Kavach: Cab Signalling & Automatic Train Protection System for Digital Railways

CHAPTER 1

KAVACH – An Overview

1.0

Introduction

KAVACH is an indigenously developed Automatic Train Protection (ATP) System meant to provide protection to the trains against Signal Passing at Danger (SPAD), excessive speed and collisions. KAVACH provides continuous update of Movement Authority (distance up to which the train is permitted to travel without danger). Hence during unsafe situations when brake application is necessitated, and the Crew has either failed to do so, or is not in position to do so, automatic brake application shall take place. KAVACH has additional features to display information like speed, location, distance to signal ahead, Signal aspects etc. in Locomotive cab and generation of Auto and Manual SOS messages (Distress messages) from Locomotive as well as from the Station unit in case of emergency situation. The communication between Stationary KAVACH and Loco KAVACH units shall be Safety Integrity Level 4 (SIL 4) certified as per the CENELEC standards for railways. Communication between two or more Loco KAVACH systems, Non-Signalling based additional collision protection (i.e. Head-on, Rear-end & Side Collisions) and Manual SoS are non-SIL based (i.e. not failsafe).

Spot or Intermittent update type system affects Line Capacity adversely due to inherent limitation of design. Continuous Update type of system like KAVACH is Line Capacity friendly by design. Continuous Update type European system has been using commercially off-the shelf mobile communication such as GSM-R for long. KAVACH uses innovative radio communication system designed by RDSO to achieve continuous communication between the Train and Track-side systems.The radio communication system operates in UHF band.

Safety Integrity Level (SIL): The concept of Safety Integrity Level (SIL) is a direct result of the IEC 61508 standard, which is not specific to railways. For the railway industry, CENELEC (European Committee for Electrotechnical Standardization) has developed the standards EN 50126 (The Specification and Demonstration of Reliability, Availability, Maintainability and Safety (RAMS)), EN 50128 (Communication, signalling and processing systems - Software for railway control and protection systems), and EN 50129 (Communication, signalling and processing systems - Safety related electronic systems for signalling) which have been derived from the IEC 61508 standard to meet the specific requirements for the design, development, and assessment of safety-related electronic systems used in the railway industry.

SILs are assigned based on the level of risk associated with a particular system. The risk is determined by the likelihood and severity of a hazardous event occurring. The likelihood is calculated based on the probability of a component or system failure, while the severity is assessed based on the potential consequences of a hazardous event.

There are four Safety Integrity Levels, labelled from SIL 1 to SIL 4: The latter has the highest level of safety integrity and SIL 1 the lowest. The costs increase significantly to reach higher levels of SIL, however the cost of not implementing the appropriate SIL far exceeds the cost of the overall implementation.

The standard associates Safety Integrity Levels with numerical probabilities of hazardous failures for systems that operate continuously like Kavach (

Table 1.1

)

Table 1.1

SIL for Continuous Demand Mode

As the SIL level increases, the Dangerous Failure Rate must decrease accordingly. Therefore, higher SIL levels require a higher level of reliability and safety, and more rigorous design and testing procedures.

1.1

KAVACH

Features

1. Prevention of Signal Passing at Danger (SPAD)

2. Cab-Signaling, Loop Line Speed Control

3. Prevention of Over speed: Section Speed, Train Speed, Permanent Speed Restriction (PSR)

4. Protection of Roll back and Reverse movements

5. Prevention of Side-collision in block section

6. Prevention of Head-on & Rear end collisions

7. LC Gate Automatic Warning

8. Save Our Souls (SOS) Messages

9. Computation of Train Length

10. Shunt Limits Validation

11. Centralized live monitoring of Train movements in Networking Monitoting System (NMS).

1.2

System

and Sub Systems

The brief overview of functioning of KAVACH is as given below:

•The trackside sub-system of KAVACH consists of Radio Frequency Identification (RFID) tags fitted on track in station section and block section for giving Trackside information to Loco KAVACH unit installed in the locomotive. Portions of track including berthing tracks, point and block sections are assigned unique IDs called Track Identification Number (TIN).

•The system also consists of Stationary KAVACH unit installed at Station with radio tower to communicate with locomotives in the jurisdiction of Stationary KAVACH which commence on approach of its first Signal. Stationary KAVACH is interfaced with station interlocking to acquire real-time dynamic information related with signalling such as various signal aspects. Route information of all the signals monitored by a specific stationary KAVACH unit is configured on the basis of KAVACH Control Table (excluding shunt signals and overlaps). Stationary KAVACH unit gets real-time information regarding Locations, Speed etc of various trains in its jurisdiction through UHF Radio Communication.

•Separate Stationary KAVACH unit is provided at Mid–Section interlocked Level Crossing Gate and Intermediate Block Signalling (IBS) locations if they do not come within the coverage of station radio