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SYLLABUS NO S 5B

POWER SIGNALLING

INDIAN RAILWAYS INSTITUTE OF SIGNAL ENGINEERING AND TELECOMMUNICATIONS

TARNAKA ROAD SECUNDERABAD - 500 017

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CHAPTER – 1 S5B

INTRODUCTION 1.1 All electric circuits essentially consist of a power source, a load and a pair of conductors to connect them with or without a control switch. In a track circuit, a portion of rail track is electrically isolated from adjoining rails and included in a circuit to energise a relay. The occupation or vacancy of the track portion is detected by the condition of track relay. The length of the track confined within one circuit depends on its working feasibility and the required separation between two running or stalled vehicles on the track. Two types of track circuit were designed. One is continuously live and is called a 'Closed Track Circuit.' The other one is made live only when occupied by vehicles and is called an 'Open Track Circuit.' The latter type is rarely used due to its serious limitations. According to the nature of supply source, the track circuits are categorised as (1)D.C.Track Circuits (2) A.C.Track Circuits and (3) Electronic Track Circuits. They are comparable as below: - ____________________________________________________________________ S.No. D.C.T.Cs. A.C.T.Cs. Electronic T.Cs. ----------------------------------------------------------------------------------------------------------------- 1. These work on the principle Reduction in track only track voltage gets of relay voltage regulation voltage and its phase reduced in these when when vehicles shunt the difference with a shunted to drop the relay. track. local reference voltage act together to de- energise the relay. ----------------------------------------------------------------------------------------------------------------- 2. These are simple in design These involve more These require more and less costly. components and are sophisticated and costly costlier. components. ---------------------------------------------------------------------------------------------------------------- 3. These are more stable and These can fail to detect These require less more dependable to detect track occupation if not monitoring. track occupation. closely monitored. ---------------------------------------------------------------------------------------------------------------- 4. Their working is more In these, the affect of Their working is less predictable and voltage is external factors on unpredictable. the only factor to be phase shift of relay monitored. voltage from the track is not easy to predict. ---------------------------------------------------------------------------------------------------------------- 5. They can be fed from small Reliable 3 Phase mains Track feed is given batteries or rectifiers connect- supply is used which through individual ed to AC mains. Batteries needs less attention. conversion units that need need more maintenance. additional surveilance. ----------------------------------------------------------------------------------------------------------------- 6. The maximum workable These can work upto The maximum workable length of these track circuits a maximum length of length of these track is about 750 metres. 2.3 Km. circuits is 2 Km. ----------------------------------------------------------------------------------------------------------------

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7. Insulated Rail joints at These also have track Maintenance and failures track ends are additional end insulated joints get reduced as there are sources of failure in these. which frequently fail. no track end insulated joints. _____________________________________________________________________ 1.2 Types of DC Track Circuits :- a) Open DC Track circuit b) Closed DC Track circuit 1.2.1 a) Open Track Circuits, wherever they are provided are D.C.Track Circuits. A

schematic diagram of an 'Open Track Circuit' is given below :-

The components of the track circuit are :- (1) Battery (2) Adjustable Resistance (3) Track Relay (4) Track Lead Cables (5) G.I.wires connecting cables to the rails (6) Continuity rail bonds (7) Insulated rail joints. The circuit gets completed when the track is occupied through the net resistance of the vehicle axles occupying the track circuit. The series resistance is so adjusted as to give sufficient voltage to the relay when track rails are shunted by axles with a high contact resistance. It is also to be ensured that the relay does not get, without shunt, a voltage enough to pick it up due to leakage currents through track bed ballast when damp. Otherwise, the track circuit can fail frequently. In this type of track circuit, if any connection breaks, its occupation goes undetected. Hence, it is used only for limited purposes where its failure does not lead to unsafe conditions. Block Section clearance and Approach proving for Calling on Signal Clearance are such occasions. 1.2.2 b) Closed Type D.C.Track Circuits which are most commonly used are connected as

below :-

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The components of the track circuit are the same as provided in the 'Open Track Circuit' as shown earlier, but their mode of connection is different. They are so connected as to keep the relay normally energised. The feed is connected at one end of the track and the relay at the other end so that any breakage of rail continuity shall drop the relay. In this track circuit, the series resistance is called a Regulating Resistance. It regulates the relay voltage so that it falls below the drop away value when the track is shunted. The fall is caused by increased voltage drop across the regulating resistance due to rise in circuit current when shunted by the vehicles. Sufficient regulating resistance is essential because the battery internal resistance can not cause much difference to the relay voltage with track occupation. Regulating resistance also protects the feed equipment when the track is shunted by avoiding a short across it. 1.3 TRACK CIRCUIT PARAMETERS: The factors which influence the working of this track circuits are shown in an equivalent electric circuit below:-

RT = Regulating Resistance RB = Ballast Resistance Rr = Rail Resistance RR = Relay Resistance RS = Resistance of the shunting vehicles Rfc = Resistance of track lead cable at feed end Rrc = Resistance of track lead cable at relay end In this, Rr shown inclides the resistance offered by the continuity rail bonds which is rather more than the resistance of the rails themselves. It is in fact negligible under normal conditions, but varies according to bond conditions. RB is the net resistance offered by the ballast and sleepers across the track to leakage of rail currents. It varies according to the dry or wet condition of the ballast and soil RR is fixed for a relay and type of its coil connections. RS is the resistance offered by the shunting vehicle axles. It varies according to the condition of rail table (top), weight of the vehicles and their speed. RT is the regulating resistance which is adjustable when used with a fixed voltage battery and connected in series with the track. Rfc is generally very low and Rrc is the main constituent of cable resistance. Rs gets connected only when the track is occupied. All other factors are always present, but change in value under different conditions. Their changes affect the relay voltage directly. Limitations are imposed on the maintainable values of the variable factors, as prescribed in the IRISE Manual, to make the working of track circuits safe and reliable.

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These limitations called the 'Track Circuit Parameters' can be better appreciated if only the effect of their change on the relay voltage is separately and cumulatively studied. A track circuit is as reliable as its components and its ability to withstand the external influences like weather, keeping its relay properly energised. It is dependable for train working safety as its capacity to detect its occupation when shunted by a vehicle with high rail contact resistance. The highest resistance which, when applied across the track, can open the track relay front contacts is known as its 'Train Shunt Resistance' value. It is the measure of its dependability. The relations between the various factors mentioned above and the TSR value of a track circuit have to be clearly understood so as to maintain the track circuits properly under adverse conditions. A higher T.S.R is always aimed at to ensure safety in train working on these track circuits. 1.4 MINIMUM PERMISSIBLE T.S.R:- It is specified as:- (i) 0.5 Ω for (a) D.C. Track Circuits: (b) Audio frequency Track Circuits outside their tuned lengths; and (c) Jeumont type High Impulse Track Circuits with wooden sleepers in them. ii) 0.25Ω for all the above types with concrete sleepers and (proposed to be revised as 0.5Ω

with RB min. as 2Ω/km and) (iii) 0.15Ω for conventional AC Track Circuits and the tuned portions of Audio Frequency Track Circuits. 1.5 PICK UP SHUNT AND DROP SHUNT RESISTANCES: In case of 'Open Track Circuits', the shunting resistance causes the track relay to pick up. If this shunting resistance is very high, the track relay may not pick up properly. Hence, the highest resistance value that can cause the track relay to pick up is called the 'Pick Up Shunt Resistance Value'. In case of 'Closed track Circuits', the track relay is normally kept energised. Here, the application of a proper shunting resistance drops the track relay. The highest value of shunting resistance that can cause the track relay to drop is referred to as 'Drop Shunt Value'. Once the track relay is dropped, it requires a considerable increase in its voltage to pick up again. This increase can be effected by increasing the shunting resistance. This least resistance value at which the track relay picks up again is called the 'Pick Up Shunt Value' of this track circuit. 1.6 IMPORTANCE OF PICK UP SHUNT ON A CLOSED TRACK CIRCUIT In longer track circuits, sometimes effective shunting by a lighter vehicle may not take place throughout their length. At vulnerable points, the track relay may again pick up momentarily under occupation. This may be due to rusty rails in a portion of track on less frequently used lines. This may also be caused by the drop shunt being of critical value and the ballast condition in the track not being uniform.

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So, it is necessary that at the time of installation and often during maintenance, the 'Pick Up Shunt' value is also noted for such track circuits. 1.7 BALLAST RESISTANCE It is the net resistance of various leakage paths across track circuit rails offered by ballast and sleepers. The longer the track circuits, more is the number of these leakage paths in parallel with each other and hence lesser becomes the net ballast resistance. Also leakage current through each path goes up with increase in dampness added to the ballast dust coat. A clean ballast free from dust or soil is not a good conductor. The ballast resistance falls to its lowest value during the first showers of monsoon. When rain water flows over it and washes dust off, the ballast resistance improves again. 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. It also improves the track circuit ballast resistance. 1.7.1 HOW IS BALLAST RESISTANCE CALCULATED? IN A D.C. TRACK CIRCUIT:

Measure the voltages and currents as shown. The Ballast Resistance can be calculated From :- VF + VR - - -- - - - - -

2(IF – IR) (i.e. Average Rail Voltage) Leakage Current. Knowing the length of track circuit, RB per kilometre can be found out. In the case of a Track Circuit working on AC., the ballast resistance can be found from:- RB = V0.4/I0

Where V0.4 = Voltages across rails at 0.4 length from the Feed End I0 = The Feed End current when the relay end leads are not connected.

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1.7.2 MINIMUM PERMISSIBLE BALLAST RESISTANCE FOR WOODEN SLEEPER TRACK CIRCUITS:-

It is specified as :- (i) 2 Ω per kilometer track length within station section; and (ii) 4 Ω per kilometer track length - outside the station section (as here, better drainage can be provided, the track being free from all line connections). 1.7.3 MINIMUM PERMISSIBLE BALLAST RESISTANCE FOR CONCRETE SLEEPER

TRACK CIRCUITS:- (i) 1Ω per kilometer - in Non-RE areas (both within and outside station sections) (ii) 0.6 Ω per kilometer - in RE areas (both within and outside station sections). As water seeps through wooden sleepers more easily than passing over the hard surface of concrete sleepers, the ballast resistance of a concrete sleeper track circuit is always less than that of wooden sleeper track circuits in monsoon. Also, the capacitance effect of reinforcing rods in a concrete sleeper drain some more current from the rails to charge itself. Hence, leakage currents are more in concrete sleeper track circuits. With this in view,the minimum permissible value of ballast resistance in a concrete sleeper track circuit prescribed is low. The basis for arriving at the Minimum Ballast Resistance value of 1 W/Km in non-RE areas is as follows:- In 1 Km length of track, about 1500 sleepers are provided. If on an average, each sleeper, with rubber padding under the rails and neoprone liners under pandrol clips offers at least 1500 Ω resistance in parallel with damp ballast, the net resistance amounts to 1 Ω per Kilometre. In RE area, as one rail of single rail track circuit is maintained at earth potential, that rail leaks more current to earth. Hence, the minimum permissible ballast resistance of a concrete sleeper track circuit in RE areas is prescribed as 0.6 Ω per Kilometre. However, the latest instructions for installation and maintenance of D.C. Track Circuits in RE area, vide RDSO's circular NO.STS/E/DC.Track Circuit dated 25.1.95 stipulate that the minimum permissible TSR for all D.C.Track circuits shall be 0.5Ω irrespective of the type of Sleepers used and that the minimum permissible RB shall be 2Ω/Km. 1.8 MINIMUM PERMISSIBLE RESISTANCE OF A CONCRETE SLEEPER: It is (a) In Non - RE and AC RE area :- (i) 500Ω after six months from the date of manufacture, and (ii) 200 Ω at the manufactures shop within fifteen days of its manufacture. (b) In DC RE area. (i) 800 Ω for Single Rail Track Circuits of upto 200m length and Double Rail Track circuits of upto 400m length. (ii) 1000 Ω for Single Rail track circuits of more than 200m length and Double Rail Track circuits of more than 400m length. 1.8.1 METHOD OF MEASUREMENT:- Measurement shall be made with a sensitive multimeter of not less than 20 KΩ/Volt resistance of coil. Megger not be used.

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After cleaning a spot on the surface of each insert, measurement shall be made between inserts A & B, A&C,A &D, B & C,B & D, and C&D. The lowest of these readings shall be considered the sleeper resistance.

1.9 BALLAST RESISTANCE AND THE TRAIN SHUNT RESISTANCE (T.S.R):- If the ballast resistance of a track circuit is more, the leakage currents across rails are less resulting in lesser voltage drop across the regulating resistance. Due to this, the track voltage and the relay voltage are higher. To bring this voltage down to a value below the relay drop away, the track is required to be shunted by a smaller resistance. It means that an increased ballast resistance of a track circuit causes a decrease in Train Shunt Resistance value.

The relationships of Ballast Resistance (1) with the track relay voltage and (2) with the Train Shunt Resistance are depicted in a graph here with Ballast Resistance on the X - Axis and the other two on the Y - axis. As can be seen, at higher values of RB, the effects of its change on VR and T.S.R are not so prominent as at its lower values.

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1.10 RAIL & BONDING RESISTANCE : What is generally referred to as 'Rail Resistance' is the combined resistance of the track circuits rails and the continuity bonds at rail joints. 8 SWG G.I wire bonds are provided by the signalling staff to reduce resistance at these joints. In DC RE areas, Traction Power department also provides larger cross-section multi-strand copper bonds for good conduction of traction return currents at these joints. These also serve to limit the rail drop of track circuit voltage. The resistance of these bonds is considerable enough as compared to the resistance of rails themselves which is negligible. Due to continuous battering of rail ends by the moving wheels and due to the interference of External factors, these bonds sometimes get loosened, become rusty at the ends or may even break. This causes further increase in their resistance. Obiviously, the longer the track circuits, the higher becomes their rail resistance. 1.11 HOW TO CALCULATE THE TRACK CIRCUIT RAIL RESISTANCE Measure the rail voltages and currents at the feed end and relay end of the track circuit. Then the rail resistance value can be deduced as below:- 2(VF – VR) where VF = Feed End track voltage Rr = - - - - - - - - - - VR = Relay End Track Voltage IF + IR) IF = Feed End Track Circuit current & IR = Relay End Track Circuit current i.e. (Voltage drop in the rails) (Average Track circuit current) 1.12 RAIL IMPEDANCE OF AN AC TRACK CIRCUIT:- In track circuits where alternating currents are fed to the track rails, rail inductance also plays a part along with rail resistance to cause voltage drop in rails. Also, due to their 'Skin Effect' rails offer more resistance to AC currents. To know the total effect of both these factors, rail impedance is considered instead of rail resistance in the working of these track circuits. 1.12.1 CALCULATION OF RAIL IMPEDANCE:-

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First, remove the relay end connections of the track circuit as shown in Fig.1. Take the readings of feed end voltage across the track and the feed end current. Let these readings be V0 and I0 Calculate, open circuit impedance, Z0 = V0/ I0

Then short the track circuit at relay end as shown in Fig.2 and take the readings of voltage and current at feed end. Let these readings be VS and IS Calculate, Short circuit impedance ZS=VS/IS. Also, calculate RB of the track circuit. From these values, the rail impedance can be deduced as Zr = (Z0 x ZS) / RB. 1.12.2 RAIL RESISTANCE / IMPEDANCE AND THE T.S.R. : Rail resistance and the rail impedance are directly proportional to the length of a track circuit as all the rails are connected in series. T.S.R. at the relay end of track circuit is lesser than that at its feed end due to the reduced track voltage there. It means that the rail resistance or rail impedance has an adverse effect on the T.S.R. Because of this the track circuit rail resistance shall be kept low. 1.12.3 MAXIMUM PERMISSIBLE RAIL RESISTANCE: For track circuit lengths upto 700m, the maximum permissible rail resistance is 1.5 Ω per kilometre. For track circuit lengths more than 700M, the maximum permissible rail resistance is 0.5 Ω per kilometre. Vide RDSO's letter No.STS/E/DC Track Circuit dt.25/27.1.95, Rail Resistance shall not be more than 1 Ω /Km (with no reference to length of track circuit). Generally the track circuit length is limited to 700m (C.S.R length) within station yards. Outside the station sections, track circuits may be longer. The condition of rail bonds cannot be checked as frequently outside the station yards as inside them. Hence, the need for keeping the rail resistance minimum there. 1.13 RELAY RESISTANCE AND T.S.R :

Upto about 40 Ω higher relay coil resistance has an improving effect on the T.S.R. Beyond that, if the relay resistance is increased, T.S.R starts falling.

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However, in the British practice of railway signalling which is predominant on our railways, the realy resistance is limited between 2.25 and 9 Ω. This facilitates their lesser operating values. Due to this, the relays' percentage release is high, contributing to better T.S.R. of track circuits. But to keep the T.S.R. within limits in these track circuits, a higher regulating resistance in series is required. Siemens DC Track Relay has a 50 Ω resistance. It works on a lesser current comparatively allowing for higher track leakage. Due to this a 2 Ω regulating resistance is enough to give a good T.S.R. In practice, track circuits with Siemens Relays are found to give a better T.S.R. always. 1.14 REGULATING DEVICES: The internal resistance of any power source is necessarily less. Due to this, there cannot be any considerable drop in the source voltage of a track circuit on application of shunt that can cause the relay to positively drop. Reduction of relay voltage to a value below its drop away with shunt across is achieved by using a 'Regulating Device' in series with track circuit power source externally. This also serves to avoid a direct short across the source that can cause damage to it. A series resistance of suitable value is used as 'Regulating Device' in track circuits of almost all types. With AC Track Circuits, sometimes an inductor or condensor is used in its place. Since the regulatory nature of all the three is the same, studying the effect of regulating resistance on the working of a track circuit serves as an example.

The effect of increase in the regulating resistance on the T.S.R. of a track circuit is similar to that of increase in the relay resistance. Upto an extent, increase in the regulating resistance results in an increase of T.S.R. But beyond a limit, it starts having an adverse effect. 1.15 TRACK LEAD CABLES: Voltage drop in the track lead cables shall be kept within limits so as to work sufficiently long track circuits with minimum power application. Generally, feed sets are kept in location boxes very close to the track circuits to get better track voltages with minimum applied source. But longer track lead cables at the relay end cannot be avoided at way - side stations because of the need to keep the track relays in the cabins and avoid thefts. However, longer track leads due to their high resistance in series with the track relays make their operations and release quicker. This is an advantage in case of shorter track circuits.

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CHAPTER – 2 S5B

D.C TRACK CIRCUITS 2.1 D.C. TRACK CIRCUITS IN NON - RE AREAS (BRITISH PRACTICE) The smallest closed type track circuit that is provided is of 2 rail length (i.e. 26m). These track circuits are used as block clearance and occupation detection track circuits of Absolute Block Territories. On running lines at the platforms where trains are stopped and on stabling lines, the track circuits provided are called as 'Berthing Tracks' and these are fairly longer. Similarly longer track circuits are provided in signal and block overlaps and also in automatic block sections. The longest track circuit workable in a station section is about 600m in length. Longer track circuits than these may be sometimes provided in Intermediate block sections, and automatic sections. But with the advent of axle counters, the usage of track circuits outside of station sections is now-a-days very limited. For the study of these track circuits, a distinction may be made between smaller track circuits of upto 100m length and the others. --------------------------------------------------------------------------------------------------------------------- S.No Small Length Track Circuits Long Track Circuits --------------------------------------------------------------------------------------------------------------------- 1. In these, power loss is less. T.S.R also There is a considerable difference is fairly uniform from feed end to relay end. between their feed end track voltage and relay end track voltage, particularly in point track circuits. Hence, to keep T.S.R at the feed end high enough, rail resistance shall be kept within limits. 2. Track relays with 9 Ohm resistance shall Shelf type track relays of 2.25 Ohm be used in these. A higher relay resistance resistance and Q series track relays of yields higher T.S.R, 2.25Ω relay resistance 4 Ohm resistance are used in these. here may cause unsafe conditions. Otherwise, with higher operating values of 9 Ohm relays, it is difficult to keep leakage and rail voltage drop within limits. 3. These can work under worse ballast Ballast resistance shall be kept as conditions as the number of their ballast high as possible. Frequent screening leakage paths is less. of ballast in these is necessary. In places with poor drainage, it is almost impossible to work longer track circuits in monsoon. 4. Since a fast moving light engine may Relays with greater release time lag clear this track circuit very soon, its relay also may not pose problems shall have the least release time lag. ordinarily with these track circuits. 5. Relay end track voltage is better in these. Track lead cables cannot be very Track lead cables can be longer with more long causing more voltage drop in voltage drop in them. Higher lead them. Track circuits are occupied by resistance in series causes quicker relay running trains sufficiently long to operation.This is necessary as these are make their relays drop. cleared by running trains more quickly.

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6. In these, a higher regulating resistance Regulating resistance can be kept at a is necessary to get a good T.S.R lower value. Particularly in for their safe working. When ballast monsoons it becomes necessary. resistance is high, a regulating However, when it is resistance nearly equal to relay too low, track circuit shall be closely resistance (about 8.5Ω ) is necessary. monitored for shunting. 7. Smaller feed voltages are required for Larger feed voltages are required. these.These can work with primary cells Either secondary cells or track feed like soda cells and 6I dry cells also . rectifiers are preferable for these. 8. Track circuits with plug in type relays of Shelf type track relays with lesser higher operating values also can work operating values are preferable with satisfactorily. these. -------------------------------------------------------------------------------------------------------------- 2.2 STAGGERING OF ADJOINING TRACK CIRCUIT RAIL POLARITIES AND THEIR IMPORTANCE :-

In the arrangement shown above, similar feed polarities are connected to the adjoining track circuit rails. Here, failure of one of the two block joints No.1 or No.2 can go undetected as it does not drop the track relay on either side. But later, if the second block joint also fails, both the track circuit feeds come in parallel. When 1T is shunted by a vehicle at the feed end, its own feed is effectively shunted. But 1TR may not drop due to its proximity to the feed of 2T, while the shunt is remotely connected making it less effective. This is an unsafe condition which should be avoided.

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In this arrangement, the polarities of track feed across the block joints in between are not similar. So, when both the block joints No.1 & No.2 fail, both the track feeds get connected, +ve to -ve and -ve to +ve with high circulating current in between. The track relays 1TR and 2TR also come across this circuit separately in parallel. With this, the voltage across the relays gets reduced. As a result, either 1TR or 2TR or both may drop, according to the fall of track voltage, even without a shunt across. However, the track relay across which there is a shunt, can not pick up in any case. Hence, to make the track circuit working safe at the time of block joint failures, it is necessary that the track feed polarities are staggered in continously track circuited sections. 2.3 D.C.TRACK CIRCUITS IN AC RE AREAS. In RE areas, traction return current also has to flow through track circuit rails to the substation in parallel with earth return path. Also, for the purpose of working a track circuit, its rails have to be insulated from the adjoining rails. Track circuit can work even if rails connected to one polarity of its supply are insulated. These track circuits in which one of the two track circuited rails carries traction return current are called 'Single Rail Track Circuits'. With DC track circuits in RE area, this is the only possible arrangement. In the case of isolated track circuits, insulated rail joints are provided on rails carrying positive polarity of track circuit voltage only. The other rail carrying negative polarity is not provided with any insulated joints. 2.4 TRACTION BONDS :- 1). Structural Bond. 2). Transverse Bond. 3). Cross Bond. 4). Longitidunal Bonds(Continuity) However in between two consecutive track circuits insulated joints are provided on both the rails so as to be able to maintain 'Staggered' track circuit polarities. Also the negative rails of adjoining track circuits are provided with a cross connection bonding strip in between, known as 'Transverse Bond'. This transverse bond (i) facilitates passing of traction return current ahead from one track circuit to the other and also (ii) helps in detecting a block joint (insulated rail joint) failure between the two track circuits.

When block Joint No.1 fails, 1TR drops as its feed gets short circuited and when block joint No.2 fails, 2TR drops as its feed gets short circuited. The rail at whose block joint, traction return current flow is stopped is called the 'Insulated Rail'. The rail at whose block joint, traction return current is given an alternate path through transverse bonds is called the 'Un-Insulated Rail'.

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2.5 CROSS BONDING OF UNINSULATED TRACK CIRCUIT RAILS: Uninterrupted flow of traction return currents through track circuit rails shall be ensured to avoid their interference with track circuit working.

In case there is a break in the traction return path of track circuit as shown, the heavy traction return current passes through the track feed source to the insulated rail and returns to the uninsulated rail through the track relay at the other end to go further ahead.

This can cause unsafe conditions in track circuit working. To avoid this, an alternate path shall be available for traction return current in such circumstances.

In multiple line sections traction return rails in track circuits are cross connected with bonding straps at an interval of about 100metres in between them. Also, beyond the last track circuit very close to the block joints, a cross bond is provided across to connect the two track rails.

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2.6 DC. SINGLE RAIL TRACK CIRCUITS (BRITISH PRACTICE)

Components 1. Battery charger 110v /2-10V D.C. 2. Feed Battery (1 to 4 sec. cells). 3. Fuse & link 4. Variac (0-25 Ohms) (Type 'F') 5. Type 'B' choke (R=3 ohms &Z= 120Ω ). 6. Track lead cable (2 X 2.5 mm2 copper). 7. Track lead J.B. 8. Track lead steel wire ropes. 9. Transverse bonds. 10 Block joints. 11. Track Relay (ACI). Certain precautionary arrangements are necessary for the safe working of a D.C. track circuit in R.E. area as detailed below, due to the passage of traction return current through one of its rails. (1) Only an AC.I track relay (of shelf type, QTA 2 type or QBAT type) shall be used with this track circuit. Even though small track circuits of upto 100 metre length can work safely in normal conditions with a non-immunised track relay, they may be unsafe for a while when the catenary snaps and falls on the track circuit rails or their connections. This is because at that time, the heavy short circuit current through the uninsulated rail can cause an abnormal AC. voltage across the relay. ------------------------------------------------------------------------------------------------------------------------------- (2) The length of track circuit shall be restricted according to the immunity level of track relays as below:- ------------------------------------------------------------------------------------------------------------------------------- S.No. Type of AC Max. Type of TC Max. Remarks Track relay Imm.of Catenary Sleepers Length Track Current of TC Relay in Section permitted ------------------------------------------------------------------------------------------------------------------------------- 1. ACI shelf 50V 600Amp. Wooden 450m type or QTA2 A 10V drop is type considered in 90m long rail length @

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600Amp current. 2. QBAT type 80V 600Amp. Wooden 750m (with relay end choked) 3. ACI shelf 50V 800Amp. Wooden 200m type or QTA2 in S/L Sec. 1000Amp. Wooden 300m The voltage drop in D/L Sec. will be correspondingly 4. QBAT type 80V 800Amp. Wooden 450m more in S/L Sec. 1000Amp. Wooden 450m in D/L Sec. 5. ACI shelf 50V 600Amp. Concrete 350m The workable length type or QTA2 1000Amp. is restricted to a esser type value due to 0.6 /Km Ballast Resistance minimum permitted. 6. QBAT type 80V 600Amp. Concrete 350m 1000Amp. (3) QSPAI relay only shall be used as repeater for QTA2 or QBAT track relay due to its lesser operate time lag. However, for ACI shelf type track relay any AC. immunised line relay can be used as repeater due to its greater operate time lag. (4) When shelf type ACI track relay is used, track feeding shall not be done directly from a rectifier, without a battery in parallel. Also their connection shall be so done that whenever battery gets disconnected, rectifier also shall automatically be isolated from the track. Otherwise, AC interference voltage coming across the charger output terminals gets half wave rectified and reemerges on the same terminals. Sometimes when this gets applied across the relay through track may not allow it to drop easily when shunted. (5) A 'B' Type protection chock of (3 ohm resistance and 120 ohm impedance for 50Hz)shall be connected in series with track feed to the uninsulated rail. This prevents damage to the feed source in case of a catenary snap resulting in heavy currents in the uninsulated rail. A similar choke shall be connected in series with the relay also for its protection. In the case of shelf type ACI track relay with this choke in series, 450m long track circuit can be worked even with traction return current going upto 1000 Amps. Without this choke, 450 m long track circuit can be worked only when the traction return current is within 600 Amps. As per 68th signal standard committee – Restriction on track circuit length due to use of concrete sleepers can be relaxed upto 450mts with QTA2 / Shelf type ACI track relays and 750mts with QBAT (4 cells at feed end 8.8 Volt DC) if adequate ballast resistance is maintained. (6) A 5A 250V rated fuse also is provided at the feed end of the track for additional protection. (7) A 0-25 Ohm variac is used for regulating purpose so that minor adjustments can be made on the track feed voltage which is considerably higher than that of a track circuits in non RE area. Here, the relay operating values are greater. (8) Whenever somebody has to work on the track circuit equipment, before starting the work, a surge discharge shall be connected across the track at the site of work. This is to protect the

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staff from excessive AC current that may parts through the equipment in times of a catenary circuit short. (9) A transverse bond shall be connected joining the uninsulated rails of two adjoining track circuits as already discussed before. 2.7 SAFE & RELIABLE WORKING OF D.C. TRACK CIRCUITS IN BRITISH PRACTICE: Safe working of a track circuit is ensured if the track relay does not fail to drop with application of minimum permissible TSR across it, under the most adverse condition. The relay gets maximum voltage when current through leakage paths is minimum and this is the most adverse condition for shunting of the track relay. This condition is caused by maximum ballast resistance and optimum feed source voltage of the track circuit. Without a shunt across the track, its relay excitation shall not exceed 250% of its pick up value this is to see that the residual flux in the core dives not cause a reduction in the relay drop away value of more than 15%. Also, when minimum TSR is applied, the relay voltage shall fall to its drop away value minus the permissible margin of 15% so that with any marginal change in the relay drop away value over a period, the relay does not fail to drop with the shunt across. This sums up the required conditions for safe working of these track circuits. Also, for making the track circuit reliable, minimum excitation of the track relay when track is not occupied shall be 125% of its pick up value. This alone can cause the required front contact pressure on the relay. Relay excitation is the minimum when its feed source voltage is normal and the net ballast resistance is minimum allowing for heavy leakage currents. Adjustment of the track circuit voltage to satisfy the above conditions simultaneously is possible with a careful choice of tapping on the regulating resistance. This is commonly referred to as 'the fail safe adjustment of D.C. track circuits. This is done in three stages to satisfy the conditions stipulated in the IRSE manual and given as below:- (1) With optimum feed voltage and maximum ballast resistance of the track, its relay voltage:- (a) When the minimum permissible shunt resistance is connected across, shall not be more than 85% of its drop away value; (b) Without a shunt across, shall not be more than 250% of its pick up value, and (2) With normal feed source voltage and minimum permissible ballast resistance of the track, its relay voltage shall not be less than 125% of its pick up value. 2.8 PROCEDURE FOR FAIL SAFE ADJUSTMENT: (1) First the highest possible (infinite) ballast resistance condition is erected by directly connecting the feed and regulating resistance in series to the track relay excluding track rails from the circuit , incase the length of track lead cables is more, the voltage drop in them shall be reckoned and the relay voltage readings shall be corrected to exclude this voltage drop.

(a) Minimum permissible TSR (0.5 Ω for wooden sleeper track and 0.25 Ω for concrete sleeper track)shall be connected across the relay.The relay voltage shall be adjusted to 85% of its drop away value by choosing the correct tapping on the regulating device.

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(b) Now, the shunt resistance shall be disconnected and the relay voltage shall be measured. It is more than 250% of its pick up value it shall be brought down by increasing the regulating resistance suitably.

(2) It is now necessary to check whether the minimum required voltage is available on the relay under minimum ballast resistance and normal feed voltage conditions. Also, in this condition, rail voltage drop cannot be ignored, as the relay voltage is just sufficient. Hence, the track is included in the circuit, by connecting the feed set and the relay to it at their respective ends. It shall now be checked if the relay has a voltage not less than 125% of its pickup value. However, the relay voltage shall not be increased now if found to be less, as in that case an improved ballast resistance condition can make the track circuit working unsafe. During the time of minimum ballast resistance condition, the track circuit shall be divided into two or more portions with separate relays. The feeding of these track portions is done as below:-

This arrangement is known as 'fed over' or 'cut section' track circuit arrangement. The relay connected to the last portion of the track is treated as the track relay of the entire. Section involved for the purpose of detection and other controls. 2.9 D.C. TRACK CIRCUITS (SIEMENS PRACTICE) A reliable source of 110V AC. power supply is a pre-requisite for provision of these track circuits as batteries are not used in this practice. A 110V/3-18V transformer is used for feeding each track circuit with different tappings for varying the output as required. The transformer output is fed into four bridge connected silicon diode rectifies. The rectifier output is connected to the track in series with a 2 Ohms 50 watt (fixed value) damping resistance for regulation. The feed set is located close to the track. A Drs 50 Siemens DC track relay is fed from the track. The same relay is used for track circuits of this practice both in non RE area and AC RE area.

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Since the pick up current of this relay is about 30 mA, it never draws more than 100 mA from the track. The feed end current of the track circuit is also correspondingly less as compared with track circuits in the British practice. So, with a lesser damping (regulating) resistance of 2 Ohms, satisfactory regulation is achieved in this when track is occupied. This makes it possible for longer track circuits of upto 600 metre length of this type to work well in non-RE area. Also, longer relay end track lead cables of 1.5 mm cross section copper conductors having more voltage drop can be connected without trouble. These track circuits can have a very good T.S.R due to the higher relay resistance connected. 2.10 D.C. TRACK CIRCUIT IN NON - RE AREA (SIEMENS PRACTICE)

Components: (1) Gl - Drs Track Relay - 66046/01f with coil 255 or risk 30/0071 (2) RD – Damping Resistance – 2 Ohm 50 W (3) GR - Rectifier - 4X6FMR60 silicon diodes connected in bridge with surge suppression. (4) Tr - Feed end transformer - Bs Br 9112/53. (5) f - fuse 1A. 2.11 D.C. TRACK CIRCUIT IN R.E. AREA (SIEMENS PRACTICE)....

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Additional components (1) Ch I - Relay end choke - Bs Br 9115/69 (2) Ch II - Feed end choke - BS Br 9115/70 Ch II can be omitted having a 100Ohm - resistance for RD

in place of 2 Ohms for track circuit lengths upto 200 metres. Minimum permissible ballast resistance in these track circuits (of RE area) is 0.65 Ohms/Km. When these track circuits are provided in AC RE. area where maximum traction current does not exceed 600 A and short circuit current does not go beyond 3000A, the following are the permissible track circuit lengths:

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CHAPTER – 3 S5B

AC. TRACK CIRCUITS 3.1 A.C.Track Circuits are provided where D.C. Track circuits cannot work. The working of an AC Track relay requires not only a good voltage from the track but also a considerable phase difference in track voltage with reference to the voltage applied to one of the relay windings locally. Even as a good phase difference is maintained at the track feed end, it gets reduced at the relay end due to the transformers, impedance bonds, relay winding and the ballast resistance in the circuit. Also, the phase angle gets shifted when the ballast resistance changes according to weather. These effects create problems for efficient and safe maintenance of the track circuit. Hence A.C. Track Circuits are provided exclusively in DC traction areas confined to Bombay Divisions of Western and Central Railways. It is possible to work A.C. Track circuits with A.C. traction also, provided the track circuit supply frequency does not have even a harmonic relation with the traction power frequency of 50Hz. 83 1/3 Hz frequency is chosen for this purpose and these track circuits are used in A.C.Traction areas including the places where DC electric traction ends and AC traction starts. In areas of exclusive AC traction of our railways, the usage of AC track circuits is tried out for some time due to the tempting possibility of working very long AC track circuits. However, this practice is not continued for long there, due to the problems in maintaining a good phase angle on these track circuits. DC track circuits are preferred there now. Introduction of electronic track circuits of high impulse type and audio frequency type on our railways created prospects for gradual and widespread replacement of many conventional DC and AC track circuits. AC and Electronic track circuits in RE areas can be broadly classified as (1) Single Rail track circuits and (2) Double Rail Track Circuits conventional AC track circuits of both the types are dealt with here.

Single Rail track circuits as already seen in the case of DC track circuits in AC RE area, are those in which traction return current also passes through one of the two track circuit rails. In these the traction return current passes from one track circuit to another through transverse bonds provided by the traction power department .

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Double Rail track circuits are those in which the traction return current passes (in the same direction) through both the track circuit rails (even as the track circuit current passes in the same direction in one rail and in the opposite direction in the second rail). Traction return current from both the track circuit rails passes into the adjoining rails through the centre tap of an 'impedance bond' provided by the S&T department. But the track circuit current is confined within its limits by the block joints provided on both the rails at its ends. Most of the current from the feeding transformer flows through the relay and the ballast, even though small leakage currents through the impedance bonds cannot be avoided. British practice of AC track circuits which was initially followed on the Bombay divisions of Western and Central Railways has given way to the Siemens practice as progressively Siemens installations have been introduced there. As Railways switched over to AC. traction, Siemens practice is the only prevailing one on our railways at present. Hence, our study will be confined to this. 3.2 SUPPLY ARRANGEMENTS FOR TRACK CIRCUIT FEEDING:- A reliable 3 phase AC supply is a pre-requisite for working AC track circuits in Siemens practice. All the track relays are fixed in the cabin relay room. In DC traction areas, a 440/110-130V transformer is provided in the cabin for this purpose. A 3 phase 130V 50Hz output from this transformer is taken on a ring main busbar to the track relay racks. Where 83 1/3 Hz AC. track circuits are provided 440V 3 phase 50Hz AC supply is fed into a frequency convertor (preferably static). 165V 83 1/3 Hz 3 phase output from this converter is taken to the track relay racks in the relay room. Another 110V 3 phase feed is taken as output from the transformer or inverter, as the case may be, and fed to a ring mains busbar taken to various location in the yard for track circuit feeding. 'Track feed phase distribution plan' for the yard is prepared well in advance to nominate phases between which individual track feed transformer connections at site and their corresponding relay local coil phase connections in the cabin are to be made. While making this plan, (i) load on each phase is sought to be balanced as far as possible and (ii) Staggered phase connections are made on adjacent track circuit rails to avoid unsafe conditions at the time of block joint failures.

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3.3 A.C SINGLE RAIL TRACK CIRCUIT

110V 50 Hz AC supply or 110V 83 1/3 Hz AC supply between the nominated phases in the location box is connected as input to the track feed transformer for stepping down. l Its output from a suitable tapping on its secondary is taken with a 3 Ohm damping resistance in series to the track lead J.Box or Bootleg on a 2 core cable of 1.5 mm2 or 2.5 sq. mm copper conductors. Multistrand wires ropes connect the feed to the track rails. At the relay end, track leads are taken similarly to the J.Box or bootleg. From these, a 2 core 1.5 mm2 cable takes this feed to the relay end step up transformer with a 2 ohm protective resistance in series. From the secondary of this transformer feed is taken on a common cable from location to the cabin to be connected there to the relay control coil. The relay local coil is connected in the cabin between the nominated phases of the ring main busbar of 130V 50Hz or 165V 83 1/3 Hz, as the case may be . At the end of this track circuit a transverse bond is connected by the traction power department if there is a track circuit or there is no track circuit on the adjoining rails. If there is a double rail track circuit adjacent to this, a multistrand wire rope known as neutral connection is joined between the uninsulated rail of this track circuit and the centre tap of impedance bond by the side. 3.4 IMPEDANCE BOND It is a device used for bonding the rails of a Double Rail track circuit with adjacent track rails for the purpose of conducting traction return current while blocking the track circuit current to pass within its relay circuit. The construction of an 'impedance bond' is as given below :-

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There are two copper coils in the bond wound on a shell type core. One is called the 'Main or Buffer coil' which consists of about 8 to 10 turns of a heavy cross section. This carries the large traction return current when connected between adjacent rails across block joints at the end of a track circuit. The second winding is called as the 'Auxiliary Coil' which has a large number of turns of a smaller cross section with different tapping for connection. This windings is used along with a 10 ∝f condenser to resonate the output circuit. This circuit resonation makes it possible to draw maximum current from the given input voltage and improves the output phase angle also. A surge anestor is also connected to protect the condenser in the auxiliary coil. Higher inductance of the auxiliary coil having many turns facilitates the usage of a small condenser. The impedance bond coils are included in the track circuit with a transformer type connection. At the track circuit feed end, the auxiliary coil with the condenser in series acts as the primary circuit to draw power from the track feed transformer secondary. Hence, the series resonating Condenser also serves as the 'Regulating Device' for dropping a large voltage across it under track occupation. The main coil acting as the secondary steps down the feed voltage to less than 5V on open circuit and feeds it to the track rails when connected across them.

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At the relay end of track circuit, the track rail voltage gets impressed on the main coil of the bond which form the primary. On the secondary side, the auxiliary coil steps up the voltage to over 25V and feeds the relay control coil. On the relay end impedance bond, a 10 ∝f condenser is connected in parallel on a carefully chosen tapping of the auxiliary coil. This condenser is known as the 'phase shifting condenser' as it serves to improve the output phase angle of the bond so that the relay rotor gets the best possible torque, by the choice of right tapping on the auxiliary winding for its connection. 3.5 FLUX SYSTEM IN THE BOND CORE:

AS can be seen from the diagram, half the number of turns in the bond main coil carry traction return current in one direction and the other half in opposite direction. Due to these currents, the fluxes established in the core are in opposite direction. They are also equal if both the rails carry equal current to the bond. In that case, no flux due to traction return current remains in the core. Hence, when track circuit current tries to pass through all the coil turns in the same direction a very high inductance causing reactance of the order of 3 Ohms or more is encountered by this current. A very low current only can leak through this path while sufficient current passes through the relay coil in parallel and operates it. 3.6 EFFECT OF UNBALANCED TRACTION RETURN CURRENTS THROUGH BOND IN

DC RE AREA. Due to some loose bonding on one of the rails or some such reasons, if traction current through the rails is unequal, bond core retains the difference of fluxes due to the unbalanced traction return currents. This can saturate the core if the retained flux rises to a high level. Such a condition may occur when a train is started in approach of the track circuit. In saturated condition of the bond core, the track circuit current through bond coil encounters a very negligible inductance as it cannot create any further flux in the core. This causes a heavy leakage current through the bond coil making the track relay to drop. To obviate this, saturation of the core by unbalanced traction currents in the bond coil is prevented by increasing the core reluctance. This is done by means of a thin sheet of nylon on the core limbs above as shown in the diagram.

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3.7 IMPEDANCE BOND IN AC.RE AREA (1) The Impedance bonds in AC. RE area carry lesser traction currents due to higher voltage of 25 KV as against 1500V of DC used for traction. Because of this, the cross section of the main coil conductor required is less and hence these bonds are smaller. (2) Due to the higher frequency of track circuit current used in this area (83 1/3 Hz instead of 50Hz) the impedance of the bond increases to nearly 5 Ohms from about 3 Ohms of those in D.C traction. (3) No provision of nylon sheet in the core for increasing its reluctance is required in these bonds as core does not get saturated by the traction currents. The reason for this is that the traction currents through the two halves of the bond main coil exhibit a self balancing features as explained below:- When unequal currents flow through the two half windings of the bonds main coil, unequal fluxes are created in the core by these. But since traction current is AC and the flux created is alternating, back emf's are induced in the two half coils in such a manner that the currents balance themselves out. 3.8 AC DOUBLE RAIL TRACK CIRCUIT

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A 110/25-75V step down track feed transformer draws its input from two nominated phases of supply in the location box. Its secondary output is taken on a cable to the impedance bond provided on the track at feed end. The supply is connected to suitable tapping on the auxiliary coil of the bond with the 10 ∝f regulating condenser in series. The main coil of the impedance bond is connected across the track rails with two multistrand steel wire ropes known as 'side connections' of the bond. The voltage is stepped down on the bond at the feed end. The center tap of the bond main coil is connected to the adjoining track circuit by means of a 'neutral connection' wire rope. At the relay end of the track, the main coil of another impedance bond is connected across the rails to draw about 1V from the track. This will be stepped up suitable on the auxiliary coil of the bond. Also, the phase angle of this voltage gets corrected as required by the connection of 10 ∝f bond condenser on suitable tapping of its auxiliary coil. This output voltage at a phase angle above 60

o with respect to source is fed to the relay end track lead cable on the bond which is laid upto the cabin relay room. This voltage is applied to the track relay control coil. The relay local coil is connected on the rack to nominated phases of local supply. At the relay end also, the center tap of impedance bond main coil is joined with the adjacent track circuit. In all the AC track circuits, a voltage between 130% and 200% of relay safe pick up value is maintained on the control coil of the relay. The local coil voltage is 130V @ 50Hz or 165V @ 83 1/3Hz as already mentioned. A phase difference of 60o – 90o is to be maintained between the control coil and local coil voltage of the relay for reliable working of the track circuit. A minimum T.S.R of 0.15 Ohm is permitted to be maintained on these track circuits. Whereas a good T.S.R can be easily obtained on a single rail track circuit, it requires careful adjustment of track voltage and phase angle on the double rail track circuit to get the required minimum T.S.R of 0.15 Ohms.

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CHAPTER - 4. S5B

TRACK CIRCUIT PRACTICE. 4.1 INSTALLATION AND MAINTENANCE. Before installing a track circuit, the portion of track to be included is made properly conductive and exclusive so as to make it fit for track circuiting. A straight track portion of welded rails does not need any props 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. The rails have to be additionally connected with Continuity Rail Bonds. 4.2 Rail Bonds

8SWG Galvanised Iron wires are shaped as shown to make 'Rail Bonds'. To fix a pair of bonds at each rail joint, holes are drilled on the rails with a 6.9mm drill. The bond wire ends are inserted in these holes and channel pins are driven to hold them tight. Two bonds are used together so as to get lesser bond resistance at the joints. This also ensures that one of these bonds at least is always secure. Two types of channel pins are in use. One has only one grove to hold bond wire. The other one has two groves so that two wires can be held by the same pin. Two bond holding clamps called 'Bond Wire Protectors' fixed on the fish bolts of joint as shown ensure that the bond wires do not loose-hang, swing under the train and get entangled with any hanging part of vehicle. The following precautions shall be taken while providing these rail bonds: (1) The bonds shall be fixed without much delay after drilling holes so that the holes do not get rusty. (2) Drilling of holes and driving the channel pins through them shall be done in the same direction to ensure proper riveting of the pins.

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(3) Channel pins shall be driven with a 1 1/2kg. hammer for their proper hugging in the holes. (4) Bond wires shall not be provided between the rails and fish plates as they can not be easily checked. (5) Holes for bonding shall be as close to the fish plates as possible. At switches and crossings, additional bonding is also required between :- (1) The heel of a cut-heel switch and lead rail (2) The lead rail and the stock rail. (3) The wing rail and the point rail. (4) The wing rail and the splice rail (5) The splice rail and the nose rail.

In addition to these 'Continuity Rail Bonds' provided by the S&T department in RE areas, traction power department also provides high current capacity bonds at the rail joints for traction return current passage. Traction bonds can be found throughout the length of track whether track circuited or otherwise. In AC RE areas, mild steel flat is used for this purpose whereas multi-strand copper wire ropes are used in DC RE areas. In fact, traction power bonds also can serve the purpose of track circuit continuity. But their becoming loose or breaking at one or two places does not affect traction as much as it fails the track circuit. Hence, providing of rail bonds by the S&T department is considered essential at all places. (2) Secondly, the track portion to be detected has to be electrically isolated from adjoining rails so as to block the track circuit current, within its boundaries by providing 'Block Joints' at each end of the track circuit. This is, however, not necessary in case of coded Track circuit such as Audio Frequency track circuits in which frequency coding takes care of this need. Also on track circuits in which additional rail connections such as turnouts are to be included more block joints are required to include them without shorting track circuit rails. These joints have to be provided in all types of track circuits including coded ones. 4.3 BLOCK JOINTS (INSULATED RAIL JOINTS). Two types of these joints are presently in use, viz(1) Nylon Insulated Rail joints and (2) Glued Rail Joints. 4.4 NYLON INSULATED RAIL JOINTS In this type, insulation components are supplied by the S&T department, which have to be inserted in the rail joint when track circuit is being installed and also whenever they get crushed under traffic resulting in insulation failure. To prevent failures under normal conditions block joint insulation is checked electrically by means of a meter by the S&T staff according to a time schedule. The metallic components of the rail joints as supplied by the civil engineering department for this

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purpose are not the usual ones. The fish plates are planed so as to accommodate insulation liners between the rails and themselves. The fish bolts have to be of 140mm length instead of 115mm. Also, four steel backing plates have to be provided for support over the nylon backing plates held by fish bolts.

The insulation components of the rail joint are: (1) End post 1No (2) Left hand Side channels 2 Nos. (3) Right hand Side channels 2 Nos. (4) Ferrules or Bushes 8 Nos. (5) Nylon backing plates with coller 4 Nos. (6) Nylon backing plates w/o coller or as required for packing. nylon washers. These insulation components are available in different sizes to suite different weightages of rails, Viz. 60 kg, 52 kg, 90 R, 75R etc. Proper components only shall be used according to the rail weightage. Even left hand side channels and right hand side channels shall not be interchanged after locally sizing them up to avoid insulation break down on these joints. Certain precautions have to be taken while installing and maintaining these block joints as detailed below :- (1) The rail ends at these joints shall be cut straight as otherwise, the nylon end post may break very quickly. (2) All the holes on the rails shall be drilled at the same height. (3) The holes in the rails and in fish plates shall be in correct alignment. Bolts shall not be forced into the rails, nor shall they be bent and pushed in as the bushes can thus get crushed. (4) Rail chairs are replaced by steel bearing plates on one sleeper each holding rails on either

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side of the joint. These plates shall be fixed sufficiently clear of rail ends to avoid their short circuiting . (5) Dog spikes that hold the bearing plates on to sleepers shall not touch the fish plates and they shall be tightly driven in the sleepers. (6) Packing of a couple of sleepers on either side of these joints shall always be good and no water logging shall be allowed near them. (7) The fish bolts of these joints should not roll due to swing under the traffic. For this, the steel backing plates shall be properly bent on the sides to hold the nuts and bolt heads. 4.5 GLUED RAIL JOINTS (As per RDSO Manual of 27.9.90). Glued Rail Joints are available in two types: (1) G3(L) type having 6 bolts and (2) G3(S) type having 4 bolts. The drawings for the same of different rail sections are: ---------------------------------------------------------------------------------------------------------------- S.No. Rail Section Drawing No.of ------------------------------------------------------------------------------- G3(L)type G3(S)type ----------------------------------------------------------------------------------------------------------------- 1. 75R RDSO/T-1283 RDSO/T-3008 ----------------------------------------------------------------------------------------------------------------- 2. 90R RDSO/T-1276 RDSO/T-1278 ----------------------------------------------------------------------------------------------------------------- 3. 52kg RDSO/T-671 RDSO/T-1259 ----------------------------------------------------------------------------------------------------------------- 4. 60kg(UIC) RDSO/T-2572 RDSO/T/2576 ----------------------------------------------------------------------------------------------------------------- The joints are fabricated in a workshop and transported to the site for insertion in the track. G3(L) type joints shall be used with CWR and LWR of 75R, 90R, 52kg and 60kg(UIC) rail sections in all temperature zones. I, II, III, & IV, both in B.G. and M.G. G3(S) type joints may be used in Fish plated track and SWR panels of 75R,90R, 52kg and 60kg (UIC) in temperature zones I, II, III & IV both in B.G and MG. Laying of these joints involves civil Engg. works viz.destressing of welded rails, welding of the joints into running track etc.. Hence these are laid by the civil Engg. Dept. 4.6 Materials used for fabrication of Glued Joints. ----------------------------------------------------------------------------------------------------------------------------- S. Description Quantity for Remarks No. G3(L) G3(S) ----------------------------------------------------------------------------------------------------------------------------- 1. Rail Piece of min.4m length.1No. 1No. 2. Fish Plates 2Nos. 2Nos. Steel to conform to IRST-1/M.37 3. Punched Washers 12Nos. 8Nos. or IS 1875-class IV. 4. Insulating Bushes 6Nos. 4Nos. To be fabricated as per 5. Insulating end post 1No. 1No. procedure described below. 6. Insulating Liners 2Nos. 2Nos. 7. HTS Bolts with nuts. 6Nos. 4Nos. Bolts:24X140mm-IS 1363-1967. Nuts Hexagonal M24-IS1363-1967 8. Adhesives As required. 9. Glass cloth carrier 4 pieces 4 pieces Cut to sizes as specified below and used for fabrication. -------------------------------------------------------------------------------------------------------------------------------

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The insulating components viz. bushes, liners and end-posts are fabricated using glass cloth reinforcement and epoxy of an RDSO approved quality with hardener by a hand laying process or pressure moulding technique. These are built up layer after layer to achieve sufficient thickness. Generally end posts are made of 20 layers, liners of 4 layers and bushes of 5 layers. After making a rectangular piece of glass cloth reinforcement and allowing it to cure, it is cut and profiled to the shape of an end post. The liners are fabricated in the hollow of a rail web. The bushes are cut to size from a long ferrule made by winding a wide piece of glass cloth on a bolt shank layer after layer with adhesive in between. The fabricated component is able to be separated from the surface on which it is made due to a coat of a releasing agent applied beforehand. All the insulating components of the joint are stuck in place with an adhesive layer and the bolts are tightened for a permanent setting.

4.7 Maintenance of Glued Joints. 1. The ballast used on track in the vicinity of these joints shall be cleaned to ensure efficient packing and drainage. Care must be taken to see that the ballast is clear of rails and rail fastenings. The clearance from the underside of rail must not be less than 50mm. 2. The joint does not need any special maintenance than that required for normal track. 3. As in the case of standard insulated joints, the metal burrs at the ends of rails shall be removed well in time to avoid short circuiting through them. This work shall be done skillfully avoiding damage to end posts. 4. Normally no relative movement occurs between rails and fish plates at these joints. In case failure occurs with separation of rail/fish plate surfaces and relative movement takes place, the damaged joint must be replaced soon. The electrical resistance of the joint does not decrease appreciably for a considerable time even after this separation. 5. Live cinders shall not be dropped near these joints which can cause damage to them. Protective boxes of asbestos or some such things shall be provided for these joints at places where this can not be avoided. Testing of Glued Joints i.e., Insulation Resistance test in Dry condition: Resistance shall not be less than 25 Megohms when a meggaining voltage of 100V DC is applied across the joint. In wet condition: Resistance shall not be less than 3 kiloohms when obtained with application of 100V DC and by dividing the voltage reading with that of current. Precautions needed while inserting a glued joint. (1) At least 10 sleepers on either side of the joint must be well packed before the joint is inserted

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to avoid damage /fatigue of the joint. (2) No damage shall be caused to the joint while inserting. (3) While welding the joint with adjoining rails, the heat shall not spread to the joint. Heating appliances shall not be applied at a distance of less than 1m from the joint. 4.8 TRACK CIRCUITING TURN-OUTS Additional block joints and rail bonds need to be provided on track circuits having point turn-outs in them. They are required in order to avoid electrical short on each road by the rails of the other on diversion and also to ensure that the track relay gets shunted in all portions of the track. Also, while providing end position block joints on turnout track circuits, protection to running or stabled vehicles shall be ensured near fouling marks by spacing them with care. It is also preferable, wherever possible to provide for detection of rail breakage in a track circuit by including all the track circuit rails in series between the feed and the relay ends. For track circuiting turnouts, depending on the mode of connection between the rails of different track circuit portions three types of arrangement are possible, viz. (1) Parallel connection (2) Series connection and (3) Series Parallel connection. The choice between the three depends on the location of track circuit and the required degree of safety for traffic or economy. 4.9 PARALLEL CONNECTION OF A SIMPLE TURNOUT

After providing two block joints in the middle of track circuit, the feed is extended on to the insulated rail by means of a small two core cable or a mild steel strap called 'Feed extension jumper'. This makes it possible for a vehicle to shunt the track relay while on the parallel portion of the track circuit. It is preferable to have the block joints in the middle on a less used track (i.e., diversion) to increase their life of insulation. 4.10 SERIES CONNECTION OF A SIMPLE TURNOUT.

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Here, three block joints are provided on the turnout and the track circuit ends of the two roads are joined by means of two cable jumpers. The relay is connected near the turnout as shown. The relay end and the connecting end of that track circuit portion may be interchanged if necessary to minimise the length of cable required. One block joint in this arrangement separates the rails of same feed polarity. The failure of this block joint brings the insulated portion of track circuit in parallel and this may not be detected till the block joint is tested. 4.11 SERIES - PARALLEL CONNECTION OF TURN-OUT.

In this arrangement of track circuit, only positive or phase polarity rails are connected in series at the turnout, keeping the rails of other polarity deliberately in parallel. This is necessary in electric traction areas to provide multiple paths for traction return current in the track circuit. Then only, interruption in one path does not force the traction currents to pass through the track circuit equipment and interfere with its working. In non RE areas also, sometimes this arrangement is preferred in view of economy in cable expenditure.

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4.12 TRACK CIRCUITING AT FOULING MARKS & PROTECTION

(1) A track circuit shall extend beyond fouling marks on both straight road and diversion portions to afford protection to the standing vehicles. In case, it is not possible to provide the block joints beyond fouling marks on any portion, the point operation to a position connecting the fouled line is prevented until the time the fouling vehicle clears the adjoining track circuit also. (2) With parallel connection of turnout track circuits, the nonclearance of fouling mark by a vehicle may not be detected when any connection in the parallel portion is broken. This shall be checked and avoided especially in case of the 1 in 8 1/2 and 1 in 12 turnouts. Hence, it is preferable to have series connection track circuits to have fouling mark protection on running lines. (3) The end position block joints on turnout track circuits shall be so located that not only the last axle wheels but also the overhanging portions of vehicle (1.8m) clear the fouling mark before the track relay picks up. 4.13 TRACK CIRCUITS ON A CROSS- OVER

Both track circuits end in the middle of cross-over as shown. Each half of the cross-over forms part of a multiple(parallel connection) track circuit on the main line adjacent to it. The thick lines indicate traction return rails in RE area. In non RE area the transverse bonds are not provided. Positive feed jumpers in RE area and all feed jumpers in non RE areas are provided by the S&T staff. Each track circuit has 6 block joints on the turn outs with two more block joints in between. 4.13.1 TRACK CIRCUITS ON A DOUBLE (or) SCISSORS CROSSOVER

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(a) Parallel connection:

In this arrangement also, the cross-over portion has two parallel connection track circuits including the adjoining main line in each . In RE area, the transverse bonds and two traction power jumpers on each track circuit are provided by the traction department. In non-RE area, negative feed jumpers are provided in place of traction jumpers by the S&T staff and no transverse bonds are needed. Each track circuit has, in addition to four end-position block joints on main line, four block joints exclusively on cross overs and four block joints in between to separate the track circuits. The cross over portions have twelve block joints in all. b) Connection with positive rails i(n series.

In this arrangement the positive feed of track circuit (1) is interrupted at (A) and (B) by two separating block joints. A positive cable jumper is connected as shown to extend the feed on to the extreme portion on the right. Another Positive jumper (2) is connected between (c) and (d) to bring the positive feed back to the turnout portion. In the second track circuit, one positive cable jumper (3) is connected between (E) and (F) as shown to make the positive rail connection a series one. Negative rails of these track circuits on the turnouts are not separated. 4.13.2 (3)TRACK CIRCUIT ON A DIAMOND CROSSING: (a) Parallel Connection

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In this four block joints are provided on the turn-out portion as shown and two positive feed jumpers are connected to include the parallel portions in the track circuit. (b) With positive rail in series.

In this arrangement, the feed and relay connections of the track circuit are shifted inside to the turnout portion. The positive rail ends on straight road and turnout are joined by means of two cable jumpers. (c) With both positive and negative rails in series.

The arrangement is almost similar to the one shown in (B) except that the negative rail on the turnout is brought in series by means of two separation block joints. 4.13.3 (4) TRACK CIRCUIT ON A SINGLE SLIP LAYOUT (a) Parallel Connection.

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The layout has block joint positions and positive jumper connections similar to those of a diamond cross over without slip and with both rails in parallel. (b) With positive rail in series.

On this layout the block joint positions and positive jumper connections are similar to those of a diamond cross over without slip and with positive rail in series. (c) With both positive and negative rails in series.

The same arrangement of connections as with a diamond cross over without slip can be repeated here.

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4.14 TRACK CIRCUIT ON A DOUBLE SLIP LAYOUT (a) Parallel wiring:

In this arrangement, 4 block joints are provided on turnout portion of straight roads and 4 more block joints on adjacent slip turnout portion. Two positive rail jumpers are provided. The feed and relay connections are made on one of the two tracks at the extreme ends. (b) With positive rail in series:

In this arrangement also, the 8 turnout block joints are placed exactly as in parallel connection. The positive rails at one extreme end of the layout are joined by a positive cable jumper. The feed and relay connections are made at the other extreme end. 4.15 TRACK CIRCUITS ON LADDER LAYOUTS:- (a)Parallel connection:

Here, for two turnouts on a ladder, 4 block joints and two positive feed jumpers are provided, while having the feed and relay connections on the first line.

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(b) With positive rail in series:

In this arrangements also, four block joints are provided on the turnout portions. The second line turnout block joints are provided on the straight road. The positive rails are connected in series by means of two long feed jumpers as shown. The feed and relay connections are close to each other on the first turnout. (c) With both positive and negative rails in series:-

In this arrangement, three block joints are provided on each turnout so that the negative rails are cut in the middle and included in series. For this purpose, one long and one short negative feed jumpers are connected as shown. The position of negative connection to the relay also gets shifted to the right of block joint as can be seen above.

Series parallel connection of track circuit on Double line layout where both the lines branch off to a side:-

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Three track circuits are provided on this double line layout. 1T has two block joints on the turnout with one positive jumper. The feed and relay of this track circuit are connected at extreme positions on either side. 2T has four block joints on the turnout with two positive feed jumpers connected as shown. Feed and relay are connected on the turnout close to each other. 3T has two block joints on the turnout. Its relay is connected at one extreme end of the line. Its feed is connected on the turnout as shown. In all the above layouts, the negative rails are shown with thick lines. In RE areas, these rails carry traction return current which is passed on to the adjacent track circuit through transverse bonds shown. In non RE areas, these bonds are not required. While the negative feed jumpers are provided by the traction power department in RE area, they are provided by the S&T department in non RE areas. 4.16 ADDITIONAL INSULATIONS ON POINT TURNOUTS IN A TRACK CIRCUIT: (1) Two or three William's stretcher bars provided on point turnouts have to be insulated in the middle to avoid a direct short across the track. Two half pieces of each stretcher are joined with two small support plates and three bolts. The insulation components of each stretcher bar are:- (i) Nylon Backing plates 2 Nos. (ii) Nylon bushes for bolts 3 Nos. (iii) Nylon washers for bolts & nuts 6 Nos.

(2) Gauge tie plates provided on wooden sleepers have to be insulated. Two pieces of this plate are joined with insulation between them. The insulation components for each plate are:

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(i) Nylon end post with 3 holes 1 No. (ii) Nylon bushes for bolts 3 Nos. (iii) Nylon washers for bolts & nuts 6 Nos. 4.16.1 (3) (a) With Electrical detectors provided on mechanical points: Insulation to be provided between detector rods and drop links:- 1 bush & 2 washers per rod. (b) With IRS type point machine: Insulation components provided between each switch rail and tongue attachment are: (i) Nylon liner plate 1No. (ii) Nylon Bushes 2Nos. (iii) Nylon washers 2Nos. c) With Siemens type point machine: Insulation components provided between each switch rail and D-bracket for rodding attachments are: (i) Nylon insulation plate 1 No. (ii) Nylon Bushes for bolts 2 Nos. (iii) Nylon washers for nuts 2 Nos.

(4) In addition, any rodding laid across the track and which is likely to short the two track rails has to be insulated. The rodding insulation joint has the following nylon components:

(i) Liner plate 1 No. (ii) Bushes for bolts 2 Nos. (iii) Washers for bolts & nuts 4 Nos.

4.17 DEAD SECTIONS IN TRACK CIRCUITS: These are defined as those portions of track circuits in which occupation by a vehicle cannot be detected. This may be due to the vehicle shunting rails of the same track feed polarity. This may also be due to one or both rails of that portion being bypassed by the track feed. The following are some of the examples where dead sections occur :- (i) The block joints position on track rails is staggered either (a) due to unequal rail creep,

particularly on curved tracks.

or (b) due to rail ends on cross-overs being out of square:-

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(2) A track portion is excluded from track circuit either (a) due to a level crossing road not allowing track circuiting of the covered area of track :-

or (b) due to a bridge or culvert being under the track.

or (c) due to a tram line passing across the railway track.

While allowing for dead sections in track circuits, the following precautions shall be taken so as to avoid unsafe conditions of traffic over them:- (1) The dead section shall not accommodate a four wheeler vehicle entirely in itself without shunting any 'live' portion of the track circuit at the same time. In B.G sections, the distance between the two axles of a four wheeler is 6m (20') and in MG /NG sections, it is 3.6m(12').

(2) If one trolley of an eight-wheeler gets entirely accommodated in a dead section, the second trolley of the same vehicle shall not go beyond the live portion of that track circuit in either direction.

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In B.G sections, the distance between the two axles of this trolley is 1.8m (6') and in MG/NG sections, it is 1.125m (3'9").

In this case, the track circuit shall extend on either side of dead section by more than 12m(40'). (3) If the dead section is longer than 10.8m(36') as in the case of long bridges underneath the track, a 'Trap Circuit' shall be provided including the control of dead section track by two other track circuits on either side as shown:-

4.18 TRAP CIRCUIT

The controlling relay contacts of BTR may be connected in series with the battery instead of relay, if desired. The working of Trap Circuit:

When the train coming from the left is trapped in the dead section, BTR which has dropped cannot pick up as ATR has already picked up and CT is not yet occupied. Similarly, when the train coming from the right is trapped in the dead section, BTR which has dropped cannot pick up as CTR has already picked up and AT is not yet occupied. BTR picks up only when the train passes over AT or CT after completely clearing BT and the dead section. Once picked up, it is kept energised through its own front contact till it is shunted again by a vehicle. If the last vehicles of a train get trapped in the dead section after parting from the train and the front portion goes ahead over the track circuit in advance, this cannot be detected. But this is very unlikely to occur. Also the vehicle trapped in the dead section of BT doesot detected at the time of AT or BT failing. 4.19 CUT SECTION TRACK CIRCUITS OR FED OVER TRACK CIRCUITS. This is an arrangement in which a track circuit is split into two or more sections with individual track relays and the feed for each latter section is controlled by the relay of former section.

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This is generally adopted when it is not possible to work a long track circuit due to the deteriorated condition of its ballast resistance, till the ballast condition is improved. The higher net ballast resistance of each portion as compared to its net value of the whole length of track makes this arrangement workable. This is also adopted in automatic signalling sections wherein the last control track circuit of each automatic signal is fed over the overlap track circuit of that signal. This method of control is termed as 'Automatic overlap system'.

In this arrangement, when 101 ATR goes down, 103TR which also controls S103 is still picked up but when 103TR goes down, 101ATR cannot pickup until 103T is also cleared by the running train. Thus while 101AT controls only S101, 103T controls both S101 and S103. 4.20 STRAY CURRENTS IN D.C 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 develops on the track. This can be observed when a voltmeter is connected across the track after disconnecting the concerned track circuit feed.

Beyond a certain limit, this voltage may prevent the track relay from dropping when track is shunted by a vehicle. The incidence of this phenomenon may be frequently observed in rocky territories where some power cables may have been laid in the vicinity. To obviate this problem immediately one of these methods may be tried:- (1) Interchanging the positive and negative connections of the rails, as in that case the stray voltage polarity becomes opposite to the proper feed polarity. (2) Interchanging the feed and relay ends of the track circuit as in that case, the stray voltage may disappear at the relay end. (3) 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, the track circuit may be replaced with an Electronic track circuit.

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4.21 REGULAR CHECKS AND PREVENTIVE MAINTENANCE OF TRACK CIRCUITS. (1) T.S.R: - It shall be ensured that under no circumstances, the failure of a track circuit results in a train passage under prohibitive conditions. Regular checks of TSR on each track circuit shall be carried out without fail. Any change of their components or adjustments shall be immediately followed by a test of TSR. For this, a fixed resistance of minimum TSR value is always available with the maintenance staff. (2) TRACK CIRCUIT HISTORY CARDS: Exact entries shall be made in them and no detail shall be neglected. Inspectorial staff shall carefully check these on every visit. Ballast resistance value shall periodically be calculated and monitored to avoid failures on this count in the near future. (3) TRI-MONTHLY JOINT INSPECTION OF SSE/JE(S) with JE/SE/SSE (P-Way) helps in carrying out timely preventive maintenance. The joint inspection involves block joints, condition of track ballast and drainage, clearance of ballast under the track circuit rails and packing of block joint and point sleepers. The broken and crushed insulations of block joints shall be replaced soon. (4) The condition of rail bonds shall be ascertained by taking track voltage readings on every fourth track circuit rail at least once in three months to avoid intermittent track circuit failures. This shall be recorded in the inspection reports. (5) Although the point rodding, stretcher and gauge tie plate insulations do not fail often, the packing underneath the point sleepers shall be well maintained to keep them in good condition always. A visual inspection on every visit to the site, particularly of tongue attachment liners and the recesses under the gauge tie plate joints helps in detecting a failure condition about to develop. (6) Just before the onset of monsoon, track relay voltages shall be checked once, not to be taken off guard in avoiding track circuit failures with the first showers. Also, on clearing of weather after monsoon, it shall be seen that the track relay voltages do not shoot up beyond safe limits. Particularly, early attention shall be paid to those track circuits on which adjustments are made during monsoon. (7) It is a healthy practice to keep all the section track relay voltages of recent inspection noted in the personal work schedule files or dairies of the concerned JE/SE/SSE. Whenever a new reading is noted, it shall be invariably tallied with the previous reading so that any unusual changes do not escape the attention of all concerned. (8) 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. (9) All the track circuit tail cables shall be meggered once in six months and replacements shall not be delayed in the case of cables showing less than 1 mega ohm insulation resistance. The condition of cable sheathing at the location entries shall not be missed during inspections. (10) Track circuit battery condition shall always be good and its voltage shall be measured after switching its charger off. (11) In busy yards, most of the track circuit maintenance, other than taking of voltage readings shall be carried out under permitted block except in cases of post failure maintenance works. 12. In no case, the regulating/damping/protective resistance’s shall be bypassed to avoid track circuit failures, particularly in monsoon. 13. Anti-tilting devices shall be provided with shelf type track relays and they shall not be tampered with. 14. Chargers used with track circuit batteries shall be rated for not less than 3 ampers.

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4.22 TRACK CIRCUIT FAILURES These failures are basically of two kinds: (1) Track circuit does not get shunted properly by vehicles. (2) Track relay drops when track is not occupied, either (a) intermittently or (b) continuously. Some guidelines are given below for finding out and rectifying certain general faults in track circuits. 4.22.1 (A).COMMON FAILURES Shunting Failures: --------------------------------------------------------------------------------------------------------------------- S.No. Symptons Check for Remedy --------------------------------------------------------------------------------------------------------------------- 1. Failure occurs in certain (1) Loose or missing Replace the missing bonds parallel portions of track rail bonds or their high or drill new holes on rails to circuit. resistance. reconnect them. (2) Broken or loose feed Reconnect them. jumpers. --------------------------------------------------------------------------------------------------------------------- 2. Failure at feed end or relay (1) Excessive relay voltage end of D.C. track circuits. caused by---- (a) Charger boost. Decrease charger output suitably. (b) Drastic increase in Readjust the track voltage ballast resistance. suitably. --------------------------------------------------------------------------------------------------------------------- 3. Failure at relay end or feed (1) Excessive relay voltage Readjust the feed end end of AC track circuits. due to increase in ballast transformer tappings and if resistance. necessary bond condensor connections at feed and relay ends in a Double rail track circuit. (2)Highly increased phase Monitor source phase angle angle due to increase in for some time after adjusting ballast resostance. track voltage to avoid futher failures. (3) Improved phase angle at source. --------------------------------------------------------------------------------------------------------------------- 4.22.2 II. Track relay repeater drops intermittently. --------------------------------------------------------------------------------------------------------------------- S.No. Symptom Check for Remedy. --------------------------------------------------------------------------------------------------------------------- 1. Sluggish track relay operation Low track relay voltage with its low voltage. caused by (a) Mains voltage reduction. 1) Restore the health of track battery in a DC track circuit(or)

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(2) Increase feed transformer tappings and monitor source voltage of AC track circuits. (b) Defective block joints. Replace the defective insulation if found.Remove rail burr or iron filings on end post. (c) Defective point rodding Replace the defective or stretcher or other insulation if found. Check insulations( a rare carefully for any small occurence) metallic object wedged under guage plate insulation, when relevant sleeper packing is loose. --------------------------------------------------------------------------------------------------------------------- 2. Track relay drops 1) Loose or broken rail Replace or reconnect the occasionally with no bonds defective bonds. constant reduction in its voltage. 2)Loose series feed jumper Reconnect them properly. connections or track lead connections. 3.Relay voltage disappears (1) Block joint or other Locate and replace the for a particular setting of insulation defect in the defective insulation. points in the track circuit. track portion connected with that point setting only. (2) Loose bonding or other Replace or reconnnect the connections or bad jumper defective bonding or other cable insulation in the track connections and repair the portion connected with that defective cable. point setting. --------------------------------------------------------------------------------------------------------------------- 4. Track voltage disappears Defective block joint Replace the defective soon after a vehicle movement insulation over which the insulation and is restored after another previous train has just movement. passed before failure. --------------------------------------------------------------------------------------------------------------------- III. Track relay dropped Low track relay voltage Necessary voltage continuously caused by faults mentioned adjustments or insulation above. replacements or repairs to defective connections as mentioned above. --------------------------------------------------------------------------------------------------------------------- 4.22.3 (B.) D.C Track Circuits faults. --------------------------------------------------------------------------------------------------------------------- 1. Intermittent dropping of (1) Low battery voltage after Replace the defective cells and track repeater relay. switching the charger off. boost the charger output for the time being, if necessary. (2) Loose battery connection Remake a secure connection.

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(3) Loose connection on Secure and resolder the loose regulating resistance connection, if possible or particularly on the coil replace the defective regul- side of a pot type resistor. ating device, if necessary. --------------------------------------------------------------------------------------------------------------------- 2. Continuous dropping of Dry solder developed on shelf Resolder the defective coil

track relay. type track relay coil connection and check for connection. restored continuity and relay

operation. Replace the relay if necessary.

--------------------------------------------------------------------------------------------------------------------- 4.22.4 (C.) A.C.Track Circuit faults. --------------------------------------------------------------------------------------------------------------------- S.No. Symptoms Check for Remedy --------------------------------------------------------------------------------------------------------------------- 1. Intermittent dropping of(1) Low relay control (1) Readjust the feed end transformer track repeater relay. voltage. tappings. (2) Low control phase (2) Changing the impedance bond angle. auxiliary coil connection of

condensor, check for improvement, first at the relay end and then at the feed end.

(3) Check the Impedance bond coil insulation with a megger. If low, check again after changing the insulation oil. If there is no improvement, replace the bond.

4) Boost the relay end transformer or impedance bond output if necessary. 2. Track relay dropped In addition to the continuously above checks, also check the following:- (1) Surge discharge Surge discharge is affected by an condition in the impe- excessive traction return current in dance bonds of a that path. Check and repair broken double rail track circuit. traction bonds in parallel paths with

the help of traction power department.

(2) Insulation resistance Replace or repair the defective track of track lead cables lead cable if found. Repacking and and their multilation at drainage clearance may be the entry into the necessary under the sleepers impedance bonds. between which the impedance bond is placed. Faults peculiar to electronic track circuits are dealt with in their respective studies.

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Nevertheless, trouble shooting shall be carried out without ruling out any sort of open circuit and short circuit conditions on all components of track circuit with an open mind, however. Remote the chances of fault occurrence may seen. Some of the fault conditions obtained on track circuits in electric traction areas call for very keen observation and reasoning for comprehending them quickly. Particularly in conventional AC track circuits the vagaries of shift in phase angle of a double rail track circuit of good length may be perplexing sometimes. Recording of all the voltage readings at different locations and their comprehensive study together may clarify many doubts at the time of failure. A definite pattern of checks shall be followed to localise the fault quickly without many presumptions. A more daunting work than others is the localisation of a short circuit on the track portion. For this purpose, the relay end leads shall be isolated first and the track voltage reading taken with a meter across rails near the insulation joint under check. It is advisable to start checking the track circuit from its relay end by taking voltage readings at different locations. In the case of poor phase angle in an AC double rail track circuit, first, it may be ascertained if the track relay picks up with reversal of track lead connections. If it picks up, it calls for a reduction of phase angle. If it does not, it requires an increased phase angle., The chances of increasing or reducing the phase angle by changing the relay end impedance bond connections shall be exhausted, first. This is because any change in the feed end bond condensor connections alters the track voltage also considerably. After making this change at the feed end, the feed transformer connections also may need a readjustment.

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CHAPTER - 5 S5B

ANNEXURE-1

DETERMINATION OF REGULATING REGISTANCE AND MAXIMUM. WORKABLE LENGTH FOR A GIVEN TRACK CIRCUIT IN BRITISH PRACTICE. This is done in the light of three stipulated track relay excitation conditions as per IRSE Manual. (Q) 1. Find the value of regulating resistance for a track circuit with the following data: (1) Normal Bat. Voltage = 2V (2) Max. Bat. Voltage = 12.V. (3) Length of track circuit = 400m. (4) Max. Ballast resistance = 20Ω (5) Min. Ballast res. = 1Ω / km. (6) T.S.R = 0.25 Ω (7) Relay end track lead cable res. = 2Ω (8) Feed end track lead cable res. = 0.5 Ω (9) Relay coil res. = 2.25 Ω (10) P.U. V. of relay = 0.2V (11) D. A. V. of relay = 0. 14V Note: If DAV is not given, % Rel may be presumed as 68%.

(A) (1) With Max. Bat voltage and RB (max) on track relay voltage shall be not more than 250% PUV, VR = 2.5 X 0.2 = 0.5V. (250% of PU value) Max. Ballast res. of track @ 20 ohm /krn, RB = 20/0.4= 50Ω (RB for 400 meters) Relay current, IR = VR/ RR = 0.5 / 2.25 = 0.222A (voltage across TR when RB max = 50 Ω) Voltage drop in relay end cable, VCR = RCR. I R = 2X0.222 = 0.444V. Track Voltage, VTr = VR + VCR = 0.5 + 0.444 = 0.944V (i) Ballast current, IB = VTr / RB(max) = 0.944 50 = 0.019A Feed end track circuit current, IT = IR - IB = 0. 222 + 0.019 = 0.241A Voltage drop in feed end lead cable, VCF = RCF. IT = 0. 5 x 0.241 = 0.1205V (ii) Voltage drop in Reg. resistance, VT= EMax - (VCF + VTr) = 2.2 - (0.12+0.944) = 2.2 - 1.064 = 1.136V. Regulating resistance, RT = VT / IT = 1. 136 / 0.241 = 4.71 ohm (B) Under the same Emax and RB (max) conditions, with a TSR of 0.25 ohm across, the relay voltage shall be not more than 85% D.A.V., i.e., 0.85 V, i.e 0.85 x 0. 14 0 = 0.12V

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Resistance across AB = RB. RS. (RCR + RR) / [ RB-RS+RB(RCR +R R)+RS(RCR+RR)] = 50 x 0.25 x (2+2.25) / [(50xO.25) + 50(2+2.25) + 0.25(2+2.5)] = 50 x 0.25 x 4.25 / [ 12.5 + 212.5 + 1.06] = 0.235 Ω Total circuit resistance = 4.71 + 0.5 + 0.235 = 5.445 Ω Feed end track current, IT = 2.2 = 0 . 404 A 5.445 Total circuit resistance = 4.71 + 0.5+0.235 = 5.445Ω Feed end track current, IT =2.2 = 0. 404AΩ 5.445 Voltage drop in reg. resistance VT = IT. RT = 0.404 X 4.71 = 1.903V Voltage drop in feed end cable, VCF = IT . RCF = 0.404 X 0.5 = 0.202V Total voltage drop at feed end = VT + VCF= 1.903 + 0.202 = 2.1015V Track voltage, VTr = E(Max) - 2.105 = 2.2-2.105 = 0 . 095V. This is less than the max. permitted voltage under this condition, i.e 0. 12V. Hence RT of 4.7 1 ohm is a safe value (C) With normal battery voltage and min. RB on track, the relay voltage shall be not less than 125 % PUV., i.e. 0.25V.

Min. RB @ 1 ohm / km = 1 / 0. 4 = 2.5 ohm Resistance across AB = 2.5 X (2+2.25) / 2.5 + 2 + 2.25 = 2.5X4.25 / 6.75 = 1.574ohm

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Total circuit res. = 1.574 + 0.5 + 4.71 = 6.784Ω Feed end track current, IT = E / 6.784 = 2 / 6.784 = 0.295 A Voltage drop in reg. res, V T = IT. RT = 0.295 X 4.71 = 1.385V Voltage drop in feed end cable, VCF = IT.RCF = 0.295 X 0.5 = 0. 148V Total Voltage drop at feed end = VT + VCF = 1.385+0.148 = 1.533V Track volt age VTr = 2-1.533 = 0.467V Ballast current = IB = VTr / RB = 0.467 / 2.5 = 0. 187V Relay current, IR = IT - IB = 0.295 - 0.187 = 0. 108A Relay voltage, VR = IR.RR = 0. 108X2.25 = 0.243V This is slightly less than the min. required relay voltage for reliability. Hence, the track circuit length shall be reduced accordingly. Actually, the same has been stipulated as 350m. (Q)2. What is the required regulating res. of track circuit with the data given below and what is its max. workable length? 1 . Relay used - QTA2 with one choke of 3 Ω res. at feed end. 2. P. U. V. of the relay = 1.38V 3. D. A. V. of the relay = 0. 97V 4. Max. Bat. Voltage = 6.6V 5. Normal Bat . Voltage = 6V. 6. Feed end cable res. = 0.5 ohm 7. Relay end cables res = 1.0 ohm 8. T. S.R = 0. 5 ohm 9. Nfin. Ballast res. = 2 ohm /Km. A. (i) With max. battery voltage and Infinite ballast res. on track (since max. RB is not specified), the track relay voltage shall be not more than 250% P.U.V. i.e., 2.5 x 1.38V = 3.45V

Relay voltage, VR = 3.45V Relay cur-rent, IR = VR / RR = 3.45 / 9 = 0.383A = IT also

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Voltage drop in relay end cable, VCR = 1 X 0.383 = 0.383V Voltage drop in feed end cable, VCF= 0. 5X0. 3 83 = 0. 1915V Voltage drop in choke, VCH = 3X0.383 = 1. 149V Voltage drop in reg.res. = E(Max) – (VR+VCR+VCF+VCH)

= 6.6 - (3.45+0.383+0.1915+1,149)

= 6.6 - 5.174 = 1.426V Regulating Res., RT = VT / IT = 1.426 / 0.383 = 3.81 ohm (ii) With the same conditions of track and a 0.5 ohm shunt across it, the relay voltage shall be not more than 85% D.A.V. i.e., 0.85 X 0.97 = 0.82.5V

Resistance across AB = 0.5X10 / 10.5= 0.476 ohm Total circuit res. = RT + RCH + RCF + RAB = 3.81 + 3 + 0.5+0.476 = 7.786 ohm Circuit current at feed end, IT = 6.6 / 7.786 = 0.851A Voltage drop at feed end = IT(RCH+RCF + RT)

= 0.851 (3+0.5+3.81)

= 6.22V. Track voltage, VTR = Emax - feed end voltage drop = 6.6-6.22 = 0.38V This is less than the max. permissible relay voltage, i.e., 0.825V. Hence, a regulating res. of 3.81 ohm is safe. (iii) With normal battery voltage and min. permissible RB on track, the relay voltage shall be not less than 125% P.U.V., i.e., 1.25X1.38 = 1.725V.

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Min. Ballast res. of track @ 2 ohm /Km 2/l ,where ‘ l’ is the track circuit length in Km. Relay voltage, VR = 1.725V. Relay current, IR = VR / RR = 1.725 / 9 = 0.194A Voltage drop in relay end cable, VCR = 0.194 X 1 = 0. 194V Track voltage, VTr = VR + VCR = 1. 725 + 0.194 = 1. 919V Feed end voltage drop = Bat voltage - Track Voltage = E-VTr = 6-1.919 = 4.081 V Total resistance connected at feed end = RT + RCH + RCF

= 3.81+3+0.5 = 7.31 ohm Feed end current, IT = 4. 081 / 7.31 = 0.558A Ballast current, IB = IT-IR = 0.558 - 0.194 = 0.364A Ballast Resistance, RB = VTr 1 IB = 1.919 / 0.364 = 5.272 ohm But, min. RB = 2 ohm i.e., 2 / l = 5.272 or l =- 2 / 5.272 = 0.379 km or 379m

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CHAPTER – 6 S5B

AUDIO FREQUENCY JOINTLESS TRACK CIRCUIT 6.1 INTRODUCTION: The Audio Frequency Track Circuit (AFTC) is the Jointless type of track circuit specifically designed to meet the onerous immunity required in AC or DC electrified areas against the high levels of interference present mainly due to traction harmonics. The equipment is classified as universal since it can be used-in AC, DC or Non-electrified sections and meets all the requirements of the known track circuits. 6.2 ABB – AUDIO FREQUENCY JOINTLESS TRACK CIRCUIT – STYLE TI –21

The basic block diagram of AF track circuit is shown below. The transmitter feeds in the AF voltage to the track through tuning unit which is received at the other end by the receiver. A standard miniature line relay is directly operated by the Receiver.

The track circuit operates on a frequency shift principle where the basic frequency is shifted between two frequencies close to each other (+ 17 Hz. & - 17 Hz.). - Both the frequencies are detected independently by the receiver for energising the track relay. This modulation is made to enable transmission of AF without getting distorted. There are eight nominal frequencies (A to H) in the range of 1.5 KHz. to 2.6 KHz. that are employed to have eight. types of track circuits. This enables two types to be used per track and with the available eight types, track circuit requirement of quadruple lines can be met.

Block Diagram of A Basic Audio Frequency Track Circuit 6.3 ELEMENTS OF AFTC: AFTC consists of

Description Quantity

i) Transmitter 1 ii) Tuning Unit 2 iii) End Termination Unit 1

(in centre fed TC only)

iv) Receiver 1

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iv) Power Supply Unit 2 v) Output Relay 1

6.4 Transmitter – TX : A block diagram of transmitter is shown below:

TRASMITTER

A bi-stable multivibrator (1) produces a square wave output of 4.8 Hz. An oscillator (2) produces the nominal frequency f(A or B or ..........H). The square wave output of the multivibrator modulates the output of oscillator (f) to produce a signal which varies by +/- 17 Hz. about the nominal frequency (f) at a rate of 4.8 Hz in modulator (3). The output amplifier (4) increases the signal to a power level suitable for transmission down the track. The transformer (5) provides a means of matching the amplifier output to the load. Filter (6) is provided to isolate the unit from unwanted ACIDC currents from the track. The transmitter output wave form is shown below :

TRASMITTER WAVE FORM

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6.5 RECEIVER – RX: Block diagram of receiver is shown below :

Signal received from the (receiver end) tuning unit is fed to the input isolating transformer (1) of the receiver. This has, tappings to obtain different turn ratios for the adjustment of receiver gain. Interwinding earth screen is provided to afford protection from the common mode interference’s. Different taps as provided on the input side to be connected to the tuning unit are shown ' below. The connected tap is for a gain of 7. Receiver input wiring & pick up current for different gain settings are given in Annexure I. One ohm resistance is provided to enable direct measurement of input current.

Terminal Arrangement of Receiver for Gain Adjustment

The higher frequency of signal is filtered at 2A and the lower frequency of signal at 2B. Thereafter, they are amplified at amplifiers (3A & 3B), filtered at (4A & 4B) and demodulated at 5A & 5B. The two demodulated frequencies are combined in a sequential 'AND' gate (6) which gives a constant output only when both the frequencies are out of phase by 180 degrees. This output after an initial time delay of about two seconds provided by (7) is extended to the relay driver to energise the relay. 6.6 Track Tuning Unit - TTU The electrical separation of adjacent track circuits is obtained by tuning a short length of track (about 20 meters) using tuning units to which a transmitter/receiver is connected. Each tuning unit present offers a low impedance to the frequency of adjacent track circuit and prevents its influence. Thus tuning unit forms a part of electrical separation joint. Block schematic of the tuning unit is given below :

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Tuning unit, in addition to acting as a selective band pass filter provides a means of connecting transmitter/receiver to the rails. Receiver is always connected to terminals 1 & 2. Transmitter is connected to terminals 4 & 5 for normal power mode while it is connected to terminals 1 & 2 for low power mode (short track circuits of 50 to 250 mtrs.)

6.7 End Termination Unit - ETU: End Termination Unit is used at the start and the end of section on which AFTC is provided. A rail insulated joint is normally provided beyond the ETU within one meter. It is also used in place of TTU for centre fed arrangement. Two types of end termination units - one with 3 parallel branches of circuits for frequencies A, C, E & G and the other with two branches of circuits, for frequencies B, D, F & H. The schematic arrangement of each is given below :

END TERMINATION UNIT

A common power supply unit generally feeds 2 adjacent AF Track circuits. It supplies power to the Transmitter and Receiver ok adjacent Track Circuits. This works on 110V AC and gives out 24V DC.(nominal) for the working of the track circuit. Detailed specification requirement is spelt out in item number 15 of technical specification of AFTC. Since the system works on

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110V AC, an uninterrupted AC power supply central system is to be Provided when we go in for this type of track circuit. Output Relay: 50 V / 1350 ohm, DC neutral relay to BRS : 930. TECHNICAL SPECIFICATION OF AFTC: 1, Track, circuit length

a) End Fed Low mode : 50 - 250 metres. Normal mode : 200 - 1000 metres. b) Centre fed : 300 - 900 metres. (each half) 2. Minimum ballast resistance : 2 OHM / km 3.Minimurn Train shunt resistance : 0.5 ohm (outside tuned area) : 0. 15 ohm (inside tuned area) 4. Boundary of track circuit : +/- 5 metres (max.) (from centre of tuned area) 5. Length of electrical separation Joint : 18.0 - 22.0 metres. 6. Output relay 50 V / 1350 ohm. DC neutral relay to BRS : 930. 7. Track circuit Frequencies :

Actual Frequency band

Type

Nominal Frequency

Lower Limit Upper Limit

A

B

C

D

E

F

G

H

1699 Hz.

2296 Hz.

1996 Hz.

2593 Hz.

1549 Hz.

2146 Hz.

1848 Hz.

2445 Hz.

1682 Hz.

2279 Hz.

1979 Hz.

2576 Hz.

1566 Hz.

2163 Hz.

1865 Hz.

2462 Hz.

1716 Hz.

2313 Hz.

2013 Hz.

2610 Hz.

1532 Hz.

2129 Hz.

1831 Hz.

2428 Hz.

8. Current consumption on 24 V DC side

Transmitter : 2.2 A (Max)

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Receiver : 0.5 A (Max)

9. Transmitter power output (max)

Low Mode : 3 W

Normal Mode : 40 W. 10. Maximum length of connecting cable between a) Transmitter & feed end tuning unit - 30 meters b) Receiver & Receiver end tuning unit -350 meters 11. Receiver output = 40 V - 65 V DC. 12. Receiver Sensitivity = 15 mA. 13. Maximum length of cable (19/1.8 mm Sq. Al.) between the tuning unit and track Long Cable = 3.25 M. Short Cable = 1.45 M. 14. Resonated impedance bond: Resonated impedance - 12 ohm (Min.) Traction impedance - DC 0.75 m. Ohm. AC 3.00 m. Ohm. .15. Power Supply Unit. = Input (Nominal) = 110 V, 50 Hz. Input tappings = 5 - 0 - 95 - 105 - 115 V. Output voltage = 22.5 to 30.5 V DC. Output current = 4.4 A (Max.) Ripple Content = 3 V peak to peak. 6.8 ADJUSTMENTS OF AFTC: 1. Adjustment of Jointless AFTC EQUIPMENT :

a) Ensure that the equipment has been installed and connected properly.

b) Ensure that the AFTC of proper frequency units has been installed.

c) Set the, power supply input tapping to match the 110 VAC supply.

d) Adjust the Receiver gain as per the Annexure No. 1 and the under mentioned procedure

shall be followed :

2. Transmitter (Normal mode)

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a) (i) Connect one ohm TSR across rails at receiver end tuning unit connections. Go on reducing the gain setting till the relay drops.

(ii) Now, increase the TSR to 1. 1 ohm. The relay should pick up.

b) If the relay does not pick up, repeat steps (i) & (ii) above for TSR- of 1.2 ohm and 1.3 ohm. c) Increase the gain, if the relay is still de-energised. Now the relay should pick up. d) Reduce the TSR in steps of 0.1 ohm. The relay should definitely drop for TSR greater than

or equal to 0.5 ohm. 3. Transmitter (Low mode)

a) (i) Connect 1.5 ohm TSR across rails at receiver end tuning unit connections. Go on reducing the gain setting until the relay drops.

(ii) Now increase the TSR to 1.6 ohm, the relay should pick up.

b) If the relay does not pick-up repeat steps (i) & (ii) above for TSR of 1.7 ohm and 1.8 ohm. c) Increase the gain if relay is still de-energised. Now the relay should pick up. d) Reduce the TSR in steps of 0.1 ohm. The relay should definitely drop for TSR greater than

or equal to 0.5 ohm.

6.8.1 RESTRICTIONS:

1. No receiver shall be positioned less than 200 m from any Transmitter on normal mode and 50 m from low power mode of the same frequency.

2. Centre fed track circuit is to be used only where track needs to be longer than permitted for

an end-fed arrangement.

3. Tuned zones should not be located at level crossings.

4. If a level crossing lies in the track circuit, receiver should be located nearer to the LC and the length should be restricted to 75% of its normal length. Transmitter shall be connected only in normal power mode.

5. Track magnet of AWS and impedance bond shall not be located in the tuned zone.

6. Track devices of axle counter should not be located within 5 m of tuned zone or 15 m of

ETU.

7. Inside the track circuit having frequency A - 1699 Hz. (nom.), track device of the axle' counter shall be located beyond 200 m from the TX of the track circuit. For track circuits of frequencies E - 1549 Hz. (nom) & G - 1848 Hz. (nom.), the distance between Tx of the track circuit and track device of the axle counter shall not be less than 100 m.

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8 An earthing rod is to be provided at every location box and all earth connections from PSU, lightening arrestors of TX & RX are to be made to this earth. It may also be necessary to provide such earthing arrangements near TTUs s in lightening - prone areas.

9. Tx and Rx locations must be positioned as close as possible to the units. 10. Two units of the same frequency may be housed in the same location provided they are fed

from separate PSUs.

6.8.2 TESTING AND COMMISSIONING:

1. Transmitter / Receiver Input Supply Voltage / Current :- Check Transmitter and Receiver input supply voltage and current between terminals B-24, N-24 of transmitter and receiver.

The voltage and current should be as below :

Current (A) Voltage (DC)

Description

Min.

Max.

Min.

Max.

Transmitter Input Low Mode Normal Mode

0.2 1.3

0.4 A 2.2 A

22.5 22.5

30.5 30.5

2. Transmitter output & Transmitter Tuning Unit Input Voltage Check Transmitter Voltage at OP1 & OP2 and tuning unit input voltage at terminals 1 & 2/4 & 5 for low and normal mode respectively, using frequency selective meter unit. The voltages should be as below :

Transmitter output voltage Transmitter Tuning Unit Input Voltage Voltage

Type

Min. V (AC)

Max. V (AC)

Min. V (AC)

Max. V (AC) A.C.E. & G B.D.F. & H

10 15

11 16

8

13

11 16

3 Transmitter & Receiver end Rail Voltage :

Check the Transmitter & Receiver end rail voltage at terminals T1 & T2 of the respective tuning units, using frequency selective meter unit. Voltage should be as below :

Transmitter End Tx Type Receiver End Rx Type TC

Length

Mode

ACEG Volts BDFH Volts ACEG Volts BDFH Volts

50 m

150 m

Low Power

Low Power

0.8

1.2

0.8

1.4

0.8

0.9

0.8

0.8

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250 m

200 m

400 m

900 m

Low Power

High Power

High Power

High Power

1.4

4.5

5.0

5.3

1.8

6.4

7.0

7.2

0.5

1.2

1.0

0.4

0.5

1.6

1.2

0.5

6.8.3 DO's AND DONT's,: DO’s :

1. Rail Bonding in the tuned area should be done with 50 Sq.mm Aluminum Cable.

2. Drop shunt test should be carried out at RX end.

3. Only one pair of frequencies (A/B or C/D or E/F or G/H) shall be used on CWR/LWR sections. Combination with other frequencies can be done when provided with insulated rail joints.

4. Frequency selective meter unit (FSMU) shall be used for measurement (except for power supply measurement) as far as possible. If measurement is to be done with digital multimeter, it shall be done after disconnecting power supply to the adjoining track circuits.

5. During Measurement,

a) Companion transmitter shall be switched off.

b) Rx end of the adjacent track to be shorted or power supply to be switched off. DONT's:

1. Same PSU shall not. be used for feeding more than one transmitter or Receiver of the same frequency.

2. In electrified sections, measurements should not be made when a train is in the vicinity.

3. There shall be no impedance bond, level crossing or switch expansion joint inside the tuned area.

4. Axle counter transmitter and receiver should not be located in the tuned area. No track device of axle counter of 5 KHz. system shall be located within 200 rnts. of AFTC transmitter of frequency A and within 100 rnts. of frequency E & G.

6.8.4 FAULT DIAGNOSIS AND RECTIFICATION: a) If both adjoining track circuits have failed together, first of all check items common like

power supplies, tuning unit or interconnection. b) Transmitter End 1. Check for "Singing Noise" produced by Transmitter and tuning unit. 2. Check rail to rail voltage at the Transmitter end. If this is OK, application of a 0.5 ohm TSR across the feed end tuning unit rail connections will lower Rail to Rail voltage by approximately

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50%, if the transmitter end is working OK. As such no further tests needed to be done at Transmitter end. 3. Test 24 V DC Power Supply Voltage and current to Transmitter and the Transmitter output voltage. If readings from these tests show a deviation from the normal limits, the power supply unit, Transmitter or tuning unit may be faulty. 4. For the integrity of interconnections, check tuning unit input and output voltages. c) Receiver End: 1. Check companion tuning unit voltage. If it is not within limits, the companion tuning unit is faulty if the rail to rail voltage at the tuning unit of the failed track becomes OK when T1 and T2 terminals of companion tuning units are shorted. 2. Check the Receiver input current. If this is very less for the Receiver to operate (less than 15 mA), the Receiver tuning unit is faulty. If it is adequate but the Receiver output at R + R - is very less with a satisfactory power supply, change the, Receiver. 6.8.5 SPECIAL REQUIREMENTS: 1. Centre fed arrangement When the length of track circuit is required to be more than 900 meters, centre fed arrangement shall be provided as indicated below:

2. Termination with other types of Track Circuits: A special arrangement using ETU shall be provided as indicated below when an AFTC is followed by other types of track circuits. Insulated rail joints are, to be provided at a distance not greater than 1 meter.

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3. Termination of AFTC with non-track circuited portion: Both the rails are to be shorted with 50 sq. mm Alu cable at 18.5 meters from the last tuning unit as indicated below:

6.8.6 A POINT TO REMEMBER:

AFTC shall be adjusted to correct level as given in Para 6. In the event of overenergisation caused inadvertent change from low power mode to high power mode or by other reasons, the level of AF signal received at Rx will be beyond the specified level of demodulator and there will be neither demodulation nor detection of AF signal. This will result in the dropping of relay when the track is free. While shunting, the signal level is bound to come down and fall within the range of demodulation resulting in detection and output will be extended to energise the relay when the track is actually shorted. Hence, when adjustment in any part of the track circuit is done, all the parameters given in Para 6 shall be checked for their correctness within the limits specified therein. 6.8.7 INSPECTION SCHEDULES: 1. Fortnightly. 2. Ensure that the "Singing Noise” produced by the equipment is present. 3. Measure the power supply output voltage and current.

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4. Measure the Transmitter output voltage. 5. Measure track voltages across the Transmitter and Receiver tuning units. 6. Measure the Receiver input current. If any adjustment is needed, it shall be done as per

Annexure - 1. 7. Measure the relay voltage. 8. Inspect the track circuit connection with the rails and inter-connections between power

supply units, transmitter, tuning units receiver and relay. Ensure they are in order. 9. Conduct drop shunt test with TSR of 0.5 ohm outside the tuned area and 0.15 ohm inside

the tuned area. 10. Fill in the details of track circuit parameters as indicated below

ANNEXURE - I TRACK NO. : FREQUENCY : TYPE OF ADJACENT TRACK CIRCUIT:

RX TX Track

PS P S

Date

V I

Track Volts

Track

shunt

Gain

setting

I p

sig.

Relay

V V I

O/P

volts

Track

volts

Conditions Remarks

Receiver input wiring and pick-up current for different gain settings:

Input Connections

Gain

Pick Up

Current

Input 1 Input 2 Loop 1

Loop 2

1

2

3

4

5

390 mA

195 mA

134 mA

98 mA

78 mA

1 H

1 L

3 H

1 H

1 L

1 L

3 L

3 L

3 L

9 L

1 H – 3 H

1 L- 3 H

1 H – 3 L

3 H – 9 H

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6

7

8

9

10

11

12

13

65 mA

56 mA

50 mA

45 mA

39 mA

35.4 mA

32.4 mA

30 mA

3 L

1H

1 L

9 H

1H

1 L

3 H

1 H

9 L

9 L

9 L

9 L

9 L

9 L

9 L

9 L

3 H – 9 H

1 L – 3 L

1 H – 9 H

1 L – 9 H

1 H – 3 H

3 L – 9 H

1 L – 3 H

3 H – 9 H

3 L – 9 H

3 L – 9 H

Note : The above values are based on a minimum ballast resistance of 2 Ohm/Km.

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TRANSMITTER CIRCUIT DESCRIPTION

T1 along with R1, R2 and C1 acts as a relaxation Oscillator, output of which is given to a bistable multivibrator comprising of T2 and T3. Initially when T2 is ON, base of T3 is pulled down through.R19 forcing T3 to enter into cut-off state. Simultaneously, base of T2 is pulled up through R17 and R20 till it goes into saturation. Next pulse from relaxation oscillator causes T3 to switch to switch ON thereby reducing base potential of T2 and driving it to OFF state. This causes base bias of T3 to increase further forcing it to enter into saturation and T2 to cut-off state.

Another pulse from relaxation oscillator again changes the states of T2 and T3 and the cycle repeats thus generating a square wave of 4.8 Hz at MOD.

The main carrier frequency oscillator is made up of transistor T5 driving a tuned inductor Ll. The biasing is so arranged that the transistor T5 remains cut off for major part of the oscillatory cycle, thereby giving rise to a high 'Q'. Multivibrator drives the transistor T4 which in turn switches capacitor C6 across main capacitor C8 (in tuning limb) of carrier oscillator to generate a waveform of two frequencies separated by 34 Hz from each other.

The regulator stage consisting of T6 and T7 which is mutually coupled to oscillator, maintains the output of transmitter substantially constant irrespective of power supply change within specified limit. The signals from T6 and T7 are square waves at carrier frequency which are fed to the output stage amplifier with signal from T6 inverted through T 11.

An output transistor (T9 or T10) will only switch ON when T6 or 17 conducts. T9 and T10 are switched alternately with an OFF period between switched on times.

D3 and D4 act as supply voltage regulators for multivibrator and oscillator circuits respectively.

D8 and D4 protect the circuit from overload transients from track and inductive switching surges.

The output transformer coupled with C9 and L3 acts as a tuned filter for particular frequency to be transmitted.

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RECEIVER CIRCUIT DESCRIPTION

The signal from the track tuning unit is fed into the isolation transformer, which has three input windings so arranged that variation of the input connections gives a range of gain settings from 1 to 13 in steps of 1. The isolation transformer is screened to eliminate the effect of common mode transients from the track such as lightening and interference. The screen is connected to an external earth terminal. A separate surge arrestor must also be provided (connected across the input leads) to complete the protection of the receiver.

The secondary winding of each input filter is tuned to select one signal coming from the associated transmitter. By convention, L1 and C1 are tuned to the high frequency and L2 and C2 are tuned to the low frequency, e.g. The 'A' frequency receiver has L1,C1 tuned to 1716 Hz. L3, C2 tuned to 1682 Hz.

Protection from series mode overload signals is provided by clipping diodes D1 and D2.

The signals are amplified by transistors T1 and T2 and filtered by tuned circuits L3 C3 and L4 C4. L3 C3 and L1 C1 are tuned to the same frequency, similarly L4 C4 and L2 C2. Thermistors TH1 and TH2. serve to stabilize the amplifier against gain changes with temperature.

D3 CS & D4 C6 form modulation detectors. The demodulated signal, a square wave of 4.8 Hz from CS or C6, switches the level detectors formed by T3, T5 and T4, T6. The output of the level detectors on the cathodes of D7 and D8 is a negative voltage rising and falling with the modulation rate. The signal from the two channels are out of phase with each other so that when one output is rising the other is falling and vice versa.

The negative outputs from the two levels detectors are combined by D7 and D8 and the resulting steady negative potential on T12 gate allows the high frequency oscillator-T9, T10, L5A and C12 to oscillate and also allows C13 to charge via R25. R25 and C 13 form a delay timer with a delay time of approximately two seconds and a reset time of 1 ms. The reset is activated either by removal of the input signals or by the power supply to the receiver being reduced.

T11 is used to sample the timing capacitor C13 and when the capacitor is sufficiently charged (after two seconds) a threshold circuit T13 is triggered. The output of the threshold circuit drives an amplifier T14, T15, T16 and T17. This powers a transformer whose output is rectified by D 13 and used to energise the output relay. Short term short circuit output protection is provided by R37 and R38.

The power supply is regulated by the shunt stabilizing devices D5 and D10 and protected against transient overloads by D 14. The 1 ohms terminal resistor is wired in series with the transformer input for monitoring the input current without disconnecting the input signals. Voltage across the resistor is 1 mV/ mA.

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CHAPTER-7 S5B

SIEMENS REMOTE-FED, CODED AUDIO FREQUENCY TRACK

CIRCUITS (FTG-S TYPE)

7.1 The German abbreviation for FTG-S is F= Remote fed, coded T= Audio Frequency G= Track Circuit S= Siemens Remove fed, coded Audio Frequency track circuits can be used in place of conventional track circuits, to overcome shortcomings of the latter. 7.1.1 Features of FTG-S: 1. FTGS is remote fed with a frequency modulated AC voltage. Both transmitter and

receiver are centrally provided in Relay Room/huts, upto 6.5 km away from the track section.

2. Centralised electronic equipment consists printed circuit boards provided in frames on racks.

3. Highly reliable - since mechanical stress and climatic influences have less effect as electronic components are installed in Relay room/hut.

4. Have maximum availability since extensive operating state indications (diagnostic aids - LEDs) permit fault localisation and immediate replacement of defective PC-boards.

5. Have transmitter, receiver, and demodulation and relay PCBs of plug in type. Ten (10)

FTGS track circuit components can be accommodated in one track circuit rack.

6. Maintenance free tuning units are provided in the track side connection boxes. 7. Continuous availability of two rails for traction return current. 8. Immune to AC/DC traction interference's. 9. Jointless track circuit except in point zones. 7.1.2 Types of FTG-S: Two types of track circuits are developed with twelve (12) operating frequencies, one to be provided within station limits and the other for outside the station limits. 7.1.3 Operating frequencies: FTG-S 46 (For longer track circuits outside station limits) F9 = 4.75 KHz., F10=5.25 KHz, F11=5.75 KHz, F12=6.25 KHz

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FTG-S 917: (For shorter track circuits within station limits) F1= 9.5 KHz, F2=10.5 KHz, F3=11.5 KHz, F4=12.5 KHz. F5=13.5 KHz. F6=14.5 KHz, F7=15.5 KHz. F8=16.5 KHz. 7.1.4 Technical parameters and data: 1. Transmission reliability - Frequency modulation coding with 15 types of 8 bit pattern per

track circuit frequency.

2. Minimum Ballast Resistance - 1.5 ohms/km (ideal is 2.5 ohms/Km) 3. Maximum recommended TSR - 0.5 ohms (other than the tuned zone) 4. Electric traction - AC/DC tractions. 5. Rail cross section: Any 6. Power Supply - (i) 220V AC + 22V/-33V, 50Hz. + 1 Hz. (OR) (ii) 110V AC +/- 15%;50 Hz + 1 Hz. 7. Power Consumption: FTGS - 46 - Standard Configuration (st) 80VA Central feed-in (M) 90VA FTGS - 917 - Standard (ST) 65VA Central feed in (M) 75VA Points (W) 75VA Crossisng(K) 85VA 8. Cable for feed in and feed out: - Star quad cable of 0.9 mm core diameter (from cabin to tuning unit) - Copper ropes of diameter 25 mm2 (From tuning units to track rails) 9. Minimum effective length of TC:30 Mts. 10. Maximum effective: (Table - 1)

11. Diagnostic LED indications on all PCB's ensure quick fault detection (Refer Annexure No.1 & 2).

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12. Comparison of transmitted and received signals using magnetic memory in addition to electronic memory (Magnetic memory has an infinite fault free life). 7.1.5 System consists of the following components:

1. Indoor equipment 2. Outdoor equipment 7.1.6 Indoor Equipment:

It consists of two units: a) CPU (Central Processing Unit) frame with printed circuit boards (Refer Fig.No.1 a,b,c,d,e) i) Transmitter card (T-PCB) ii) Amplifier and filter card (A-PCB) iii) Receiver I card (RI-PCB) iv) Receiver II card (R2-PCB) v) Demodulator card (DEM-PCB) vi) Relay card (Relay - PCB)

Mounting frame for standard track circuit (St) or central feed-in (M)FTG S46

Fig.1(a) Mounting frame (St) FTG S 46

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Fig 7.1(b) Mounting frame (M) FTG S 46

Mounting frame (St) FTG S 917

Fig.1(c) Mounting frame for standard track circuit

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Mounting frame (W/K/M)FTG S 917

Fig. 7.1 (d) Mounting frame for point track circuit or track circuit with central feedin.

Fig.7.1 (e) Mounting frame for crossing or double-points track circuit. The term "double points" is used here to designate two adjacent sets of points combined to form a single vacancy detection circuit.

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b) Power supply Unit: (Refer Fig. No.2(a),(b))

Input voltage = 110V AC or 220 V AC Output voltage = + 5V DC, + 12 V DC

Fig 7.2 (a) Front view

Fig.2(b) Rear view

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7.1.7 Outdoor Equipment: (Fig.No.3) i) Tuning units in track connection boxes - 2 Nos. ii) Star quad cables (9m m dia. ) - for connecting T.U to Rx Tx iii) 25 mm 2 copper lead ropes - for connecting TU to rail.

7.2 S BOND TRACKSIDE ARRANGEMENT:

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7.2.1 Principle of Working: (Refer block diagrams No.4 (a), (b):

Audio frequency modulated and coded signals are generated by the transmitter card. These signals are fed to the feed end track through a tuning unit. When the track is unoccupied, transmitted Audio Frequency modulated AC voltage reaches the receiver end tuning unit through rails. From receiver end T.U. signals are sent to the receiver card provided in the cabin through telecom. cables. Here the signals are demodulated and evaluated in two separate channels for redundancy. The codes of received signal is compared for matching with the preset code there in. If there is a match, two track relays, connected at the end of the channels in relay card (GF1, GF2) picks up.

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Whenever the track is occupied, the transmitted signal voltages get shunted through the vehicle axle. Receiver card detects this and drops the two track relays (GF1,GF2).

Various LED indications are provided on each card to facilitate failure detection.

Various testing voltage at measuring sockets are listed on page. SCHEMATIC REPRESENTATION:

Fig. 4 (a)

BLOCK DIAGRAM

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Fig. 4 (b) 7.3 Function of PCB's in FTG-S Frame:

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1. Transmitter Card :

Transmitter PC board consists of a quartz oscillator with modulator. In this card a particular audio frequency voltage is generated and modulated with a bit pattern. The particular track circuit frequency is generated by means of a variable frequency divider, which steps down the clock pulses of the quartz oscillator (16,336 MHz). Bit pattern & frequency can be selected by means of two code plugs.

2. Amplifier and Filter Circuits:

For FTG-S917, these are provided in one PCB and for FTG-S46, these are on separate PCB's. In this card, the modulated audio frequency signal from the transmitter is raised to the required level by the amplifier and transmitter to the feed end point of the track via a selective filter.

3. Receiver Circuits: These are provided on two PC Boards.

a) Receiver 1 PCB :

It assesses the track voltage amplitude received through cable from the track tuning unit. When the track is clear, this card transmits pulses to the demodulator card and extends DC voltage to receiver card 2.

4. DC Modulator PCB:

When the track circuit is vacant, this card compares the bit pattern received from Receiver 1 with an internal reference pattern. If both are identical, the received bits are sent to the logic comparator on the Receiver 2 PCB.

5. Receiver 2 PCB:

This card combines the output signals of receiver 1 resulting from amplitude assessment there and those of demodulator after bit pattern check. The output signal resulting from the dynamic AND operation, is amplified and fed to the Relay PCB. For reasons of safety, Receiver I, demodulator and the Receiver 2 circuits are of two identical channels picking up two relays independently.

6. Relay PCB:

There are two relays one in each channel. The interlocking circuits regularly checks the switching state of both track relays. For operational reasons, the track occupied signal is delayed by 170 milli seconds and track clear signal is delayed by 1300 milli secs.

7.4 TRACK CIRCUIT DELIMITATION BY SECTION DIVIDER BONDS.

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S-BOND - This connector is built of two semi loops each delimited between its centre tap and its connection point to the rail. This along with the rail of this region forms the inductive branch of a parallel resonated circuit. The discrete capacitors of tuning unit make its capacitive branch.

The more distant semiloop of the two S-bonds delimiting a track section is tuned to the perating frequency of track circuit. Feed is applied to the resonated semiloop circuit causing its transmitter to consume little energy. The other semiloop of section divider is tuned to the operating frequency of neighbouring track circuit. Due to the layout of semiloops in the S-bond, an axle standing on the S-bond occupies both the near and advance track circuits. This S-bond causes overlapping, of the two track circuits so that there is no detection gap. In the last AFTC of a region, End bonds (alfa bonds) are provided at their exact delimitation or for their transition to other types of track circuits with block joints in between.

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7.5 Three modes of connections are adopted for FTGS-depend on the length of section and location.

1. STANDARD LAYOUT

ANNEXURE - 1

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7.6 Meaning of the Indications The tables below Annexures 2 & 3 show the various possible combinations illuminated indicators for the operating states "section clear". "section occupied" and possible fault conditions. The indicator combinations (Annexure – 2) and associated remarks or instructions for remedying the faults (Annexure – 3) have the same sequence numbers. All the information refers to the standard track circuit with one receiver. For sections with more than one receiver, eg. points or crossing track circuits, there is more than one receiver-1 and demodulator board. Each receiver section has its own set of 1 L5, II L5, I L6 and II L6 LEDs. The same work is required on the additional receivers and demodulators as for the standard track circuit. LEDs I L7 and II L7 of the receiver-2 board S25533-B39-A3 only light up if all L5 and L6 LEDs of all associated receiver I and demodulator boards for channels I and II are also on. L1 Output of transmitter board

L2 Upper frequency

L3 Lower frequency

L4.1 Amplifier output (FTG-S 46 only)

L4 Output voltage to track

I L5 Amplitude evaluation channel I

II L5 Amplitude evaluation channel II

I L6 Bit pattern evaluation channel I

II L6 Bit pattern evaluation channel II

I L7 Combination amplitude - bit pattern channel I

II L7 Combination amplitude - bit pattern

L8 Scanning pulse for receiver-2 board

L9 Intercore short-circuit supervision (ISCS)

92

92

ANNEXURE-2

93

93

ANNEXURE-3

Seq. No.

Remarks or maintenance action required

1 Section is clear 2 Section is occupied or see No.12 3 Exchange circuit board B40-or-B41 4 Check voltages 220 V AC, 12V DC, 5V DC, if OK, exchange circuit board -30 5 Check 12V DC voltage 6 Check 220 V AC fuse for ISCS; if OK, intercore short circuit 7 Check 5V DC voltage 8 Exchange circuit board - B30- 9 Exchange circuit board - B30- 10 Exchange circuit board-B30-

11 Exchange circuit board -B40-or-B42; if fault persists, exchange circuit board -B30-as well

12 Check voltage between measuring sockets I 5 and II 8 on circuit board -B33-; if voltage < permitted : check voltage between measuring sockets 3 and on. Circuit board-B40-and outdoor equipment if voltage ≤ permitted value : exchange circuit board-B33-

13 Exchange circuit board -B33-

14 Exchange circuit board -B33-

15 Exchange circuit board -B35-

16 Exchange circuit board -B35-

17 Exchange circuit board -B35-

18 Exchange circuit board -B30-; scanning pulse is faulty

19 Connect measuring sockets E1 and E2 on circuit board -B33-

20 if LEDs I L6 and II L6 on circuit board -B35- do not switch off, exchange circuit board -B35-.

21 if LEDs I L6 and I L6 on circuit board -B35- switch off, exchange circuit board -B39- or -B34-. NOTE: Preceding track circuits in a cascade must be clear.

22 Exchange circuit board -B35- 23 Exchange circuit board -B35- 24 Exchange circuit board -B35-

94

94

ANNEXURE-4

Testing Voltages at Measuring Sockets For troubleshooting purposes, the voltage at the power unit and measuring socket the major components can be measured. The permitted values are given in the tab below. Sockets

Circuit board) Adjuster range

Permitted Value [ V ]

Measurement location

Remarks

1/ 2 (-B40/B41-)

20V AC 9 to 12* Transmitter output Square wave voltage approx.18V T=1/10= 69 to 210 υs

3/4 (-B42-)

200V AC 60 to 90 Amplifier output Square wave voltage approx.100 to 150V with peaks

3 /4 (-B40-)

200V AC 30 to 100 Filter output To track (before cable stabilizing resistor)

II 5 / II 8 II 5 / II 8 (-B33-)

20V AC > 6.5 < 5

“ Clear” track volt. “Occupied” track volt.

Without external axle shunt (see section 5.10) with 0.5

I 6/II 8 II 6/II 8 (-B33-)

20V DC 12 to 15 Receiver 1 output

I 7/II 8 II 7/II 8 (-B33-)

20 / 2V AC

1.3 to 2.0 Demodulator input

I 8/II 8 (-B33-)

20V DC 11 to 13 12 V - Supply voltage

I 9/II 8 II 9/II 8 (-B33-)

- - Receiver 1 output without modulation

I 10/II 8 II 10/II 8 (-B33-)

20V DC 5.6 Reference voltage

I 11/I 12 II 11/II 12 (-B39/B34-)

20V DC 16.5 + 1 Relay voltage

I 13/I 14 II 13/II 14 (-B39/B34-)

20V DC 4 to 5 Cascade clock pulse Output of AND element

12V /0 V 20V DC 12 + 1 Power unit Supply voltage 12V DC 5 V/0 V 20V AC 5 + 0.5 Power unit Supply voltage 5 V DC E1/E2 (-B33-)

20/2V AC

0.3 to 2.0 Receiver 1 input Via adjusting filter; according to setting