dc track circuit - rdso.indianrailways.gov.in

Maintenance Instructions
1.0 Introduction ........................................................................................................................ 1
3.0 Classification of DC Track Circuits .................................................................................... 2
3.1 DC Track Circuit (Closed type) ...................................................................................... 3
3.2 DC Track Circuit in Non- RE Area ................................................................................. 3
3.3 DC track circuit in RE area ............................................................................................. 7
4.0 Insulation material for point turnouts in track circuited area .............................................. 10
5.0 Important parameters of DC Track Circuit ........................................................................ 12
6.0 Fail safe adjustment of Track Circuit ................................................................................ 14
7.0 Relay end voltage under different conditions ..................................................................... 15
8.0 Maintenance ..................................................................................................................... 15
9.0 Joint Inspection of Track by S&T and Permanent Way Inspector ...................................... 20
10.0 Prevention from stray currents in Single Rail DC Track Circuit......................................... 20
11.0 Installation of point machine in track circuited area to the negative polarity rail side ......... 22
12.0 Monsoon precautions ........................................................................................................ 23
Maintenance Instructions for D.C. Track Circuit
1.0 Introduction Track Circuit is a low powered electrical circuit in which running rails are used as a part. With the help of track circuit, one can easily identify whether the particular section is clear or occupied by a train/vehicles or Track Circuit is in failed condition. It is highly reliable for effective and safe running of trains. A DC track circuit has mainly two ends i.e. feed end and relay end. A track circuit gives two indications on the Indication panel: Yellow/White/No light indication - When track circuit portion is clear i.e. when line is
unoccupied. Red indication - When track circuit portion is occupied by a vehicle or track circuit is
in fail condition.
2.0 Requirement of maintenance in DC Track Circuit Although DC Track circuits are highly reliable for effective and safe running of trains, there are several factors which affect the performance of DC track circuits. For smooth and safe functioning of track circuits, preventive as well as periodical maintenance of its components and associated items whether pertaining to S&T or other departments must be done. Apart from this failures due to outside interference or miscreant activities are not ruled out. Following are the items related to DC Track circuits for which maintenance is required:
(a). Power supply
Power supply equipments in power equipment room for supply of feed to the track feed charger at site. Any failure of power supply system may affect the batteries kept in location box at site.
(b). Location box Periodical checking of condition of location boxes and intactness of locks at site to avoid
damage to them and theft cases. (c). Track Relay Maintaining specified range of voltage at relay terminals and periodical replacement of
relay for safe operation. (d). Track feed charger & battery Maintaining specified Track Feed voltage and battery charging current. Maintenance of
secondary battery in location box. (e). Cables Periodical meggering of main and tail cables to minimize cable faults. (f). Bond wires/Jumper connections and Track lead wire ropes Track circuit continuity bond wires and Track lead wires connecting feed end and relay
end when broken due to rust or during P. Way or Electrical traction work at site are major source of failure. Hence these are to be checked on every visit.
CAMTECH/S/PROJ/2019-20/SP6A 2
Maintenance Instructions for DC Track Circuit March 2020
(g). Traction bonds Various types of bonds provided by Electrical Traction department are to be checked for
their intactness and rigid connection with rail to avoid the possibility of high resistance. (h). Insulation rail joint & glued joint Insulation material in insulation rail joints are prone to damage if the packing of sleepers
on either side of them is loose, creep in rail, fish plate bolts are bent or loose or due to frequent movement of trains. Formation of iron burr, or dropping of iron dust or iron filing over both insulation rail joints and glued joints are likely sources of failure of track circuits. Hence burrs are to be cut and iron dust/filings are to be cleaned frequently. Change of rail connected to insulation rail joint/glued joint by P.Way staff is also required to be attended by S&T staff or disconnection and reconnection.
(i). Track lead junction box
TLJBs are in the vicinity of track and are prone to damage during P. Way work. Hence need attention.
(j). Insulation in point zone Insulation materials in track circuited point turnout portion for gauge tie plate and point
rodding/ground connections are to be checked periodically to prevent track circuit failure and replaced whenever required.
(k). Ballast, ballast resistance and drainage Clean ballast and specified ballast resistance is required to be maintained throughout
track circuited portion. Water logging, mud and muck result in failure of track circuit hence proper drainage is to be ensured.
(l). Train shunt resistance (TSR) TSR is to be maintained to ensure proper shunting of track by Motor trolley, Light
engine or Train. Hence to be checked periodically.
The important parameters of DC Track Circuit, their specified range and maintenance guidelines are given in the following sections.
3.0 Classification of DC Track Circuits Based on normal status of track relay.
(i) Open track circuit (ii) Closed track circuit
The Open Track Circuit is a normally de-energised track circuit. The circuit gets completed when the track is occupied through the net resistance of the vehicle axles occupying the track circuit. This not used currently as any break in connection goes undetected which is unsafe. Closed DC Track circuit is used on Indian railways which is normally in energised condition and de-energises when occupied by a vehicle or train. Based on use of one rail or both rail for passage of track circuit current.
(i) Single rail track circuit used in RE areas. (ii) Double rail track circuit used in Non- RE areas.
Single rail track circuit In RE area, single rail track circuit is used where one rail carries traction return current and other rail carries positive polarity of DC track circuit. This positive polarity rail is insulated from either side. It is also used in NON-RE area, where special condition exist, such as in a yard on point and crossings as it is cheaper. Double rail track circuit In double rail track circuit both the running rails are insulated from adjoining sections by insertion of block joints.
Double rail track circuits shall be provided on non-RE areas, as far as practicable. Single rail or double rail type as convenient may be provided in RE areas. (SEM Part II Para 17.1.2)
3.1 DC Track Circuit (Closed type) A closed type D.C. track circuit has two ends i.e. feed end and relay end. Both the
ends are insulated by a Nylon joint or glued joint. Feed end is connected to power source and relay end is connected to track relay.
Fig. 1: Closed type DC Track Circuit
The circuit is completed by positive and negative feed going through separate rails
from feed end and coming to relay end to pick up the connected track relay Track relay will be in de-energised position under following conditions :
A vehicle occupies any part of the track circuit or Rails removed or Rails clearly broken or It is short circuited by any means.
Otherwise track relay will be in energised position. Since it is a vital safety circuit, hence installation is to be made according to the approved
interlocking plan.
3.2 DC Track Circuit in Non- RE Area Following are the main parts of a DC track circuit in Non-RE area:
(a) Relay
Relay must conform to British Standard Specification No.1659, unless otherwise specially permitted. The approved type issue relays are Shelf type Q series type
The resistance of the track relay should be 9 ohm for the length of track circuits up to
and less than 100 Mtrs.
The resistance of the track relay should be 2.25 Ohm for a length of track circuit above 100 Mtrs. if the track is laid on wooden sleepers and 9 Ohm if laid on concrete sleepers.
(b) Track Feed Power supply given to DC track circuit at feed end Approved type of primary cells or lead acid secondary cells shall be used. Where primary cells are used, two batteries in parallel shall be used to increase
reliability. Where secondary cell(s) is/are used, they shall be used with battery charger/solar
panels of adequate capacity. Track feed battery charger shall conform to specification no. IRS S 89 – 2013 Rev. 1.
Separate feed shall be provided for each track circuit. The polarity of a DC track circuit must differ with adjacent DC track circuit.
Fig.2: Track Feed Battery Charger
(c) Adjustable Resistance 0-15 ohm This resistance is used at power source and feed end voltage is adjusted according to the condition of ballast and pickup voltage of track relay.
(d) Cables
The cable from feed location/cabin to feed end junction box and relay end junction box to relay location should preferably be made of copper conductors of min. 2.5 Sq.mm. cross-section.
(e) Bond wires
A straight track portion of welded rails does not need any special means to enhance its conductivity. But if smaller panels or individual rails are to be included, the ordinary fish plated and bolted joints themselves cannot give good electrical continuity. In such cases, the rails are to be connected with continuity Rail bonds. Bond wires shall be of an approved type or 8 SWG
GI bond wires may be used for rail bonds. These bond wires are fitted with channel bond pins,
which have grooves to hold the wires. It is desirable to used bond wire clips to secure the
bond wired. (f) Insulation Rail Joint Two types of insulated joints are presently in use :
Nylon insulated rail joints [Supplied by S&T dept.]
For one Nylon insulation joint, following insulation components are required as shown in Fig. below : 1. Bushes - 8 nos. 2. End post -1 no. 3. Channel side plate LH - 2 nos. 4. Channel side plate RH - 2 nos 5. Nylon insulating plate - 4 nos. 6. Steel backing plate - 4 nos.
Fig. 3: Insulated rail Joint and its exploded view
Glued joints [Supplied by Engg. dept.]
Glued Rail Joints are available in two types: (a) G3 (L) type consisting of 6 bolts (b) G3 (S) type consisting of 4 bolts These are available in various sizes to suit Rail sections of 90 R, 52 kg., 60 Kg. etc.
Fig. 4: Glued Joint on PSC sleepers
(g) Track lead junction box (TLJB)
Track Circuit is provided with two track lead junction boxes, one at feed end insulation joint and another at relay end insulation joint. Jumpers are used for connecting track feed to rails from feed end junction box. Similarly jumpers are used for connecting rails to relay end junction box. Cable from power source and feed end jumpers are terminated in feed end junction box. Similarly cable from track relay and relay end jumpers are terminated in relay end junction box. As far as possible TLJBs consisting of 2 terminals and single support should not be used.
Fig. 5: TLJB with 2 terminals and single support
1
2
3
4
TLJBs with two supports in the ground and consisting of 4- way terminals as per RDSO specification no.RDSO-SPN-151-1997 should be used.
Fig. 6: TLJB with 4 terminals and 2 supports
Advantages of 4 terminal TLJB: Refer Fig. 7 below. Cable from location box is terminated on two terminals i.e conductor carrying +ve polarity on terminal no.1 & -ve polarity on terminal no. 3). Terminal no. 1-2 & 3-4 are made parallel with wire loops at both ends so that if there is break in one of the terminals the other is available. Track lead wire ropes connected to track are terminated at other end of if TLJB terminals. Double wires are used for both +ve and -ve track lead wire ropes so the if one of the wire breaks the feed is continued through other.
TRACK LEAD JUNCTION BOX
Wire loop
Fig. 7: Wiring arrangement in 4 terminal TLJB
Typical Parameters Of D.C Track Circuits in Non-RE area
3.3 DC track circuit in RE area In RE area, all parts are similar to that of Non-RE track circuit, except choke & relay.
Choke B type 0-3 ohm, impedance 120 ohm. This is used for the safety of track circuit. This prevents damage to the feed source at the time of a catenary snap resulting in heavy currents in un-insulated rail. The "B' type choke shall conform to specification no.IRS S 65 – 83 Ver 2.
Fig. 8: 'B' type choke Relay
Relay must be AC immunised. Track relay resistance must be 9 ohms only for any length of track circuit. Plug in type AC immunized Track relay QTA2 with 2F/2B contact configuration instead of 2F/1B should be used for availability of spare contacts. QTA2 Relay shall conform to BRS Spec. 939A and 966 Appendix F2.
Fig.9 : QTA2 AC Immune DC Track Relay
Type of Relay
Resistance of Track Relay (L= Length of the Track Circuit)
Cells at Feed end
Non ACI shelf type
For L < 100 m → 9 1 cell (2 V) 0.4 V 40 mA For L > 100 m → 2.25 1 cell (2 V) 0.2 V 80 mA
Non ACI Plug in Type (QT2)
For L < 100 m→ 9 1 cell (2 V) 1.4 V 150 mA For L > 100 m → 4 2 cells (4 V) 5.4 V 125 mA
The layout of a typical Single rail DC Track Circuit is given below:
Fig.10: Arrangement of DC Track Circuit in RE area
Components
1. Battery charger 110V /2-10V D.C 2. Feed Battery (1 to 4 secondary cells3) 3. Fuse & link (5A / 250V). 4. Regulating Resistance (adjustable) 0-30 5. Type 'B' choke (R=3 & Z= 120 at 50 Hz). 6. Track lead cable (2 X 2.5 sq mm copper).
7. Track lead J.B 8. Track lead steel wire ropes 9. Transverse bonds 10. Block joints. 11. Track Relay (ACI). 12. Continuity Bonds.
Typical parameters of DC Single Rail Track Circuits in 25 KV AC RE Area Type of Track Relay
Track Relay Resistance
PU Current Approx
ACI Shelf type
ACI Plug in Type QTA2
9 2 cells up to < 100m 3 cells > 100 m
1.4 V 140 mA
ACI Plug in Type QBAT
9 2 cells up to < 100m 3 cells > 100 m to 450m 4 cells up to 750m
1.75 V 175 mA
Note: Continuity bonds are provided to give good electrical continuity at ordinary fish plated and bolted joints. In every adjacent track circuit the polarities are reversed to avoid extension of feed of one track circuit to another in case of failure of insulation joint. Transverse bonds are provided to give continuity of traction return current through negative polarity rail which is staggered for every adjacent track circuit. Both type of bonds are provided by S&T and Electrical Traction departments. Bond wires provided by S&T deptt. shall be 8 SWG GI wire or of approved type and those provided by Traction deptt. shall be mild steel flats of not less than 200 mm2 cross sectional area.
As per SEM Part II Para 17.15.5, the permissible lengths for different types of track relays are shown in table below.
Sr. No.
TSR in
1 Non- RE
Wooden/ PSC
Block 4 0.5 1000 m QT2 of 4 or 9 / Shelf type track relay of 2.25 or 9
If L ≤100m, 9 QT2 or Shelf type Track relay.
If L>100m, 4 for QT2 or 2.25 for Shelf type Track relay
2 Wooden/ PSC
Yard 2 0.5 670 m QT2 of 4 or 9 / Shelf type track relay of 2.25 or 9
If L ≤100m, 9 QT2 or Shelf type Track relay.
If L>100m, 4 for QT2 or 2.25 for Shelf type Track relay.
3 RE Wooden/ PSC
Block 4 0.5 450 m QTA2 / Shelf Type 9 AC Immunised Track Relay
QSPA1 Relay shall be used as a 1st repeater relay for QTA2 Track Relay.
4 Wooden Yard 2 0.5 450 m QTA2 / Shelf Type 9 AC Immunised Track Relay
5 PSC Yard 2 0.5 350 m QTA2 / Shelf Type 9 _ AC Immunised Track Relay
6 PSC Yard 2 0.5 750 m QBAT (ACI level = 80V AC, PU. 1.75 V, 175 mA ) in conjunction with QSPA1 With B-type Choke at relay end.
QSPA1 Relay shall be used as a 1st repeater relay for QBAT Track Relay.
Note :- (i) B type choke shall be connected in series with the relay also for its protection to
enhance the AC immunity of the track relay. (ii) In the case of shelf type ACI track relay with this choke in series, 450 m long
track circuit can be worked even with traction return current up to 1000 Amps. Without this choke, 450 m long track circuit can be worked only when the traction return current is within 600 Amp
4.0 Insulation material for point turnouts in track circuited area
William stretcher bars Nylon Backing plates 2 Nos. Nylon bushes for bolts 3 Nos. Nylon washers for bolts & nuts 6 Nos Gauge tie plates Nylon end post with 3 holes 1 Nos. Nylon bushes for bolts 3 Nos. Nylon washers for bolts & nuts 6 Nos. Electrical detectors provided on mechanical points Between Detector rods and drop links 1 bush & 2 washers per rod IRS type & Siemens point machine Between tongue rail and tongue attachment (D bracket) Nylon insulation plate RH (RDSO S3265) 1 No. Nylon insulation plate LH (RDSO S3266) 1 No. Nylon Bushes for bolts (RDSO S 23199) 2 Nos. per D bracket Nylon washers for nuts (RDSO S 8640) 2 Nos. per D bracket Between 1st William stretcher & Drive lug Insulating bush (RDSO S 8813 ) 2 Nos Insulating plate (RDSO S 8804) 1 No. 220 mm throw point machine with clamp lock Between tongue rail and tongue attachment (P bracket) Nylon insulation plate RH (RDSO S3592) 1 No. Nylon insulation plate LH (RDSO S3593) 1 No. Nylon bush between lock /detector slide & lock /detector rod lug (RDSO S 23199)
1 No. per detector/lock rod
Nylon washer between lock /detector slide & lock /detector rod lug (RDSO S8640 )
2 Nos. per detector/lock rod
Nylon bush between drive bar and drive rod lug (RDSO S 3463)
1 No.
Rodding passing across the track likely to short the two track rails Liner plate 1 No. Bushes for bolts 2 Nos Washers for bolts & nuts 4 Nos
In addition to above, for 220 mm throw point machine with clamp lock it is to be ensured that
(i) Spring setting device (SSD) is Insulated from both the rails.
(ii) Clamp lock assembly is insulated from both the rails
D-bracket insulation bush
Drive lug insulation plate
Gauge tie plate insulation
5.0 Important parameters of DC Track Circuit (a) Ballast resistance
Ballast Resistance is the net resistance of various leakage paths across track circuit rails offered by ballast and sleepers. Ballast resistance is inversely proportional to length of Track circuit and it also varies with the condition (Dry/Wet) of the ballast and soil. Ballast resistance reduces with increase in the length of track circuit as there are more
leakage paths in parallel. Clean ballast is not a good conductor hence offers a higher ballast resistance. Water across the tracks cause leakage hence ballast resistance falls during rainy
season. A good drainage is essential to avoid water logging and for maintaining a higher ballast resistance.
Periodical screening of the ballast is not only necessary to improve the strength of track bed but it also improves the track circuit ballast resistance.
Minimum permissible ballast resistance for track circuits With wooden sleepers (a) 2 per Kilometer track length in station yard, and (b) 4 per Kilometer track length - block section (as here, better drainage can be
provided, the track being free from all line connections). With Concrete Sleepers (a) For Double Rail Track Circuit - 1 per Kilometer (b) For Single Rail Track Circuit - 0.6 per Kilometer
Minimum permissible resistance of a concrete sleeper
Type of Area Minimum Permissible Resistance Of A Concrete Sleeper
(a) In Non - RE and AC RE area
500 after six months from the date of manufacture.
(b) In DC RE area. 800 for Single Rail Track Circuits of up to 200m length and Double Rail Track circuits of up to 400m length. 1000 for Single Rail track circuits of more than 200m length and Double Rail Track circuits of more than 400m length.
Note: Measurement shall be made with a sensitive Multimeter of not less than 20 KW/Volt
resistance of coil. Megger should not be used. Wherever PSC Sleepers are used, availability of insulated liners upto a minimum level of
97% shall be ensured. (SEM Part II Para 17.28). GFN liners shall be provided in the track circuited area using concrete sleepers. (SEM
Part II Para 17.5.3) Rubber pads are also provided at both ends of PSC sleepers below rail.
Rubber pads GFN Liners
Fig.13: Rubber pads below rail and GFN liners below pandrol clips
(b) Train Shunt Resistance (TSR) This is the maximum value of resistance, which when applied across the track, drops the
track relay. For DC track circuit, the minimum permissible value of TSR is 0.5 Ohm. A higher value of TSR > 0.5 Ohm is always desirable to detect any vehicle such as Motor Trolley, Light engine , Full train provided the wheels and rails are not in rusty condition.
Drop Shunt value The highest value of shunting resistance that can cause the track relay to drop is referred to as 'Drop Shunt Value'. The drop shunt value must be higher than the minimum permissible TSR (0.5 Ohms for DC T.C) for safe working of Track circuit. Pick up Shunt value Once the track relay is dropped, it requires a considerable increase in its voltage to pick up again. The least resistance value of TSR at which the track relay picks up again is called the 'Pick up Shunt Value' of this track circuit.
(c) Rail resistance
The resistance of rail and bonding per 1000 mtrs. of track should not exceed 0.5 Ohm for track circuits longer than 700 Mtrs.
A rail and bond resistance up to 1.5 ohm per 1000 meters of track may be allowed for length of track circuit less than 700 Mtrs.
(d) Insulation Resistance of Glued Joint Before installation insulation of glued joint must be tested. Glued joint should be kept in dry wooden sleepers.
Insulation test in dry condition The value of resistance shall not be less than 25 Mega ohms when a meggering voltage of 100 V DC is applied across the joint and resistance is calculated by dividing the voltage by current.. Insulation test in wet condition Wet sand can be applied on the joint for 24 hr. and thereafter the value of resistance shall not be less than 3 Kilo ohm when obtained with application of 100V DC megger. Precautions Joint must be well packed 10 sleepers on either side of glued joint. No damage shall be caused to the joint while inserting in the track. Only 'J' type clip shall be used in glued joint portion of track. (SEM Prt II Para
17.13.4)
6.0 Fail safe adjustment of Track Circuit Select the required track relay and calculate and record 250%, 125 % of Pick Up value
and 85 % DA value of the relay.
Connect the relay directly to cell with regulating resistance in series. (Cell voltage must be 2.2 Volts).
Connect a resistance equivalent to min. ballast resistance across the relay and adjust the regulating resistance so that the voltage across the relay is just above 125 % of rated pick up value.
Now disconnect the equivalent ballast resistance connected and take reading across the relay without changing the value of regulating resistance and the voltage shall not be more than 250 % of rated pick up voltage, if voltage is high, increase the value of regulating resistance and ensure the voltage is not exceeding 250 % limit.
Shunt the relay with 0.5 Ohm TSR and check the voltage at relay terminal, it shall be less than 85 % of DA (drop away) value of the relay.
Now disconnect the relay and power supply and connect the same without any alteration in regulating resistance to the rails at the respective end i.e. relay to the relay end and power to the feed end.
Test the track circuit with 0.5 Ohm shunt and check up the relay voltage which should be less than 85 % of DA (drop away) value and relay is in dropped condition.
Measure and record the actual value of voltage and working current.
If the track relay voltage is less than 125 % of rated pick up value it means ballast resistance is less than minimum required value and if it is impossible to improve the value of ballast resistance than split the track circuit.
7.0 Relay end voltage under different conditions Following are the conditions for which the relay voltage should be adjusted for its safe working: (a) To keep Relay in Picked condition when track is not occupied under Max Leakage
(RB –Minimum) & Max Rail Resistance (Rr - Maximum). This condition generally
occurs in rainy season.
(b) To drop Relay when Track is occupied & Voltage across relay is maximum (RB -
Max i.e min leakage)
(c) Precaution against over energisation.
The specified range of track relay voltage for above conditions is summarized below: Description Condition Track Relay Voltage VR Minimum Excitation at Track Relay
Max leakge (RB Minimum) & Minimum Battery voltage
Not less than 125% of rated PU voltage for all Track Relays except QBAT.
Not less than 122% of rated PU voltage for QBAT Maximum Excitation at Track Relay
Min Leakage (RB Maximum), Rr Minimum and Fully charged Battery voltage
Not more than 250% of rated PU voltage for Shelf Type Track Relay
Not more than 300% of rated PU voltage for Plug in Type Track Relay except QBAT
Not more than 235% of rated PU voltage for QBAT Dropping of Track Relay
Irrespective of RB conditions, with the application of TSR=0.5 Ohm
Not more than 85% of rated DA voltage
8.0 Maintenance (a) Insulation joint
Every joint must be tested by maintainer to ensure high resistance. If the value of I.R.
is below 5 Mega ohm, such joint should be marked and insulation must be replaced on
priority as it may fail intermittently.
Sleeper should be avoided below joint of insulation rail joint or glued joint.
Fig.14: Sleeper below joint
Sleepers edge from insulation joint must be 4.5 " so that dog spikes/pandrol clip may
not short the insulation.
Fig.15: Sleeper clear from joint of insulation joint

Remove accumulation of brake-dust, dirt, other foreign matter on insulation joint with
a brush on each visit.
Fig.17: Cleaning of insulation joint with brush
Ensure provision of anti-creep devices on either side of the insulated joint, specially
which are in block section and nearby long welded rail (LWR). Interpose two rail
length of 13m/12m to isolate SWR from insulated joint.
Fish bolts at the joints must be kept tight and the sleepers well packed in the vicinity
of the joints.(SEM Part II Para 17.5.4).
Ensure proper drainage to prevent joint being flooded with rain water.
Ensure sound condition of gauge tie plate insulation, stretcher bar insulation, D type
insulation and rodding insulation.
Ensure no leakage of current on account of muddy portion between feed end and relay
end. If leakage is more, then advise to PWI for deep/shallow screening of ballast.
For glued joints on wooden sleepers, ensure provision of dog spikes. The spikes
should not protrude below the sleeper.
Ensure that the rail ends of the nylon insulation joints are square and smooth.
Fig.18: Rail ends of nylon insulation joint
(b) Bond wires/Jumper connections
Bonds shall be inspected frequently and maintained in good condition.(SEM Part II Para 17.26.1)
Bonds shall be painted with aluminium paint, where bond corrosions are excessive. (SEM Part II Para 17.26.2)
Following bonds must be checked on every visit for their good condition, intactness and rigid connection with rail to avoid the possibility of high resistance: Cross bond
Transverse bond
Structure bond
Longitudinal bond
Note: All the above bonds except Structure bond are provided both by S&T deptt. and
Electrical Traction deptt.
To avoid failures, two bond wires (S&T) in parallel may be provided.
Jumper connections shall be inspected frequently and maintained in good condition. Long jumper connections shall be properly secured. SEM Part II Para 17.27).
(c) Tail cables Voltage drop in the tail cables shall be kept within limits so as to work sufficiently
long track circuits with minimum power application.
All the track circuit tail cables shall be meggered once in six months and to be replaced if insulation resistance is less than 1 Mega ohm. The condition of cable sheathing at the location entries shall not be missed during inspections.
(d) Track Lead wire ropes Check that track lead wire ropes/cables of relay and feed end are intact at both rail
web and TLJB.
(e) Track Lead Junction box
Check that the Track Lead wires connections in TLJB are intact and tight
(f) Insulation in point zone track circuit Insulation for stretcher bars and point rodding (including guage tie plate insulation and D
bracket insulation ) shall be periodically checked to see that they are in sound condition.
All defective insulation shall be changed. (SEM Part II Para 17.25).
Rail Structure bond Fig.:21
Fig.23: Insulation in point zone track circuit
(g) Track feed charger and battery Check and note down the current & voltage at feed end and relay end with & without
charger on each visit.
Specified value of track relay voltage < 250% of pick up voltage for shelf type relay. < 300% of pick up voltage for plug-in type relay except QBAT relay. < 235% of pick up voltage for QBAT relay.
Ensure that the date of overhauling / replacement of track relay is not overdue.
Check the battery connection, specific gravity and voltage periodically. Measure the
voltage after switching off the charger.
Check the battery condition regularly.
Fig.24: Checking of specific gravity of electrolyte of battery and relay voltage in location box
(h) Ballast
Ballast must be maintained clean throughout the track circuited section and care should be taken to see that clearance of ballast from the foot of the rail shall not be less than 50 MM. Ballast shall be kept free from vegetation.
The ballast resistance of the track with both rails insulated should not be less than 2.0 Ohm/Km. with wooden sleepers and 1.0 Ohm./Km. with concrete sleepers in non-RE area and 0.6 Ohm/Km. with concrete sleepers in RE area.
In case of concrete sleepers ensure provision of rubber pads & availability of insulated liners up to 97%. (SEM Part II Para 17.28).
(i) Relay
As per Para 19.141 of SEM Part II, all types of track relays should normally be overhauled every 10 years subject to a maximum of 12 years. The duration may be reduced depending on local conditions and prevailing zonal railway instructions.
The due date of overhauling shall be noted in paint on every track relay prominently in the front so that it is not retained in circuit even for one day after the overhaul falls due.
Check the arching of contacts, corrosion and presence of fungus after every six weeks.
Ensure that there is no moisture/leakage of water near relay.
9.0 Joint Inspection of Track by S&T and Permanent Way Inspector As per SEM Part II Para 17.30, the track-circuited portion of the track shall be jointly inspected by Sr. Section Engineer (Signal) and Sr. Section Engineer (P-way) at least once in six months. This is in addition to routine inspections to be carried out by each Branch. The condition of rail and insulation at the rail joints, ballast and sleepers, abnormal collection of brake dust, rusting of the rail and drainage system of the yard shall be particularly noted, it shall be ensured that percentage of missing liners for track circuit length not to exceed 3%. Maintenance work found necessary on insulation joints after such inspection should be carried out jointly.
10.0 Prevention from stray currents in Single Rail DC Track Circuit In DC Track circuits, due to high soil resistivity under the track bed between the two ends of a track circuit and complete earthing of only one of the two track rails, sometimes some stray voltage/current develops on the track. It is therefore necessary that DC stray current and rail earth voltage tests shall be carried out to ensure that DC track relays shall not operate with stray currents. The length of the track required to be track circuited shall be insulated by means of Block Joints on either end of the rails. As per Annexure 32 of SEM Part II, for measurement of stray current set up the circuit as shown below and measure the current simultaneously. Two suitable earths, one on either end of the track shall be provided and these are connected to the rails by leads of negligible lead resistance. The earth resistance shall not exceed 5.
Fig.25: Arrangement for measurement of stray current
The total stray current as measured, shall not exceed: i) 10 milli-amperes, if length of track circuit is less than 100 meters
ii) 100 milli-amperes, if length of track circuit is 100 meters and above
For measurement of rail earth voltage set up the circuit as shown below: Where 9 ohms, 4 ohms or 2.25 ohms relays are used, use 9 ohms, 4 ohms or 2.25 ohms resistance and measure the voltage once at 'X' and next at ' X1.
Fig.26: Arrangement for measurement of rail earth voltage If measured value of stray current/rail earth voltage exceeds the specified limit as above one of these methods may be tried to prevent eliminate stray current/voltage:
(i) Interchanging the positive and negative connections of the rails, as in that case the stray voltage polarity becomes opposite to the proper feed polarity.
(ii) Interchanging the feed and relay ends of the track circuit as in that case, the stray voltage may disappear at the relay end.
(iii)Splitting of the track circuit as in that case, the stray voltage in each portion may become negligible.
If none of the above solves the problem, other type of track circuit suitable to work in A.C. traction area shall be used.
11.0 Installation of point machine in track circuited area to the negative polarity rail side As we know that track circuit consists of positive and negative polarity rails. The ground
connections of point machine pass below one of the rails and are likely to touch the rail bottom. If that rail is carrying positive polarity then there are chances of earthing of positive feed through connected point machine.
Although insulation is provided between tongue rail and D brackets connected to lock
rods and detection rods and the stretcher bar connected to throw rod is also insulated, there are likely chances of ground connections touching the rail bottom resulting in track circuit failure as the point machine is partially grounded. .Also if any metal piece or aluminium foil is stuck between the rail bottom and ground connections crossing below it, the track circuit may be shorted
In view of the above, it is recommended that point machine may preferably be installed towards the side of rail carrying negative polarity.
Point machine to be installed towards negative rail of track circuit
Fig. 27: Installation of point machine towards negative rail of track circuit
Objects like crushed metal can and aluminium foil can stuck between ground connections and rail bottom and earth the positive polarity rail.
12.0 Monsoon precautions (Ref.: Annexure to Railway Board letter no. 2015/Sig./SF/Monsoon Precautions dated 18.05.2016)
(1). Provision and cleaning of drainage system in yards to avoid water accumulation in points and track circuited area. Temporary drains need to be provided wherever required. Cross and longitudinal drains are made effective and are cleaned regularly during monsoon and rainy season.
(2). Joint inspection of major yards prone to water logging by a team consisting of ADEN, ADSTE, AOM, ADEE and ADMO be carried out and action to be taken to improve the drainage before onset of monsoon. the concerned department shall take necessary action to ensure proper drainage.
(3). Joint inspection by SSE/P. Way and SSE/Sig to ensure: (a). Cleaning of ballast and ensuring at least 50 mm clearance of ballast from
bottom of rail to avoid leakage of track circuit currents. (b). Provision of 100% GFN liners and rubber pads in track circuited area with
PSC sleepers. (c). Replacement of worn out wooden sleepers, if any, and proper packing of
ballast/sleepers below insulated joint. (d). Removal of vegetation, mud and muck from track circuited portion of track
as well as on either side of tracks and in vicinity. (e). All nylon pieces of insulated joints, insulation of stretcher bars and point
rodding are intact and replace those in bad condition. (f). Defective/worn out glued joints are replaced before onset of monsoon. (g). Provision of 'J' clips at all insulated joints on PSC sleepers.
(4). Track lead junction boxes in flood prone areas are raised without infringing SOD
so that water does not enter in them.
(5). Adjustment of track circuit parameters to keep track relay pick up voltage within safe working limits.
(6). Proper working of track feed charger failure alarm wherever provided.
(7). Provision of self restoring type PPTC fuses at all lightning prone stations.
(8). Checking of all traction bonds in track circuited portion of track and attending deficiencies through Electrical Traction department.
(9). Checking and ensuring all connections like rods, transverse bonds, feeds of adjacent track circuits etc. do not touch the bottom of the rail.
(10). Timely replacement of old rusted track circuit bond wires.
13.0 Do's and don'ts Do's Check all safety parameters and record the exact values in track history card. Check insulation joint regularly and at the same time see its previous value. If
changing, then replace such insulation joint promptly. Check the due date of overhauling of each track relay and send them timely for
overhauling. Megger the track circuit tail cable after every six months and if the value is less than 1
mega ohm then such cable should be replaced promptly. Check the bond wire connections to avoid high resistance which are cause of voltage
drop. Prefer to provide track lead junction box vertically to avoid water accumulation in the
junction box. Apply glue/epoxy on the rail and fish plate of those joints which are shorting due to
iron filings and iron powder. At the time of replacing the insulation joint apply quick drier paint on the rail and fish
plate. Use double wire for track circuit bonding. Try to replace the insulation joint when the temp. is between 200 -350 C. At insulation joint pandrol clip should be opposite in direction so that pandrol clip’s
small portion should be towards fishplate or use J Pandrol clip to avoid touching of pandrol clip with the fish plates.
Fig.28: J type Pandrol clip Don't Bypass the regulating resistance at any time. Tamper with the track relay at the time of track circuit failure. Disturb the anti-tilting arrangement of shelf type track relay. Forget to give disconnection memo to on-duty ASM/CASM at the time of attending
failure. Adjust the track circuit beyond the limit of track circuit parameters given earlier.

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dc track circuit - rdso.indianrailways.gov.in

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