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AUTOMATIC TRAIN PROTECTION (CAB SIGNALLING) FOR DELHI METRO
RAILWAY
A CASE STUDY
By:
Raj Kumar Vijay kumar
CSTE / DMRC Dy CSTE/ DMRC
Synopsis
Delhi Metro Railway has been designed for headway of 120 seconds for rail corridor and
90 seconds for metro corridor. The Train control & Signalling system consists of ATP,
ATO, ATS & CBI and provides cab signals to Train drivers and protects against any
hazards ahead in the line.
This paper describes the Automatic Train Protection system for Delhi Metro and the
experiences during its design and implementation
1. Introduction
The first phase of Delhi MRTS consists of two corridors, the underground corridor called
the Metro corridor (Approx 11 Km) and, the surface & elevated corridor called the Rail
corridor (Approx 22 Km).
1.1 Headway
(a) The design headway of Rail corridor is 120 seconds for a sustained
operating headway of180 seconds.
(b) The design headway of Metro Corridor is 120 seconds for a sustained
operating headway of 120 seconds.
1.2 Train Control & Signalling System overview for Delhi Metro:
Delhi Metro railway system consists of 18 stations on Rail corridor and 10 stations
on Metro Corridor with two Depots , one for Rail Corridor at Shastri park and the
other at Khyber Pass for Metro Corridor.
Automatic Train Protection System(ATP) with Cab Signalling. The Track to
train communication is through Coded Audio frequency Track Circuits
Automatic Train Operation System (ATO)(Only for Metro Corridor)
Automatic Train Supervision System (ATS)with Automatic Route Setting
and Automatic train Regulation.
Solid state Interlocking System (SSI)both on the Main Line and Depot
1.3 The main function of the ATP system is to ensure safe train separation and safe
train movement. The ATP system's intelligence and safety decision making process
is placed mainly on the on board ATP equipment. The wayside ATP equipment.
Safety information is provided by the Solid State Interlocking for track circuit
occupancy and by the wayside ATP equipment which performs the ATP block
function using the status of the track circuits ,position of the point and the track
profile e.g curves , gradients , permanent & temporary speed restriction etc.
1.4 The main function of the Automatic Train operation system (ATO) is to run the
trains in between stations automatically without the intervention of Train driver.
The ATO system generates speed generates speed control to the traction and
braking system of the train with respect to the computed speed profile. The ATO
system ensures that the train achieves timely, accurate and smooth station stops
or stopping ahead of a restrictive point. The ATO system also controls the train
doors during station stops under the supervision of the ATP system without the
intervention of the train driver.
2. System Architecture
The Signalling system being used for Delhi MRTS project are based on fail safe
computers and safety critical software.
3 Modes For Train Operation
Operational Modes
3.1 ATO Mode
The normal mode of operation for the Metro Corridor is ATO Mode. In this mode
the trains shall operate automatically between stations while remaining within the
safety envelope calculated and enforced by the ATP and open its doors at the next
station.
3.2 ATP Mode
The normal mode of operation for the Rail Corridor is ATP Mode. This mode will
also be used on the Metro Corridor if the ATO equipment fails. In this mode the
train driver will operate the train manually. Indications shall be provided in the cab
of the train with onboard displays for Maximum Safe Speed (MSS) current speed,
target distance/speed as deduced from the most restricting ATP condition,
signalling mode etc. and routes established though interlocking. The braking curve
is to be computed continuously along the line, so as to enable a minimum safety
distance to be maintained. This computation is based on line characteristics as
well as the parameters of the train with dynamic monitoring and enforcement of
the change of target distance and speed. The maximum speed shown in the cab
shall be enforced by the ATP equipment. The ATP equipment shall also indicate
which side doors may be opened when a train enters a station. The ATP equipment
shall not allow the doors to be opened on the wrong side, unless an emergency
override control is activated.
3.3 Cut-Out Mode
The Cut-Out Mode will be used when the on-board ATP equipment on the Rail
Corridor fails or both the on-board ATO and the on-board ATP equipment on the
Metro Corridor fails.
In cut out mode lineside signals will be used to provide information to the train
driver that the route is clear to the next interlocking or to enter the depot
connecting track. Accordingly the train driver will operate from interlocking to
interlocking following the aspects of the lineside signals. In this mode the train
driver will operate the train at a maximum of 25 km/hr and this speed limit
enforcement will be ensured by onboard rolling stock equipment.
3.4 RM Mode
RM Mode is used to drive the trains in the absence of any cab signal input. In this
position, the train will operate without any cab signal input, but the speed shall be
limited to 25 km/hr by the on board ATP equipment.
3.5 ROS (Run on Sight) Mode
ROS mode of operation is with the mode Selector on ATP position and ROS mode
being then selected by a ROS button/Key and the driver Runs On Sight The only
control is concerning the train speed which cannot exceed a maximum speed ROS
- speed limit( 25 KMph) (Emergency breaking triggered by ATP system). The
running monitoring is the same as for RM. The ATP will give Cab Signal indications
as soon as the train reaches a track position where normal running can be
resumed. The ATP authorizes the ROS request
4 Automatic Train Protection System
The ATP system for DMRC is a "Distance to GO" system.
The basic idea used is to transfer to the train the responsibility for train movement
definition and monitoring. The train borne equipment will act as a driver does. It
will receive simple information from which it deduces orders such as 'stop at this
point' or 'reduce the speed to this level at this point' and will calculate the speed
versus location profile, which must be respected to obey these orders.
To be able to do that, static description of the track in which all the locations of
the critical points are indicated is necessary. This description can be named the
"route map". Data contained in the route map are named the "invariants".
The train must be able to know at all times where it is located. To do that, an
odometer function calculates the train displacement. Absolute positions in the
route map are defined by the location of beacons. When the train passes over
these beacons, it is capable of relocating itself the corresponding beacon
possesses an unique identifier which can be read by the train. The invariants are
transmitted to the train from the wayside. The data transmitted to the train also
contains the status of the stopping points (stop or not), and the status (normal or
reversed) of each set of points. From this data, the train can deduce the orders it
has to obey, and can follow its movement along the route map. This dynamic data
is called the variants.
4.1 Principle of Automatic Train protection System
The on board ATP has the information of the route map in the form of invariants
and the state of route and movement authority in the form of variants i.e status of
track circuits, route set , points etc .The on board ATP calculates the speed -
distance profile with supervision to a fixed target point based on the above
information and the characteristics of the rolling stock which is stored in the on
board ATP equipment . This is illustrated in the following set of figures
4.2 FIXED BLOCK ATP OPERATION
The fixed block system is fitted with a continuous track-to-train transmission
allowing the trackside ATP computer to continuously send to the train the track
occupancy configuration. Consequently, the intelligent ATP train borne computer
continuously calculations its next point to protect: in this case the beginning of
next occupied track-circuit.
4.3 Challenges Faced during design of ATP system for Delhi Metro
4.3.1 Interface with Rolling stock:
The design of ATP system is dependent on the mechanical and electrical
interface with Rolling stock . The issues which had to be studied in great detail
by both the Rolling stock and Signalling contractors to fulfill the required
mechanical and electrical interface.
4.3.1.1 Mechanical interface:
The mechanical interface included the fixing and mounting of the pickup coil ,
antenna and odometer and the associated cables from these equipments to the
on board ATP equipment while satisfying the EMC requirement as per EN50121
norms.
The space for housing the on board ATP equipment in the driving cab was
another critical issue keeping in view the space constraint in the driving cab.
This was resolved in line with the design of driving cab arrangement in line with
those used in other metro systems.
4.3.1.2 Electrical interface:
The most critical interface of the ATP system with the Rolling stock is the
electrical interface as this interface controls the emergency brake , zero speed
detection and door authorization circuits of the Rolling stock and are safety
critical circuits. The requirement of adequate number of train lines and their
specific characteristic needed from the front cab to the rear cab to meet the
head - tail redundancy of the onboard equipment from Rolling stock is another
issue, which has to be kept in view while designing the ATP system. Apart from
matching the electrical parameters, the most important issue was the electrical
interface with Rolling stock while ensuring that this meets the functional and
safety requirement of the head- tail redundancy of the on board ATP equipment.
This is illustrated by the following schematic of the emergency brake circuit
interface with Rolling stock.
4.3.1.3 Rolling stock characteristics:
The design of ATP system is completely dependent on the Rolling stock
characteristics. Some of the important parameters are the length of the train,mass of
the train ( both tare and fully loaded), Initial acceleration (average, nominally
constant 0-30 km/h), Acceleration curve to be applied, Resistance to motion
(formula, curve, starting resistance), Service braking: deceleration rate, Service
braking: traction cut off delay, Service braking: full braking delay (from 0% braking
to 90% braking) Electric Brake, Service braking: full braking delay (from 0% braking
to 90% braking) Pneumatic Brake, Emergency braking: deceleration rate, Emergency
braking: traction cut off delay, Guaranteed emergency brake rate
4.3.2 Specific features of ATP for Delhi Metro
4.3.2.1 Redundancy of On board ATP equipment
The availability of the signalling system during revenue service has to be the order
that there is minimum interruption to train services. A very critical aspect during
design was the redundancy of the on board ATP equipment. Delhi metro finalized for
the head tail redundancy meaning thereby that in the event of failure of the front cab
ATP equipment , the train will switch over to the rear cab ATP equipment and
continue its service . This ensure high availability of the ATP system. The two on
board ATP equipments are in hot standby state and no driver action is required to
switch from the front cab ATP equipment to rear cab ATP equipment. This is
illustrated by the following figure.
4.3.2.3 Service brake intervention as a first level of intervention before
Emergency Brakes
The Automatic train protection system has the responsibility of protecting the train
from any hazard ahead and also from any unsafe situation like overspeeding etc.
This is ensured by application of irrevocable emergency brakes which brings the train
to a stop before the emergency brakes are released and service can be continued
ahead. Generally the application of modulated braking command is a function of
ATO( Automatic train operation system) which controls the traction and braking
system of the Rolling stock. Since Delhi metro had only ATP in Line 1 , the design
progressed to implement the specific ERTMS specification of service brake as a first
level of intervention with the option of release of service brakes by driver when the
actual speed of the train is brought below the maximum safe speed by the
application of full service brake by the on board ATP equipment.The same has been
designed and is under implementation by DMRC. This is illustrated by the following
figure:
4.3.2.4 Monitoring of Station stop :
The monitoring and ensuring that a train stops at each station t the correct location
on the station is also a ATO function. However in order to ensure this function in line
1 of DMRC which does not have ATO , the design for the same has been done in line
with the ERTMS specification for advisory speed indication to the driver and ensured
by Full service brake . This feature is also under implementation. This function is
illustrated by the following figure.
4.4 Challenges during testing and commissioning of ATP system for DMRC
4.4.1 Electro magnetic compatibility with Rolling stock
One of the critical aspect for the correct track to train transmission is for Rolling
Stock to ensure that around the following frequencies currents rejected by the train
in the track do not exceed 30 mA peak value in a bandwidth of 600 Hz and do not
exceed 40 mA peak value in a bandwidth of 1200 Hz in the band of the AFTC i.e from
9 to 21 KHz. This has been extensively tested by both the Rolling stock and
signalling contractor and improvements made by both in order to meet this criteria.
Further improvement on the same is in progress.
4.4.2 Commissioning of all the functions of the ATP system in one stage
Since all the functions of ATP required for Delhi metro were not fully developed
validated for safety part from the extensive testing of the ATP system with Rolling
stock, Delhi metro decided to commission the functions of AATP in two stages. All the
safety functions were commissioned in stage 1 on 29th Sept 2003 for the Shahdra to
Trinagar section and in March 2004 for Trinagar to Rithala section , thus completing
the entire line1. The second stage of commissioning is underway and will be finished
by June 2004 for the following functions:
a. Head -Tail redundancy with ERTMS type screen for drivers
b. Service brake as a first level of intervention before emergency brakes.
c. Monitoring of station stop.
4.4.3 Other challenges during testing and commissioning of ATP system
The issues which are to be effectively monitored and tuned for successful
commissioning of ATP system are :
a. Track to Train transmission through rails. The rails are required to be cleaned so
that effective level of transmission to the train is ensured.
b. The measurement of the actual location of the S-bonds for Track circuits, point,
Platform.
c. Testing that the on board ATP system software functions correctly with the Rolling
stock with respect to all vital ( like Emergency brake application , correct door
authorization etc.) and non vital functions.
5. Conclusion
The installation and testing of ATP system has been completed for entire Line 1 from
Shahdra to Rithala- a stretch of 22 Kms with 18 trains running on date . The ATP
system designed and commissioned by DMRC will be the trendsetter of all ATP system
in India with its operational and safety features for safe journey of passengers on the
DMRC network.
