Signaling In Re Area

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SIGNALLING IN RE AREA (PRECAUTIONARY MEASURES) 1.

Introduction In electrified section, Signalling circuits are affected by induced voltage. This induced voltage may cause hazardous effect on working of Signalling equipments as well as Railway staff dealing with it. It is, therefore, necessary that suitable protective measures are adopted to minimise the effect of induced voltage. This handbook covers signalling in 25 KV-50 cycle AC electrified section.

2.

Effect of A.C. Traction Any circuit in the vicinity of 25 KV AC electrified section is likely to be influenced by electrostatic and electromagnetic induction. a) Electrostatic induction is practically eliminated by transferring a circuit into underground cables protected by a metal sheath. b) Electro-magnetic induction causes various current and voltage to develop in conductors parallel to the track. The value of this induced voltage depends on various factors such as: i) Length of parallelism between the cable conductors and the electrified track. ii) Soil conductivity iii) Screening efficiency of the cable sheath.

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iv) Return current through the rails and the return conductor, where provided. v) Mutual inductance between catenary and the cable conductors which depends on separation between the two. vi) The current carried by the catenary etc. 3.

Precautionary measures As a high voltage conductor, is provided, induced voltages may cause effects on the functioning of signal equipment and may be dangerous to the maintenance and operating staff, so precautionary measures are adopted for each signalling gears to minimise the effect of induced voltage as described below.

3.1

Signal Unit Electrical clearance required to be provided to safe guard, is specified as 2000 mm from the live conductor. Under no circumstances, a signal post or any of its fittings must be allowed to infringe in this portion. When the signal have to be so located that they fall with in 2m from the electrified track, the iron screen of wire mesh should be provided between the signal post and the OHE and properly earthed to protect the staff who may have to work within the infringing portion.  All

signal units and cables connected with it are earthed near the signal.  The screen shall be provided on the side adjacent to the catenary and for signal post between two wired track, a screen on either side of the post will be required.

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 The

screen shall be so fixed that its top edge is 2 meters above from the catenary and the bottom edge is 2 meters below from the contact wire. 2 met ers

Catenary Wire

Protective Screen

Signal Post

Contact Wire 2 met ers

Less than 2 meters

Screen adjacent to catenary  Screen

shall be connected to an earth, not exceeding 10 Ohm in resistance.  Provision

of such screen is mandatory in all cases where the distance from OHE wire is less then 2 m.  Signal

unit and screen should be connected to earth.

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2 meters

Protective

Signal Post

Catenary Wire

2 meters

Contact Wire

Less than 2 meters

Less than 2 meters

Screen between two wired track

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Insulation of Rod and Wire Transmission Traction return current pass through rails and rods/wires are in contact with the rail at some point. The rod and wires in AC electrified areas are subject to a certain amount of induced voltage. To protect the operating staff from the effects of the voltages, the rod and wires are provided with insulation both at cabin and the function end.

3.2.1 Insulation of Rod  In

case there is a large number of rodding in the same alignment, the insulated joints shall be provided on each rod run between the same sets of rod roller guides as shown in figure below.

Roller Guide

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Rod Insulation

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If this is not done any voltage appearing in one rod will be transmitted to another rod through the rod roller guide as in the figure given below: HIGH VOLTAGE AFFECTED ROD

JOINT INSULATION

ROD ROLLER GUIDE ASSEMBLY

TO CABIN

INSULATION JOINT

Insulation joints wrongly provided Voltage appears on all rods  For

rod running under the track, the top of the rod shall not be less than 25 mm below the bottom of the rail in order to ensure that the rails do not come in contact with the rod during the passage of the trains.  Ensure that the rod transmission is more than 300 m. Additional insulators shall be provided on each rod at every 300 meters. 3.2.2 Insulation of Wires The insulation of wires is obtained by provision of hard rubber wire insulators on the wire transmission at both cabin and function end.

Rubber Wire Insulator

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 The

wire insulators shall be provided on each wire as close to the cabin as possible or inside the cabin to ensure that the insulator is not exposed to sun and rain directly.  In case the distance between the two insulators at either end is greater than 300 meters, additional insulators shall be provided on each wire so that the distance between two consecutive insulators on the same wires is not greater than 300 meters.  Any contact between the wire transmission and the rails must be avoided.  A minimum distance of 40 mm shall be maintained between the wire and nearest edge of the rail or mast.  The insulators shall be provided with split links or disconnecting links on either side for easy replacement. 3.3

Track circuit Following type of track circuits are used in RE area.  DC Single rail track circuit.  Electronic track circuit.  Audio frequency track circuit  AC track circuit.

3.3.1 DC single rail track circuit  In

single rail DC track circuit, one rail is used for traction return current and other rail is insulated, noninsulated rail is connected with OHE mast. AC induced voltage is 10V per meter. A 9 Ohm AC immunized relay with chock at both feed and relay end works up to 350 meters.

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 Maximum

length permissible is 450 meters with QABT1. AC immunized relay with wooden sleepers are provided with train shunt value of 0.5 Ohm.  Maximum length of track circuit is 350 meters with concrete sleepers, with train shunt value of 0.25 Ohms.  At feed end one chock and resistance is provided in series on – ve side of battery, which is connected to traction return rail and other chock is provided at relay end.  In single rail track circuit, in the event of a break in the non-insulated rail, very heavy current will flow through the track relay as well as the equipment at the feed end as in fig below.

To avoid, the following precaution should be adopted.  The

non-insulated rails of adjacent tracks shall be cross bonded at interval of 100 m.  If track circuit is less then 100 m, in length, cross bonding at both end shall be provided.  If track circuit is more then 100 m. in length than cross bonding to be provided at every 100 m.

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 Staggered

polarity is provided for adjacent track circuits and if return rails are staggered, insulated joints on both the rails are provided with transverse rail bond, so that continuous path is available for the return current as shown in figure below.

 As

par as possible crossing of point should be connected to the – ve polarity.  Closed and open track circuit adjoining each other shall not be provided. 3.3.2 Electronic track circuit. Jeumont high voltage Impulse track circuit are used in railways, which may be either single rail or double rail type.  Maximum  Maximum

length of single rail track circuit is 200 m. length of double rail track circuit is 800 m.

3.3.3 AC Track circuit In this type of track circuit, 831/3 cycle is used for track feed and the relays used are either the van type or motor

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type. The 831/3 track circuit may be either the single rail type or the double rail type.  Impedance  The length

bonds are used on the double rail types. of single rail track circuits shall not exceed

200 m.  The length of double rail track circuit shall not exceed 1000 m. 3.4

Block Instrument Since the block circuit is very much longer then ordinary signal circuits, comparatively high voltage will be developed in the circuit. Protective devices shall be provided at either end of block circuit for protection. The principal protective device used is called “Block filter.”  A relay

unit is required for single line block instruments.

 In

single line Neal’s block token Instruments, the rest contact is substituted by the contacts of a slow release relay. The relay is energised during the operation of the plunger but gets de-energised only after the condenser has discharged in a 5000 Ohm. 3.4.1 Filter Unit A

filter of approved design shall be installed between the block instrument and line wire.  The filter acts as a low pass filter which allows DC current to pass through but offers very high impedance for the induced voltages.

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Wiring diagram of filter unit

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Filter unit

 When

a block section originates at a station in RE area and other terminates on non RE area; filter should be provided with block instruments at both ends of such a block section.  Block telephone line should be separate from block circuit.  Separate battery set shall be used for each block instrument.

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3.4.2 Block bell unit  In

SGE double line block instrument the bell circuit is taken separately in another pair of wire, the bell beats are transmitted by AC through the separate pair of the block quad. The AC supply is generated by the block bell equipment, which works on 12 volt DC.

Bell unit equipment consist of a transistor oscillator generator AC at 150 cycle and rectifier for converting AC impulse received from other station. The rectified impulse are applied to the block bell through a relay.  The

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Wiring of block bell equipment

3.5

Equipment not immunised Equipments not immunised for AC shall not be used directly on line circuits. The following is the list of such equipments:  Electrical Key transmitter  Arm and light repeater  Telephone type relays  Lever locks  Slots indicators  Color light signal repeating Indicator.  250 ohms relay. To make use of these equipments, relays are interposed so that they are made to work locally through the contacts of these relays. The immunisation value of certain relays are as under S.No. Type of Relay 1 2 3

Immunisation value type 300 V

Shelf relay BSS-1659 Plug-in type 300 V relay. BRS-930 PI-150 A 210-260 V (Sundram clayton)

Signalling in RE area

Max. length of parallelism. 3.5 Km. 3.5 Km. 2.0 Km. Screen cable 800 m. Unscreened October’ 2001

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cable 4

Siemens type i) 5F/3BK50 B1 ii) 4F/4B iii) 6F/2B

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175 V 130 V 120 V

2 Km. 1.4 Km. 1.3 Km.

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3.6 Signal feeding system. In RE AC electrified area maximum length of direct feeding of signals shall not exceed 600 m. when screened cables are used and 240 m. in case of unscreened cables. If the length exceeds this limit the following two methods are used: ♦ Local Feed ♦ Remote Feed In RE area current transformers L-type and H-type are used to enable a 1000 Ohm line relay to be used as ECR. L-type is used in series with the supply leads where the signal lamps are directly fed from the cabin. 3.6.1 LOCAL FEED METHOD For signals located beyond 600 meters, the controlling relays HR, DR, HHR etc. in relay room are repeated through AC immunised relays at the location and the signals are fed locally from these relay contacts. All circuits which pass through a main cable must have individual returns and the controlling relay contacts must be included in both the conductors i.e. double cutting of contacts is necessary. More then one route UGPR for all the routes shall be provided in the location.

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24 VDC 24 VDC

DECPR DECR

HECPR

HECR

RECR

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24 V DC

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In the local feed method, the following equipments are provided at the location box. ♦ 2 Nos. `OFF’ aspect controlling relays (HPR, DPR). ♦ 3 Nos. ECR Relays (DECR, HECR,RECR) ♦ 3 Nos. current transformer rectifiers to feed ECR relays. ♦ A transformer rectifier set to feed DC voltage to repeat DECR, HECR, RECR. ♦ Besides the above, a power cable will be required to take power to the location to feed the signals and repeat the ECR(s). Hence local feed system has become cumbersome.

24 V DC

3.6.2 REMOTE FEED In this remote feed system, signals are fed directly from the cabin but in the signal lamp circuit, the “OFF” aspect controlling repeat relays are proved as under.

+

HR

HPR

+

DR DPR

-

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Point machine.

For various types of point machines the parameters are as under : Maximum Permissible Separates Type AC Immunity Between Point Contactor And Point Machine Value (Volts) Single track Double track SIEMENS 60 V 345 mts. 420 mts. GRS 5 E 90 V 515 mts. 630 mts. M-5 70 V 400 mts. 490 mts. M-3 200 V 1150 mts. 1400 mts. 3.8 Lifting Barrier. As far as possible lifting barrier shall be located at a minimum distance of the length of boom from the nearest rail. 4.0 Earthing arrangement. Any dangerous potential appearing on the exposed part due to electromagnetic induction is likely to cause injury to the person and may prove dangerous to the equipments; so proper earthing of S&T installation is essential. 4.1

Purpose of earthing.  Safety of the working staff against electric shocks.  To ensure safe & reliable operation of equipments

by minimising the effect of induced voltage.  To protect the equipment from unduly high EMF, which may cause DI- ELECTRIC break down mostly due to (insulation) the physical contact with live OHE

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equipment such as in case of catenary wire falling on the track or due to lightening discharge. 4.2

Equipments to be earthed. Separate earth shall be provided for the following :  Lever frame and other metallic frames.  For each Block Instrument.  In case of signals provided on bracketed

posts or gantries located above contact wire level falling within 2 meters from the electrified tracks. The protection screen shall be connected to earth.  Where the under ground cables enters the location box or cabins, the cable termination boxes, (connecting the ends of the cable) the metallic structures supporting the terminal boxes shall be connected together to the same earth as the lightening arrestors. 4.3

Earth lead wire The following type of earth lead wire should be used  ACSR

wires of size 64 Sq. mm.(19 strands of 2.11 mm dia.)  GI wire of negligible resistance. Care should be taken as under  The

lead wires shall be protected against mechanical damage.  In case buried underground, should be painted with anticorrosive paint or bitumen or varnish.

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 The

earthing leads for separate earthing arrangements should be electrically insulated from each other.  Earth lead wire should be soldered with earth pipe. 4.4

Earth electrode  Under

ordinary conditions of soil, use of GI or MS electrode is recommended.  Where

more than one earth pipes are used, the distance between each other pipes should not be less than 3 m.  The

resistance of each earth should not exceed 10 ohm.

5.0

Power supply for signal circuit

5.1

Stabiliser To ensure that correct voltage is available at all times for signalling lamps, relays sensitive to voltage variations (ECR’S relays), voltage stabilizers of adequate capacity should be used.

5.2

Transformers (220/110 V AC ) The location of transformers 220/110 V AC of adequate capacity, at the controlling point depend, upon the distance of signal from point of control. Separate transformers should be used as under.  Transformer

for all signals located with in a distance of

600 m.

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 Transformer

for all signals beyond 600 m. It must be ensured that the combined length of parallelism shall not exceed 2 Km.  Transformer for signals where length of parallelism is more then 2 Km.  Each distance shall be provided with separate transformer. 6.0

Battery arrangement Separate battery set should be used for signalling circuit as under.  Separate  Separate  Separate  Separate

battery set for external circuits. battery set for internal circuits. line battery for block instrument. battery set for local circuit of block equipment (i.e. block bell & commutator lock circuit) for both block instruments.  Separate battery set for each track circuit.

7 Protection of Railway Staff These instructions lay down the precautionary measures to be observed by railway personnel working on Signalling. Installation on lines equipped with 25 KV, 50 Cycles AC traction. Precautions are required to be taken on account of the following.  Proximity

of a live conductor

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CAMTECH/2001/SRE/1.0  Pressure of return current in rails.  Induction in all metallic bodies situated

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close to overhead

equipment. 7.1 Proximity of a live conductor  Any

contact, direct or indirect, with the 25 KV live conductors is dangerous and shall be strictly avoided.  If any portion of a signal post or its fittings where a lampman has to work falls within 2 m. of a 25 KV live conductor or metal part electrically connected to this conductor, such portion shall be protected with an iron screen of approved design solidly connected to the structural work.  In

case of signals provided on bracketed posts or gantries located above contact wire level and falling within 2 m. for the electrical connection to this conductor, then such portion shall be protected with an iron screen of approved design solidly connected to the structural work.  If

any portion of a signal post or its fittings where lampman have to work, falls within 2 meters of a live conductor, such portion shall, as far as practicable, be protected with an iron screening of approved design solidly connected to the structural work.  If for any reason, the protective iron screening is not provided as above, the railway staff shall not undertake any work on those portions of the signal or its fittings falling within the 2 meter zone from a 25 KV live part unless the power has been switched off of this 25 KV live part and a permission to work has been obtained. 7.2

Pressure of return current

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The flow of return current in the rails may cause a potential difference :  Between

two rails at an insulated joint of the track circuit or at an ordinary joint, in case, the fish plates are broken.  Between two ends of a fractured rail.  Between an insulated rail and the rail used for the traction return current.  Between the rail and the surrounding mass of earth. 7.3 Induction in all metallic bodies situated close to overhead electrical equipment Precautionary measures listed below shall necessarily be taken, as induced voltages may appear at any time on account of a sudden short circuit in the traction overhead equipment.  They

shall as a general rule, wear rubber gloves and use tools with insulated handles.  When the work to be done is of such a nature that rubber gloves cannot be used conveniently, staff must insulate themselves from the ground by using rubber mats, etc.  Before cutting the armour or the lead sheath of the cable or the wires in the cables, an electrical connection of low resistance shall be established between the two parts of the armour, the sheathing or wires that are to be separated by cutting. 8.

Insulation of Tools

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The handles of the tools shall be provided with an insulating sleeve of rubber/plastic material of an approved type sufficient to with stand 3000 Volt. 8.1

Tools to be insulated  Screw Drivers  Pliers  Electricians Knives  Spanners  Any other tools whose

handles are metallic and which are required for the above purpose. 8.2 Tools to be provided with insulating paints Some of the tools which are used in Signalling are required to be insulated as a precautionary measure to avoid bridging of rails and earth through the tools and body of the workman as a difference of potential may exist due to traction return current and electromagnetic or electrostatic induction. It is considered that painting of the below mentioned S&T tools with suitable rubber based insulating paints should adequately meet the requirements of insulation.  Crow Bar  Tommy bar  Spanner  Ratchet  Wrenches  Black-Smith’s tongs  Any other tools which

are wholly metallic or whose

handles are metallic.

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Maintenance ν Check

that wire mesh screen provided between the signal post and OHE to protect the staff is held properly with nut and bolt. ν Check caution board provided on the signal post to warn the staff. The caution board should be cleaned and varnished so that precautions are clearly readable from the foot of the signal ladder. ν Check that wire mesh screen is not broken due to dust and rust. ν Check that rod and wire insulation once in six months or as per the instructions issued by the Railway authorities. ν Check that structure bonding, cross bonding and longitudinal bonding are intact and make arrangements for joint inspection with OHE staff once in six months or as per the instructions issued. ν Check

no load current of signal transformer once in a six months. Voltage stabliser should be of adequate capacity.

ν Ensure

that correct voltage is available at all times.

ν Check

that separate power cables for feeding all signals are installed, provided the conductors are of adequate cross sectional area.

ν Ensure

that the combined parallelism of circuits does not exceed 600 meters. In case it is more than two transformers shall be provided to isolate the feed.

ν Ensure

that no rectifier for polarisation or any other purpose (such as making the relay slow to operate), shall be

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included in any external circuit as the rectifier will act as half wave rectifiers on application of AC and will effect the relay operations. ν Check

that earth lead wires are protected against mechanical damage.

ν Check

that the earthing lead is provided for separate earthing arrangements ensure that these are electrically insulated from each other through out and also from the metallic structure in contact with different earthing arrangements. ν Refer maintenance handbook on earthing No. CAMTECH/2000/S/ETH/1.0 prepared by CAMTECH/ Gwalior for maintenance of earth. ν Ensure

that the staff working on tracks equipped with 25 KV-50cycles AC traction are familiar with the instructions for treatment of persons suffering from electric shock.

ν Ensure

that the instruction board in English and in the regional language describing the methods to be adopted for treatment of electric shock must be clearly displayed in all inspector’s office.

10.

Do’s & Don’ts

10.1

Do’s

ν Ensure

the proper earthing of battery charger after replacing the defective charger.

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ν Ensure

that transfer and longitudinal bonding are provided after replacement of defective glued joint on track circuited portion.

ν Always

use tools, which are provided with insulated

sleeves. ν

Always arrange for power block before taking the work on hand for replacement of signal unit or any other work on the signal, which is infringing within two meter from the live parts of the OHE.

ν Always

use surge arrester on cable, terminated between junction box and EV of axle counter.

ν Ensure

that no portion of signal fitting lies within 2m. from OHE live conductor.

ν Ensure

that for the power cable for feeding the signals. The voltage drop is with in 5 %

ν Ensure

that individual earth must be in good condition for each signal.

ν Ensure

that a caution board is provided on signal post at the height of 3.0 meter above the rail level, if protective screen is not provided on the signal post.

ν Ensure

that the protective screen of signal post is earthed properly.

ν Ensure

that separate earth is provided for each block instrument.

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ν Ensure

that each block instrument have separate line battery set, to feed block instruments individually.

ν Insist

P-way staff to inform S&T officials before replacing the crossing and rail to ensure continuity of RE bonds.

ν Ensure

continuity of earth bonds before opening any insulation joint. ν Do inform to the OHE staff immediately if any OHE bond like longitudinal bond, structural bond, and cross bond is found open or loose. ν Ensure

continuity of armour while joints provided in the

cable. ν Ensure

that rod insulation joint is in the same span while changing the broken rod.

ν Ensure

the rods and wires passing under the track and are not touching the rail flange.

Don’ts ν Don’t

remove/disconnect screen of wire mesh provided between the signal post and OHE live conductor.

ν Don’t

remove warning board fitted on signal post.

ν Don’t

open the earthing of signalling and other metallic fittings concerned with the signalling gears.

ν Don’t

energize any circuit on overhead line.

ν Don’t

make through wire insulator with wire or wire rope.

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bypass any lightning arrester.

ν Don’t

remove any earthing wire from cable armour or metallic sheath of underground main cable.

ν Don’t

combine earth with each other.

ν Don’t

remove any OHE bonds provided for traction bond.

ν Don’t

by pass choke terminals.

ν Do

not keep the track circuit in working condition only on the battery charger.

ν Don’t

combined internal and external battery cell with each

other. ν Don’t

replace any immunised relay with non immunised

relay. ν Do

not open the earthing and connections of any part of the block filter unit. 

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References 1. RE Manual issued by CORE/Allahabad 2. Various instructions issued by IRISET / Secundrabad 3. Various instructions issued by RDSO/ Lucknow 4. CAMTECH publications a) b)

Block instrument Earthing arrangement 

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