CHAPTER-VII SIGNALLING & TELECOMMUNICATION AND PERMANENT WAY INSTALLATIONS IN ELECTRIFIED SECTIONS 20700 Introduction
The important points concerning the signalling, telecommunication and permanent way installations in electrified sections can be grouped as follow:
I. Signals and associated equipments
II. Telecommunication facilities for ac traction
III. Power supply for S&T installations
IV. Permanent way installations
Various aspects for the general information of electrical staff are covered in this chapter. The rules are covered in the Indian Railways Telecom Manual for the S&T staff and in the Indian Railway Permanent Way Manual for the civil engineering staff.
The safety rules applicable to the staff of S&T and civil engineering departments are given in Chapter IV, Vol. I of this Manual. I. SIGNALS AND ASSOCIATED EQUIPMENT 20701 Effects of 25 kV Traction on S&T Equipment
Any circuit in the vicinity of OHE for 25 kV ac 50 Hz signal phase traction system is influenced by electrostatic and electro-magnetic induction. The electrostatic induction is practically eliminated by transferring S&T circuits into underground cables protected with metal sheath. The electro-magnetic induction causes currents and voltages to develop in metallic items parallel to the track. The items include the rails, traction return conductor where provided, cable sheath and S&T circuits. The voltages that occur in the metallic items appear as potential gradients. The value of induced voltage depends on various factors such as:
a) length of parallelism between the cable and electrified track
b) soil conductivity
c) screening efficiency of cable sheath where existing
d) return current through the rails and return conductor where provided.
e) mutual inductance between catenary and cable conductors
f) current carried by the OHE.
Appropriate precautions to overcome the effects of the induced voltage, therefore, have to be taken by S&T department.
Other aspects where S&T equipment is affected are:
i) OHE masts and fittings may come in the way of visibility of signals to some extent and may come in the way of signal.
ii) Restrictions in the path of traction currents on section provided with track circuits.
20702 Types of Signals
In the double line electrified sections, the signalling system shall generally be the colour light signal (CLS) type. But the semaphore signals may be retained on single line sections (Main or branch) which are taken up for Railways Electrification.
20703 Locations of Signals
1. Signals are so located as to afford maximum visibility to drivers and the signal structures have to be clear of the moving dimensions. In electrified sections, however, the signals should have the required electrical clearance of at least 2m from the live conductor. Detailed instructions on the location of signals have been issued by the S&T Deptt.
2. Where a signal post or its fittings have to be located within 2 m of live OHE, a screen of wire mesh of approved design solidly connected with the structural work shall be provided between the signal post and the OHE for protection of staff. Provision of such a screen is mandatory where non-technical staff like lamp-man are required to climb up signal posts. The protection screen is not necessary when only the technical personnel, such as inspectors and maintainers of the S&T Deptt. are authorised to work on the signals. When a screen is not provided for any reasons, a caution board of approved design shall be provided on the signal post on the side facing the ladder at a height of 3 m above the rail level to caution such staff.
3. Technical personnel shall exercise particular care to protect themselves while working on signal posts not provided with protective screens If there is any likelihood of any part of their tools or equipment coming within 2m of live equipment, they shall take a power block as detailed in Chapter VI. The same precautions are also required in the vicinity of return conductors, which should be treated as live.
4. To ensure maximum visibility of signals to the drivers, signal posts should be located on the side opposite to that of traction masts as for as possible. Where this is not possible as in double line sections and station yards, the following steps are taken to achieve maximum visibility from the Driver's normal position in the driving cab.
i) The distance between the signal post and the traction mast shall be as large as possible. In case the traction mast is located in front of the signal post the distance between the traction mast and signal post should not be less than 30m. No traction mast shall be located beyond the signal post at a distance less than 10m.
ii) The signal post should be sufficiently high so as to be seen clearly.
iii) For deciding setting of mast near signals, para 20.5 of Appendix 1 may be referred to.
iv) On curved tracks or in areas where other obstructions such as buildings, trees, etc. exist the site is individually examined for deciding the most appropriate location of the signal.
v) In all cases a "Signal Siting Committee'' which includes a representative of the Electrical Department should be constituted to examine the visibility of the signal before finally deciding its location and height.
20704 Insulation of Wires and Point Rods
Normally wires and point rods would be eliminated in the signalling system in ac electrified section. However, where these exist, the wire transmission as well as point rods in ac electrified areas are subject to induced voltage which could reach high values when an OHE fault occurs. This induced voltage or rail voltage is transmitted through the wires and point rods to the lever frame. Insulators are therefore, provided on the wires and point rods for insulating them from rail potentials and induced voltages, in accordance with detailed instructions on the subject laid down in Chapter XXII of Indian Railway Signal Engineering Manual issued by S&T Department.
20705 Earthing of S&T Equipment
Earthing of the following equipment is essential on sections electrified with 25 kV ac 50 Hz single phase system the earthing being done in accordance with prescribed instructions.
a) Signal posts provided with protective wire-mesh screens
b) The lever frames and other metallic parts of the cabin in contact with the lever frame, (This includes rail staging wherever they are used. Where the electrical conductivity of the joints of the rail staging is doubtful the members are to be bonded at the joints.)
c) Metallic sheath wherever applicable and armouring of all underground cables. The earthing of the sheath and armouring of main cables at either end is a matter of paramount importance because unless the cables are earthed properly at both ends it will not be possible to obtain the screening effect of the cable from induced voltages.
d) Block instruments working on earth return through the respective block filters.
e) All telecommunication equipment.
f) The surge arrestors provided in block filters as well as those provided for telecommunication equipment in switching stations.
The telecommunication equipment may be connected to the same earth as the lever frames. Surge arrestors may be connected to the earth for the cable sheath. In all other cases separate earths shall be provided. The resistance of an earth shall not exceed 10 ohms.
20706 Signalling & Telecommunication Cables
The main S&T cable in ac electrified sections are usually of the PVC insulated, screened and armoured type to IRS Specification No. S-35. These cables are laid in accordance with instructions issued by the S & T Department. Instructions which are likely to affect traction installations are given below : -
(i) The cable is laid so that it is not less than lm from the nearest edge of the traction mast foundation provided that the depth of the cable does not exceed 0.5 m. When the cable is laid at a depth greater than 0.5 m a minimum distance of 3 m shall be maintained between the cable and the nearest edge of the traction mast foundation. If it is difficult to maintain these distances the cable shall be laid in concrete pipes for distance of 3m on either side from the mast. When so laid the distance between the cable and foundation may be reduced to 0.5m. These precautions are necessary to avoid damage to the cable in the event of the failure of an overhead insulator.
(ii) In the vicinity of traction substations and feeding posts, the cable shall be laid at least lm away from any metallic parts of the OHE and other equipment at the sub-station/ feeding post as well as from the substation earthing system. In addition, the cables shall be laid in concrete pipes for a length of 300m on either side of the feeding post . As far as possible the cable shall be laid on the side of the track opposite to the feeding post.
(iii) In the vicinity of switching stations, the cable shall be laid in the ground at least lm away from any metallic structure of the switching station and at least 5m away from the station earthing system. The distance of 5m can be reduced to lm provided the cable are laid in concrete pipes.
(iv) Where an independent earth is provided for an OHE mast/ structure i.e., where the mast is connected to a separate earth instead of being connected to the rail, the cables shall be laid at least one metre away from the earth.
v) Where there are traction masts/structures along the cable route, the cable shall be laid in the trench which should be as far as possible but not less than 5.50 m from the centre of the track.
(vi) Where cables have to cross the track, concrete or GI pipes must be used for the crossing. The use of GI pipes or any form of metallic pipes is prohibited within a distance of 300m from the feeding post. Similarly galvanized iron metallic pipes are prohibited in close proximity to switching station earths or traction masts.
20707 Block Instruments and Block Circuits
On replacement of overhead communication lines with cables, block instruments working with overhead lines with earth return are transferred to special PVC insulated quads in the underground cables. Special protective devices are provided at both ends of block circuits for protection of the instruments as well as the operating staff.
20708 Track Circuits
Any of the following types of track circuits may be used on ac electrified sections :-
(i) dc single rail track circuits.
(ii) ac track circuits working at a frequency other than 50 Hz so as to be unaffected by the latter.
(iii) Voice frequency and other forms of electronic track circuits.
The track circuits of (ii) and (iii) above may be either the double rail type or the single rail type.
20709 Bonding in Track Circuited Zones
The track bonding for the passage of traction current requires modifications in the track circuited zones. Appendix II may be referred to in this regard.
20710 Signalling and Inter-locking Circuits
In view of the high level of electro-magnetic and electro-static induction in overhead lines, all overhead lines used for signalling and inter locking circuits in ac electrified sections have been replaced by underground cables. The replaced lines, if not dismantled before energization of the OHE, shall be cut into sections and earthed at several places.
The length of a circuit in a cable shall be such that the induced voltage in the circuit does not exceed 120 volts (corresponding to a parallelism of 3.5 km). If for any reason parallelism of a circuit exceeds 3.5 km, a relay is inserted in the circuit so that the physical continuity of the cable is broken and the parallelism of each portion is reduced to less than 3.5 km. If the parallelism in excess of 3.5 km is due to feeding two circuits from a common battery or power supply source, separate batteries are provided to feed the circuit on each side so as to limit the parallelism to less than 3.5 km. II. TELECOMMUNICATION FACILITIES FOR AC TRACTION 20711 Telecommunication Circuits
The telecommunication facilities provided in electrified sections have been detailed in Chapter II of Volume I.
On ac electrified sections all overhead telecommunication lines running parallel to the track have to be replaced by underground cables. When the induced voltage in the cable is expected to exceed 60 volts; way station and subscriber's equipment, exchanges are protected from the induced voltage by providing isolating transformers. When transformers are provided it will not be possible to transfer dc circuits such as CB and auto telephones, dc telegraph circuits etc., into the cable.
The attenuation of speech in an overhead line of 56.8 kg per km copper is approximately 0.039 dB per km whereas the attenuation in an underground long distance cable is approximately 0.22 dB per kin. The telecommunication circuits are therefore subject to about five times the attenuation when transferred to underground cables and consequently repeaters are required for these circuits at intervals of about 50 to 60 km for satisfactory working. Where the cables are laid by the DOT all repeaters and isolating transformers are provided by them.
20712 Principles of Tapping
Traction Power centre, Traction loco Control and emergency telephone circuits are specifically installed for electric traction. Control regarding utilization of these circuits rests with the Chief Electrical Engineer. All tappings of these circuits will, therefore, be provided with the specific approval of CEE. Adequate capacities on all these circuits shall be provided taking into account future requirements. Usually the following tappings are provided :
1. Traction Power Control Circuit
(i) Traction Power Control of the adjoining Remote Control Centres,
(ii) All switching stations,
(iii) All railway traction sub-stations,
(iv) All grid sub-stations,
(v) Central repair shop,
(vi) All OHE, PS1 and RC maintenance depots,
(vii) Offices of all Station Masters/ ASMs,
(viii) Offices of Yard Master who control movement of trains,
(ix) Offices and residences of Traction Distribution officers,
(x) Residences of CTFO, TFO/ATFO of OHE, PS1, Substation, RC maintenance depots.
2. Traction Loco Control Circuit, (i) All electric loco sheds,
(ii) All electric loco stabling sidings,
(iii) Offices of Station Masters of originating, and junction stations,
(iv) Offices of Yard Masters of large yards,
(v) Office of CTFR and TFR,
(vi) Offices and residences of Rolling Stock officers,
(vii) Residences of CTFO(RS), TFO(RS), CTFR and TFR provided their residences are more than 500m from their offices and no other telephone facilities exist at their residences.
3 Emergency Control Circuit
(i) At regular intervals along side the track not exceeding lkm of running track.
(ii) At all traction sub-stations, switching stations, and maintenance depots.
(iii) Near booster transformer locations and isolator switches provided for isolation of OHE.
If the distance between two successive emergency telephone sockets determined as above is less than 100 m, only one socket shall be provided, at such locations.
However, in large yards having more than four tracks which are likely to be occupied most of the time, an additional emergency socket may be provided on the opposite side of the yard near an isolator provided for isolation of traction OHE.
Where the transverse distance between two tracks involves walking of more than 300 m, separate tapping shall be provided for each individual track. If not already done, this circuit should also be extended to the TLC to enable him to guide loco/EMU crew in the event of failures enroute.
4. Railway's local telephone (i) Remote Control Centre, (ii) Traction Loco Controller, (iii) Traction Power Controller,
(iv) Offices and residences of all officers of Traction Distribution and Rolling Stock - operation and maintenance,
(v) Offices and residence of CTFO & TFO(RS) and CTFR & TFR,
(vi) Office and residence of CTFO and ATFO of OHE, PS1 and RC maintenance depots,
(vii) Office and residence of ELC of sub-depot,
(viii) SEB's Grid Substation, if feasible. ,
5. P & T Telephones
(i) Remote Control Centre, (ii) All Traction sub-stations,
(iii) Offices and residences of Sr.DEE & DEE(TrD), Sr.DEE & DEE(RS), Sr.DEE & DEE(RSO), AEE(TrD), AEE(RS) and AEE(RSO).
20713 Power Supply Arrangement
1. To ensure reliability of ac 240V, ac 50 Hz single phase power supply a 25 kV/240V auxiliary transformer shall be connected to 25 kV OHE.
(a) At a station where a reliable local power is available, the main supply is taken from this source. The stand-by supply is obtained by tapping the 25 kV catenary and installing a 25 kV/240 V auxiliary transformer.
(b) At stations where no reliable local supply is available, the main and stand-by power supplies are obtained by installing two 25kV/240 V auxiliary transformers, each connected to independent sub-sectors of the OHE.
(c) At stations where an auxiliary transformer is installed at a traction switching post situated within 350 m of the signal cabin or the station building 240 V supply from the auxiliary transformer is treated as the main supply and a second 25W/240V transformer is installed on another sub-sector for giving the stand-by supply.
2. Following works shall be carried out by the Electrical Department:
(i) At each way side station, 2 nos. Auxiliary Transformers, one each connected to OHE of UP & DN lines shall be provided. A 2 x 25 mm2, aluminium cable shall be laid from each AT to ASM's room and shall be terminated at the CLS supply panel. Local supply, if available, shall also be terminated at the panel as third source. A manual three-position change-over switch shall be provided on the CLS supply panel. The CLS panel shall be provided with MCBs and neon indication lamps for the incoming and outgoing supplies, Change-over shall be effected by ASM on duty. From the CLS supply panel, power supply will be extended to either cabin by S & T department, through 2 x 25 mm2 aluminium cables.
(ii) At big yards, where a number of cabins are located, 2 to 3 cabins shall be grouped together and a set of two ATs, one each connected to OHE of UP & DN lines shall be provided at a convenient location to feed each such group. CLS supply panel having a three-position manual change-over switch shall be provided at one of the cabins by the Electrical Department, from where the supply shall be extended by S&T department to other cabins.
(iii) Provision of 2 nos. Auxiliary Transformers, one each connected to OHE of UP & DN lines, shall be arranged at each level crossing located more than 2 km away from the Railway station. If any other level crossings are located within 2 km of the level crossing where a set of ATs have been provided, then supply from the same ATs shall be extended to these level crossing through 2 x 25 mm2. Aluminium cable to be laid by S & T Deptt. The CLS supply cable alongwith manual change-over switch shall be provided at the gate lodge. Change-over shall be effected by the Gateman on duty.
(iv) In case of IBH, separate set of ATs shall be provided. As IBHs are unmanned, a two-position automatic change-over switch shall be provided.
(v) In single line sections, one AT connected to the OHE will be provided for supply to CLS. The LT supply will be extended from the AT to ASM's- room by means of 2 x 25 mm2, aluminium cable terminated at the CLS supply panel. Local power supply, if available, will also be connected to this panel, which will be provided with a change-over switch. This arrangement will be adopted for the way side stations, level crossings beyond 2 km. from the nearest Railway Station and at the IBHs.
(vi) At way-side electrified stations, where local supply is prone to prolonged interruptions, an emergency light point shall be provided in ASM's room and in each cabin from the AT supply, through a separate circuit protected by a fuse of proper rating. At non-electrified stations, a separate lighting circuit shall be provided in ASM's room and in each cabin from the AT supply. From the lighting circuit in the ASM's room, one light point each in ASM's room, on the platform outside the station building, at the ticket window/waiting hall and in the cable hut shall be provided. On the lighting circuit at the cabins, one light point each in the cabin, relay room, battery room and cabin basement shall be provided.
(vii) All the power supply installations provided by the Electrical department as detailed in paras (i) to (vi) above, will be maintained by the Electrical department.
3. Following works shall be carried out by the S&T department:
(i) A 2 x 25 mm2 aluminium cable will be laid from the ASM's room to each cabin alongwith the signal control cables in the same trench. An integrated power cubicles including a voltage stabilizer, inverter and battery chargers will be provided in the relay room for signal and relay supplies. A 240 V ac outlet from this power pack will be made available to Electrical Department for provision of light points. Similar arrangements will be made at each level crossing and IBH.
(ii) An 80 Ah battery capacity, sufficient to cater for two hours failure of supply, will be provided at each cabin and level crossing. One extra 80 Ah battery set shall be provided temporarily at these points until AT supply becomes available. At IBH 200 Ah battery capacity may be provided to cater for four hours failure of supply.
(iii) At large yards, two standby diesel generating sets of 10 kVA rating each will be provided for standby power supply to the signalling installations. The supply from these generators will be brought to the CLS supply panel in the ASM's room or in the cabin, where a change-over switch will be provided by the S&T Deptt. to enable the ASM/Cabinman to affect the change-over supply from the normal mode to the generator mode. A push-button control will also be provided in the ASM's room/cabin to enable the ASM to start/stop standby diesel generator whenever required.
(iv) On sections where automatic block is planned, S&T will lay a power cable all along the section with suitable feeding arrangements to suit local conditions.
(v) At station where telecom repeater stations are located, a 2 x 25 mm2 aluminium cable will be laid from the CLS supply panel in the ASM's room to the repeater station to avail AT supply to work battery chargers and repeater equipments in the event of failure of local supply. Electrical Department will provide a change-over switch at the repeater station between AT supply and local supply. An emergency light point shall also be provided at Repeater stations by Electrical Department from the AT supply.
2. In the event of power block being given on both the OHE sub-sectors from which the signal supply is derived, electric traffic would necessarily have to be suspended on the line. During such periods, colour light signalling will not also be in operation. Such cases are likely to arise very rarely at any station and the duration of the block is not like to exceed one hour at a time. Therefore, no additional power supply arrangement need be made by the Electrical Department at wayside stations. However, to cater for this condition, portable stand-by sets should be kept by the S&T Department to be operated until 25 kV supply is restored. At large stations with considerable shunting movements, a stand-by diesel generator set may be installed by the S&T Department to meet emergencies, if considered essential. III. PERMANENT WAY INSTALLATIONS 20714 Major Track Maintenance Works
1. An authorised OHE staff should invariably be present, when relaying work or any major work on track is carried out, in order to ensure the following points:
(i) Power block is correctly taken and permit to work is issued;
(ii) The structure bonds, track bonds, cross bonds, longitudinal rail bonds etc. are not disturbed and if disconnected for the work, they are reconnected properly when the work is completed.
(iii) The return feeder connections to the rails at the feeding posts are proper and not disturbed.
(iv) The setting distance of the structure is not affected during slewing;
(v) The track level is not raised beyond the permissible limits during the work;
(vi) Excavation or digging near a mast foundation is done in such a manner that the foundation is not exposed;
(vii) The clearance particularly at over line structure is maintained to the required standards; (viii) Precautions for the safety of staff working under the OHE are taken correctly.
The Engineering officials in charge of such major work shall ensure that intimation to their counterparts for OHE maintenance work is given with adequate notice.
20715 New Sections to be Electrified
Engineering staff working in section being electrified should be specially trained and instructed in regard to working in electrified sections well in time (Para 20972).
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SWITCHGEAR INSPECTION AND TEST PROCEDURE PKR ELECTRICAL ENGINEERING CONFIDENTIAL TABLE OF CONTENTS 1) VISUAL INSPECTION 2) W...
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