INTERLOCKING AND ISOLATION

INTERLOCKING AND ISOLATION

INTERLOCKING has been defined in the General Rules as an arrangement of points , signal and other appliances operated from a panel or Lever frame so interconnected by mechanical locking or electrical locking or both that their operation must take place in proper sequence to ensure safety. 

Necessity 

• Eliminates the dependence on human element to achieve safety.
• Ensures that signal can be taken “OFF” only after the relevant facing points are correctly set and locked and trailing points are correctly set. 
• Ensures that once the signal has been taken “OFF”, it should not be possible to change the position of the points or unlock them. 
• Prevent conflicting signals.  Increases speed over main line. 

Principles/Essentials: - 

• It must not be possible to take off a fixed signal to receive a train on a line unless 
• All facing points over which the train will pass are correctly set and locked and trailing points are correctly set, 
• Isolations and signal overlaps are correctly set/locked, 
• All points giving access to the running line from the siding / non running line are set and locked against such line, 
• Interlocked level crossing gates are closed and locked against road traffic. 
• It must not be possible to take off the conflicting signal at one and the same time. 
• After the signal has been taken off it must not be possible to move any point or lock on the route including isolation nor to release any interlocked gates unless the signal has been replaced to the ‘ON’ position. 
• Operation of levers/switches must take place in proper sequence. 
• Signal levers/switches when operated must lock or back lock as necessary. 
• It must not be possible to take off the Warner signal until all the relevant Stop signals have first been taken off and when ‘Off’ it must back lock all such signals. 
• When all signals are in the ON position all relative points must be free for shunting purposes. 

Types of Interlocking:-

Direct -When the points and signals are operated directly from one lever frame/panel. 

Indirect – When the points are set and locked from one place and the signals are operated from another place. It is affected by means of keys carried from one place to another.

Necessity of interlocking:-

1) To ensure more safety
2) To increase speed
3) To increase the section capacity

 Normally Interlocking arrangement is between: 

1. Points and Signals
2. Signal and Signal
3. Signal and Gate
4. Signal and Block Instruments
5. Points and block Instruments
6. Key and Key 7. Lever and lever
8. Slide and Signal
9. Slot and Signal Methods -

a) Mechanical :- Direct & Indirect.
b) Electrical :- Using Electrical locks & relays.
c) Hybrid: - Combination of Mechanical &Electrical Interlocking. Using relays.
d) Electronic:- Solid State Interlocking. It uses micro-processors and logic circuits with electronic components. It saves Building construction, relays etc.

Non-interlocked station 
There is no relation between signal, points and other appliances.
Signal can be taken off without correct setting and locking of relevant points and points can be altered before putting back of signal.
Speed over facing points on main and loop line should not exceed 15 kmph.

NON-INTERLOCKED

Modified non-interlocked station

• Developed stage of Non-interlocked station. 
• Home signal cannot be taken off without proper setting and locking of points at the approaching end and Outer signal cannot be taken off before taking off Home signal. 
• But, Home signal cannot give the guaranty of the points at the trailing end. 
• Speed over facing points on main and loop line should not exceed 15 kmph. 
• Points are locked by Triples Hand Plunger Key-lock.
• 
  

Interlocked station 

• There is a relation between signal, points and other appliances such as L.C. Gate, Track circuit, lock bar, detector etc. 
• A signal cannot be taken off until the relevant points are correctly set and locked and interlocked L.C. Gate is closed against the road traffic. 
• The relevant points cannot be altered and the interlocked L.C. Gate cannot be opened until the signal has been put back to ON. 
• Speed over facing points on turn out, cross over and loop line is generally not exceeding 15 kmph; but under approved special instructions speed over loop line may be exceeding 15 kmph. 

Panel Interlocking 

• All points and signals at a station are worked by the switches/push buttons provided at the panel in the SM’s room. 
• The lay-out of the station is indicated on the panel. 
• The route which is set is indicated on the panel by appearance of white light on the signaling section concerned. As soon as the train enters a signaling section, red light is indicated on the section. 
• Provided in ASM’s room and operated by ASM/SM on duty. 
• No staff except SM/ ASM on duty shall operate the panel. 
• Indications of signal, points and lines are shown in the panel. 
• There is considerable time saving in the train operation at a panel interlocked station. 
• SM himself controls the operation of point and signals and no co-ordination with the cabin man or lever man is required as is the case in mechanical signaling. 
• Panel interlocking also result in the considerable saving of staffs such as lever man, cabin man, etc.. 

Route Relay interlocking 

• The entire geographical diagram is drawn on a single panel board. 
• A number of buttons of different colors are used for different operations as follows-

              Blue- Points
              Red- Signals
              Grey- Routes
              Yellow- Shunt Signals

• All the points, isolations of a route are set and locked at once on a single operation of concerned route button and signal button within a short period of time. 
• Provided for major yards and large junction stations where the traffic is busy. 
• Provided in ASM’s room and operated by ASM/SM on duty. 
• No staff except SM/ ASM on duty shall operate the panel. 
• Indications of signal, points and lines are shown in the panel. 
• Operation of signal and concerned route button set and lock the desired route automatically and clear the signal.
• Facilities like taking ON the signals, cancellation of the route already set, taking OFF the calling-on signals to receive train on an obstructed line, operation of points even in case of track down, cancellation of signal overlap etc. are also the important advantages of RRI. 
• Whole of the lines are track circuited and they are divided into smaller part on the panel so that any defects in the track circuit can be easily detected. 
• Any defects can be detected by audio visual indication on the panel. 
• The route in the rear of the train is automatically cleared on the progress of train on the route so that other train may be allowed to proceed.

Solid State Interlocking

• Micro-processor (computer) based interlocking. 
• Provided in ASM’s room and operated by ASM/SM on duty. 
• No staff except SM/ ASM on duty shall operate the panel/ computer. 
• Indications of signal, points and lines are shown in the panel/ monitor of the computer. 
• It saves building construction and relays. 
• Ensures greater safety at less expense 

DETECTOR: 

It is an appliance, provided at the facing points to ensure the points being correctly set before the relevant signal can be taken off. There are mechanical and electrical detectors. Mechanical detectors are of two types –Box (Slide) type and Rotary type. Detector also prevents the points being moved until the relative signal has been put back to ‘ON’. Electrical detector gives the visual indication in Panel/Lever frame (Normal/ Reverse).

Track Circuit 

Whenever a train or vehicle entries on a track which is provided with continuous track circuit, the presence of the train/vehicles on the track is immediately known due to short  circuiting of the track circuit by the axles of the locomotives/vehicles. The interlocking is so controlled electrically that the signals for a signalling section which is already occupied by a train or vehicle cannot be taken OFF for the movement of any other train or vehicle till the signalling section is clear. The track circuiting, therefore, ensure that two trains cannot enter the same signal line section simultaneously.

Axle Counter

Axle counters are fixed at specific locations in the track so as to count in and count out the numbers of axles of the vehicles passing over them. An Axle counter fixed near the Advance Starter will count the total number of axles of a train which is despatched from that particular station. The axle counter fixed near the home signal of the station in advance at the end of the Block Section will count again the total number of axles when the train is received at the station in advance. Both the axle counters will be so electrically connected that the number of axles “counted in” at the station in rear should tally with the number of axles “counted out” at the station in advance for the same train. This will ensure complete arrival of the train at the station in advance and that no portion of the train is left behind in the section. Axle Counter may also be fixed at the entrance and exit of a running line. This will indicate that a train which had been received on that line has cleared that line without leaving behind any vehicle on the line.

Difference between Track circuit and Axle counter

Block Proving Axle Counter:

 1. Block Proving Axle Counter for last vehicle check is provided at station for ensuring clearance of block section as well as to ensure the complete arrival of train.

2. It is a device for ‘In-count’ of axle when a train passes over the transducer provided near Advanced Starter signals / Commencing point at block section entry point at sending end station and for ‘Out-count’ of axle when a train passes over the transducer provided near Advanced Starter signals / terminating point at block section clearance point at receiving end station . The Block Proving Axle Counter is interlocked with the concerned Block Instrument.

3. The SM on duty at station provided with BPAC shall ensure complete arrival of the incoming train by seeing the ‘Green’ indication on ‘Reset Box’ of BPAC. If the ‘In-count’ and ‘Outcount’ of the axles at the entry end and exit end are equal , a ‘Green’ indication will be displayed in the ‘Reset Box’ and which indicates that the nominated portion of track between two detection points is clear of any obstruction. After acknowledging the ‘Green’ indication by pressing the acknowledgement button, the concerned Block Instrument can be normalized.

4. When the BPAC fails , a ‘RED’ indication will appear on the ‘Reset Box’ concerned Block Instrument also fail in that case the SM on duty must obtain complete arrival certificate from the Guard of the train on T/1410 then shall informed details to the SM at the other end under exchange of private number .

5. The SM on duty after ensuring the block section is clear then inserts resetting key turn clockwise and presses the key along with the resetting button and record the counter number on the appropriate register. After getting this information from the other end, the SM on duty at the other end shall do the same resetting operation and preparatory green indication will appear after few seconds at both ends.

6. However the first train must be passed with PLC T and T/369(3b) for the last stop signal and concerned Starter Signal. After the train has cleared the portion being monitored by the axle counter, the section clear Green indication will appear at the resetting box and the axle counter system is resumed. Reset Box consists of reset button, counter and indications.

7. If by above procedure, the axle counter is not restored and the green indication does not appear in the reset boxes, this should be reported to the concerned JE/SE/SSE (Signal) of the section on written message for rectification and PLCT working shall be continued.

8. Reset Box:- Reset Box consist of reset button , counter and indications. The following indications are provided in the Reset Box :-

 i. Red for ‘ Occupation of track ’

 ii. Green for ‘ Clearance of track ’

iii. Preparatory green for reset operation.

iv. Yellow for ‘ Power on ’

N.B:- The Key of the reset box shall be kept locked in a separate box with Station Master on duty under his personal custody.

DATA LOGGER- 

It is such a system based on computerization that saves all the activities and real time operations of the panel and RRI. Introduction of this system in train operation makes it more transparent and any controversy during the train operation can be settled easily by this system.

ISOLATION 

To prevent collision between trains while the same are being received or running through a station, the running lines are normally isolated from the adjoining lines. This ensures that while a train is being received on a running line or is running through the same, it will not be possible, even by mistake to foul the passage of the train by the other operations such as shunting etc. The various methods of providing isolation are as follows

1. De-railing Switch,
2. A Sand Hump of approved design,
3. A siding of adequate length (short dead end and long dead end)
4. Scotch Block

Note- the sand hump/long dead end are used for simultaneous reception of train and on double line, simultaneous dispatch train on the main line and reception of train on the loop line.