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Vaibhav Tiwari

B. Tech 2nd

Year

SRM University, SRM Nagar

Kattankulathur 603203,

Kancheepuram District,Chennai Tamilnadu

Summer Training Report

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This is to certify thatVaibhav Tiwari

(1041210250) student of

2011-2015 Batch of Electronics & CommunicationBranch in 2nd

Year of SRM University, Kattankulathur , Chennai has

successfully completed his industrial training at Delhi Metro Rail

Corporation Ltd., Yamuna bank depot, New Delhi for six weeks

from 16th June to 15st July 2014. He has completed the whole

training as per the training report submitted by him.

Training In-charge

Delhi metro rail corporation Ltd.

Yamuna bank depot, New Delhi

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TABLE OF CONTENT:-

1.Acknowledgement

2.About the company

3.SYSTEM OVERVIEW OF METRO

Braking system

Traction Power supply

C-VIS

HSVCB

SCMS

Energy storage

SCADA

Signaling system

Rolling stock

4.OB communication overview

Train radio system

TCMS

CCTV

ATO/ATP

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Acknowledgement

Its a great pleasure to present this report of summer training in Delhi Metro

Rail Corporation (A Joint Venture of Govt. Of India and Govt. Of Delhi) in

partial fulfillment of B.Tech

Programmed under

SRM University SRM Nagar Kattankulathur - 603 203

Kancheepuram District Tamil Nadu.

At the outset, I would like to express my immense gratitude to my training

guide, Mr. Amit Giri, guiding me right from the inception till the successful

completion of the training.

I am falling short of words for expressing my feelings of gratitude towards

him for extending their valuable guidance, through critical reviews of project

and the report and above all the moral support he had provided me with all

stages of this training.

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ABOUT THE COMPANY

Delhi Metro Rail Corporation (DMRC) was established by the

Government of India and the Government of Delhi in March 1995 to

build a metro system in the capital.

The metro network consists five lines with total length of 125.67kms.

The metro has 80 stations and 28 are underground.

Construction work in progress for the phase-IV.

Finances and Funding

From government of India and government of Delhi contribute equal shares,

trough soft loan from Japan bank for international cooperation.

Revenue and Profits

Revenue from advertisements and property development, leasing out trains

stations for film shoots.

Security

Central industrial security force (CISF)

Closed circuit cameras

Dog squads

Emergency communication b/w passengers and driver.

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DMRC NETWORK:-

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SYSTEM OVERVIEW OF METRO:-

Braking system in Delhi Metro Train

Its normal braking actuated by train operator using TBC during normal

train operation.

Its a mixture of regenerative braking and electro pneumatic friction

brake

Traction Power supply to Delhi Metro Train

Power is supplied by 25 kv, 50 Hz ac through overhead catenary.

Power supply

qu pm nts

1. (C- VIS)- Cubicle type Vacuum Insulated Switchgear

2. (HSVCB)- High Speed Vacuum Circuit Breaker

3. (B-CHOP)- Energy Storage for Traction Power Supply System

4. (SCMS)- Stray Current Monitoring System

SCADA system for power supply and network equipment surveillance.

C-VIS (Cubicle type Vacuum Insulated Switchgear)

25 kV vacuum insulated switchgear in order to eliminate the risk of

greenhouse gas emission, to meet customer requirement such as

compact design and low maintenance.

CHARACTERISTIC

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1. Dual Contact design (High reliability of interrupt and disconnect)

2. SF6 gas free -Vacuum Insulation

3.

Compact design

4.

Grease free

HSVCB (High speed vacuum circuit breaker)

Hitachi contributes the electric railroad system demanded to the safer

service through HSVCB which is unique to us.

Characteristics

1. Low noise

2. No arc emission

3. Very short time interruption

4.

Low maintenance

Stray Current Monitoring System (SCMS)

This system provides evaluation of the stray current conditions of the track,

which facilitates early detection of insulation deficiencies and allows necessary

measures to be taken to prevent potential damages caused by stray current

corrosion

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B-Chop (Energy Storage for Traction Power

Supply System)

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SCADA (Supervisory control $ data acquisition)

SCADA is a software system which is in charge of surveillance and data

collection by personal computers.

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Signaling system of Delhi metro

Signaling used on high density metro (or subway) routes is based on the same

principles as main line signaling. The line is divided into blocks and each blockis protected by a signal but, for metros, the blocks are shorter so that the

number of trains using the line can be increased. They are also usually

provided with some sort of automatic supervision to prevent a train passing a

stop signal.

ATO

1. Control all operation from acceleration to stopping.

2.

Realize driverless operation.

ATC

1. Used for making high speed operation.

2. It detect train position and transmit signal to control unit.

Figure 1: Diagram showing simple Metro-style two-aspect signaling.

Originally, metro signaling was based on the simple 2-aspect (red/green)

system as shown above. Speeds are not high, so three-aspect signals were not

necessary and yellow signals were only put in as repeaters where sighting was

restricted.

Many metro routes are in tunnels and it has long been the practice of some

operators to provide a form of enforcement of signal observation by installing

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additional equipment. This became known as automatic train protection (ATP).

It can be either mechanical or electronic.

The older, mechanical version is the train stop; the latter, electronic versiondepends on the manufacturer. The train stop consists of a steel arm mounted

alongside the track and which is linked to the signal. If the signal shows a

green or proceeds aspect, the train stop is lowered and the train can pass

freely. If the signal is red the train stop is raised and, if the train attempts to

pass it, the arm strikes a "trip cock" on the train, applying the brakes and

preventing motoring.

Electronic ATP involves track to train transmission of signal aspects and

(sometimes) their associated speed limits. On-board equipment will check the

train's actual speed against the allowed speed and will slow or stop the train if

any section is entered at more than the allowed speed.

The Overlap

If a line is equipped with a simple ATP which automatically stops a train if itpasses a red signal, it will not prevent a collision with a train in front if this

train is standing immediately beyond the signal.

Figure 2: Diagram showing the need for a safe braking distance beyond a

stop signal.

There must be room for the train to brake to a stop - see the diagram above.This is known as a "safe braking distance" and space is provided beyond each

signal to accommodate it. In reality, the signal is placed in rear of the entrance

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to the block and the distance between it and the block is called the "overlap".

Signal overlaps are calculated to allow for the safe braking distance of the

trains using this route. Of course, lengths vary according to the site; gradient,

maximum train speed and train brake capacity are all used in the calculation.

Figure 3: Diagram showing a signal provided with an overlap. The overlap

in this example is calculated from the emergency braking distance required

by the train at that location.

This diagram (Figure 3) shows the arrangement of signals on a metro where

signals are equipped with train stops (a form of mechanical ATP) and each

signal has an overlap whose length is calculated on the safe braking distance

for that location. Signals are placed a safe braking distance in rear of the

entrances to blocks. Signal A2 shows the condition of Block A2, which is

occupied by Train 1. If Train 2 was to overrun Signal A2, the raised train stop

(shown here as a "T" at the base of the signal) would trip its emergency brake

and bring it to a stand within the overlap of Signal A2.

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Track-Circuited Overlaps

Figure 4: Diagram showing a train standing in the signal overlap.

Nothing in the railway business is as simple as it seems and so it is with

overlaps. A line which uses overlaps and has closeheadways could have a

situation as shown above where the train in the overlap of Signal A121 has a

green signal showing behind it. Although it is protected by Signal A123

showing red, the driver of Train 2 may see the green signal A121 behind Train

1 and could "read through"or be confused under the "stop and proceed"rule.

Figure 5: Diagram of the track circuited overlap, sometimes known as a

"replacing track circuit".

So, where there is a possibility of a green signal being visible behind a train,

overlaps are track circuited as shown in Fig. 5. Although there is no train

occupying the block protected by Signal A121, the signal is showing a red

aspect because the train is occupying the overlap track circuit or "replacing"

track circuit, as it is sometimes called.

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This will give rise to two red signals showing behind a train whilst the train is

in the overlap. The block now has two track circuits, the "Berth" track and the

"replacing" track.

Absolute Block

Figure 6: Schematic showing the principle of the Absolute Block system. Signal

A127 is clear because two blocks in advance of it is clear. A125 shows a

danger aspect because one of the blocks ahead of it is occupied by a train.

Many railways use an "Absolute Block" system, where a vacant block is alwaysmaintained behind a train in order to ensure there is enough room for the

following train to be stopped if it passes the first stop (red) signal. In Figure 6,

in order for Signal A125 to show a proceed aspect (green), the two blocks

ahead of it must be clear, with Train 1 completely inside the block protected by

Signal A121.

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ROLLING STOCK

The first wave of rolling stock was manufactured by a consortium comprising

Hyundai Rotem, Mitsubishi Corporation and Mitsubishi Electric Corporation.Initial sets were built by ROTEM in South Korea, with later examples

completed in India by public sector undertaking Bharat Earth Movers Limited

(BEML). BEML is also responsible for the manufacturing coaches under

technology transfer agreement.

The air-conditioned trains consist of four 3.2m-wide, stainless steel,

lightweight, although eight is possible. The trains have automatic doors,

secondary air suspension and brakes controlled by microprocessor.

Delhi Metro has a fleet of 280 coaches, which DMRC runs as 70 trains every

day. Each train can accommodate about 1,500 people, 240 seated. Maximum

speed is 80km/h (50mph), with a 20-second dwell time at stations. Train

depots are located at Khyber Pass, Najafgarh, Shastri Park and Yamuna Bank.

In May 2011, BEML received a contract worth Rs9.2bn ($205m) from DMRCto supply 136 intermediate metro cars. The delivery is expected to be

completed by December 2013.

In March 2008 Bombardier Transportation announced an 87m ($137m)

contract for 84 MOVIA metro cars, a follow-on to an order for 340 placed in

July 2007. The new vehicles are being deployed as part of the Phase II

expansion.

In September 2011, Bombardier received a $120m order for 76 additional

MOVIA metro cars. This was a follow-on contract to an order placed for 114

vehicles in the middle of 2010. Deliveries under the new order are expected to

be completed between the third quarter of 2012 and early 2013.

DMRC received the first MOVIA metro car from Germany in February 2009.

The first 36 vehicles will be manufactured in Gorlitz, Germany, and theremaining 388 cars will be built at Bombardier's Indian manufacturing facility

in Savli, South Gujarat.

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A Phase I broad gauge train, supplied byHyundai Rotem-BEML.

A Phase IIbroad gauge train, supplied byBombardier.

The Metro uses rolling stock of two different gauges. Phase I lines use1,676 mm (5.499 ft)broad gauge rolling stock, while three Phase II lines use

1,435 mm (4.708 ft)standard gauge rolling stock. Trains are maintained at

seven depots at Khyber Pass and Sultanpur for the Yellow Line, Mundka for

the Green Line, Najafgarh and Yamuna Bank for the Blue Line, Shastri Park for

the Red Line and Sarita Vihar for the Violet Line.

Broad gauge

The broad gauge rolling stock is manufactured by two major suppliers. For the

Phase I, the rolling stock was supplied by a consortium of companies

comprisingHyundai Rotem,Mitsubishi Corporation,andMELCO.The coaches

were initially built in South Korea byROTEM,[116]then in Bangalore byBEML

through atechnology transfer arrangement. These trains consist of four 3.2-

metre (10 ft) wide stainless steel lightweight coaches with vestibules

permitting movement throughout their length and can carry up to 1500

passengers, with 50 seated and 330 standing passengers per coach. The

coaches are fully air conditioned, equipped with automatic doors,

microprocessor-controlled brakes and secondary air suspension, and are

capable of maintaining an average speed of 32 km/h (20 mph) over a distance

of 1.1 km (0.68 mi). The system is extensible up to eight coaches, and

platforms have been designed accordingly.

The rolling stock for Phase II is being supplied byBombardier Transportation,

which has received an order for 614 cars worth approximately US$ 1100

million. While initial trains were made in Germany and Sweden, the

remainder will be built at Bombardier's factory in Savli, near Vadodara These

trains are a mix of four-car and six-car consists, capable of accommodating

1178 and 1792 commuters per train respectively. The coaches possess several

improved features likeClosed Circuit Television (CCTV) cameras with eight-hour backup for added security, charging points in all coaches for cell phones

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and laptops, improved air conditioning to provide a temperature of 25 degrees

Celsius even in packed conditions and heaters for winter.

Standard gauge

The standard gauge rolling stock is manufactured by BEML at its factory in

Bangalore. The trains are four-car consists with a capacity of 1506 commuters

per train, accommodating 50 seated and 292 standing passengers in each

coach. These trains will have CCTV cameras in and outside the coaches, power

supply connections inside coaches to charge mobiles and laptops, better

humidity control, microprocessor-controlled disc brakes, and will be capable

of maintaining an average speed of 34 km/h (21 mph) over a distance of

1.1 km (0.68 mi)

position. This prevents any kick from the pipe as it is disengaged. Closing the

angle cocks also has the effect of bleeding off the air trapped in the hose. The

angle cock has a special bleed hole for this purpose.

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OB COMMUNICATION

Train radio system

The train radio system is the main link for non-safety critical vehicle

communication. The system can handle both voice and data communication

in order to

Allow operation control center (00C) to read status information

from the vehicle.

Allow the driver to speak with OCC and/or depot.

Allow OCC to perform remote operation of the vehicle PIS. Allow OCC to passively supervise cab activities, i.e. the current

voice/sound of the active cab

Train radio system component

Train radio system units in driving cab

The train driver will see five items, in the driving cab. that make up the train

radio system:

19" sub-rack. located behind the co-driver's seat

Train radio control panel (1RCP) mounted on the left hand

Components

DT car hifT-car

19 Trainborne rack 1

Radio centre/ bead (RCF-1) 1

Train radio control panel (TRCP) 1 -

Speaker 1 _

Handset 1

Antenna 1

Fist microphone 1 -

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sidewall of the driver.

Radio control head (RCN) mounted on the left hand sidewall

of the driver.

Handset mounted on the console in front of the driver seat to be

used as default option for voice input.

Fist microphone mounted on the left hand sidewall of the

driver to be used as backup option for voice input.

Train Control and Management System

TCMS)

:-The function of TCMS is to control and monitor on board

systems and sub systems connected to the train

communication network. The TCMS system incorporates

unit and train level functionality for the different

systems that has interlaces with the TCMS system. it is

a distributed and modular system.

The following functions/systems are supervised

/controlled by TCMS:-

Propulsion

Brakes

Auxiliary electric system

Train operation control

Doors

Passenger information system

ATP/ATO

Train radio

Air supply

Carbody fittings

Interior

Coupler

HVAC

Line voltage

Battery

Fire detection

CCTV

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Units in TCMS

Unit

DT

CAR

M-

CAR

T-

CAR

CCU-0 Central computing unitoperational 1 1 1

CC U-C Central corn utin unitcomfort 1MOBAD Mode/Batter /Address unit 3MIO-DX2 Modular di ital in ut/out ut unit 2 1 1MIO-DX3 Modular di ital in ut/out ut unit 1 1 1MIO-DX4 Modular di ital in ut/out ut ur.: 1AX Analo ue in ut /out ut unit 1MCG Mobile communication atewa 1

Antenna 1Dual-

1

11M1 Human machine interface

TCMS software

Train diagnostic system TDS)- uploader: Offers the user aninterface for uploading or reading the information stored in the

diagnostic system.

Maintenance of vehicle information and statistics MAVIS):

It enables the maintenance staff to view and analyze the information

uploaded from the on-board TDS system.

Drivers control unit DCU) term: It is a software tool for the maintenance

personnel.

Software is used to view analog and logical signals in real-time in a

graphical environment, to analyze the system status, to analyze the

operation-recording of signals, to enable test procedures through

buttons and scripts.

Version control arid download tool MTVD):

MTVD is a tool

mainly for the maintenance personnel.

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CCTV System Closed-Circuit Television):-

The main function of CCTV system is to record the events in the saloon

area & Platform.

Cameras are directly connected to the DVRs in the DT-car

It, other cars cameras are connected to remote units.

All images are streamed to the DVRs where they are stored.

The DVRs and remote units are connected to the TCMS via IP backbone.

The CCTV system via DVF-i will communicate with the TCMS via IP

backbone.

Live camera images can be viewed on monitors in both cabs.System activation:

When the vehicle is activated, it performs a system start-up and supplies

power to the CCTV system.

After the system start-up, tile video system starts recording images.

System de-activation:

When there is no power, the CCTV system de-activates.

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AUTOMATIC TRAIN PROTECTION

(ATP)/AUTOMATIC TRAIN OPERATION (ATO):-

Functions of AT0

To drive trains between stations and slop them with high precision.

To give consistent speed profile for at trains to improve both traffic

regularity and Line capacity.

ATO

ATP is the safety system which ensures that trains remain a safe distance a part

and have sufficient warning to allow them to stop without colliding with

another train. ATO (Automatic Train Operation) is the non-safety part of train

operation related to station stops and starts.

The basic requirement of ATO is to tell the train approaching a station where

to stop so that the complete train is in the platform. This is assuming that the

ATP has confirmed that the line is clear.The sequence operates as shown

below.

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The train approaches the station under clear signals so it can do a normal run

in. When it reaches the first beacon - originally a looped cable, now usually a

fixed transponder - a station brake command is received by the train. The on

board computer calculates the braking curve to enable it to stop at the correctpoint and, as the train runs in towards the platform, the curve is updated a

number of times (it varies from system to system) to ensure accuracy.

Modern systems require less wayside checking because of the dynamic and

more accurate on-board braking curve calculations. Now, modern

installations can achieve 0.15 meters stopping accuracy - 14 times better.

Metro Station Stops

ATO works well when the line is clear and station run-ins and run-outs are

unimpeded by the train ahead. However, ATO has to be capable of adapting to

congested conditions, so it has to be combined with ATP at stations when trains

are closely following each other. Metro operation at stations has always been

a particular challenge and, long before ATO appeared in the late 1960s,

systems were developed to minimize the impact when a train delayed too longat a station.

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To provide a frequent train service on a metro, dwell times at stations must be

kept to a minimum. In spite of the best endeavors of staff, trains sometimes

overstay their time at stations, so signaling was been developed to reduce the

impact on following trains. To see how this works, we begin with an example(left) of a conventionally signaled station with a starting Signal A1 (green) and

a home Signal A2 (red) protecting a train (Train 1) standing in the station. We

can assume mechanical ATP (train stops) is provided so the overlap of Signal

A2 is a full speed braking distance in advance of the platform.

As Train 2 approaches, it slows when the driver sees the home Signal A2 at

danger. Even if Train 1 then starts and begins to leave the station, Signal A2will remain at danger until Train 1 has cleared the overlap of Signal A1. Train

2 will have to stop at A2 but will then restart almost immediately when Signal

A2 clears. This causes a delay to Train 2 and it requires more energy to restart

the train. A way was found to allow the second train to keep moving. It is

called multi-home signaling.

Multi Home Signaling - Approach

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Where multi-home signaling is installed at a station (left), it involves the

provision of more but shorter blocks, each with its own signal. The original

home signal in our example has become Signal A2A and, while Train 1 is in

the platform, it will remain at danger. However, Block A2 is broken up intothree smaller sub-blocks, A2A, A2B and A2C, each with its own signal. They

will also be at danger while Train 1 is in the platform. Train 2 is approaching

and beginning to brake so as to stop at Signal A2A.

When Train 1 begins to leave the station, it will clear sub-block A2A first and

signal A2A will then show green. Train 2 will have reduced speed somewhat

but can now begin its run in towards the platform.

Multi Home Signaling - Run In

At this next stage in the sequence, we can see (left) that Train 1 has now

cleared two sub-blocks, A2A and A2B, so two of the multi-home signals are

now clear. Note that the starting signal is now red as the train has entered the

next block A1. Train 2 is running towards the station at a reduced speed but it

has not had to stop.

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When Train 1 clears the overlap of signal A1, the whole of block A2 is clear

and signal A2C clears to allow Train 2 an unobstructed run into the platform.

ATO/ATP Multi Home Signalling

Fixed block metro systems use multi-home signalling with ATO and ATP. A

series of sub-blocks are provided in the platform area. These impose reduced

speed braking curves on the incoming train and allow it to run towards the

platform as the preceding train departs, whilst keeping a safe braking distance

between them. Each curve represents a sub-block. Enforcement is carried out

by the ATP system monitoring the train speed. The station stop beacons still

give the train the data for the braking curve for the station stop but the trainwill recalculate the curve to compensate for the lower speed imposed by the

ATP system.

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ATO Docking and Starting

In addition to providing an automatic station stop, ATO will allow "docking"

for door operation and restarting from a station. If a "driver", more often

called a "train operator" nowadays, is provided, he may be given the job ofopening and closing the train doors at a station and restarting the train when

all doors are proved closed. Some systems are designed to prevent doors being

opened until the train is "docked" in the right place. Some systems even take

door operation away from the operator and give it to the ATO system so

additional equipment is provided as shown left.

When the train has stopped, it verifies that its brakes are applied and checksthat it has stopped within the door enabling loops. These loops verify the

position of the train relative to the platform and which side the doors should

open. Once all this is complete, the ATO will open the doors. After a set time,

predetermined or varied by the control centre as required, the ATO will close

the doors and automatically restart the train if the door closed proving circuit

is complete. Some systems have platform screen doors as well. ATO will also

provide a signal for these to open once it has completed the on-boardchecking procedure. Although described here as an ATO function, door

enabling at stations is often incorporated as part of the ATP equipment because

it is regarded as a "vital" system and requires the same safety validation

processes as ATP.

Once door operation is completed, ATO will then accelerate the train to its

cruising speed, allow it to coast to the next station brake command beacon andthen brake into the next station, assuming no intervention by the ATP system

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Functions of ATP

To prevent trains from running too fast.

To prevent collisions between trains and buffer stops. To safeguard the movement of trains through points.

To maintain a safe distance between following trains on the same track.

Preventing the train to switch "mode" when not appropriate.

Automatic Train Protection

To adapt metro signaling to modern, electronic ATP, the overlaps are

incorporated into the block system. This is done by counting the block behind

an occupied block as the overlap. Thus, in a full, fixed block ATP system, there

will be two red signals and an unoccupied, or overlap block between trains to

provide the full safe braking distance, as shown here (click for full size view).As an aside, remember that, although I have shown signals here, many ATP

equipped systems do not have visible line side signals because the signal

indications are transmitted directly to the driver's cab console (cab signaling).

On a line equipped with ATP as shown above, each block carries an electronic

speed code on top of its track circuit. If the train tries to enter a zero speed

block or an occupied block, or if it enters a section at a speed higher than that

authorized by the code, the on-board electronics will cause an emergency

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brake application. It was a simple system with only three speed codes -

normal, caution and stop. Many systems built since are based on it but

improvements have been added.

ATP Speed Codes

A train on a line with a modern version of ATP needs two pieces of

information about the state of the line ahead - what speed can it do in this

block and what speed must it be doing by the time it enters the next block. This

speed data is picked up by antennae on the train. The data is coded by the

electronic equipment controlling the track circuitry and transmitted from the

rails. The code data consists of two parts, the authorised speed code for this

block and the target speed code for the next block. The diagram below shows

how this works.

In this example (left), a train in Block A5 approaching Signal A4 will receive a

40 over 40 code (40/40) to indicate a permitted speed of 40 km/h in this blockand a target speed of 40 km/h for the next. This is the normal speed data.

However, when it enters Block A4, the code will change to 40/25 because the

target speed must be 25 km/h when the train enters the next Block A3. When

the train enters Block A3, the code changes again to 25/0 because the next

block (A2) is the overlap block and is forbidden territory, so the speed must be

zero by the time train reaches the end of Block A3. If the train attempts to

enter Block A2, the on-board equipment will detect the zero speed code (0/0)

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and will cause an emergency brake application. As mentioned above, Block A2

is acting as the overlap or safe braking distance behind the train occupying

Block A1.

Operating with ATP

Trains operating over a line equipped with ATP can be manually or

automatically driven. To allow manual driving, the ATP codes are displayed to

the driver on a panel in his cab. In our example below, he would begin

braking somewhere around the brake initiation point because he would see

the 40/25 code on his display and would know, from his knowledge of the

line, where he will have to stop. If signals are not provided, the signal positions

will normally be indicated by trackside block marker boards to show drivers

the entrances to blocks.

If the train is installed with automatic driving (ATO - Automatic Train

Operation), brake initiation for the reduced target speed can be by either a

track mounted electronic "patch" or "beacon" placed at the brake initiation

point or, more simply, by the change in the coded track circuit. Both systems

are used by different manufacturers but, in both, the train passes through a

series of "speed steps" to the signaled stop.

When the first train clears Block A1, the codes in Blocks A2, A3 and A4 will

change to the next speed up and any train passing through them will receive

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immediately a new permitted speed and a new target speed for the next block.

This allows an instant response to changing conditions and helps to keep

trains moving.

Distance-to-Go

The next stage of ATP development was an attempt to eliminate the space lost

by the empty overlap block behind each train. If this could be eliminated, line

capacity could be increased by up to 20%, depending on block lengths and line

speed. In this diagram, the train in Block A1 causes a series of speed reduction

steps behind it so that, if a following train enters Block A6, it will get a reduced

target speed. As it continues towards the zero speed block A2, it gets a further

target speed reduction at each new block until it stops at the end of Block A3.

It will stop before entering Block A2, the overlap block. The braking curve is

shown here in brown as the "standard" braking curve.

To remove the overlap section, it is simply a question of moving the braking

curve forward by one block. The train will now be able to proceed a block

closer (A5 instead of A6) to the occupied block, before it gets a target speed

reduction. However, to get this close to the occupied block requires accurate

and constant checking of the braking by the train, so an on-board computercalculates the braking curve required, based on the distance to go to the

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stopping point and using a line map contained in the computer's memory. The

new curve is shown in blue in the diagram. A safety margin of 25 meters or so

is allowed for error so that the train will always stop before it reaches the

critical boundary between Blocks A2 and A1.

Speed Monitoring

Both the older, speed step method of electronic ATP and "distance-to-go"

require the train speed to be monitored. In Fig 8 above, we can see the

standard braking curve of the speed step system always remains inside the

profile of the speed steps. The train's ATP equipment only monitors the train's

speed against the permitted speed limit within that block. If the train goes

above that speed, an emergency brake application will be invoked. The

standard braking curve made by the train is not monitored.

For the distance-to-go system, the development of modern electronics has

allowed the brake curve to be monitored continuously so that the speed steps

become unnecessary. When it enters the first block with a speed restriction in

the code, the train is also told how far ahead the stopping point is. The on-board computer knows where the train is now, using the line "map" embedded

in its memory, and it calculates the required braking curve accordingly. As the

train brakes, the computer checks the progress down the curve to check the

train never goes outside it. To ensure that the wheel revolutions used to count

the train's progression along the line have not drifted due to wear, skidding or

sliding, the on-board map of the line is updated regularly during the trip by

fixed, track-mounted beacons laid between the rails.

Operation with Distance-to-Go

Distance-to-go ATP has a number of advantages over the speed step system. As

we have seen, it can increase line capacity but also it can reduce the number of

track circuits required, since you don't need frequent changes of steps to keep

adjusting the braking distance.

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The blocks are now just the spaces to be occupied by trains and are not used as

overlaps as well. Distance-to-go can be used for manual driving or automatic

operation.

Systems vary but often, several curves are provided for the train braking

profile. This example shows three: One is the normal curve within which the

train should brake, the second is a warning curve, which provides a warning

to the driver (an audio-visual alarm or a service break application dependingon the system) and the third is the emergency curve which will force an

emergency brake if the driver does not reduce speed to within the normal

curve.