Lecture 23 Final

CE-363

Lecture 23: Interlocking and

Construction of Track

Dr. Ankit Gupta, Assistant Professor

Department of Civil Engineering

National Institute of Technology Hamirpur

Lecture Outline

Interlocking

Principles of Interlocking

Standards of Interlocking

Methods of Interlocking

Interlocking Devices

Methods of Construction of Track

Interlocking

Definition:

An arrangement of signals, points and other

appliances so inter-connected by mechanical

or electrical locking that their operation takes

place in a pre-determined sequence to ensure

that conflicting movement of signals and

points do not take place and train runs safely

Interlocking

Necessity:

Increase in number of points and signals

Increase in speeds (high speeds tracks)

This makes the arrangement of points and

signals foolproof. Their locking eliminates the

possibility of conflicting movements of trains.

Helps in proper and safe working of the

system.

Interlocking

Interlocking Principles:

It must be impossible to take OFF a signal for approaching train unless the route to which

the train is taking is properly set, locked and

held. At the same time it must be impossible to

operate the points while the train is moving on

it.

This means that points should be set and each

facing point is locked

Interlocking


It must be impossible to take OFF position at one and same time for two fixed signals which

would lead to conflicting movements

Means points and signals are locked against

such movements

Interlocking


It must be impossible for loose wagons to

interfere with the route for which the points are

set and signal has taken OFF position.

Means the levers connecting to points and signals

should be interconnected and operated in a

particular sequence (pulling / putting back)

The route for which the points are set and signal

taken to OFF position should be clear of any obstruction.

Interlocking

Interlocking Standards:

Standard I

Interlocked station has mechanical interlocking.

These are usually branch line stations.

The points are worked by point levers situated near the points, and the signals are worked from interlocking frames in the signal cabin.

Interlocking


Standard I

The mechanisms use keys such that a key obtained from the points mechanism after setting the points must be used on the signal post locking mechanism to pull off the corresponding signal (s) and also to operate the block instrument.

Through running speed for trains is restricted to 50km/h.

Interlocking


Standard II

Interlocked station may be mechanically or

electrically interlocked (usually the latter).

These are usually non-trunk main line stations.

The main running line at such a station can be

completely isolated from the loops and

shunting sidings on both sides.

Interlocking


Standard II

In electrically interlocked systems, setting the

points activates electrical circuitry that enables

or disables the appropriate signal levers and

block instruments.

Through running speed for trains is restricted

to 75km/h.

Interlocking

Interlocking Standards: Standard III

Interlocked station has points and signals that are either interconnected mechanically within the same mechanism, or electrically as with route-relay and panel interlocking.

These are usually stations on trunk routes.

Usually two signal cabins whose signal and points controls are interconnected are provided.

Interlocking

Interlocking Standards: Standard III

These stations usually have the full complement of home and starter signals for receiving and dispatching trains.

Through running speed for such stations is limited only by the speed limit for the section.

The loop lines at such stations have to be completely isolated from the main running line by means such as sand humps, over-run lines, trap points, or derailing switches, etc.

Interlocking


Standard III.I (or III/I)

This is another designation found for some

stations, which indicates that the station is rated as

for Standard III, but the loop lines are not

physically isolated on one side of the station.

Similarly, a Standard II.I (or II/I) station is rated as

in Standard II, but has loop lines or sidings that are

not completely isolated on one side of the station.

Interlocking - Methods

Methods of Interlocking:

Based on the functions to be performed

Key interlocking

Mechanical or electrical methods of interlocking of

signals

For principles 1, 2 and 3.

Track circuiting

For principle 4

Interlocking Methods

Key interlocking

Simplest method of interlocking

Provided with standard I interlocking with speed limit below 50 km/hr

For an example of a main line and a branch line, points can be set for either of the two

The point has two keys Key A: to be taken out when the point is set and

locked for main line

Key B: taken out when point is set and locked for loop line


Key interlocking (Indirect Locking)

At one time only one key can be taken out (depending upon which route is to be set)

Lever frame operating the signals has two levers. Lever for main line can be operated by only key A and similarly lever for loop line can be operated by only key B.

Therefore, if main line points are set and locked then key A is released and used for unlocking main line signal thus bringing it to lower position.


Mechanical Interlocking

It works with lever frames connected by wire to the signals and points

It requires lesser staff and improves safety as compared to key interlocking

It consists of locking frame (signal levers, point levers, point locks), point fittings, plungers, tappets, lock bars, etc. Plungers have notches and tappets are connected to tie bars.



The lever, plunger, tappet and tie bar connection works on Wedge Action

Due to this the tappet moves out of the notch at right angles to the movement of plunger. This movement is transmitted to other tappets.


Mechanical

Interlocking



Principle of interlocking

Signal 1 for main line is operated by lever 1; signal

2 for loop line is operated by lever 2; point (3) is set

for main line by lever 3 (normal position) and for

loop line by lever 3 (pulled position); and lever 4 in

pulled position locks point (3) in both positions

The normal setting of points, signals and levers is

for the main line.

The point will set for main line if lever 3 remains in

normal position and lever 4 is pulled.



Principle of interlocking In normal position of lever 4, tappet D butts against the

plunger and thus not allow tappet B or C to get released

from notch

Pulling of lever 4 brings notch in front of tappet D, thus releasing tappet B or C as required. Also tappet E will move in notch of plunger connecting lever 3

Now after setting point for main line, signal for main line is set to OFF position. For this lever 1 is pulled. This will move tappet A out of the notch of plunger connected to lever 1 and it will enter the notch on plunger related to lever 2. Therefore, lever 2 becomes inoperable (i.e. signal for loop line can not be set to OFF)



Principle of interlocking The movement of tappet A also causes the movement

of tappet F, which moves into the notch of plunger connected to lever 3 thus locking it in position

To adjust the track for branch line

Putting back lever 1 in normal position will allow

tappet A to enter notch on plunger connected to lever

1.



Principle of interlocking

Now lever 3 is pulled to set points for the loop line.

This will cause tappet E to move back and lock lever

4 and tappet F to move out of notch on plunger of

lever 3. this will lock lever 1 due to moving of tappet A

in notch on plunger of lever 1.

Now lever 2 is pulled causing movement of tappet C

in notch and bringing signal to OFF position.


Electrically operated interlocking

In the more advanced electrical or electronic

interlocking schemes, the points and signals are

worked from one integrated mechanism in a signal

cabin which features a display of the entire track

layout with indications of sections that are occupied,

free, set for reception or dispatch, etc.

The interlocking is accomplished not by mechanical

devices but by electrical circuitry -- relays and

switches in older electrical or electro-pneumatic

systems, and computerized circuits in the newer

electronic systems.


Panel Interlocking (PI) is the system used in most medium-sized stations on IR. In this, the points and signals are worked by individual switches that control them.

Route Relay Interlocking (RRI) is the system used in large and busy stations that have to handle high volumes of train movements. In this, an entire route through the station can be selected and all the associated points and signals along the route can be set at once by a switch for receiving, holding, blocking, or dispatching trains.


In recent years interlocking accomplished by modern integrated electronic circuitry instead of electromechanical relay systems has come into use (Solid State Interlocking ('SSI').

By year 2001, SSI was in place at 14 stations in India. SSI equipment is manufactured by RDSO. 247 stations now have RRI installations and the number of stations with Panel Interlocking has risen to 2,426. (Year 2003)

Interlocking

Mechanical Devices for Interlocking

Purposes Ensure that the route is set, proper signal is taken

OFF and route cannot be changed after the signal is OFF.

Hold the route properly at a diverging point.

Ensure that the route cannot be changed while the train is on the point

Ensure correct routing, setting and avoiding conflicting movements.

Interlocking - Devices


Detectors

It at once detect any defect or failure in the

connection between switches and the lever or an

obstruction between stock and tongue rail

The signal remains at danger position and cannot

be taken to OFF position until the defect is set right.

Detectors are used on all points over which signal

controls the train movement.



Stretcher Bar The two tongue rail are connected to each other by

means of two stretchers known as William Patent stretchers

The front stretcher extends under the stock rail to prevent jumping at switches.

Point Lock It ensures that each switch is correctly set

It is placed in the middle of the track, a little in front of the toe of tongue rail.



Point Lock

It consists of two stretcher blades, a plunger, plunger

casing, and a three way crank

The different types are

A bolt and cotter, each individually fitted to switch rail and

padlock or clamp, and a padlock for locking switch rail to

stock rail. (If V < 16 km ph)

Key of approved design for locking each rail independently

(if V > 16 km ph and < 48 km ph)

A plunger type of facing lock (if V > 48 km ph)



Lock Bar Its purpose is to ensure that the point is not

operated while the train in on it.

Therefore, it is little longer that the longest wheel base of any vehicle.

It is provided near and parallel to the inner side of rail.

When the point lock is worked from the signal cabin, the lock bar rises slightly above the rail level and then comes down.



TEMPERATURE

COMPENSATOR



Tappet Locking

Slotting of Signals It is an arrangement in which the lever operating a

signal is in one cabin but the actual taking OFF of the signal requires releasing of a control from another cabin.

Both of these cabins can unilaterally put back the signal to danger position.

The arrangement of slotting is done either electrically or mechanically

Interlocking


Connecting devices Usually consist of 3.8 cm diameter pipe or solid rod

These move on rollers in frames fixed in concrete at 2m to 3m intervals.

The distance between a cabin to points or signals should not exceed 275 meters.

Temperature Compensator Used to neutralize the effect of expansion or contraction

of rods due to variation in temperature

It consist of a pair of cranks (one of acute angle and another of obtuse angle) connected by a pipe.


Three stages:

Earth Work

Formation and consolidation

Plate laying

Laying of railway track

Laying of ballast on the track


Earth Work

Formation

Formation up in embankment is always preferred to a

formation in cutting

Height of embankment above highest water level in the

area should be at least 60 cm.

The economical limit of moving the earth in longitudinal

direction is decided by Mass Haul curve.

Cost of earth work is related to three factors

The type of soil used, Hauling distance, Lift required


Earth Work

Consolidation

Required to pack the track so that larger quantities of

stone ballast are not lost by sinking into loose earth

formation

Addition of admixtures

Compaction using vibratory or impact methods

Small earthen walls 15 cm high are built at an interval of

3 to 4.5 m

Rain water so collected helps in further consolidation

Embankment should be left open for two monsoons

before proceeding to second stage of construction


Plate Laying

The operation of laying out sleepers and rails over the

ready formation is known as plate laying

Placing of ballast is not included here. It ois placed

after two-three monsoon of plate laying

The point from where the laying of the track starts is

known as the base

The point up to which the new track is carried out is

known as the rail head


Methods of Plate Laying

Tramline method or side method

Telescopic method

American method



Tramline method or side method

The name is derived from the temporary tramline laid by

the side of proposed track for carrying out the material

Economical where existing single line track is to be

converted to double line track

Sometimes a road parallel to the proposed track is

constructed for transporting the material at site.

This method is usually adopted in flat terrain

Progress of work is slow, not more than 1.6 km per day



Telescopic method

Extensively used in India

Material is transported in material trains to the

farthest point of new track, unloaded and carried to

rail head



Telescopic method: Operations

Collections and preparation of material at depot

Transportation of material from depot to work site

Unloading of material at worksite and carrying them

to the rail head

Fixing the rails to the sleepers and joining the two

rails with fish-plates

Packing of track for correct level and alignment



Telescopic method: Operations Collections and preparation of material at depot

If due to distance the material train is unable to make a round trip on the same day then a second depot near rail head is established

Preparation of materials like adzing of wooden sleepers etc is done at the depot.

Transporting material to the rail head

Initially when lead does not exceed 1.6 km, the material is transported in trolleys




Transporting material to the rail head

When lead exceeds 1.6 km, the material is

transported by trains

Minimum two sets of wagons and one locomotive is

used for quick and efficient transportation

Unloading of material at the site

Labour known as Material Gang is used for this purpose.

They unload the material and supplies it to rail head.



Telescopic method: Operations Unloading of material at the site

Linking Gang fixes the rails to the sleepers and joins the rails with fish-plates

16 labourers are required to carry one rail

Use of Anderson rail carrier saves this labour and time

Depot should be as near as possible to the rail head, supply should be regular, on-site transportation should be quick

Around 37.5 percent of total labour force should be for material gang



Telescopic method: Operations Fixing and joining of rails

Center line of track is marked by pegs and a string is stretched along that

Sleepers are then placed below string at appropriate spacing

Rail is either marked with chalk or marked rod for sleeper spacing is used

Suitable chairs or bearing plates are provided below rails to attain specified cant




Fixing and joining of rails

Rails on both the sides of the sleeper are fixed one after

the other to maintain gauge. Rail gauge is used to check it

Fixing of rails to the sleepers is continuous

Liners or shims (pieces of metal plates, 1 mm to 4 mm

thick) are used to provide expansion joint between the two

rails. Thickness is controlled by day temperature.

Fish-plates are then placed in position and tightened

Labour force of 37.5% to total labour should be employed

as linking gang




Packing of ballast

Packing gang is employed for this.

They first straighten the newly laid track

Track is brought to required gradient by packing or

removing earth or ballast under each newly laid

sleeper

If there are chances of consolidation, then level of

track is kept higher by a few millimeters than the

actual track level desired



American method: Operations

Machines are used for track laying

Truck mounted, projecting arm or jib

Used for laying the material received at rail head

Wagon mounted, cantilevered arm or jib

Assembled panels of two rails and sleepers required

are prepared in workshop; delivered to rail head;

unloaded by special machine; linked with rail head, till

the required length of track is laid



American method: Operations Laying of ballast on track

Ballast is transported by ballast train and unloaded into a number of heaps at suitable intervals

Packing of ballast to get firm foundation is done using shovels

It can also be done directly by ballast train using a brake van. When train moves slowly the ballast is spread uniformly through openings of wagon floors

Plough is used to spread the ballast uniformly

Documents

Lecture 23 Final