BASIC CONCEPTS OF SIGNALLING, AND INTERLOCKING. Signaling in Indian Railways ensures safe running of trains. Unlike road transport, where two vehicles cross easily, on railway track it is not possible to cross two vehicles on the same track. This has lead to block station, where a point is inserted in the running line. “Point” is a place where a train is diverted from one line to another line. Depending upon the need of the traffic, there may be more than two lines in a block station. To inform the driver on which line he is being received has lead to signaling system. Set of signals which lead a train in to the station is called as “RECEPTION SIGNALS”, and the set of signals which lead a train out of station are called “DISPATCH SIGNALS”. Apart from these two categories, there is a need to have signal which guide the train in the station for shunting purpose. A signal is not independent equipment. It is depending upon various other equipments, and systems like point, track circuit, locking of the point etc. In the following pares let us discuss about these equipment and system in detail. TYPES OF SIGNALS. Main Signals. Subsidiary signals. Hand Signals. Detonators. Signals are generally displaying danger aspect. This danger aspect is called as “ON” position of the signals. When a signal displays other than ‘ON’ aspect, either ‘Yellow’ or ‘Green’, it is called as “OFF” aspect of the signal. There are some signal which are generally displaying “ON” aspects, and are called as “STOP” signals. The
driver of the train is not supposed to pass such ‘Stop’ signals at ‘ON”. There are few more signals, which can be passed at ‘ON’ and are called as “Permissive signals’. MAIN SIGNALS.: As the name indicates, Main signals govern the movements of trains between two block stations. SUBSIDIARY SIGNALS.: Subsidiary signals are generally movements of a train within the station.
govern
the
Hand signals and Detonators are used for specific purpose, and are beyond the purview of this discussion.
SYSTEMS OF SIGNALLING.: 1. Lower Quadrant Signals, 2. Upper Quadrant Signals. These two types of signals are shown to the driver either in the form of a ‘Physical Arm’- which is called as “SEMAPHORE SIGNALLING”, or in the form of COLOUR LIGHT SIGNALLIN”
LOWER QUADRANT SIGNALS: RECEPTION SIGNALS. 1. Warner signal. - Permissive Signal. 2. Outer signal. - Stop Signal, and a First Stop Signal. 3. Home signal -Stop Signal, and a Second Stop Signal. DISPATCH SIGNALS. 4. Starter signals. -Stop Signal,
5. Advanced Starter. Signal
-Stop Signal, and Last Stop
UPPER QUARDRAN SIGNALS. RECEPTION SIGNALS 1. Distant signal. 2. Home signal. Signal.
-Permissive Signal. -Stop Signal, and a First Stop
DISPATCH SIGNALS. 3. Starter signals. -Stop Signal, 4. Advanced Starter.-Stop Signal, and Last Stop Signal SUBSIDIARY SIGNALS. 1. Shunt signals. - Used for shunting in the station. 2. Calling on signal. - Used for specific purpose. 3. Co-acting signals. - Used for specific purpose. 4. Repeater signals. - Used as repeaters (only in LQ) COLOUR LIGHT SIGNALLING A colour light Distant signal shall be provided with “P” marker, to facilitate the driver to identify it as a ‘Permissive signal’ in case of signal becoming blank. Shunt signals are of position light type in colour light signaling system. Calling-On signals are provided “C” markers.
OVERLAPS. To ensure safety in running the trains an adequate distance is kept free ahead of the signal or block section.
In the signaling system mainly there are two overlaps are referred to as “Signal Overlap” and “Block Overlap” Signal overlap carries importance while taking ‘Off’ a signal. The ‘signal overlap’ to be kept clear before a signal is taken ‘Off’. Block overlap carrier importance while granting line clear to a train approaching the station. The block overlap should be kept clear before the line clear is granted. Depending upon the type of signaling the distance of both these overlap varies. MISCELLNEOUS SIGNALS. Apart from above discussed signals there are few signals which are used in Railways. GATE SIGNAL: Used for interlocked level crossing gates, when the signal is protecting only the level crossing. The gate signal is provided with “G” marker, so that the driver of the train can pass the signal when it is at “ON”. AUTOMATIC SIGNALS.: These signals are provided in Automatic Signaling Territory. Automatic signals are provided with “A” marker, so that the driver can pass the automatic signal at “ON” duly following some rules. INTERMEDIATE BLOCK SIGNALS: IBS are provided on double line section. They are provided with “IB” markers, so that the driver can pass the signal duly observing some rules. STATION SECTION:
The area between two advanced starters (last stop signals) of a station is called as ‘Station Section’. Shunting can be performed in the station section. The station section also plays an important role in classifications of stations. STATION LIMIT: An area between the outer most signals of the station is called as ‘Station Limit’. The station master is an authority for the station limit.
CLASS OF STATIONS: Stations are classified based on availability of station section, shunting in the face of an approaching train, line to be kept clear before granting the line clear etc. There are four class of stations viz. A, B, C, D. Out of which ‘D’ Class station is called as cattle crossing, and is not provided any type of signals. ‘A’ class stations are provided under special conditions, where shunting in the face of an approaching train is not permitted. There is no separate station section in ‘A’ class station. Maximum stations are classified under ‘B’ class stations. There is ‘Station Section’, and shunting in the face on an approaching train can be performed. ‘C’ class stations are provided for increasing line capacity. STANDARDS OF INTERLOCKING: Standards of interlocking determines the maximum speed of a train through a facing point in a station, when a train is being received on main line. To suit the speed of the train on the facing point, safety equipments are standardized. Standards of interlocking also determines
type of signaling, operation of points, locking of points, detecting of points, isolation etc. There are four types of standards of interlocking. PRINCIPLES OF INTERLOCKING: Principles of interlocking ensures safe operation of signals. These principles by and large are applicable to any type of signaling. Interlocking is a sequential operation of different equipments like points, lock, level crossing gate etc. before a signal is taken ‘OFF’. The principles are discussed broadly in the following paras. The conditions discussed should be fulfilled not only in the route of the train but also in the overlap. Overlap is an adequate distance kept for safety. There are two types of overlaps namely, “Block Overlap” and “Signal Overlap”. • A signal cannot be taken “OFF” unless all points are set including isolation, all facing points are locked and all level crossing gates are closed and locked for the road traffic. • Once the signal is taken “OFF” it should not be possible to operate any point including isolation, un lock the facing point and open the level crossing gate for the road traffic. • It should not be possible to take “OFF” any two conflicting signals at the same time. • It should also not be possible reverse any two conflicting points at the same time Irrespective of type of signaling the above principles of interlocking have to be fulfilled. In Mechanical signaling it is achieved by interlocking different levers operated from the cabin. In Relay interlocking it is achieved through relay interlocking, and in Electrical Interlocking it is achieved through microprocessors. BLOCK SYSTEMS.
To run many trains on the given section, entire stretch of track is divided in to smaller sections by introducing “Block Stations”. The distance between any two adjacent ‘Block Station’ can be any where between 5 Km to 15 Km depending upon the requirements. To ensure safe running of trains between these block stations, “Block System” have been evolved. On ‘Indian Railway’ mainly two types of block systems are employed. 1. Absolute Block Working: This system is used on single
line and on double line. The system is supported by a “Block Instrument”. The system ensures that one train at a time in the block section. An authority is issued to the driver to enter the block section called as “Line Clear” 2. Automatic Block Working: This system is used in busy
sections where number of trains are more. The signals are governed and operated by the passage of the train. No authority as “Line Clear” is issued to the driver.
