Railway signalling

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IRSSE : An Organized Gazetted Service of

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About Railway Signalling

Railway Signalling

Signalling is one of the most important parts of the many

components which make up a railway system. Train movement

safety depends on it and the control and efficient management of

trains depends on them. Over the years many signalling and train

control systems have been evolved. The journey started with very

simple systems such as simple coloured flags and semaphore arms

to that today a highly technical and complex electrical and

electronic systems. Here is an attempt to explain, in simple terms,

how railway signalling really works.

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Fig-2 Semaphore Signals that raise (upper quadrant)

Nowadays IR has converted what are known as Color Light Signals (CLS) with

Multiple aspects where the color of Light indicates meaning to Drivers ( Now called

Loco Pilots)

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Why Signalling is required?

In road transportation the direction and speed of a vehicle are

controlled by the driver and the different vehicles share the same

way at the same time in both the directions. However in Rail

transport the the driver controls only the start / stop and speed of

the train and the direction is controlled by the track components

themselves. There is no steering wheel. One more factor to be

considered is that the trains are very large vehicles and hence need

large distances to increase and decrease speed i.e to start and stop

also. Hence they need to be separated by considerable distances

while traveling behind one another.

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:-1. Arranging safe reception and dispatch of trains onto required

lines at stations.

2. Ensuring that trains are not received on occupied lines

3. Ensuring that two trains donot enter the same part of the track

between two stations (Also called block signaling)

4. Optimizing the utilization of track and other assettes by

allowing the dealing of maximum no of trains at highest speeds

permitted by track and train vehicles safely.

5. Achieve all the above in a manner called

" Fail Safe"

which makes signalling a

unique field of Engineering as every component and particularly the combination

shall not fail to an unsafe end result at any cost.

To achieve the above functions the follwing devices are used

:

1. Track circuits : are simple electric gadgets that are filtted to

tracks and detect the presence of trains over that portion of the

track. They prevent allowing of signals on the same portion by fixing

the signals at Danger (RED) position till such time the trains leaves

that portion. Thus this gadget allows dealing of trains without

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Fig 3b - The Track Circuit - Occupied by train (Signal goes to Red)

The diagram above shows how the track circuit is applied to a section or

block of track. A low voltage from a battery is applied to one of the running rails in the block and returned via the other. A relay at the entrance to the section detects the voltage and energises to connect a separate supply to the green lamp of the signal. The signal turns and remains RED.

The track circuit requires that the two rails are insulated from each

other electrically and therefore can work only when we have either

wooden or concrete sleepers. The same purpose of detecting train

presence is achieved by another new electronic gadget called “axle

counter” which works by counting the axles entering and the axles

leaving the given section of track.

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Fig 4 - The Functioning of Axle Counters

Other Components :

○

Point machines ( to change points; read below about points)

○ Relay or Electronic Interlocking for correlating all field gears before clearing signals)

○ Panels with yard diagram for taking orders from Station master

○ Block Instruments for ensuring that two trains donot enter the space between two

stations in an unsafe manner.

○ Lifting barriers to ensure road vehicles are not allowed during train movements ○ Signals of different types to inform driver to move or stop

○ Dataloggers to monitor correct sequences and pre warning or analyzing unsafe

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○ Automatic Signalling which works without humanintervention in busy sections esp in

suburban transport

○ Advanced Train wraning and train protection systems

○ Powersupply systems to support reliable and safe working of Signalling

Signalling at Stations

:-We are aware that though there are only one or two lines between

stations (called block section); at stations there are many lines onto

which the trains are allowed to be received and dispatched. We

have also learned that a train driver cannot steer his train in the

required direction. Thus railway is called guided transportation. The

track itself modifies its components dynamically to lead the train to

required line (platform). An important part of the track that achieves

routing of trains is a point.

Point also called

Turnout

Fig 5 : A point is capable of changing the route of a train , a train by itself cannot do

so

Points are switched ie changed from one position to another to change the couse of

train. Of course all required points are to be switched to the required positions to lead

to a given line before lighting up the signal and shall remain so untill complete arrival

of train.

The railway signalling does the change over of points, their locking and holding of the

route without any unsafe discretion of the station master.

All such points and connected line at a station is known as a yard. A typical simplified

signalling diagram is indicated below:

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Fig 6 : Yard Signalling sketch of a small station on Double Line (Double

Line Means seperate tracks between stations for UP and DOWN direction trains).

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FAILSAFE ENGINEERING

INTRODUCTION : Fail-safe or fail-secure describes a device or feature which, in the event of failure, responds in a way that will cause no harm or at least a minimum of harm to other devices or danger to personnel. Fail-safe components of a system are distinguished from fail-secure components in that, in the former, component failure allows but does not cause or invite a certain improper system behavior, whereas in the latter, component failure does not allow a certain improper system behavior, although some proper behaviors are impeded.

For example, . a pass word improperly fed may prevent access (by OS) which is a failure for the genuine owner/user but will not allow undue access without thorough verification of authenticity. ... for detailed explnantion visit the related page on this site.

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Copyright ©2009

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Create a Free Website

IRSSE : An Organized Gazetted Service of

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FAIL SAFE ENGINEERING

INTRODUCTION : Fail-safe or fail-secure describes a device or feature which, in the event of failure, responds in a way that will cause no harm or at least a minimum of harm to other devices or danger to personnel. Fail-safe components of a system are distinguished from fail-secure components in that, in the former, component failure allows but does not cause or invite a certain improper system behavior, whereas in the latter, component failure does not allow a certain improper system behavior, although some proper behaviors are impeded.

For example, . a pass word improperly fed may prevent access (by OS) which is a failure but ensures safety for the genuine owner/user but will not allow you to reset it without thorough verification of authenticity. Multiple trails with wrong pass word lead to access lock up which is failsafe

outcome since it protects the data or other assettes of customer.

Also a power controlled access control door is so designed that if power fails , the door will allow egress(exit) but not ingress.(entry). This failsafe concept.

All Railway Signalling installations are required to meet this meticulously. That means when any

failure in any component takes place, the signal shall be fixed at RED bringing train to a stop but

shall NEVER allow the signal to go to YELLOW or GREEN under such condition.

Electronics in Failsafe Design : Electronic devices are not inherently failsafe and tend to behave

erratically. Designers are using the power of microprocessors for control of railroad, aircraft, and space vehicles to minimize the dangers of complex transportation systems.

A mean time between unsafe failures (MTBUF) for transportation is one billion hours, or once

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Good safety architecture includes redundancy in various forms, such as additional equipment. Redundancy is achieved by duplicating components, or by use of diverse components or use of

redundant software.

It is critical that the first failure of a controller be detected, so that human monitors can take action before a fault-induced catastrophe occurs. A microprocessor's highly reliable circuits can continuously confirm the operating status of components, and automatic monitors can interrupt the system when an error occurs. The first microprocessor interlockings for railroads have entered service in

the US, Canada and Europe and in India (In india they were first introduced since 1993). Use of microprocessors for aircraft safety is also described.

.

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FAILSAFE ENGINEERING

INTRODUCTION : Fail-safe or fail-secure describes a device or feature which, in the event of

failure, responds in a way that will cause no harm or at least a minimum of harm to other devices or danger to personnel. Fail-safe components of a system are distinguished from fail-secure components in that, in the former, component failure allows but does not cause or invite a certain improper system behavior, whereas in the latter, component failure does not allow a certain improper system behavior, although some proper behaviors are impeded.

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Welcome to all Railway Signal Engineers by irsse | 7 comments

Copyright ©2009

IRSSE : An Organized Gazetted Service of

the Government of India

(Un official web site of IRSSE)

Tags : IRSSE, Indian Railways, Railway signalling, irsse,

rvb babu, iriset, irste, IRSTE

• HOME

(13)

• About Railway Signalling • Fail Safe Engineering • IRSSE Blog

I

ndian

Railway Service of Signal Engineers

Wha

t is IRSSE ?

Secunderabad, India

IRSSE

stands for

Indian Railway Service of Signal

Engineers

, an Organized Gazetted Government service of the

Government of India.

The incumbents are selected by the Union Public Services

Commission, the apex gazetted recruitment body of the Goverment

of India. The examination consists of CESE ; all india written test

followed by interview for selected candidates. Based on the marks

obtained, a choice can be made to join this service. It has been

common in the past 20-25 years for toppers from EEE/ECE streams

of CESE to join this service.

This site is created by one of the mebers of this service with a view

to creating public awareness about this important service

responsible for safe and speedy train travel and creating user

friendly Passenger information systems and public interfaces.

Brief Role

Signal Engineers in Railway take care of Train safety in Operations,

Capacity enhancement, Corporateand Operational Telecom and IT

services, creation of Electronic interfaces for Passenger information

dispersal and creation of advanced Signal and Telecom (and IT)

assettes as per Operational Requirements.

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This Day in History

The First Defenestration of Prague (1419)

In 1419, a mob of Czech Hussites stormed the town hall of Prague and killed several members of the town council by throwing them out of a window—an act known as "defenestration." Spurred by discontent at the inequality between the peasants and the Church and nobility, the First Defenestration of Prague led to the prolonged Hussite Wars, which broke out shortly afterward and continued until 1436. What was the Second Defenestration of Prague?

UNDER CONSTRUCTION

Under Construction... may take about a month. Site building started on 26-07-2009

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the genuine owner/user but will not allow undue access without thorough verification of authenticity. ... for detailed explnantion visit the related page on this site.

Recent Blog Entries

Welcome to all Railway Signal Engineers

Copyright ©2009

IRSSE : An Organized Gazetted Service of

the Government of India

(Un official web site of IRSSE)

Tags : IRSSE, Indian Railways, Railway signalling, irsse,

rvb babu, iriset, irste, IRSTE

• HOME

Role and Function

Functional Role : The service abbreviated as IRSSE has the job of

Managing the vast Signalling and Telecommunication (S&T)

infrastructure of the Indian Railways. This basically is

techno-managerial in nature.

The Signalling is a function essential for Safe Train operations and

Maximizing the utilization of fixed and moving assets (Train rakes,

locos, Track, Over Head Power Eqpt etc). Telecom on the other hand

caters for Both Safety related , Operational and Administrative

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communication needs of the Huge IR network. The Copper Cable,

Optical Fibre Telecom and Microwave Links span several Lakh km.

General Management: Like all other IR Engineering (IRSE, IRSEE,

IRSME) and Civil service Cadres (like IRTS, IRPS and IRAS) ,

the IRSSE has the responsibility of contributing to the General

management of railways. In IR, the general management posts are

GM (general manager), DRM (Divisional Railway Manager), SDGM

(Senior Deputy General Manager and CVO and the posts of Chief

Safety Officers(CSO) and SrDSO.

Organization

The Engineers recruited for IRSSE are normally part of Signal & Telecom (S&T)

Department of Indian Railways (IR).

APEX LEVEL

:The S&T Organization is headed at apex level (ie Railway Board) by

ML (Member-eLectrical)who heads Electrical and S&T branches. He is assisted by

two Addl Secy rank (equivalent to GM) officers v.i.z Additional Member (Signal) and

AM(tele).

ZONES

:The Indian Railways has 16 Zonal Railways with an average Track length of

about 4000 km and average staff strength of about 80,000 headed by GMs. The Zonal

Organizational structure of Signal Engineers is headed by CSTE (Chief S&T Engr)

who is assisted by CSE (Chief Signal Engr), CCE (Chief Telecom Enr), CSTE

(Planning), CSTE(Projects) and CSTE(Construction) and DyCSTEs, SSTEs etc.

DIVISIONS :

Each Zone is divided into 4-7 Divisions each with an average track

length of about 1000 km and staff strength of about 15000 headed overall by DRM

(Divisional Railway Manager). The Division is the basic operational Unit and a Profit

Centre.

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At this Level the Signal Engineers are Headed by SrDSTE (Senior Divisional S&T

Engineer) who is in turn assisted by DSTEs and ADSTEs. An IRSSE officer starts

his career as an ADSTE who is the Team leader of about 100-200 staff.

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Railway Signaling

[ 1. Introduction ] [ 2. Track Circuit ] [ 3. Relays ] [ 4. Signals ] [ 5. Moter Points ] [ Gate6. barriers ] [

7.

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Career Photo Album Railway Sri Lanka

Hello Railway Enthusiast, Welcome to my site of Railway

Signaling. During one of my undergrad training, I was attached to the Signal and Telecommunication Department of the Sri Lanka Railways. It was amazing to learn how a set of simple engineering techniques put together form the bottom line safety gear of the railways. Believe

me; no Differential Equations or Discrete Cosine Transforms! Just relays, sensors, power supplies and of course signal heads. Yes, it is a centaury old system, but, still serves its purpose.

Following are the elements of signaling as used in Sri Lanka Railways.

1. Introduction 2. Track Circuit 3. Relays 3.1 Types of Relays 4. Signals 4.1 Automatic Signals 4.2 Controlled Signals 4.3 Call-on Signal 4.4 Typical Signal Layout 5. Moter Points 6. Gate barriers 7. Automatic Blocking System 7.1 Route Establishment 7.2 Train on Line 7.3 Release of Route

You can visit the Model Rail Club of Sri Lanka web site here.

[ 1. Introduction ] [ 2. Track Circuit ] [ Relays3. ] [ 4. Signals ] [ Moter5. Points ] [ 6. Gate barriers ] [ 7. Automatic Blocking System

]

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1. Introduction

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The heart of the signaling system is the interlocking plant. This can be claimed as the decision making part of the system. The signal outputs are based on the track occupancy, motor point status, output of the remote end signal and the input from traffic controller.

This plant ensures that before a signal goes in to 'clear' (green) state, it is absolutely safe for a train to enter into the track segment. The traffic

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controllers commands are not executed if it is not safe to do so.

The interlocking plant is built out of electromechanical relays. We will discuss the type of relays under the respective section. Now we will move on to the first element: Track Circuit; which is used to sense the presence of a train on a track segment..

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2. Track Circuit

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Track circuit is one of the primary input for a signal interlocking plant. Opps ! hold on. What is an 'interlocking plant'? It is the control logic behind the signaling system. The signal cannot be 'green' while there is another train on track segment ahead. The system should able to detect the condition of the track segment: occupied or not.

The tracks are segmented into 'blocks'. Each block is track circuited separately. The figure below illustrates a track circuit.

The track circuit consists of a power supply on one end and a directional (polarized) relay on the other end. The power supply has a 6V battery kept charged by a 6V/6A rectifier. In case of power failure the battery will supply power to the circuit.

The track relay (TR), which has a resistance of 30 ohm and a pickup voltage of 1.4 volt, is normally held in picked-up state the circuit being completed via the rails. When a train enters the segment the axels of the train short circuit the supply to the relay and the relay drops. The contacts of the track relays appear in most of the safety circuits of the interlocking plant. The interlocking logic is arranged such that only one train can be permitted to enter a section. If you carefully observe, the track circuit is fail safe; if the circuit fails it will indicate occupancy.

The variable resister is introduced into the circuit such that it can be tuned to make the system works under all weather conditions.

The rails are insulated to separate the adjacent track circuits. The polarity of the adjacent track circuit is always reversed, so that the power supply of one circuit cannot operate the relay of the other circuit should the insulate between the circuits breakdown. Within one track circuit the rails are electrically connected by two wires (for safety).

The minimum length of track circuit is depends on the degree of control necessary and the maximum length is limited by the weather conditions. On the Northern line from Loco Junction (Maradana) to Veyangoda, the

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segments have a maximum length of 2000 feet. On the Southern line from Loco Junction to Wadduwa, due to the saline atmosphere along the cost line, the track circuits are limited to 1500 feet max.

Now that we have looked upon the track relay we will get into discuss the types of Relays used in the railway signaling.

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3. Relays

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Career Photo Album

Railway Sri Lanka

Relays are electro-mechanical devices used for switching. Relays are used to make the signaling logic circuits in the interlocking plants. They consists of one or two magnetic coils (electro magnets) and a set of contacts.

Magnetic System

The magnetic system of the relay illustrated below (JRK 10 type) consists of a cylindrical iron core with coil (pale blue near the bottom), two pole pieces and an armature. Larger relays (JRK 11) have two iron cores united at the rear with a yoke and the front end being provided with pole pieces. The armature extends across both pole pieces.

Iron core, pole pieces and armature are made out of iron with excellent magnetic properties. The armatures are so balanced that the vibration on the unit will not affect the relay operation. [Move the mouse over the

relay to activate it!]

Contacts

The relay contacts can be classified into four types. A relay unit will contain a combination of these types .

Front contact - NO

Back contact - NC Front/ Back contact Make before break contact

The contact springs are made out of nickel and the contacts tips are silver. The front contacts are of twin contacts and the back contacts are single contact type. The rear end of the contact springs are fixed between two blocks of transfer molded carbonate plastic reinforced with glass fibre. The stationary contact springs are supported at their free ends by a strip with notches, which limits the spring movement. The lower end of this strip is attached to the magnet support.

The movable contact springs are guided by an actuating strip which at the lower end attached by bearings to the armature and at the upper end to the upper most movable contact spring. The front edge of the actuating strip provided with slots, which lock the spring and guide the movement of the contacts.

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The rear end of every contact spring has eight forked terminals. This provides a very dependable connections to the plug board terminals, when the relays are plugged in.

[ Up ] [ 3.1 Types of Relays ]

[ Introduction1. ] [ 2. Track Circuit ] [ 3. Relays ] [ 4. Signals ] [ Moter5. Points ] [ 6. Gate barriers ] [ 7. Automatic Blocking System

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3.1 Types of Relays

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Railway Sri Lanka

Neutral Relays

This is the most elementary type of relay. The neutral relays have a

magnetic coil, which operates the relay at a specified current, regardless of the polarity of the voltage applied.

Biased Relays

Biased relays have a permanent magnet above the armature. The relay operates if the current through the coil winding establishes a magneto-motive force that opposes the flux by the permanent magnet. If the fluxes are in the same direction, the relay will not operate, even for a greater current through the coil.

Polarized Relays

Like the biased relays, the polarized relays operate only when the current through the coil in one direction. But there the principle is different. The relay coil has a diode connected in series with it. This blocks the current in the reverse direction.

The major difference between biased relays and polarized relays is that the former allows the current to pass through in the reverse direction, but does the not operate the relay and the later blocks the current in reverse

direction. You can imagine how critical these properties when relays are connected in series to form logic circuits.

Magnetic Stick Relays or Permopolarized Relays

These relays have a magnetic circuit with high remanence. Two coils, one to operate (pick up) and one to release (drop) are present. The relay is activated by a current in the operate coil. On the interruption of the current the armature remains in picked up position by the residual magnetism. The relay is released by a current through the release coil.

Slow Release Relays

These relays have a capacitor connected in parallel to their coil. When the operating current is interrupted the release of relay is delayed by the stored charge in the capacitor. The relay releases as the capacitor discharges through the coil.

Relays for AC

These are neutral relays and picked up for a.c. current through their coil. These are very fast in action and used on power circuits of the point motors, where high current flows through the contacts. A normal relay would be slow and make sparks which in turn may weld the contacts together. All relays have two operating values (voltages), one pick-up and the other other drop away. The pick-up value is higher than the drop away value.

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4. Signals

[ Up ] [ 4.1 Automatic Signals ] [ 4.2 Controlled Signals ] [ 4.3 Call-on Signal ] [ 4.4 Typ ical Signal Layout ] Career Photo Album Railway Sri Lanka

Signal posts carries signal light units consisting one or more aspects. This is the final stage of communication that gives the driver necessary orders and warnings about the track segments ahead. The signal aspects are powered individually by 110 V a .c. and each aspect has its own step down

transformer. In the secondary circuit a relay is connected in series with the lamp to get the indication back to the interlocking plant. The figure below illustrates the circuit of a signal aspect.

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Signal can be classified according to their mode of operation as follows: Automatic Blocking Signal

Automat ic

Automatic Approach Signal Signals

High Controlled Signal

Controll ed

Dwarf Controlled Signal

[ Up ] [ 4.1 Automatic Signals ] [ 4.2 Controlled Signals ] [ 4.3 Call-on Signal ] [ Typical4.4 Signal Layout ]

[ Introduction1. ] [ 2. Track Circuit ] [ Relays3. ] [ 4. Signals ] [ Moter5. Points ] [ 6. Gate barriers ] [ 7. Automatic Blocking System

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4.1 Automatic Signals

Automatic Signals can be identified by the circular number plate bearing the distinctive number of that signal post and the gray color mast. They may contain one, two or three aspects of one or more units. Only one aspect can be lit in a unit at a given time. The automatic signals are approach lit; i.e. light up only when a train approaches. This arrangement is used to conserve power. The automatic signals operates according to the track conditions ahead and are not controlled by the controller.

4.1.1 Automatic Block Signal

Automatic block signaling is used to control trains between two stations. A detailed discussion about automatic block signals can be found here. These signals have one unit of three aspects and have the following meanings:

RED Dange

r; train on immediate block

AMBE R

Cautio n;

train on the block after the next, prepare to stop at the next signal

GREE N

Proce

ed: line clear for the next two or more blocks

4.1.2 Automatic Approach Signal

These signals are placed immediately before the controlled signals. These signals have one unit with three aspects on the main post and another unit with two aspects on a support bracket below the main unit.

These signals indicate that a controlled signal is being reached and show the route that will be taken at a controlled speed. These are also called distance signals or outer home signals. The aspects of the signals are as follows.

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ger;

AMBER over AM BER

Caut ion;

controlled signal ahead is Danger

AMBER over GR EEN

Proc

eed; going on the loop line

GREEN over AM BER

Proc

eed; going on the main line

The upper unit (three aspects) refers to the main line and the lower unit refers to the loop line.

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4.2 Controlled Signals

The controlled signals normally show 'danger' aspect (RED) and are controlled by the train controllers. They have a square number plate and their mast and base are painted with red and white stripes.

4.2.1 High Controlled Signal

The high controlled signals control and guide the trains into the yard. These signals will normally have two units of three aspects in line. The upper unit corresponds to the main line and the lower unit corresponds to the immediate loop line. Some high controlled signals will also have, below the second unit, a third unit of one aspect (AMBER). These are found at the points where there are more than one turn out. The second unit have a speed restriction of 48 km/h and the third unit has 16 km/h. The meanings of the aspects are given below.

RED Danger ; Stop

AMBER over RED Going on main line; starter not given

RED over AMBER Going on loop line; starter

not given

GREEN over RED Going on main line; starter

given

RED over GREEN Going on loop line; starter _given

In three unit signals

RED over RED over

AMBER

Caution; more than one turn out

4.2.2 Dwarf Controlled Signal

Dwarf controlled signals may have one unit of two or three aspects. They are used as exit (starter) signals, where there is a general speed restriction.

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4.3 Call-on Signal

To enter locomotive in the yard while shunting, the high controlled signals cannot be given because of the presence of the coaches on the same line (platform). In this situation a call-on signal is used. The call-on signal, which is mounted above the base of the high controlled signal, has three lamps and two aspects as illustrated below.

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4.4 Typical Signal Layout

The simple station layout below depicts the positions of the respective signals in a typical yard.

The first signal a train will see when arriving from left is the one before last ABS signal. It will inform the track condition ahead. It may show 'caution' if a train is awaiting to enter or just entering the station yard. The second will the last ABS which is also the outer home signal. It will hint about the platform the train will be stopping or passing through (if it is an express train). The third will be the inner home (high controlled) signal. This will allow the train to enter the

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station yard or pass through the station if it is an non-stopping station for that particular train. If the train stops at the station, when ready the starter (dwarf controlled) signal is given to proceed.

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5. Moter Points

Point is a place where the track branches off. The points can be either manually switched (lever frame) or motor driven. Most of the points in the color light area are motor points and can be controlled by the Maradana control office.

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The point motor is powered by 110V d.c. supplied by the nearby relay house. When an order is given to switch the point, power is given to the motor in the respective direction. The motion is used to either push or pull the drive rod. Point machine has contacts for detection of the switching. These contacts are operated by the long and short detection rods. When the point is set properly an indication is obtained by the relay house through these contacts. The allowable gap between the stock rail and the switch blade is 3mm. When a foreign material such as a stone prevents the point from setting properly, the indication contacts stay

neutral and no indication is sent. The clutch mechanism in the point

machine will start slipping in order to protect the machine from mechanical damages. The safety relay attached to the motor circuit will cut off power in 15 seconds. When no indication is obtained at the control office, the

controller will inform the Signal and Telecommunication Inspector (STI) in charge of the respective yard. On receipt of the information, STI will go to the motor point in question and remove the obstacle. The point machine has a facility to operate it by manual cranking. Once the point is cranked, the operation is finished and the indication will received by the control office. Some points in the color light area are of lever frame type. They are not frequently switched during routine operations. These type of points are

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protected by a device called "magnetic lock", which has to be released by the controller at the central office to enable station master to switch the point. After the operation is completed station master will switch the point back to its normal position and it is locked by the controller. This ensures that all the points are under the controller at the central office.

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6. Gate barriers

Gate barrier protects the level crossing. In the color light area gate barriers are automatically operated when a train approaches it from either direction. The gate machine has 110V d.c. motor to operate the gate. It also consists of contacts to get indication of the status of the gate. The figure below illustrates a gate barrier system.

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The gate barrier has two signals on the track on either side of the road. The signal at the distance is called an early warning. It has two aspects of amber and green. The five lamps are arranged in a manner to represent letter "W" for Warning. The amber aspect means the gate is not protected. This signal is located at a distance to allow the driver of the train to apply brakes and stop the train if necessary. The green aspect means the gate is protected and the train can pass the gate at its normal speed. The signal near the gate has a similar

arrangement; red on top unit and green on lower unit. If the gate is protected the green aspect will be lit and if not the red.

The gate barrier system also has flashing two unit warning signals on either side of the track for the road traffic. A warning bell is also fixed on the mast. It rings before and while the gate is closing. The circuits are wired in such a manner a failure on the gate motor circuit will result in the continuous ringing of the bell. In such an occasion the gate-man will inform this to the nearest station master using the gate telephone and he in turn will inform the STI.

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7. Automatic Blocking System

[ Up ] [ 7.1 Route Establishment ] [ Train7.2 on Line ] [ 7.3 Release of Route ]

Automatic block signaling (ABS) safeguards the train operations between stations and an effective means of increasing the line capacity. In the color light area, where the trains are worked on the ABS, each running rail is divided into a series of blocks sections (track between the stations) and station sections (track between entry and exit signal). Each section is track circuited separately. Entry into each block section is governed by the automatic block signals at the entry point of the section. (Signals 1, 2 and 3 in the coming pages). The train leaving station block A and entering station block B will be controlled by the controlled signals at respective stations. The color light area has dual tracks and under normal operation the up trains will be using up line and the down trains will be using the down line.

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[ Up ] [ 7.1 Route Establishment ] [ Train7.2 on Line ] [ 7.3 Release of Route ]

[ 1. Introduction ] [ 2. Track Circuit ] [ Relays3. ] [ 4. Signals ] [ Moter5. Points ] [ 6. Gate barriers ] [ 7. Automatic Blocking System ]

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7.1 Route Establishment

Operation

In the figure below consider the line between station A and Station B, which is divided in to 4 blocks. The signals at A and B are home signals (controlled signals) and the signals 1, 2 and 3 are automatic blocking signals. In the reverse direction the entire track segment is treated as one block.

Establishment of route

In the idle condition controlled signals show 'danger' and the ABS signals are extinguished.

When a train is to be dispatched from station A to station B, a "black" current is sent from station A to station B.

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If the line is free, i.e. all track relays are picked up, the "black" current arrives at station B and blocks there the dispatch of a train from station B to station A. Station B acknowledges by sending a "yellow" current. The first block post (signal 3) signal lights up and show 'caution'. This block post send the current on, but now as "green" current.

The "green" current passes to the remaining block posts and their signal switch on to 'proceed'. When the current reaches station A, the home signal (starter) shows 'proceed'. There after the black current is cut off. The direction of movement is now locked.

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7.2 Train on Line

As soon as the train passes the controlled signal at station A, the signal switches to 'danger'. Note that the "green" current is short circuited by the train axle and does not reach signal A.

Sooner or later the the controlled (home) signal at station B will be set to 'proceed' by the controller. As a result signal 3 switches to 'proceed' as well. When the train leaves the first block, the the signal 1 switches to 'danger' since the "green" current is now cut off by the train. This signal post sends a "yellow" current backward. Since the signal A is a controlled signal it ignores the

"yellow" current and remains 'danger'.

As the train enters block 3, the "yellow" current set the signal 1 to 'caution'. "Green" current is sent to the previous signal. Now a new train can be dispatched on the line from A to B and ABS ensures at least on block space between the two trains.

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Now you can deduce the aspect meanings of the ABS signal.

Red Stop! Train on next block

Amber Train on block after next; proceed with caution Green Normal speed; next two blocks are unoccupied

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When the train has passed the home signal at station B and the signal is turned 'danger' and the release of the route is automatically started. The release current ("black") is sent from station B to station A.

When the release current reaches station A, it checks that the exit signal does not show 'proceed', i.e station A is not intending to dispatch another train toward station B. If it does show 'proceed', release of route will not take place. If signal A shows 'danger', a black current is sent back to station B.

Route is released when the current reaches station B. The signal aspect currents ("yellow" and "green") are cut off and the block signal are extinguished. The "black" current from A is also cut off and the system returns to idle condition.

Design

All the information is transmitted on a two wire under ground cable. The aspect currents "yellow" and "green" are d.c. with opposite polarity and the locking and releasing current, "black", is a.c. The wires are connected with filters in block posts. This enables simultaneous transmission of d.c. and a.c. on the same wire pair.

The locking relays in the block posts are of magnetic stick type and once picked up by the locking current, they remain picked up until the release current is applied. If a ABS post is locked and it receives no

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aspect current it shows 'danger' and sends a "yellow" current to the post at the back. If it receives "yellow" or "green" aspect current it will show 'caution' or 'proceed' aspect and send a "green" current to the post at the back. When the releasing take place all aspects are extinguished. The controlled signal do not respond to aspect current but take it into consideration when a order to is given. It turns

'danger' as soon as the train passes it.

The spacing of block signals varies from 4000 to 8000 feet according to the curvatures on the running rail and the visibility. On double line area only one block is provided between station in the reverse direction.

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«

Supply Chain Management

Indian Train Accidents-Reasons and Solutions

»

Railway Signalling using Wireless Sensor Networks

Railway Signalling is safety critical domain, where still traditional technology is in

use. There are many reasons for using traditional technology; one of the main reasons

being the proven Safety performance of the older systems (Relay Based). As the rail

traffic is increasing and with higher speed of trains there is an acute need for

modernization of Railway Signalling Technology. Even with the advent of

Microprocessor based technology, the problems have not been solved. The current

railway signalling technology involves huge amount of physical wiring used to

receive inputs and drive outputs to the field functions, which is very difficult to

maintain and up-gradation of this infrastructure is every signal engineer’s nightmare.

This paper proposes the use of Wireless sensor networks in Railway Signalling

(45)

domain which combines the Ground base signalling and the On–Board Signalling

using customized routing algorithm, which is suitable for high Speed Railway Traffic

which reduces the physical wiring to the bare minimum by applying distributed

architecture to the field functions which are connected by Wireless Network.

The most important part of the railways is to carry out operations like safe movement

of trains, this is achieved by Signalling. The Railway signalling is governed by a

concept called Interlocking. Many interlocking system still in use follow either relay

based technology or the Microprocessor based technology called Electronic

Interlocking System (EIS). Relay based systems are very huge in size and have

cumbersome wiring to perform operations. The advent of Electronic Interlocking

systems reduced the relays and wiring to some extent, but still uses traditional copper

cabling to be connected to the field functions such as signals, Track Detection

equipment, points (Switches). In modern signalling systems, the signal and switch

status needs to be sent to the On-Board Computers in the locomotives, this involves

traditional radios connected to the wayside field functions that communicate this

information to the OBC. This involves laying out track loops or balises that send this

information to the OBC, these loops are venerable to climatic conditions such as

ballast resistance, water flooding during rains, etc. Due to the failsafe nature of these

systems the cabling has to be redundant, this results in large maze of complex wiring

that is very difficult to maintain and upgrade. There is need to upgrade the existing

Railway Signalling Infrastructure and addition of new technologies like failsafe

wireless communications which shall combine both the ground based signalling

(Interlocking Systems) and the Locomotives (On Board Computers of the train) which

directly leads to simple distributed architecture which are highly maintainable and

easy to upgrade in future.

(46)

Sandeep Patalay

(47)

Tags:

Railway Signalling

,

Signal Designer

,

Signal Engineer

,

Signalling

,

Wireless Sensor Network

This entry was posted on Saturday, July 10th, 2010 at 7:36 pm and is filed under Signalling. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

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.

« Supply Chain Management

Indian Train Accidents-Reasons and Solutions »

(48)

Railway Signalling is safety critical domain, where still traditional technology is in use. There are many reasons for using traditional technology; one of the main reasons being the proven Safety performance of the older systems (Relay Based). As the rail traffic is increasing and with higher speed of trains there is an acute need for modernization of Railway Signalling Technology. Even with the advent of Microprocessor based technology, the problems have not been solved. The current railway signalling technology involves huge amount of physical wiring used to receive inputs and drive outputs to the field functions, which is very difficult to maintain and up-gradation of this infrastructure is every signal engineer’s nightmare. This paper proposes the use of Wireless sensor networks in Railway Signalling domain which combines the Ground base signalling and the On–Board Signalling using customized routing algorithm, which is suitable for high Speed Railway Traffic which reduces the physical wiring to the bare minimum by applying distributed architecture to the field functions which are connected by Wireless Network.

The most important part of the railways is to carry out operations like safe movement of trains, this is achieved by Signalling. The Railway signalling is governed by a concept called Interlocking. Many interlocking system still in use follow either relay based technology or the Microprocessor based technology called Electronic Interlocking System (EIS). Relay based systems are very huge in size and have cumbersome wiring to perform operations. The advent of Electronic Interlocking systems reduced the relays and wiring to some extent, but still uses traditional copper cabling to be connected to the field functions such as signals, Track Detection equipment, points (Switches). In modern signalling systems, the signal and switch status needs to be sent to the On-Board Computers in the locomotives, this involves traditional radios connected to the wayside field functions that communicate this information to the OBC. This involves laying out track loops or balises that send this information to the OBC, these loops are venerable to climatic conditions such as ballast resistance, water flooding during rains, etc. Due to the failsafe nature of these systems the cabling has to be redundant, this results in large maze of complex wiring that is very difficult to maintain and upgrade. There is need to upgrade the existing Railway Signalling Infrastructure and addition of new technologies like failsafe wireless communications which shall combine both the ground based signalling (Interlocking Systems) and the Locomotives (On Board Computers of the train) which directly leads to simple distributed architecture which are highly maintainable and easy to upgrade in future.

(49)

Sandeep Patalay

(50)

Tags: Railway Signalling, Signal Designer, Signal Engineer,Signalling, Wireless Sensor Network

This entry was posted on Saturday, July 10th, 2010 at 7:36 pm and is filed underSignalling. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

Leave a Reply

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A Snapshot of Railway Signalling

Monday, January 25th, 2010

Complex Railway Signalling Simplified

In Railway Signalling the term ‘interlocking’ is very important.

Interlocking means operation or status of one signalling apparatus is decided by another or depends on the status of other.

A railway signalling is a highly safety critical system,which are fail safe(even if any thing fails ,fails in safe condition).

In order to achieve a safe operation (to give a green signal),the signalling system assure that the track ahead of the signal to the next is free.

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In other words signals may not be operated to permit conflicting train movement to take place at the same time.

The interlocking ensure the switches(the electric or pneumatic equipment lead the train to different track) and other appliances in the route must be set in position before a signal allow the train to enter in to that route(between two signals).

When a route is set ,the train is given a the signal(yellow for example ,the first proceed aspect or green) to proceed with the movement and the interlocking ensures all the switches and other movable appliances(say trainstop for an example,a simple electro mechanical or pneumatic device mounted just outside the track which make the train to apply break automatic , if the driver overshoot a red signal) in the route are locked in position ,until either the train complete the journey of the route set or the proceed signal is withdrawn and sufficient time has passed to ensure that a train approaching that signal replaced or withdrawn(green to red by an operator or a system) has had an opportunity to stop before over shooting that signal.

Mechanical Interlocking

The above mentioned operations can be achieved either mechanical(outdated),electrically(with the help of relays) or electronically(with the help of computer ,named as solid state interlocking).

In olden days signals are controlled by manually operated levers ,which operates signals,swtiches ,derailer (forcefully derail the train before a standstil the train enter in to another track in operation).Reliability ,time delay in operation ,inefficiency,wear and tear t more mecanical devices were some of the drawbacks.

Electrical Interlocking

It was later replaced by better relay interlocking,which was achieved by electrical highly reliable relays ,make and break depends on the status of other relays/appartus.

In a complex interlocking 20’s of relays will be operating to ensure a single route is free before the signal goes ‘clear’.

There may be 100’s of relays operating for a complex yard or station for a secure operational requirement.

Based on the route request from an operator (entry exit) or OCS or GUI or ATS ,the relays will start checking the availablility of that route,based on the status of the track,other signals,points(switches)etc and make the route “locked’ for a safe operation by ensuring all the elements are “Set”,”locked’ and “detected” in desired condition.

One of the disadvantages of this system is large requirement of signalling hut(Where signalling control appartus housed) to mount 100’s of relays for a single area.

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This is the most modern interlocking ,(before anything could replace!!!)started installing in late 80’s,are generally soild state(Appartus made out of solid materials!!!) where wired network of relays are replaced by software logic running on a special hardware(a microcontroller assembly).

Modification of the network with a solid state interlocking is easy compared to relay interlocking as the software logic modification is easy compared to the hard wired elements.

SSI(Solid State Interlocking) is used as a product name as well,which is the first generation electronic interlocking,jointly developed by British rail,GEC(Alstom) and Westinghouse.

Second generation SSI is known as CBI(Computer Based Interlocking),where SmartLock(Alstom,France),Microlok(Ansaldo,Italy/USA),Westlock(Westinghouse,UK) are some of the product examples.

Each system uses its own style of programming ,and has merits and demerits.

Generally,a PBI(Processor Based Interlocking) or a CBI consists of a CPU card(where the system software process according to the application logic), a power supply card,

Input/Output Cards(I/O cards) a device driving card to mention a few..

There are flash memories,EEPROM(Electrically Erasable Program Read Only Memory) where an experienced application logic person write the logic(replacing the hard relay functions with software)and load into the flash memory.(Burn an EPROM or load through a serial port)

The I/O cards are responsible for Input and Outputs.Input card read the status of the the field equipments(Switch position,Track Occupancy,Trainstop Position,Route Request and Cancel,Point Call etc).

Where as Output cards drives the output to set the route in desired condition,after the application logic is processor based on the input status.

The system is programmed in such a way that,it takes the most solid input before changing the status to ensure a fail safe operation.

(For example a track is showing ,occupied and free alternatively ,known as bobbing,the system will consider that track as occupied until the Input card read a stable un occupied status)

There are serial communication ports available in the PBI for communicating with other systems,to make hot stand by arrangement,and with adjacent interlocking.

Serial communication ports are 485,232/432

Depends on the application ,modem are used to communicate with a long distance train control system or other PBI.

For the sake of explanation,I can generalize the discussion and stick to Microlok ,one of the cheap and popular systems.

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The Boolean operators (AND,OR ,NOT are most commonly used,where as other operators like XOR are also available)

Microlok syntax for AND is ‘ * ‘ ,for OR ‘+‘ , and NOT is ‘~‘ For explanation I can show a simple logic here,

ASSIGN ~A42VSNR * ~42VSNJR * I2_42MA_HR * ~ACE19.6U_VSNR * ~CE19.6U_VSNJR * CE19.6U_VCSR TO 42MA_HR;

Here ,to drive the software relay for controlling the yellow aspect of 42 signal A route various status of other relay has been proved…

Some of the logic can be very complex…Another example below

ASSIGN (37M_RUR + 37S_RUR + 39MA_RUR + 39SA_RUR) * ((40ATP1 + 302NLR) * 37ATP1 * I1_37BTP * I1_CE20.1ATP * I1_CE20.3ATP * I1_CE20.5ATP * I1_CE20.5BTP *

I1_CE20.7ATP * I1_CE21.1ATP * I1_CE21.3ATP * I1_CE21.5ATP * I1_CE21.5BTP * I1_CE22.1ATP * I1_CE22.1BTP * I1_CE22.9ATP * I1_CE22.9BTP * I1_201ATP * I1_203ATP * I1_205ATP * I1_207ATP * (I1_207BTP + I1_303RLR) * (I1_216ATP + I1_303NLR) * I1_218M_NLR * I1_218M_USR * I1_218S_NLR * I1_218S_USR * I1_216MB_NLR * I1_216MB_USR * I1_216SB_NLR * I1_216SB_USR +

I3_MP_EG_DL_DDSR + MP_EG_DL_SEC_JR) TO 37_39A_YR,O3_37_39A_YR;

Depend on the interlocking there could be around 5000 Assign statements….for each interlocking data….

This is an example taken from a data detailing just two assign statements,apart from this we need to assign ports for communication,re direct logic,log bits define all the Boolean bits ,baud rate and many other things..

Processor based system explained above is the brain of the system…which operates on the status of the external situation ,commands from the operator or an automated system..

Technology is moving forward…Introduction of Automatic Train Operation(ATO),Automatic Train Protection(ATP),and Automatic Tran Supervision (ATS) make the system work with out human interface.

As per the train schedule loaded on to the ATS system ,a train located miles away in a yard come to the platform on right time,open the door and set to go when you are in.