Interlocking In Railway And Their Methods

This Article Covers About Principle Of Interlocking In Railway With Various Methods One by One.

Interlocking In Railway

Interlocking is a device or a system meant to ensure the safety of trains. With the increase in the number of points and the signals and introduction of high speeds

it has become necessary to eliminate human error, which would otherwise lead to massive losses of life and property.

The points and signals set in such a way that the cabin man cannot lower the signal for the
reception of a train unless the corresponding points have set and locked.

The signal thus interlocked with the points in a way that no conflicting movement is possible and the safety of trains ensured.

Interlocking may therefore, defined as a technique, achieved through mechanical or electrical means by which it ensured that before a signal is taken ‘off, the route which the signal controls properly set, locked and held till such time the entire route traversed by the train and at the same time all the signals and points, the operation of which would lead to conflicting movements, are locked against the feasibility of such conflicting movements.

The signal and interlocking systems designed that the failure of any equipment results in the
turning ‘on’ of the signal, thus ensuring train safety.

Essentials of Interlocking

Lever frames and other types of equipment provided for the operation and control of signals, points, etc, must interlocked and arranged as to comply with the following essential regulations

  • It should not possible to turn a signal off unless all points for the line on which the train is to received correctly set, all the facing points locked, and all interlocked level crossings closed and inaccessible to road traffic.
  • The line should fully isolated before the signal turned off, i.e., no loose wagons should be able to enter this line.
  • After the signal has taken off, it should not be possible to make adjustments in the points or locks on the route, including those in the isolated line. Also, no interlocked gates should, released until the signal replaced to the ‘on’ position
  • It should not be possible to turn any two signals off at the same time, which can lead to conflicting movements of the trains.
  • Wherever feasible, the points should interlocked as to avoid any conflicting movement.

Standards of Interlocking

The speed of a train depends on a number of factors such as the haulage capacity of the locomotive, the fitness of the track, the fitness of the rolling stock, the load of the train, the ruling gradient and standard to which the signalling system is provided.

Signaling arrangements

The signalling equipment, manner of locking points, and operation of signals and points differ in the different standards of interlocking.

The types of signalling equipment provided at different interlocked stations and other requirements to met for each of the four categories do differ.

Locking of points

The method of locking of points is the key locking in Standard-I. It is an indirect method of interlocking between signals and points. In Standard-II, a plunger type facing point lock used.

The plunger lock can operated from the cabin or from the site itself. In standard-Ill and IV, the points to centrally operated and the locking between points and signals required to be direct.

Isolation of lines

In Standard-I, isolation is optional. In Standards II, III, and IV, the main line must isolated from all the adjoining lines.

Methods of Interlocking In Railway

There are basically two methods of interlocking as explained below.

Key Interlocking

Key interlocking is the simplest method of interlocking and still exists on branch lines of small stations on Indian Railways. The method involves the manipulation of keys in one form or the other.

This type of interlocking is normally provided with standard interlocking with a speed limit below 50 km per hour.

The simplest arrangement of key interlocking accomplished in the following manner.

  1. Take the example of a station with a main line and a loop line, the point can set either for the main line or branch line.
  2. The point has two keys, the first is key A, which can taken out when the point set and locked for the main line. Similarly, key B can taken out when the point set and locked for the loop line. At any given time either key A or key B can taken out, depending upon whether the route set for the main line or the loop line.
  3. The lever frame operating the signals is provided with two levers. The lever concerning the main line signal can operated only by key A and similarly the loop line signal lever can operated only by key B.
  4. If the train received on the main line, the points set and locked for the main line and key A released. This key used for interlocking the main line signal lever, thus lowering the signal for the main line. Since key A cannot used for interlocking and lowering the loop line signal, only the appropriate signal can taken off. This type of interlocking called indirect locking.

Mechanical system of interlocking in railway

Almost 70 per cent of railway stations in the country work with the mechanical system of signalling. The interlocking arrangements for mechanical signalling system have to mechanically oriented.

Two systems of mechanically designed signals:

  • Single-wire system and the
  • Double-wire system.

A mechanically structured signal has (i) spectacle with an arm; (ii) signal post, which may be tubular or lattice.

Longer posts chosen to be lattice; and (iii) a counterweight to help pull the wire back to allow the signal to go back to its on/normal position.

Such mechanical structures of signals are: (i) two-aspect semaphore signal and (ii) multiple aspect semaphore signal.

Mechanical interlocking or interlocking on lever frames is an improved form of interlocking compered to key locking.

Electrical system of interlocking in railway

As the signal displays fixed light illuminated by incandescent lamp or a light emitting diode (LED) signal,

The operation of such system may through mechanically operated levers or by push buttons provided on the yard layout depicted on the top of panel box to be termed as the control cum indication panel.

Under the electrical signalling system the colour light signals used in any case operated by lever, points

  • operated by wrought iron solid 33 mm rod;
  • operated by electric point machines

or operated by Control cum Indication Panel operating points by an electric point machine with signals coloured light.

The system of operation of electrically operated signals by levers is hybrid and invariable an interim measure to suit 25 kV ac traction, to subsequently converted to operation by control-cum indication panel.

Typical Cases of Interlocking In Railway

The following typical cases of interlocking usually encountered.

Normal Locking

Normal locking In this case, pulling one lever locks the other lever in its normal position. Such locking shall required in situation like the signal lever locking a point lever, when the signal requires the point to moved for train movement.

Back Locking or Release Locking

Back locking or release locking In this case, when the lever is in its normal position, it also blocks the other lever in its normal position

but when this lever is pulled it releases the other lever, which can then be pulled.

Furthermore, once the second lever is also pulled, the first lever gets locked in the ‘pulled’ position

And cannot be returned to its normal position unless the second lever is restored to its normal position.

Both-Way Locking

Both-way locking In this case, once a lever is pulled, it locks the other lever in its current position that is, in the normal or pulled position.

Such type of locking is normally required in situations when the lock on point is to lock the point in either position.

Here, if the point is to be locked in normal condition, the point lever shall get locked as it is by pulling back the lever.

Special or Conditional Locking

Special or conditional locking In this case, the pulling of one lever locks the other lever only when certain conditions are fulfilled, say the third lever being in a normal or pulled position as the case may be.

Such a locking normally required when a signal leads to more than one route.

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