fault Control Setup-:
The Divisional Telecom Fault Control setup shall have two components:
For monitoring all telecom networks other than Microwave/UHF
called
Divisional Telecom Fault Control Room.
For monitoring Microwave/UHF networks called Divisional
Microwave Fault Control Room.
Each of these Contol rooms shall be headed by a Senior Section
Engineer(Telecom) in a general shift.Three section engineers
(Telecom)/Jr. Engineer(Telecom)shall man the fault control room
round the clock.
Following Telecom Networks shall be monitored by the
Divisional Fault control Room-:
Optical fibre Cable Network.
RE Telecom Cable Control Network.
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Railways Overhead wire control network.
DOT owned Overhead Wire Control Network.
Electronic Telephone Exchanges.
Electro-mechanical Telephone Exchanges.
Single channel Duplex UHF/VHF
MODULE II
Railway Signalling & Signal
Workshop
Introduction-:
Signaling is one of the most important aspects of Railway
communication. In the very early days of the railways there was no fixed
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signaling to inform the driver of the state of the line ahead. Trains were
driven on sight. But several unpleasant incidents accentuated the need for
an efficient signaling system. Earliest system involved the Time Interval
technique. Here time intervals were imposed between trains mostly around
10 mins. But due to the frequent breakdown of trains in those days this
technique resulted in rear-end collisions. This gave rise to the fixed
signaling system wherein the track was divided into fixed sections and each
section was protected by a fixed signaling. This system is still being
continued although changes have been brought about in the basic signaling
methods. Earlier mechanical signals were used but today block signaling is
through electric instruments.
When trains run on railway tracks they follow rules of operations
in which safety plays a very important role.The most important rule in
respect of safety is to ensure that two trains do not occupy the
sameposition on the track at the same time. To make this rule work
operation of trains uses signaling to controlmovement of trains on
tracks and divides tracks into several sections which are protected by the
signals.
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Fig shows a representation of a railway signaling arrangement. The
horizontal liner represents the railway track, the signals are depicted by the
symbol of the circle with a horizontal and vertical line to this circle and the
red rectangles are the trains. This representation is however to explain how
trains are run safely.
Locking-:
There are three types of locking
a) Direct
b) Approach
c) Route
Direct locking is available as long as a signal is clear or track is occupied or
a point is set. This is the most fundamental level of locking.
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When signal S1 is cleared the cleared condition of the signal locks other
signals which can cause trains to run on any part of the route over which S1
allows a train to run. Thus with S1 cleared allowing trains to move to track
T1 signal S4 cannot be cleared and willbe locked as the latter also allows
trains to occupy track T1. Other form of direct locking is the locking of the
point in the route for which signal S1 is cleared. If S1 is cleared to the
straight route T0 T1 T2 then the point P1 will be set and locked to allow
a train to move on the straight route over Point P1.Attempts to move point
P1 from this position will not be allowed and hence will be locked.
Conversly if the point P1 is not set for straight the signal S1 will be locked.
The occupation of a track also locks signals if T1 is occupied then signal S1
cannot be cleared. Signal S1 is therefore directly locked to the cleared
status of the track. Points are directly locked to track circuits over the point
zones. If the track circuit over a point zone is occupied the it is locked so
that it cannot move. This is the direct locking of the point.
Approach Locking -:
While ensuring safety for train running it is not only necessary to ensure
that safety is ensured over all portions of track for which signals have beengiven but also over portions over track which can get occupied due to trains
approaching a signal which protects these portions of track failing to stop at
this signal. Such protection is required under the condition when the signal
protecting had not been cleared.
Flank protection and isolation -:
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When a train is allowed to move by a signal it is also necessary to ensure
that no part of the train will be Involved in a side collision.
Protection in the overlap -:
When a train is approaching a signal a possibility exists that the train may
fail to stop at the signal where it is intended to stop due to mechanical
failure or due to human failure. While there is no absolute arrangement to
control against this eventuality a partial safety is ensured by providing a
small part of the track beyond the signal at which the train is to stop free of
any conflict or obstruction to the train if it fails to stop at the foot of the
signal. Typically when train TR1 is approaching S1 it will normally be
ensured that the track section onto T2 is free of any obstruction. This
includes possibility of any train from the opposite direction reaching T2.
Hence if TR1 is allowed to approach S1 it will be ensured that the train
TR2 does not at the same time approach signal S2. Any point in this portion
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of the track also needs to be set and locked in the position allowing safe
movement through it. If TR1 is approaching signal S1 it will mean point
P2A must be set and locked for the straight route. The point P2A and track
T2 is referred to be in the overlap for signal S1 and locks the signal
allowing approach of a train to signal S1 if not found free. Conversely if
signal S1 is cleared any condition which can lead to the overlap from
failing to remain in the condition to maintain safety for train TR1
approaching S1 will be locked.
Release of locking -:
Signals indicate when a route which it checks is safe for a train to travel.
The safety is checked from different angles as explained above. After a
signal has been cleared for a train it is required to be put back to danger as
the train moves past it. There are two reasons for doing this-:
a) To ensure the safety of the train which has moved past.
b) To allow clearance of other signals which has been locked by it.
The release of locking is done automatically as a train moves along the
route a signal had cleared for it. The locking is released in stages-:
a) As the train moves past the signal the approach locking is brought back
to normal.
b) As the train clears the first track after the signal the direct locking gets
released.
c) As the train moves the route locking , flank or isolation protection for the
portions of the route cleared by the train is removed.
d) After the train has come to a stop at the next signal for sufficient time to
prove that it is not moving the overlap is released. This is the normal
release with the passage of train. There can however be occasions when it is
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required to cancel a signal which has been cleared and yet to be passed by
the train. When this is required the signal is canceled. When the signal is
canceled it is necessary to ensure that the locking it had enabled also get
canceled. Here again the cancellation starts from release of the approach
locking followed by release of the route locking, locking of flank and
isolation and finally the overlap. The release is done only after it is
established that a train which had been approaching the train has come to a
stopped at the signal before the locking to other signals are released.
Detection of trains -:
Signals control movement of trains. For it to effectively control movement
of signals there is a need to know the location of trains on the track. The
railway tracks are divided into short sections normally referred to as track
sections. At any time only one train can occupy one such a section. Track
circuits or axle counters are used for the detection of trains in these
sections. Only one train can occupy a
track section at any time. Normally the detector is fed with the signal from
the
source through the rails and as long the detector receives a signal it
concludes that the track section is not occupied. If a train occupies the track
section being monitored it short circuits the track cutting off the signal
from the source to the detector. When the detector fins loss of signal from
the source it concludes that the section is occupied by a train. Principles of
fail safety is also very well demonstrated in this arrangement. In case of a
failure like a broken wire, rail fracture, power supply failure, failure of the
source the detector will lose the signal and conclude the section is occupied
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by a train. This will allow the detection to maintain safety even under
failure condition and satisfy requirments of fail safety.
Control and drive to points -:
Points are driven by electrical motors. The motors are known as point
motors and moves point using a mechanism which including the motor is
referred to as point machine. A point machine mechanism moves switches
of a point through a mechanical arrangement of rods and gears.
Signal s-:
Signals indicate to the train drivers whether the route till the next signals is
reached is safe or not. Before a signal is cleared the signal control logic
verifies that everything is safe for a train which follows it. This will mean-:
a) All track sections over which the train will be routed is unoccupied. This
is checked by checking the status of the track circuit relays. Track proving
relays of all track sections which are clear will be picked up. By checking
the status of these relays which are referred as track relays the signaling
control logic can determine
that the route is clear.
b) Routes of any signals which conflict with the signal is not cleared andthat none of the signals have been approach locked.
c) There is not route set over a track section conflicting with the route of the
desired signal. This is proved by checking that all track circuits over which
the signal reads is clear of route locking.
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Implementation of Signaling Systems
Train running and signaling the drivers of the trains depends to a significant
extent on mechanized equipment. The technologies used for this application
ranges from very rudimentary systems to highly sophisticated equipment.
The technologies are based to a great degree on mechanical arrangement at
large number of installations. Advanced technologies are in use on sections
where train densities are high and
specially where Railway Electrification has already been done.
Technologies used for this application are for two reasons :-
1) To ensure safety of train running.
2) To improve operational efficiency.
Basic Principles :
Safety of train running in practice means ensuring that two trains do not
occupy the same location at the same time. Since trains are bound onto
Railway tracks it means ensuring two trains do not occupy same location of
the track at the same time. This is ensured in two stages-:
1) By dividing the Railway track into sections.
2) Entry into each of these sections are controlled by suitable signaling
system which ensures through various means that when a train is signaled
to Basics of Railway Signaling.
3) The drivers controlling the train are signaled sufficiently in advance so
that they can stop the train before signals which are not cleared. Since trains
typically move at a speed of around 100 Km./Hr. it requires a braking
distance of 1 Km before a signal at which it is required to stop. Hence
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signaling system ensures that signals are conveyed to the Drivers
sufficiently in advance to bring the train to stop safely.
4)It should not be possible to move a point when a train is over the point or
is very near to the point having picked up signal allowing the train to move
over the point likely to be moved. In addition to above various other rules
are applied to
make a signaling system safe. These rules are results of experiences gained
after accidents. Thus one rule msays that if a passenger train has to run
through a line then this run through line should be isolated from other
connected lines in the station by suitable means. This rule has been
introduced to ensure that if there is a train standing on a connected line and
it starts rolling it cannot result in a devastating collision as it is kept isolated
from run through line on which high speed train has been signaled to go
through.
Basic Rules -:
The basic rules of safety in connection with train running is implemented
through various methods. The Railway Engineering is very old and,
therefore, implementation methods also are old. Availability of modern
electrical & electronic technology is gradually changing the implementation
of Railway signaling systems. The technologies used in Railway signaling
system depended on human element initially. Gradually mechanical
systems were introduced followed by electrical/electromechanical and now
electronics/electrical/electromechanical systems. The human element in
Railway signaling is getting reduced wore & more for improving safety and
efficiency of train operations.
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The Human element :
Signaling Systems exist where setting of the point and locking of the same
is entirely manual. The locking of the point is achieved through key and
lock system.
The signals are all hand Signals. A more mechanized arrangement is where
switches turning points are connected to levers and signals are given by
mechanical arms known as semaphore signals. In both the systems the
human element ensure that the routes a train will take is not obstructed. The
set person who is clearing the signals for passage of the trains achieves this
entirely visually. The oldest signaling Systems are entirely manual where
even the checking that a route has been properly is manual.
The 50 Hz & 83&113 Hz signal source is used in a manner similar to D.C.
voltage and requires no special mention as the detector is simply a relay. In
case of 83&1/3 Hz system normally 3 phase system is used and two phases
are used on any section. The feed end gives one phase and a second phase
is always fed to the detecting relay. When the track circuited section is free
the two phases create a rotary force as in a AC electric motor. Absence of
one of the phase via the rails due to presence of a train removes the rotating
force dropping the relay. The 83&1/3 Hz track circuits is a popular track
circuiting arrangement.
Electronics in Railway Signaling for improved
Safety-:
The audio frequency track circuit is the latest entrant in the field. This
arrangement feeds an Audio frequency signal which causes pick up of
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Relay via the detector. A simple Audio frequency generator is used and at
the detecting end a L.C. resonant circuit is used for picking up the desired
Audio frequency signal & rejecting others. Due to the use of high frequency
it is possible to use the Railway track as a
transmission line and use of physical insulating pieces electrically isolating
one section as "R' from 'A-B" is not required. By using resonant L.C.
circuits at suitable points the AF signal can be made to stop beyond any
particular point without the need of any insulating joint. This feature is a
big advantage for this type of track circuit as there is no need to cut Rails &
insert insulating pieces. Indian Railways but considerable difficulties, faced
on account of loss of track side equipment due to theft has rendered the
system ineffective. As a corollary to this simple arrangement, systems of
continuous automatic control of trains are also available. Such systems
continuously control speed of trains through transfer of signals from the
track side to the engine. The system is quite elaborate consisting of a
receiver located in the engine and suitable transmitter coils located on the
sleepers between the track. A computer computes the required speed of
trains running on the track for ensuring safety as well as for ensuring that
trains run on time speeding as necessary or slowing when needed. Such a
system is being implemented on Metro Railway Calcutta in India for the
first time. Such systems are important for Metro Railway services where
time between two successive trains is are required to be kept very small toas much as one min or less. Even with such small interval between trains
complete safety & punctuality can be attained using the continuous
automatic train control and protection system. Use of Electrical/Electronic
Gadgets for ease of operation Over and above allowing higher levels of
safety by using sophisticated controls the use of electrical/electronic
gadgets for Railway Signaling is also made for ease of train operations and
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higher efficiencies. Systems known as Panel Interlocking and its
sophisticated variety known a Route Relay Interlocking are for control of
signals and points with higher efficiencies.
Design of Signaling Circuits -:
The design of signaling circuits is based on simple principles. Railway
Signaling being one of the oldest control engineering is based on very
simple methods
and principles. One of the main reasons of its simplicity lies in the fact that
technological aids for design were not very high till late 21st century and
complicated design principles and methods could not be supported. as a
result of this the circuits are drawn using very simple symbols and names
are kept short. If looked in the context of the fact that the circuits had to be
hand drawn in times where duplicating facilities were very primitive the
reason why they are so simple
can easily be understood. Signaling circuits are based on defining relays of
the
following types-:
a) Those signifying states in progress of a command
b) Those indicating steady state of the signaling functions.c) The last operation has been completed properly .All circuits of Railway
Signaling has to ensure safety. Hence both the type of relays defined above
also always ensure safety. This fundamentally means that in absence of any
voltage to the circuit the relays shall assume safe state which is the drop
state for all neutral relays and can be dropped or one of the latched state for
relays which are latched electrically or mechanically.
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Signal Workshop-:
In the signal workshop of Indian railways,following machine are
manufactured which are used as a part of signaling system-:
1. Electric point machine.
2. Relays.
Points are provided to divert the running trains from one track to another.
The points have movable switches which can be operated electrically by a
point machine. A point can be single-ended point or double-ended point
depending on whether the movable switches are provided at one end or two
ends of the point,
The two switch rails of the point are rigidly connected together by a cross
bar so that they can be moved from one position to the other position
together by the point machine. If the position of the switches is such that
the train is moved on to the main line as shown above, then the point is said
to be in its normal (N) position. If the switch rails are moved to the other
position as shown below so that the train is diverted to the loop line, then
the point is said to be in its REVERSE (R) position.
Solid State Interlocking -:
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Solid State Interlocking is a data-driven signal control system designed for
use throughout the British railway system. SSI is a replacement for
electromechanical interlockings---which are based on highly reliable relay
technology---and has been designed with a view to modularity, improved
flexibility in serving the needs of a diversity of rail traffic, and greater
economy. The hugely complex relay circuitry found in many modern
signalling installations is expensive to install, difficult to modify, and
requires extensive housing---but the same functionality can be achieved
with a relatively small number of interconnected solid state elements as
long as they are individually sufficiently reliable. SSI has been designed to
be compatible with current signalling practice and principles of interlocking
design, and to maintain the operator's perception of the behavior and appe
arance of the control system.
A schematic view of SSI processor.
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Conclusion
This report takes a pedagogical stance in demonstrating how results from
theoretical electronics may be applied to yield significant insight into the
behavior of the devices .Electronics & communication engineering practice
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seeks to put in place, and that this is immediately attainable with the present
state of the art. The focus for this detailed study is provided by the type of
solid state signaling and various communication systems currently being
deployed throughout mainline railways. Safety and system reliability
concerns dominate in this domain. With such motivation, two issues are
tackled: the special problem of software quality assurance in these data-
driven control systems, and the broader problem of design dependability. In
the former case, the analysis is directed towards proving safety properties
of the geographic data which encode the control logic for the railway
interlocking; the latter examines the fidelity of the communication
protocols upon which the distributed control system depends.
We have covered in this report the history ,latest developments in Railway
systems as well as related fields. We have studied the various uses of
electronics and communications in railways like microwave
communication,signaling,electronic point machines etc..