Telecom Hand Book PDF

इ रसेट IRISET  TELECOM HAND BOOK ET IS IR The Material Presented in this IRISET Notes is for guidance only. It does not over rule or alter any of the Provisions contained in Manuals or Railway Board’s directives. INDIAN RAILWAYS INSTITUTE OF SIGNAL...

इ रसेट IRISET  TELECOM HAND BOOK ET IS IR The Material Presented in this IRISET Notes is for guidance only. It does not over rule or alter any of the Provisions contained in Manuals or Railway Board’s directives. INDIAN RAILWAYS INSTITUTE OF SIGNAL ENGINEERING & TELECOMMUNICATIONS, SECUNDERABAD - 500 017 April 2020  TELECOM HAND BOOK S.No Chapter Page No 1. Telecom General 1 2. Radio Propagation 6 3. Measuring Instruments 12 4. Telecom Cables 23 5. Public Address System 32 6. Passenger Information System 38 7. Power Supply Arrangements 47 8. Earthing and Surge Protection 55 9. Train Traffic Control 63 10. Telephone Exchanges 69 11. PDH Principles 84 12. 13. 14. OFC Systems ET PDH Equipment SDH Principles 87 93 101 15. SDH Equipment 104 16. Mobile Communication 114 IS 17. Data Communication & Networking 119 18. Data Networks of IR 134 19 New Topics 140 IR Compiled by Telecom Faculty of IRISET DTP K.Srinivas, JE (D) No. of Pages 168 Date of Issue April 2020 Version No. 1.0 © IRISET “This is the Intellectual property for exclusive use of Indian Railways. No part of this publication may be stored in a retrieval system, transmitted or reproduced in any way, including but not limited to photo copy, photograph, magnetic, optical or other record without the prior agreement and written permission of IRISET, Secunderabad, India” http://www.iriset.indianrailways.gov.in  Telecom General CHAPTER 1: TELECOM GENERAL (TB1) 1.1 Organization of S&T Zonal Level PCSTE CAOR CSE CCE CSTE/Plg CSTE/Proj CSTE/Con Dy CSTE/Sig Dy CSTE/Tele Dy CSTE/Plg Dy CSTE/Proj Dy CSTE/Con SSTE/Sig SSTE/Tele SSTE/Plg SSTE/Proj SSTE/Con SSE/Sig SSE/Tele SSE/Plg SSE/Proj SSE/Con Divisional Level ET Sr DSTE IS DSTE/Sig DSTE/Tele DSTE/Works IR SSE/Drg SSE/Sig SSE/Tele SSE/Works Sub Division Section (Field Units) ADSTE ADSTE ADSTE SSE/Sig SSE/Tele SSE/Sig SSE/Tele SSE/Sig SSE/Tele JE/Sig JE/Tele JE/Sig JE/Tele JE/Sig JE/Tele Tech/Sig Tech/Tele Tech/Sig Tech/Tele Tech/Sig Tech/Tele Helper Helper Helper Helper Helper Helper IRISET 1 Telecom Hand Book Telecom General IRISET - SECUNDERABAD ET 1.2 Important organizations in Telecommunications International Telecommunication Union ITU-T (CCITT) Telecommunication sector IS International Telecommunication Union Radio ITU-R (CCIR) communication sector International Telecommunication Union Development ITU-D Sector IR TEC Telecommunication Engineering Center RDSO Research Designs and Standards Organization TCSC Telecommunications Standards Committee PTCC Power and Telecommunication Co-ordination Committee WPC Wireless Planning & Co-ordination Committee Standing Advisory Committee on Radio Frequency SACFA Allocations ISO International Organization for Standardization IETF Internet Engineering Task Force ETSI European Telecommunication Standards Institute ANSI American National Standards Institute IEEE Institute of Electrical and Electronic Engineers NCSSS National Cyber Safety & Security Standards CERT-in Indian Computer Emergency Team CyCord Cyber Coordination Centre IRISET 2 Telecom Hand Book  Telecom General 1.3 Telecom system in Indian Railways a) Train Traffic Operating ckts(Block, IBS, LC gate ph, BPAC etc.) b) Train Traffic Safety Communication (VHF, MTRC, TCAS) c) Train Traffic Communication (Sec. Control, TPC, RC, TLC, ENGG, Dy.Control, Hotline, Rly auto phone) d) Data Circuits (UTS, PRS, FOIS, RAILNET, Data Loggers, PMS, COA, ICMS, CMS) e) Telephone Exchange (ISDN, VoIP) f) Passenger Amenities (PA system, TIBs, CIBs, POET, ATVM, Touch Screen KIOSK, Fare display board, BSNL phone) g) Passenger Safety System (Surveillance System & Integrated Security System - ISS) h) Accident site Communication (ART, ARMV, V-SAT, WLL Exchange, VHF,CUG) i) Alternate Communication for Train Traffic Control (BSNL Phones, CUG, 25W VHF, FWP) 1.4 MTBF and MTTR ET a) Mean Time between Failure (MTBF) is a reliability term used to provide the amount of failures per million hours for a product. MTBF = Total working hours/Number of failures of sub system IS Total working hours of Equipment = Σ number of Equipment provided X working hours of Equipment system b) Mean Time To Repair (MTTR) is the time needed to repair a failed hardware module. IR MTBF should be as high as possible and MTTR should be as low as possible. 1.5 Registers/Documentations to be maintained at Telecom Installations 1.5.1 Exchange Indoor a) Exchange layout plan b) Rack layout plan for each rack with connection details c) MDF and IDF terminal on plan d) Installation manual for equipment e) Software documentation f) Operation and maintenance manual g) Wiring diagram for power panel h) Manual for battery chargers i) Battery maintenance register IRISET 3 Telecom Hand Book Telecom General Outdoor a) Telephone No. wise subscriber’s details b) Subscriber wise Telephone Directory c) Cable/Overhead layout plan d) Subscriber premises typical wiring plan e) Outdoor cable testing register 1.5.2 OFC system a) KM wise diagram (soft & hard copy) b) Channel planning chart c) E1 allocation chart d) STM 1 equipment Test register e) PD MUX test register f) SMPS battery charger test register g) Maintenance register h) Earth measurement register ET i) Fiber joint test register with RCIL j) Installation Manual of STM1 equipment k) Operation Manual of STM1 equipment l) Maintenance Manual of STM1 equipment m) Installation Manual of PD MUX n) Operation Manual of PD MUX IS o) Maintenance Manual of PD MUX p) Equipment History Register 1.5.3 Quad Cable IR a) KM wise Cable route diagram (soft & hard copy) b) Quad cable allocation chart c) Quad cable testing register 1.5.4 Data Networks (UTS/PRS/FOIS/Railnet/MIS) a) Approved network diagram b) Actual network diagram c) E1 allocation for RCIL channels and details of BSNL channels d) E1 Ring protection for RCIL/BSNL and its channel details 1.5.5 Accident communication a) Details of EC socket b) Zonal Railway Telephone directory c) Zonal CUG mobile directory d) Satellite phone directory e) Railway Board Telephone directory f) Disaster Management Telephone directory g) OFC/Quad Cable route diagram h) Train Time Table IRISET 4 Telecom Hand Book  Telecom General 1.5.6 Passenger Amenities (at Stations) a) Approved Installation network diagram b) Actual network diagram c) AMC/ARC particulars d) Inspection registers 1.5.7 Drawings/Specifications & Circulars/JPOs (Available at Divisional HQs/ section SSE level) a) Set of all IRS (TC) drawings b) Set of all RDSO drawings c) Set of all IRS (TC) Specifications d) Set of all RDSO Specifications e) Railway Board Circulars & JPOs f) Set of all Zonal Circulars & JPOs g) ET Jurisdiction chart of Quad cable/OFC cable maintenance staff & Telecommunication equipment maintenance staff 1.6 The gauge of MG line is 1000 mm and BG line is 1676 mm 1.7 The efficiency of any circuit or equipment is [ (A-B)/A ] X 100 IS where A is total working hrs in a month B is total working hrs lost on account of line interruptions 1.8 Emergency Communication IR (EC) sockets are available at regular intervals of 1 KM along the Railway track to establish communication from site to controller Painting of EC post should be alternately Black & white paint with 15cm bands Position of EC post from centre of railway track: 4m (permitted range 2.65m to max 5.5m) Facing of EC socket: towards Control office side Nearest EC socket post is identified by Telephone symbol painted on OHE mast/Decimeter post IRISET 5 Telecom Hand Book Radio Propagation CHAPTER 2: RADIO PROPAGATION (TB5) 8 2.1 Radio Propagation: Radio waves travel 3 X 10 meters per second 2.2 Electromagnetic Spectrum 2.3 Ionosphere Regions D-Layer 50KM-90KM above the earth’s surface. It will disappear at night E-Layer 110KM above the earth’s surface ET F1-Layer 220KM above the earth’s surface F2-Layer 250-350 KM above the earth’s surface At night F1 and F2 layers make one layer. The ionization of all the layers is maximum at day time and minimum at night 2.4 Propagation mechanism IS No. Frequency Mechanism of Propagation 1 < 500KHz Surface/Ground wave 2 500KHz - 1.5MHz Surface wave for short distance IR Ionosphere wave for longer distance 3 1.5MHz - 30MHz Ionosphere wave 4 > 3 0MHz Space wave/Line of sight propagation 2.5 Frequency to Wavelength Conversion: λ = c/f where λ = the wavelength in metres, f = frequency in Hertz 8 c = speed of radio waves (light) (3 x 10 m/s) 2.6 Radio Frequency Spectrum VLF Very Low Frequency 3 - 30 KHz LF Low Frequency 30 - 300 KHz MF Medium Frequency 300 - 3000 KHz HF High Frequency 3MHz - 30 MHz VHF Very High Frequency 30 MHz - 300 MHz UHF Ultra High Frequency 300 MHz - 3 GHz SHF Super High Frequency 3 GHz - 30 GHz EHF Extra High Frequency 30 GHz - 300 GHz IRISET 6 Telecom Hand Book  Radio Propagation 2.7 Radio Frequency bands used in Railways No. Frequency Range Band Application 1 VHF 30MHz - 300MHz Walkie-Talkie a) 2GHz UHF Radio links 300MHz - 3GHz b) Train Radio through leaky 2 UHF coaxial cable in tunnels c) GSM & GSM-R 3GHz - 30GHz 7 GHz (MW) 3 SHF (MW) 18 GHz (MW) *HF communication (3 MHz – 30MHz band) was once used in Railways but now obsolete 2.8 GSM and GSM-R Frequency Allocation No. Type Uplink (MS to BTS) Down link (BTS to MS) 1 2 3 GSM-900 GSM-1800 GSM-1900 ET 890 - 915 MHz 1710 - 1785 MHz 1850 - 1910 MHz 935 - 960 MHz 1805 - 1880 MHz 1930 - 1990 MHz 4 GSM-R 876 - 915 MHz 921 - 960 MHz IS 2.9 FADING: Fading is variation or the attenuation of a signal with various variable. To avoid fading, diversity technique are used. They are 2.9.1 Frequency diversity IR IRISET 7 Telecom Hand Book Radio Propagation 2.9.2 Space diversity 2.10 Antenna An antenna is basically a transducer. It converts RF electrical current into an EM Wave of the same frequency. It forms a part of the transmitter as well as the receiver circuit. The simple antenna is called a Half Wave Length Dipole. The practical length of a half wave dipole is Lm = (142.5/MHz) meters Isotropic antenna : Actual antenna : Input Impedance : ET Radiates equal power in all directions Does not radiate power equally in all directions Typical input impedance is 50Ω Return loss : Return Loss (in dB) = 20 log10 SWR +1 SWR -1 IS Bandwidth : BW = 100 × FH - FL FC Where FH is the highest frequency in the band, FL is the lowest frequency in the band, and FC is the centre frequency in the band. IR Different types of antennas have different bandwidth limitations. 2.10.1 Antenna Gain: Gain of an antenna provides to a signal before transmitting to air. For parabolic antennas used for MW link Antenna Gain = 17.8 + 20 log (f x dia) where f = Frequency in GHz, dia = Diameter of MW antenna. dBi = used to compare the gain of an antenna with respect to an isotropic antenna dB = A dB is a short way to express the ratio of two values. As a unit for the strength of a signal, dB expresses the ratio between two power levels. To be exact, dB = log (P1/P2) dBm = It denotes an absolute power level measured in decibels w.r.t 1 mill watt (mW). dBm = 10*log (P/1 mW) IRISET 8 Telecom Hand Book  Radio Propagation dBr = The expression dBr is used to define signal strength at RF and AF frequencies. The symbol is an abbreviation for "decibels relative to reference level". If the dBr figure is positive, then the measured signal is stronger than the reference signal. If the dBr figure is negative, then the measured signal is weaker than the reference signal. 2.11 Omni-directional Antennas propagate in all directions. a) Whip antenna: The gain is 5.19 dBi and about 36.8 Ω of radiation resistance ET b) Ground-plane antenna gain is 2.15 dBi IS IR 2.12 Directional and Semi directional antennas focus radiated power into narrow beams, which increases gain. Frequently used for long distance links. a) Sector antenna: Sector antennas are semi-directional antenna. Sector antennas are used extensively for cellular communication. IRISET 9 Telecom Hand Book Radio Propagation b) Yagi antenna: Yagi antennas have beam width in the range of 30-80° and can provide excess of 10 dBi passive gain. c) Gain of Parabolic antenna (7GHz band) 2 No. Antenna Type Gain of antenna 6 (D/I) 1 Fibre Antenna 17db formula not applicable 2 2.4m dia metal antenna 43db 3 3m dia metal antenna 45 db 4 ET 3.3 dia metal antenna 46 db IS IR 2.13 Antenna Applications VHF - for fixed stations : Dipoles for Omni-bus - for fixed stations : Yagi for directional - for mobile sets : Whip antenna UHF - for fixed stations : Yagi, Grid - for mobile sets (Train radio) : Whip antenna - for GSM – BTS : Sectorized antenna - for GSM Mobile sets : Whip antenna MW - for fixed stations : Parabolic Dish antenna : Beam reflectors : Passive reflectors IRISET 10 Telecom Hand Book  Radio Propagation 2.14 Link budget of MW link Radio Link ET This is a calculation with all the possible losses in the system and subtracting the losses from the line of sight to give an estimated value of your likely link performance FM = Srx+ Ptx + Gtx + FSL + Grx - CL IS FM = Fade Margin Srx = Sensitivity of the receiver (dBm) (using + dBm instead of – dBm) Ptx = Transmitter RF output power (dBm) IR Gtx = TX Antenna Gain (dB) FSL = Free Space Loss (dB) = 32.4 + 20 Log f + 20 log d f = Frequency of Radio equipment d = Diameter of Antenna Grx = Receiver (RX) Antenna Gain (dB) CL = Cable/Connector Loss (dB) IRISET 11 Telecom Hand Book Measuring Instruments CHAPTER 3: MEASURING INSTRUMENTS (TB6) 3.1 MEASURING INSTRUMENTS Measuring instrument is commonly used to describe a measurement system to provide Information about the physical value of some variable being measured. 3.2 Types of Measuring Instruments Indicating Integrating Recording 3.3 An analog instrument gives an output that varies continuously as the quantity being measured changes. The output can have an infinite ET number of values within the range that the instrument is designed to measure. 3.4 A digital instrument has an output that varies in discrete steps and so can only have a finite number of values. IS The instruments which are most commonly used in telecommunication systems are Voltmeter, Ammeter and an Ohm meter. 3.5 Digital Multimeter - Principle of Operation IR Any given measurement cycle performed by the A/D converter can be divided into three consecutive time periods: auto zero (AZ), integrate (INTEG) and READ. Both auto zero and integrate are fixed time periods. A 3-1/2 digit meter reads 000-999 plus 1000 to 1999. Since this is twice as high as a 3-digit meter can read, it is arbitrarily called a 3-1/2 digit. IRISET 12 Telecom Hand Book  Measuring Instruments ET A seven-segment display for this only needs the two segments that make up a "1" to perform this function. 3.6 ESSENTIAL QUALITIES OF A GOOD METER Sensitivity, Resolution, Range, Linearity, Precision, Repeatability, IS Reproducibility, Lag and Setting time. Errors during the measurement process Systematic errors and Random errors. IR Some of the measuring units related to telecommunication systems: Decibel: It is often used to express power or amplitudes in logarithmic ratios (gains), in preference to arithmetic ratios or percentages. One advantage is that the total decibel gain of a series of components (such as amplifiers and attenuators) can be calculated simply by summing the decibel gains of the individual components. Absolute measurements of Power dBm or dBmW : It refers to dB(1 mW) ie., power measurement relative to 1 milliwatt. x dBm = x dBW + 30. dBW dB(1 W) – similar to dBm, except the reference level is 1 watt. 0 dBW = +30 dBm; -30 dBW = 0 dBm;.001m W = -30 dbm IRISET 13 Telecom Hand Book Measuring Instruments 3.7 OUTDOOR (FIELD) MEASURING INSTRUMENTS Various types of measurements which are carried out periodically on telecom systems are i. Insulation Resistance ii. Loop Resistance iii. Route tracing iv. Fault locating v. Earth Resistance vi. Transmission Loss 3.8 GENERAL TYPES OF CABLE FAULTS a. Earth fault: When the insulation between the earth and the conductor in the cable becomes very low. b. Low insulation fault: When the insulation between conductors in the cable or between the pairs or between pair and earth falls below a ET prescribed limit (normally 0.5MΩ). c. Disconnection Fault: When the Conductor is cut or has become open, then it is called break fault or High Resistance fault. d. Short Circuit Fault: When the resistance between the wires or between the pair of conductors becomes very low even without any IS loop in the circuit. e. Foreign potential: The existence of potential, even when the circuit is idle or isolated. IR 3.9 MEGGER: The megger is a portable instrument used to measure insulation resistance of cables and/or overhead lines. Meggers are available in 100V DC, 500V DC ranges. Insulation resistance more than 5000K ohm (5 Mega Ω) for a particular pair is considered GOOD. Insulation resistance less than 2000K ohm (2 Mega Ω) for a particular pair is considered FAULTY. IRISET 14 Telecom Hand Book  Measuring Instruments 3.10 CABLE ROUTE TRACER: It is used for tracing the path or route of underground telecommunication cables and is useful for utility mapping i.e preparing maps & to provide ready reference during emergencies. 3.11 CABLE FAULT LOCATOR is used to locate various kinds of faults in UG copper cables and can measure the distance upto fault using ET pulse reflection principle. They are of Pulse Echo Method and Time Domain Reflectometry (TDR). Using a cable fault locator, it is possible. To locate low insulation faults To detect open and short faults (distance of fault) IS For measuring insulation resistance For measuring foreign voltage on cables 3.12 DIGITAL EARTH RESISTANCE TESTER is direct replacement of IR the conventional hand generator type universal earth tester. It is basically an Ohm meter designed for measurement of the resistance of earthing used in electrical equipment as well as for measurement of ground resistivity. Measurement of effective earth resistance of earth electrodes Current C1&P1 Voltage IRISET 15 Telecom Hand Book Measuring Instruments The value of earth resistance as per RDSO standards is less than 1 Ω for screened cables and digital systems. 3.12 Transmission Measuring Set (TMS) is an accurate instrument with two in one facility of frequency Oscillator & Level meter which operate independently & hence can be used separately or can be combined to form a Voice Frequency level test set which is used for measurements on communication lines and monitoring of communication facility. They are used for following measurements. 1. Signal Levels 2. Insertion Loss 3. Transmission Loss 4. Return Loss 3.13 PSOPHOMETER is an instrument that measures the perceptible noise of a telephone circuit. The core of the meter is based on a true RMS Voltmeter which measures the level of the noise signal. As the human-perceived level of noise is more important for telephony ET than their raw voltage, a modern Psophometer incorporates a Weighting network to represent this perception. IS IR Psophometer is basically used to measure interfering effect of noise in telephone equipments caused by amplifier noise, fundamental and harmonic frequencies of AC line supply as well as by intelligible or unintelligible cross talk from neighboring lines. Pshophometric noise measurement is done by passing the subjected telephone ckt. output through a very carefully shaped (designed) frequency selective filter so that noise measurements could be taken and referred to as "a Psopometricaly weighted noise measurement". The equivalent Pshophometric noise voltage in voice circuit should be 100 MΩ/KM >100 MΩ/KM measured with 100V DC Megger 0.63 dB/KM. Transmission loss in (Unloaded) 0.3 dB/KM. 4 VF range 0.25 dB/KM. (Unloaded) (Loaded) 5 RDSO spec. ET IRS:TC: 30/2005 ver.2 RDSO/SPN/TC/72- 07 4.33 Specifications of 6 Quad Cable RDSO spec. no: IRS-TC 30/2005 Ver. 2. (w.e.f : 1-1-2006) IS Loop resistance 56Ω/L.KM Transmission loss: 0.25dB/L.KM(loaded), 0.63dB/L.KM (unloaded) IR Impedance 470 Ω (unloaded) / 1120 Ω (loaded) Insulation resistance >100MΩ/KM with100V megger Conductor diameter nominal 0.9 mm Minimum dia of insulated conductor 1.5 mm Thickness of PVC outer sheath 2 mm Thickness of G.I. Armour tape 0.8 mm Thickness of PVC intermediate 1 mm sheath(Grey colour) Thickness of inner PVC sheath 2 mm Thickness of Aluminum tape 0.2 mm ± 10% Aluminum wire screen dia of each wire 1.4 mm Mutual Capacitance of the pair 50 pF/KM * Cable armour, Al screen and poly Al moisture barrier are to be connected to earth resistance value of < 1Ω. IRISET 28 Telecom Hand Book  Telecom Cables 4.34 Colour code scheme of conductor insulation of 4/6-Quad cable Colour of conductor insulation Colour scheme Quad of the quad No A-Wire B-Wire C-Wire D-Wire whipping Quad 1 Orange White Red Grey Orange Quad 2 Blue White Red Grey Blue Quad 3 Brown White Red Grey Brown Quad 4 Green White Red Grey Green Quad 5 Yellow White Red Grey Yellow Quad 6 Black White Red Grey Black 4.35 Tentative Quad allocation of a 6 Quad Cable, when laid along with OFC or without OFC is as under: a) 6 quad cable with OFC b) 6 quad cable without OFC Quad No ET Name of the circuits Quad No 1 Name of the circuits Block Circuit 1 Block Circuit 2 Spare 2 Section Control IS Emergency Emergency 3 3 Control Control 4/1 LC gate telephone 4/1 BPAC IR 4/2 BPAC 4/2 LC gate telephone 5 BPAC 5 BPAC 6 TAWS 6 TAWS 4.36 Status of 6 Quad Cable System used in various Railways a. Conventional 6-quad cable system with loading, balancing and VF repeaters at regular intervals of 40-50 KMs. b. Equalizer Amplifier System at all stations with unloaded 6-Q cable. 4.37 Rlys are presently following laying of 6-Q cable with OFC only. Apart from 0.9mm dia conductor, 1.4mm dia copper conductor PIJF quad cable also has been introduced in Indian Railways by RDSO under specification no: RDSO/SPN/TC/72/07 for long distance (> 25 KM) Block sections. IRISET 29 Telecom Hand Book Telecom Cables 4.39 Guidelines for use of OFC & 6-quad cable on various routes in Indian Railways. On A,B,C,D & D Special routes, 24Fibre OFC(RDSO spec IRS.TC.55 or latest) with 6-Quad cable(RDSO spec. IRS.TC30/2005 or latest) will be laid in same trench. 4.40 Difference between PIJF underground Paired and Quad Cables S. PIJF telephone Pair Cable PIJF Telecom Quad Cable No IRS-TC: 41/97 IRS-TC: 30/2005 Conductors are available in Conductors are available in the 1 the form of Pairs. Twin twisted form of Quads. Twin Twisted pairs Available in 10/20/50/100 2 Available in 4/6 quads pairs 3 Dia of conductor 0.5/0.6 mm Dia of conductors : 0.9/1.4 mm 4 ET Characteristic Impedance of the pair : 600 Ω Characteristic Impedance of the pair in the quad: 470Ω(0.9mm dia)/310Ω(1.4mm dia) Induced Voltage reduction Induced Voltage reduction done in IS 5 done in two stages by three stages by earthing Al foil, earthing Al foil & armour Aluminum screen & armour. used for short distance phone/ used for long distance Signalling IR 6 Data ckts in Rly stn area as and Telecom safety circuits last mile connectivity. between two Block stations. Loop Resistance of the pair is Transmission loss in pair of quad 7 important criteria. is important criteria. Jointing is in the form of Straight Jointing is in the form of 9 Through/ Derivation/Transformer/ Straight Through Joints. Condenser/Loading Coil Joints Thermo Shrinkable Jointing Reinforced Thermo Shrinkable Kits used for different size of Jointing Kits used for 4/6 10 cables as per RDSO spec. underground Quad Cable as per no: RDS0/SPN/TC/57/2006 RDSO spec. no: IRS:TC:77/2012 Terminated in Krone/Wago Terminated in 10 Pair/20 Pair 11 type modules & terminal strips CTBs and Wago type modules Generally used by all Telecom exclusively designed for Indian 12 Service providers. Railways S&T applications IRISET 30 Telecom Hand Book  Telecom Cables Mandatory Check & Tests to be done before commissioning of BPAC/SSDAC/MSDAC applications on 4/6 Quad/ PIJF cables (RDSO lr no. STS/E/SSDAC/SPN/177 dt. 28/30.08.2006) a) Conduction test : 56 ohms/loop km b) Insulation Resistance : > 10 M Ohms. c) Transmission loss test. : At 2 KHz/600ohms Transmission loss will be 1.2 dB/Km and it shall not be more than 30 db for full length of Quad Cable d) Near end Crosstalk at 155 KHz : shall be better than -55 dB e) Far End Crosstalk at 155 KHz : shall be better than -55 dB f) Psophometric Noise : shall not be more than 2 mV g) Continuity of Armour : shall be ensured h) Earth Resistance at Armour : shall be less than 1 Ohm Schedule of Testing & Measurements in Quad Cable 1 Checking Attenuation Monthly 2 3 4 ET Loop Resistance Test Checking Cross Talk Level Checking Noise Level Monthly Quarterly Quarterly 5 Insulation Resistance Test Yearly Schedule of Quad Cable Inspections IS 1 Monthly schedules JE/SSE (T) 2 Quarterly & Yearly schedules Section incharge SSE/T 3 Annual inspection ADSTE / DSTE / Sr.DSTE IR Impedance ratio of matching transformer Name of the circuit where it is used Loaded quad cable Unloaded quad cable For V.F. circuits (Control, 1120:1120 470:1120 EC etc) For terminations of 2 wire 1120:600 470:600 circuits(LC, PD MUX etc) 470:1120 470:1120 For Block circuits. Insertion loss of VF Transformer 0.6dB max. “JPO issued by Railway Board to prevent U/G cable damages and cuts” is in the latest Telecom circular no: 17/2013 dated 24.06.2013. Guide lines on “Precautions for Thermoshrink Joints of Quad Cables” to ensure correct jointing method issued by RDSO under repot no : STT-44, March 2013. IRISET 31 Telecom Hand Book Public Address System CHPATER 5: PUBLIC ADDRESS SYSTEM (TC2) 5.1 The system through which the information is disseminated to the limited public in limited area is known as Public Address System. It mainly consists of Microphone, Mixer, Amplifier and Loudspeakers. 5.2 Application of P.A. system in Railways: 1. Passenger amenity 2. Marshalling Yards 3. 4. 5. ET Breakdown train Emergency Equipment Special functions Railway Workshops 6. Conferences 5.3 Microphone: Microphone converts acoustic energy into electrical IS energy. As per mode of operation these are classified into two. (i) Pressure operated and (ii) Velocity operated.  Pressure operated microphones are carbon, crystal, dynamic capacitor type and velocity operated is of Ribbon microphone. IR  The important specification of microphones includes Type, Sensitivity, Frequency Response, Max. Sound Pressure level, Impedance, Minimum load impedance, Cable and Connectors, Front to Back Ratio and Polar Response.  Type means whether it is a Dynamic, Ribbon, Capacitor or Crystal microphone.  Sensitivity is the amount of voltage generated by the microphone for an applied sound pressure at 1 KHz. shown as mV/Microbar.  Frequency Response is the ability to produce a proportionate output to the sound pressure applied for the specified range of frequencies.  Maximum Sound Pressure Level is the level that can produce a proportional output with a total harmonic distortion limited to 1%.  Impedance shows the Impedance offered by microphone at 1 KHz. There are low impedance (less than 600Ω) and high impedance (>10KΩ) microphones. IRISET 32 Telecom Hand Book  Public Address System  Cables and Connectors describe the type and length of the cable with a particular connector.  Front to Back ratio for a unidirectional microphone is the response of front sound to back sound. Generally it is 20 db.  Polar response describes whether it is an Omni-directional, Bi-directional or Uni-directional.  Microphone connectors are 3 pin XLR type and jack type connectors. These connectors may be of mono or stereo type. RCA type connectors are widely used with music systems and they are for stereo type only. Precautions to be observed for use of microphones are given below I. Must be handled carefully and never dropped, nor placed where there may be metal dust. II. As far as possible locate away from electrical equipments. Do not run microphone leads together with power cable. ET III Microphone should be located away preferably to rear of the loudspeakers to prevent acoustic feedback 'howl'. IV. Ribbon microphones should be placed atleast 10 feet away from the speaker. IS V. Microphones should never be mounted on a vibrating surface like piano, amplifiers, radio, recorders, etc. VI. Microphones must be protected from strong winds, otherwise 'roaring' noise will result. IR 5.4 Loud speaker: It converts electrical energy into acoustic energy. There are two types of loudspeakers; Cone type and Horn type.  Cone type is a direct radiator, where cone or diaphragm is directly coupled to air.  Horn type is an indirect radiator, where the diaphragm is coupled to the air by means of horn.  The most common type is the Moving Coil type loudspeaker also known as dynamic loudspeaker.  A system of several separate speakers mounted one above the other in a suitable enclosure is called column speaker.  Specifications of loudspeakers are sensitivity, broad directivity, low distortion over the audio spectrum, smooth frequency response, balanced response, good transient response, sufficient damping at base resonant frequency and adequate power handling capacity. IRISET 33 Telecom Hand Book Public Address System  High fidelity (hi-fi) speakers are used to reproduce the generally audible frequency range of 50 Hz to 12 KHz.  A Woofer reproduces lower notes (< 2 KHz) in a musical program.  Tweeter reproduces higher notes (2 - 20 KHz) in a musical program  The crossover network is a frequency-dividing circuit ensures that each drive unit is fed only with its correct frequency band. This circuit in a two-way system directs the high frequencies to a Tweeter and low frequencies to a Woofer. 5.5 Amplifier: It is a device which takes a low level input signal from microphones and amplifies it to a high level output signal at the desired output power, which will be delivered to the loud speakers.  Amplifiers generally have a minimum of 3 microphone inputs and maximum upto 6 no. of input devices which includes auxiliary inputs (like tape recorder, mixer unit). ET  The individual volume control knobs for each input are provided separately.  Bass control knob used to boost or cut the low frequencies as per the requirement. IS  Treble control knob used to boost or cut high frequencies.  Master control is the final output control of amplifier.  For uninterrupted operation of amplifier, 12V/24V battery can be IR connected. Changeover to battery operation is automatic when AC main supply fails. When the amplifier is working on AC mains, the battery will get charged.  For connection of loudspeakers in Voltage matching method, three terminal strips are provided viz, COM, 100V & 70V. The connection must be made only one at a time i.e., either COM and 100V or COM and 70V.  For connection of loudspeakers in Impedance matching method, four terminal strips are provided viz., COM, 4Ω, 8 Ω and 16Ω.  Pre-Amp out jacks offer output for connecting tape recorder for recording the overall program or for feeding to Aux. Input of any amplifier for obtaining combined high-powered output.  Line output jacks offer output for connecting to line input of a booster amplifier or any other amplifier. IRISET 34 Telecom Hand Book  Public Address System 5.6 Audio mixer pre-amplifier: It accommodates more number of input devices with individual controls. The combined output of all individual channels will be connected to Aux. input of the main amplifier.  The mixer has the facilities like individual Input jacks, individual gain control, Bass, Mid and Treble controls, Echo control, PAN (Left or Right output channels) control and Channel ON/OFF switch.  The metal chassis of the amplifier should be earthed to avoid noise in the output and for avoiding electrical shock to the human being.  Acoustic defects like echo, flutter and reverberation to be identified and corrective measures to be adopted before installation. 5.7 PA System arrangement for VIP functions:  Generally dynamic microphones should be used due to its good ET directivity pattern.  The microphone cables should be isolated from power, loudspeaker and telephone cables.  The output power of the amplifying system should have a desirable IS sound level of 60 to 80 dB during operation.  Earthing should be done for all the amplifier systems properly.  For better reproduction, column speakers should be used. The IR spacing between two columns in a row should be approx 8mtrs apart.  All the loud speakers in each group should be connected in parallel and in phase across the output line.  Amplifiers and Mixer should be normally operated from 230V single- phase 50Hz AC mains supply with voltage regulating device and also with 12/24V standby battery, which provides continuous operation without any interruption. 5.8 Conference system provides the required sound reinforcement for eliminating problems of poor intelligibility while controlling acoustic feedback.  Conference system mainly consists of Chairman unit, Secretary unit, Delegate unit and a central Amplifier.  Chairman unit is equipped with a lockable switch and a ring LED indicator for speaking and also visual identification of the speaker. IRISET 35 Telecom Hand Book Public Address System  It will also have a non-lockable PRIORITY switch, which interrupts and mutes the delegate’s unit microphones.  Secretary unit enables proceedings to be recorded through a cassette recorder and to take notes by the stenographer and to relay pre-recorded messages if any, to delegates.  Delegates units are similar to chairman unit with the exception of the priority switch not being provided.  Central amplifier is provided for connecting all the conference units consisting of chairman, secretary and delegate units. 5.9 In a multiple loudspeaker system, when two or more driver units/loud speakers are facing in the same direction and are installed in same area, it is essential that their diaphragms/cones act in unison. Hence, the Loudspeakers must be connected in phase with each ET other which is called as Phasing of loud speakers. Some additional points regarding PA System  When the voice coil terminals are not marked, the simplest way of determining the correct phasing is by doing as follows. Take 1.5V or IS 3V batteries (dry cell) with the polarity marking of each observed, connect them momentarily to the voice coil of the speaker. The cones or diaphragms should move in the same direction for correct phasing. IR  Two types of loudspeaker connections are employed, Impedance matching and Voltage matching.  In Impedence matching system for maximum power transfer, the effective impedance of the load should be matched with output impedance of the amplifier.  For the purpose of Impedance matching, the amplifier output tappings will be given as COM, 4Ω, 8Ω and 16Ω.  The total impedance of all the connected loudspeakers are computed and the line should be connected to the proper tapping.  In Voltage matching system, loudspeakers are connected to the amplifier through a line matching transformer to either 70V or 100V tapping.  As the distance between amplifier and LS increases, length of the cable increases, so the strength of the sound signal decreases. IRISET 36 Telecom Hand Book  Public Address System  In such installations where the length of the cable is substantial, Line Matching Transformers (LMT) are being used in voltage matching method, between the output of the amplifier and each individual speaker to be connected.  LMT is having multiple high impedance tappings on primary side and standard impedance tappings of COM, 4Ω, 8Ω and 16Ω on secondary side.  The primary side will be connected to output of amplifier to 70/100V line and the secondary will be connected to loudspeaker.  When transformer taps are marked directly in "watts", no mathematic calculations are required.  Simply choose a transformer with the correct power tap and connect to the desired terminals. ET 5.10 Comparison between Impedance matching and Voltage matching: Impedance Matching Voltage Matching For maximum power transfer, Total wattage of speakers should IS Impedence of speakers should be be less than the rated power equal to output impedance of output of amplifier amplifier IR Used for short distance for less Used for longer distance for more number of speakers. Preferably number of speakers. Preferably indoor outdoor Speakers can be connected in Speakers are connected in parallel series, parallel or series-parallel only combination Cheap Costly due to use of LMTs Impedance should be calculated No calculations required Frequency response is best Frequency response is better IRISET 37 Telecom Hand Book Passenger Information System CHAPTER 6: PASSENGER INFORMATION SYSTEM (TC3) 6.1 As per Railway Board letter No.2018/LM (PA) 03/06 dated 09.04.2018, the stations are categorised into three groups; Suburban, non-suburban and Halt stations, which is as below: Category Proposed passenger Category Proposed passenger of stns earning of stns earning Non-Suburban stations Suburban Stations NSG-1 > 500 Crore SG-1 > 25 Crore NSG-2 > 100 Crore to < 500 SG-2 > 10 Crore to < 25 Crore Crore NSG-3 > 20 Crore to < 100 SG-3 < 10 Crore Crore NSG-4 > 10 Crore to < 20 Halt Stations Crore NSG-5 NSG-6 < 1 Crore ET > 1 Crore to < 10 Crore HG-1 HG-2 HG-3 > 50 Lakhs > 5 Lakhs to < 50 Lakhs < 5 Lakhs 6.2 Minimum essential Telecom amenities at various stations are: IS Non-Suburban Stations NSG- NSG- NSG- S. No. Amenities NSG-1 NSG-2 NSG-3 4 5 6 IR 1 Clock Yes Yes Yes Yes Yes Yes Public Address 2 System/Computer Yes Yes Yes Yes Yes Yes based Announcement Electronic Train 3 Yes Yes Yes -- -- -- Indication Board Suburban and Halt Stations SG-1 SG-2 SG-3 HG-1 HG-2 HG-3 1 Clock Yes Yes Yes Yes -- -- Public Address 2 System/Computer Yes Yes Yes -- -- -- based Announcement Electronic Train 3 Yes Yes Yes -- -- -- Indication Board IRISET 38 Telecom Hand Book  Passenger Information System 6.3 POET: It is an interactive system which provides train/reservation related information to the passengers at station area. This can be operated by the passengers themselves.  It consists of a touch screen, a controller PC card and software.  It is connected to the PRS and NTES servers through network to fetch the information. 6.4 Integrated Passenger Information System: RDSO specification RDSO/SPN/TC/61/2007 Rev 1.0 specifies a system which integrates Display boards, announcement and CCTV and named as IPIS.  As per revision 1.0 and 2.0, the system consists of units like Control Console Unit (CCU), Main Data Communication Hub (MDCH) and Platform Data Communication Hub (PDCH), 8 port ethernet switch and various types of LED display boards.  CCU is a personal computer loaded with IPIS software and database ET consists of train details and voice files for announcement.  The MDCH/PDCH are having atleast 2 i/p ports and minimum 16 o/p ports.  The functions of MDCH/PDCH are: (a) Routing of data coming from CCU to various devices IS (b) Checking the correctness of data  After getting suggestions from field, RDSO revised the specification three times and the latest is Rev 4.0 done in the year 2015.  As per the latest revision, the main units in the system are IR Central Data Controller (CDC), Central Data Switch (CDS), Platform Data Controller (PDC) and various types of display boards.  The Central Data Controller (CDC) shall consist of two CPUs (PCs) connected through a Central Data Switch (CDS) for data synchronization.  CDC shall be provided with voice recording and playback facility for making live PC based announcement.  Suitable hardware & software should be provided to acquire data / required information of trains from automatic train information system like train charting server, NTES, COA, etc.  The Central Data Switch (CDS) is provided with Ethernet connectivity for data communication between CPU of CDC and multiline display board & Platform Data Controllers of the station.  CDS should be 8 or 12-port Layer-3 switch with minimum 2 SFP port.  Necessary diagnostic tools should be provided in CDC for health monitoring of various ports of CDC. IRISET 39 Telecom Hand Book Passenger Information System  Data communication between Central Data Switch to Platform Data Controller and Multiline display board should be on Ethernet using CAT-6 or Optic Fibre cable.  The Platform Data Controllers will drive Platform display boards and Coach guidance display boards.  The PDC should have one SFP port with single mode optical interface for connecting CDC and various display boards.  PDC should also have four serial ports for connecting Platform Display boards/Coach Guidance Display boards.  PDC should have provision to connect Platform Display boards and Coach Guidance Display boards on wireless using Zig-B or sub GHz module in license free band.  All the ports should have LED indications for monitoring the communication status of connected ports.  The PDC should be IP54 environmental standard compliant to protect ET it against dust, rain & other environmental hazards.  Data transfer from CDC to PDC & all display boards except CGDB should be on Ethernet using TCP/IP protocol and PDC to CGDB it should be either on wired serial port (RS-485) or on wireless using IS Zig B/sub GHz module.  Fixed titles on display boards viz. train number, name, expected time, arrival/ departure, platform number should be screen printed in capital letters and provided on top of the cabinet of display board. IR  The character size of these titles shall be minimum 6 cm height. Colour of these characters should be preferably in white or yellow.  The display board control cards should have inbuilt 2 MB min. non- volatile Flash memory for storage of data.  LEDs with uniform intensity are to be used in the display boards to ensure that the information being displayed is with excellent contrast & no black patches are visible. Display board should be flicker free.  All display boards should be constructed using 16x48 LED matrix PCB modules.  Intensity of display board should be adjustable in manual mode and automatic timer mode.  UTP CAT-6 cable should be used for data communication between System devices, where Ethernet connectivity has been provided.  Class-D surge protection device should be provided in all display boards and PDC for protection of data line against surge. IRISET 40 Telecom Hand Book  Passenger Information System 6.5 Parameters of Class-D surge protection device should be as under: Max. continuous DC Voltage 13 V DC Nominal discharge current (8/20μs) line-Ground 5 kA Impulse limiting voltage/Let through Voltage Line-Line 40V Impulse limiting voltage/Let through Voltage 1000 V Nominal load current 100 mA  Individual coach display boards should display train No &. Coach No. alternatively like GEN, D1, S10, B1, A1, H1 in English and “अना., डी-1, एस-10, बी1, ए-1, एच-1” etc. in Hindi.  All display boards should be covered with U.V. stabilized polycarbonate single sheet without any joints having minimum ET thickness of 3mm for better visibility and protection against dust.  Suitable ‘Earthing’ point should be provided for earthing the body of display board.  The faces of Coach Guidance Display board shall be tilted from the IS vertical plane downwards. The tilt from vertical plane shall be 5° nominal. IR IRISET 41 Telecom Hand Book Passenger Information System 6.6 Comparison between various revision are: CHANGES IN REV 2.0, 3.0 AND 4.0 IN SPECIFICATION No. RDSO/SPN/TC/61 S.No. REV 1.0 / REV 2.0 REV 3.0 REV 4.0 1 2007 / 2009 2012 2015 Control Console Unit Renamed as Central 2 -do- (CCU) Data Controller (CDC) Two individual One monitor, keyboard 3 Monitors, mouse and and mouse for 2 CCUs -do- keyboards for 2 CCUs. with KVM switch. Renamed as Central Any type of display Main Data Data Switch (CDS). It boards can be 4 Communication Hub should be layer 3 switch connected to any hub (MDCH) with atleast two SFP (MDCH/PDCH). ports. Renamed as Platform Platform Data Data Controller (PDC). 5 Communication Hub It should be layer 2 (PDCH) a. Dual core i5 ET -do- switch with atleast one SFP port. a) i5 processor or equivalent or higher processor (min. 2.6 processor GHz) or higher b) 8 GB RAM IS b. 4GB DDR- 2 RAM. c) 500 GB or higher c. 250GB SATA HDD. 6 SATA HDD d. Multi port serial card d) Standard I/O Ports (1 (At least four serial -do- Serial, 1 VGA and 4 communication ports) IR USB) e. Windows Xp or e) Windows 7 or higher Windows 7 version OS Red colour LED were White colour LEDs to 7 -do- used be used. Normal LEDs and SMD type LEDs and 8 components were components are to be -do- used. used. MLDB, PDB and Only MLDB and PDB 9 CGDB should be -do- were multilingual multilingual Device addresses to identify each display Display boards are 10 board and Multicast -do- assigned IP addresses addresses to identify platforms MDCH/PDCH should Display data controllers 11 be of 8 bit -do- should be of 32 bit microcontrollers microcontrollers IRISET 42 Telecom Hand Book  Passenger Information System  Multi-line Display Board will show information of multiple trains at a time, i.e. Train number, Name, time of arrival/departure, expected time and platform number.  It shall be placed at main entrance/ concourse of the station.  Platform Display Board will display the details of a single train scheduled for arrival/departure from that platform i.e. Train number, Name, expected time of arrival/departure and platform number. These boards should be provided at suitable places on platforms/ foot-over bridges.  At-A-Glance Display Board will display information of the train arriving/departing from that platform with coach composition. These boards should be provided at suitable places on foot-over bridges.  Coach Guidance Display Board will display the position of coaches scheduled for arrival/departure from that platform for guidance of passengers.  The Mechanical dimensions of display board should be as under: ET Display Board Type Multiline display board Maximum Physical Dimensions (mm) 4100 (L) x 600(H) x 150(D) - Single face 4100 (L) x 600(H) x 200(D) - Double face 4100 (L) x 350 (H) x 150 (D) - Single face Single line display board 4100 (L) x 350 (H) x 200 (D) - Double IS face 2150 (L) x 550 (H) x 150 (D) - Single face At-a-glance display board 2150 (L) x 550 (H) x 200 (D) - Double face Coach guidance display bd 540(L) X 250(H) X 200(D) IR 6.7 True Colour Video cum Train Information System (RDSO/SPN/TC/67/2013, Rev 3.0):  This is also a system similar to IPIS but the only difference is we can give different colours to the display.  The system consists of following units/subsystems (a) Central Data Controller (CDC), (b) Platform Data Controller (PDC), (c) Platform Display Board (PFD), (d) Coach Guidance Display Board (CGD), (e) Video Display Controller (VDC), (f) Indoor Video Display Board (IVD), and (g) Outdoor Video Display Board (OVD).  The system should allow programming the video information to display from a remote place through LAN/WAN.  The Central Data Controller (CDC) comprise of two Workstations (PCs) of reputed make with latest configurations, One 17” Colour LCD/TFT monitor, one Central Data Switch (CDS), one passive IRISET 43 Telecom Hand Book Passenger Information System Keyboard-Video-Mouse (KVM) switch, Audio & Video selection device and one speaker and microphone.  The workstations should be pre-loaded with all the software and services required. There shall be continuous data synchronization between these two workstations through a LAN link.  The Central Data Switch (CDS) shall provide Ethernet based IP data communication between workstations of CDC and multiple video display boards  12-port or 24-port Layer 3 switch (as per site requirement) shall be used as CDS.  Layer 2 switches shall be used as repeater in case the length of the copper cable between the CDS and field devices is more. 6.8 CCTV SURVEILLANCE SYSTEM: The surveillance system provides security of passengers and their belongings in the station premises.  In small and medium stations, analogue based CCTV surveillance system is provided and in major stations IP based system is provided. ET  Cameras are provided at waiting halls, reservation counters, parking area, main entrance/exit, platforms, foot over bridges etc. of railway station and other railway establishments as per requests of RPF.  Analogue based CCTV Surv. system (RDSO/SPN/TC/65/2006) mainly consists of fixed cameras, (P/T/Z: Pan/Tilt/Zoom) dome IS cameras, digital video recorder, keyboard, LCD monitor, colour monitors and video cable, power cable, twisted pair cable etc.  IP based CCTV Surv. system (RDSO/SPN/TC/65/2016 Rev.4) mainly consists of fixed cameras, P/T/Z dome cameras, multi channel IR encoder & decoder, video management hardware & software, network video recorder with software, hard disk arrays (RAID), key board, LCD monitor, colour monitors, switches and associated video cable, power cable, twisted pair cable, OFC cable, CAT-6 cable, etc.  Advantages of IP based surveillance system are Remote accessibility, High image quality, Event management and intelligent video, Easy integration, Scalability, flexibility and Economic. 6.9 Specifications of P/T/Z camera: Video Frame Rate Atleast 25 Frames Per Second Video Resolution 704 x 576 (4 CIF), 704 x 288 (2 CIF), 352 x 288 (1 CIF) Network Protocol RTP, Telnet, TCP, IP, UDP, HTTP, IGMP, ICMP Video Data Rate 9.6kbps to 6Mbps per channel Multiple alarm Atleast 4 Inputs Network Ethernet, 10/100/1000 Base T Connectivity IRISET 44 Telecom Hand Book  Passenger Information System  24 port Layer-3 switch as per RDSO specification No. RDSO/SPN/TC/83/2008 should be provided at control room. It should support advanced routing protocols like OSPFv3 and BPG4 plus.  8 port layer-2 switches as per RDSO specification No. RDSO/SPN/ TC/83/2008 are to be provided for connecting cameras in the field. It should have one 10/100/1000 SFP port and 7 fast Ethernet ports. These switches should be PoE compliant.  The External RAID 5 storage system should have atleast 4 interfaces of FC or iSCSI across dual redundant controllers.  Network Video Recording (NVR) Software supports recording of MPEG-2 and MPEG-4 source simultaneously. It also supports recording of video and audio. The NVR support triplex applications, recording, re-play and backup simultaneously.  The NVR records upto 100 Mbps of video and audio data. The NVR is able to record upto 64 different video streams simultaneously. It is ET accessible from any PC connected to the network.  Video Analytics Software should support Intrusion Detection, Left Object Detection, Overcrowding and Camera Tampering.  Uninterrupted Power Supply (UPS) System should be of atleast 6 KVA, ON line, N+1 configuration and should give atleast 1 hour back IS up at full load.  The latest system for security is called Integrated Security System (ISS) in which Under Vehicle Scanner System (UVSS), baggage scanners and Bomb disposal items are integrated with CCTV IR surveillance system. 6.10 Call centre maintained by IRCTC is single window interactive system to provide different service information through universal no. 139. Information on the following services is made available to the customers:  Accommodation availability  Reservation status  Arrival & Departure of trains  Fare structure  Concessions  Trains for different destinations  Summer specials  Information on passenger Amenities  Salient features of call centre includes increased availability of services, E-mail access, Fax on demand, Automatic announcing unit, Call back facility on confirmation of reservation, Accident related queries and Registration of complaints. IRISET 45 Telecom Hand Book Passenger Information System 6.11 Clocks are provided in almost all stns to give time information to passengers. It may be analog, digital, master-slave or Global Positioning System (GPS) based.  The RDSO specification for GPS based master slave clock is RDSO/SPN/TC/62/2008 Rev 3.0  The digital clock uses GPS receiver to receive correct time.  The clocks have local battery backed Real Time Clock (RTC) which will synchronized to the time information received from the GPS.  In case of failure of GPS clock’s, local RTC time will be displayed and as soon as the GPS is connected, the time will be updated. 6.12 The features of GPS based clocks are:  Microprocessor controlled  Wired/Wireless communication between master and slave clocks  Real time clock backup for GPS reception  Automatic synchronization of Real time clock, from GPS Receiver  Automatic intensity control to daylight saving ET  Master clock can also be optionally driven by PC software  Manual setting of Real time clock, 12 or 24 Hr format can be possible 6.13 Connectivity: IS IR 6.14 Electronic reservation chart (ERC) is a system established at railway stations for the convenience of passengers. Confirmation status of RAC/WL tickets will be displayed in the system. Easy readability, Bright and clear visibility in day and night. Automatic display at scheduled timing. Charts can be transferred over network to way side stations. Tampering & removing of charts by the passengers is eliminated. Present problem of placing chart by employees is eliminated. Chart is stored electronically for the future reference. Advertisement shall be displayed in the screen if required. IRISET 46 Telecom Hand Book  Power Supply Arrangements CHPATER - 7: POWER SUPPLY ARRANGEMENTS (TC4) 7.1 CELL convert chemical to electrical energy. Two or more cell form a battery. Capacity of cell rated in AH(Ampere-hour). They are of two types  Primary batteries can be used only once (chemical reactions are irreversible). Ex: carbon zinc (1.5V). Types A(1.5V – used for torchlights), AA(1.5V), AAA(1.5V – used for remote)  Secondary batteries can be charged and reused (chemical reactions are reversible). ALKALINE battery (rechargeable-1.25V) and Lead Acid (LA) battery. Lead Acid battery have been subdivided into Conventional Lead acid batteries(Flooded Lead Acid - FLA) & Low Maintenance Lead Acid (LMLA) batteries. Lead Acid battery has an efficiency of 75-85% = (Pout /Pin) x 100 7.2 LA Secondary CELL: 1. The nominal voltage of LA Secdy cell is 2V. 2. Voltage of a fully charged LA cell is 2.2V and of a fully discharged ET LA cell is 1.8V. 3. The active material of positive Plate of LA Sec cell is Lead Peroxide (Pbo2) and active material of Negative Plate is Spongy lead (Pb) 4. For increasing the current, cells are connected in Parallel and for increasing the voltage, cells are connected in Series IS 5. Electrolyte of LA secondary cell is diluted Sulphuric Acid (H₂SO₄). 6. Specific Gravity(SG) of a fully charged LA cell is 1.220 and of fully discharged LA cell is 1.180. The SG of concentrated H₂SO₄ is 1.835 IR 7. The Specfn., of batt grade concentrated Sulphuric acid IS: 266. 8. Depth of Discharge(DOD) of a Flooded type LA cell - 70% LMLA (Low maintenance LA) cell - 80% VRLA (Valve regulated Lead Acid) cell - 50% 9. C (capacity of Cell) = Load current x Back up time ÷ DOD ex: If load current is 10A and the backup time required is 10Hrs then recommended capacity of Flooded LA Cell is = 10A x10hrs/0.7 = 142AH (nearest higher capacity of cell is 200AH) Current rating of Charger : Load current I + AH cap/10 10. SG of Electrolyte varies with temp.(standard is 27°C). Temperature correction for every degree above and below 27°C, to be added or subtracted with 0.0007 to Sp. gravity as read on the hydrometer. 11. The SG of pure water is 1.0. Specfn of Distilled water is IS: 1069 12. During preparation of electrolyte, acid must be added to electrolyte. During mixing, temperature of electrolyte should not exceed 50˚ C. IRISET 47 Telecom Hand Book Power Supply Arrangements 7.3 Adv of LEAD ACID BATTERIES  Low cost. High discharge rate capability.  Can be maintained simply by adding distilled water  Long proven history and hence more reliable compared to VRLA batt 7.4 VRLA cell: It is also called Sealed Lead Acid (SLA) batteries. They are of two types AGM and GEL type. Like LA cell, +ve and –ve plates and working principle for VRLA is same except the electrolyte in AGM batt is completely absorbed in separators consisting of matted glass fibers and wrapped around +ve plate. In GEL type the electrolyte is permanently locked in a thick viscous gel state instead of liquid form. During charge and discharge, it will convert again to similar form as that of LA cell. However, in VRLA if pressure exceeds safety limits, safety valve open to allow the excess gases to escape, and in doing so regulate the pressure back to safe levels (hence "valve-regulated" in "VRLA"). GEL type costs twice that of AGM type and has a deep discharge resiliency and can deliver 2-3 times the cycle life of an AGM. ET Railways use AGM as it can handle higher I & work in cold environments 7.5 Advantages: Maintenance-free(no water topping required) No special battery rooms, No corrosive fumes, Ease of installation. Ready to use since supplied from factory in fully charged condition Codal life of re-chargeable batt used in S&T department is 4 yrs IS DC - AC conversion is called INVERTOR Changeover time is 500msec DC - DC convertor is called CHOPPER or SMPS: It converts DC to various DC voltages. IR AC - DC conv is called RECTIFIER or CHARGER. It consists of fuse, transformer, rectifier, filter and control circuitry for constant Voltage O/P AC - AC conv is called CYCLO Conv(conv. to different V & freq) 7.6 UPS is a device which stores electrical power on normal conditions and gives back power to load when EB fails to supply power and also processes for voltage regn. UPS is combination of inverter, rectifier and battery unit. Changeover time 10 - 25msec. Different types are  OFF Line UPS - which is switched ON automatically as soon as the AC power is put off. Changeover time is < 25 msec(low cost, high efficiency). widely used for personal computers < 0.5KVA  ON - Line UPS - which always remains ON thru INV, irrespective of Input AC P/S and we get pure sine wave. used for cap > 5KVA  Line interactive UPS – which works like OFF line UPS, but always interacts with AC line voltage. used where I/P supply vary frequently IRISET 48 Telecom Hand Book  Power Supply Arrangements 7.7 DIESEL GENERATOR SUPPLY (Efficiency = 65%) It converts mechanical energy to electrical energy. Provides sinusoidal waveform 1Ø,230V AC (3% regn) with 50hz freq ± 5% from NL to FL. It shall be air cooled type. The capacity of generators shall be calculated based on present load plus anticipated increase of load. Generally 10KVA, 12KVA & 15KVA rating of Generator is used by S&T dept. 7.8 Linear Regulated PSU is used in conventional chargers.  Simple in design it has Efficiency < 50% More weight, big in size and less reliable Shall work within 160V - 270V range and its of Self-regulating type In auto mode of working, If current across battery terminals increases by 8-12% of the rated current, the output voltage of the charger automatically change to 2.4V/cell (Boost mode) If batteries gets fully charged and the current drawn by batteries is less than 5% of rated current value the charger automatically changes to ET 2.15V/cell(Float mode) which is normal O/P V of charger 7.9 BATTERY CHARGERS Following information to be given while procuring the SMPS power plant a. The type of battery to be used : VRLA or Conventional Lead Acid IS b. Battery capacity and number of battery bank c. Ultimate Expandable Capacity of the Power Plant in terms of load d. Type, Number & Configuration of SMR Modules e. For 1-Ø, Incoming P/S range : either 90V-300V or 165V-260V IR f. Whether to work as Float Rectifier-cum-Float charger(FR-FC) Mode or Float Rectifier - Float charger cum Boost charger(FR-FC-BC) Mode Volts Auto Mode of Working Float Mode Boost Mode (2.15 x No. of cells) (2.4 x No. of cells) 12 12.9 15.05 17.2 14.4 16.8 19.2 24 25.8 27.95 30.1 28.8 31.2 33.6 60 64.5 66.65 68.8 72 74.4 76.8 110 118.3 120.4 122.6 132 134.4 136.8 POWER SYSTEM CONFIGURATION S.No. Load (Equipment & Battery Bank) (n+1) SMR Modules 1 25A to 50A (2+1) x 25A 2 50A to 100A (2+1) x 50A 3 100A to 150A (3+1) x 50A 4 150A to 200A (4+1) x 50A IRISET 49 Telecom Hand Book Power Supply Arrangements 7.10 Switch Mode Power Supply(SMPS)  I/P AC volt is first rectified and filtered to produce un-regulated DC V  Un-regulated DC volt is converted into square wave at high frequency using transistor based circuit  The chopper employs switch which is basically a transistor based ckt  High frequency switching (order of 100 KHz) and a fast control over duty cycle of switch, will produce desired voltage along with ripple voltage of very high freq to output side  The output from chopper is fed to a High Freq Pulse Transformer for voltage scaling & isolation  O/P DC is given as feedback to chopper to regulate through a Error Amplifier & Compensating network Block Diagram of SMPS is shown ET IS IR Adv: Less weight & size. Due to high freq switching > 20 Khz., filter becomes simple and noise due to line freq is eliminated. High conversion efficiency > 90% & Lower operating temperature. Disadv: more complex circuitry. proper measures to be taken to prevent EMI due to high freq switching "Telecom Integrated P/S System(TIPSS)" : RDSO/SPN/TC/102-2013 Valve Regulated LA Sealed Maintenance Free Batt IRS S : 93/96(A) for Low Maintenance Lead Acid Battery IRS S : 88/2004 12 V DC power supply unit : RDSO Specfn., IRS : TC-72/97 48 V DC SMPS POWER PLANT : RDSO/SPN/TL/23/99 Ver. 4.0 IRISET 50 Telecom Hand Book  Power Supply Arrangements 7.11 Transformer Its a Passive device. Steps up or step down Voltage and correspondingly Current decreases during stepup and current increases during step down of V. In other words, transfers power fm Pri to Secdy. Rated in KVA. Having 90-95% efficiency. For maximum V in Secondry, minimum Primary tap & maximum Secondary tap should be used. 7.12 Solar Cells It is a renewable source of energy. It contains Photovoltaic cell which converts light into electricity. Each PV cell is of 0.5V and of 2.2 A. Can be connected in series/parallel combination for achieving desired O/P NO moving parts, No Maint., No fuel, No noise and hence No pollution Disadv: Initial cost is more. Dependant on atmosphere and hence not reliable source of energy. Generates small amt of power, Large area ET required. For night power, batteries to be provided for storage. LIFE : between 25 to 40 years Name of Eqpt Wkg V Rated I 25W VHF Set 12V DC 2-3 Amp VF Repeater 12V DC 0.5 Amp IS Gate ph& W/S control Ph 12V DC 100mA STM1/4 OFC Equipment 48V DC 3 Amp PD MUX 48V DC 2 Amp IR Router 12V DC 3 Amp Switch 12V DC 2 Amp IPIS 230V AC 5 Amps(6 Line) Auto Announcement system 230V AC 5 Amps Digital Clock 230V AC 1 Amp/PF Clock Coach Guidance 230V AC 4 Amp /PF 7.13 LOAD CALCULATION IN TELEPHONE EXCHANGE 1. For ex: C-Dot Electronic Exchange = 5 Amps, 2. OKI Electronic Exchange = 15 Amps 3. ISDN Electronic exchange = 1.5 Amps then Total Load current = 5 + 15 + 1.5 = 21.5A Capacity of the battery required = 21.5 Amps x 10 Hours = 215 AH. As per RDSO instructions, battery should be discharged upto 50% of its capacity to make it recharge quickly. Actual capacity of battery required = 215 x 2 = 430 AH. IRISET 51 Telecom Hand Book Power Supply Arrangements Rating of SMR charger required to put the battery under Float charging = C/10 x 2.5 = 430/10 x 2.5 = 107.5 A = 108 Amps. (Min) Total Load = Voltage x Load Current = 48v x ( 21.5 + 43 ) = 5530 VA Power Factor x Efficiency 0.8 x 0.7 Rating of Generator is 5530 VA ÷ 0.65(Efficiency) = ̴ 8.5 = 10 KVA 7.14 Precautions : 1. Wire fuses must not be used and use fuse of proper rating (1.5 to 2 times of circuit current) should be used 2. Always go for minimum fuses & termination 3. Use circuit breaker instead of fuses, for easy replacement 4. Do not leave any terminal nuts without proper tightening 5. All terminations be soldered & provided with lugs for good conductivity 6. Do not bring naked flames into Battery room. 7. Dangerous growth of vegetation near equipments or feeder lines or masts must not be allowed. 8. Oils, paints should not be stored near the equipments. ET 9. All power supply systems must be properly earthed. 10. All electrical installations shall be provided with gas type extinguishers. Water should not be used to extinguish electrical fires. 11.Suitable protective guards shall be provided to prevent staff from making accidental contact with dangerous voltages. IS 12. Tools to be insulated to protect the staff from AC induced V. 13. Where cables pass thru metallic parts, insulating bushes be provided 14. Wherever standby equipment is provided, ensure its working IR 15. Ensure all equipments are not working beyond their codal life 16. Ensure all telecom equipments are working within its tolerance limits IRISET 52 Telecom Hand Book  Power Supply Arrangements Constant Voltage charging allows full current of charger to flow into battery until the power supply reaches its pre-set voltage. The current will come down to a minimum value once that voltage level is reached. The battery can be left connected to the charger until ready for use at “float voltage”. This type is used for Normal, Float & Trickle types of charging. Suitable for Lead Acid, but not for (Ni-MH) or (Li-ion) types. Constant Current charging is a simple form of charging batteries, with current level set at approx. 10% of the maximum battery rating. Charge times are relatively long with the disadvantage that battery may overheat if it is over-charged, leading to premature battery replacement. Generally used for Ni-MH type of batteries. Used fr Initial & Boost type of charging Sulphation may occur if a battery is stored for prolonged periods in a completely discharged state. It increases internal resistance of the battery. It can be corrected by charging very slowly (at low current) at a higher than normal voltage. ET Trickle charging means charging a fully charged battery under no-load at a rate equal to its self-discharge rate, thus enabling battery to remain at its fully charged level. It is done @ 2.25 to 2.30 V/cell and Current will be approximately 1 mA/AH @ 10 Hour capacity of the battery IS Float Charge (2.15 - 2.20 V/cell). In this system, battery is connected in parallel to the charger or DC source and load. It should be maintained slightly greater than the open circuit voltage of the battery IR Boost charge is done at higher rate and for shorter duration in order to prevent over-discharging of the battery. It is given at rate of 2.4V Cell. Equalizing charge: Once in a while you have to overcharge the batt so that the weaker cells are brought upto full charge. It is periodical charge given to battery @ AH/50 to correct any inequalities of Sp.Gr. among cells developed during service. Initial charging : It is done with constant current charging @ (2.7 V/cell) st 1 cycle : Charge for 80-100hrs @ 5% AH cap 2.10V@1220; dischg @ AH/10 for 9hrs till 1.98V@1190 nd 2 cycle : Charge for 6hrs@AH/10 &reduce charging current to half & charge@10hrs 2.16V@1220; dischg@AH/10 for 10hrs 1.90V@1170 rd 3 cycle : Final charge AH/10 @ 24hrs and putup fr use 2.02V@1200 Check voltage & Sp. Gr for every 8hrs. After initial charging, if battery is not connected to load for every 15days, Equalising charge is given IRISET 53 Telecom Hand Book Power Supply Arrangements VOLTAGE STABILIZERS : To avoid Voltage fluctuations, stabilizer is used. Difference between Voltage Stabilizer and Voltage Regulator Voltage Stabilizer: It is a device which is designed to deliver constant voltage to the output without changes in incoming voltage. Voltage Regulator: It is a device which is designed to deliver constant voltage to the output without changes in load current. Relay Type Voltage Stabilizers: In this type, voltage regulation is accomplished by switching relays so as to connect one of a number of tappings of transformer to the load. It compares output voltage with a built-in reference voltage source. Whenever voltage rises or falls beyond reference value, control ckt switch the corresponding relay to connect a desired tapping to output. They are of low weight & low cost. Disadv: slow voltage correction speed, less reliability, interruption to power path during regulation and unable to withstand HV surges. ET Servo Controlled Voltage Stabilizers: It uses servo motor to enable voltage correction. It incorporates servo motor, auto T/R(buck-boost), motor driver and microcontroller control circuitry. In this stabilizer, one end of buck boost transformer primary is connected to fixed tap of auto IS T/R, while other end is connected to moving arm that is controlled by servo motor. Secondary of buck boost transformer is connected in series with incoming supply which is nothing but stabilised output. Electronic IR control circuit detects voltage dip and rise by comparing input with built- in reference voltage source. When it finds error, it operates motor that in turn moves the arm on auto T/R for desired voltage output. Adv are high precision of stabilized output and high reliability. But require periodic maintenance due to presence of motors. Static Voltage Stabilizers: It uses power electronic converter circuit to achieve voltage regulation. It essentially consists of buck boost transformer, IGBT power converter (or AC-AC conv) and microcontroller. The IGBT conv generates voltage by PWM technique, and this voltage is supplied to primary of buck boost transformer. Whenever microprocessor detects voltage dip, it sends PWM pulses to the IGBT converter such that it generates the voltage which is equal to that of the deviated amount from nominal value. Adv: Compact in size, very fast correction speed, excellent V regn, no maintenance due to absence of moving parts, high efficiency & reliability. IRISET 54 Telecom Hand Book  Earthing & Surge Protection System CHAPTER 8: EARTHING & SURGE PROTECTION SYSTEM (TC5) 8.1 Surge is a transient which occurs sudden, due to which the magnitude of Voltage and Current increases several times of normal value, resulting in complete/partial damage of components/equipments. 1. As per IEC(International Electro-technic Commission), percentage of loss due to Surge is about 27.4% of total loss. 2. Causes of Surge: a. Lightning discharges b. Switching on/off of inductive loads(ex:transformers,Coils&Motors) c. Ignition and interruption of electric arcs (e.g. welding process) d. Tripping of fuses and circuit breakers e. Short circuits However, Lightning is the major phenomenon to cause Surge 3. Lightning has the following physical effects: 0 a. Heating of air upto 30,000 K b. Heavy potential difference of 10 million Volts c. High magnitudes of current of 10kA to 200kA ET 4. Surge I due to lightning has 3 parameter (ex. Surge of 10kA, 8/20µs) a. Surge amplitude b. Time taken by surge to reach to 90% of its peak value: : 10kA 8 µs c. Time taken by the surge to fall to 50% of that peak : 20 µs 5. Lightning is natural phenomenon. It is an unpredictable that occurs IS due to accumulation of electric charges in cloud and are of 3 types, a) Within-the-Cloud b) Cloud-to-Cloud c) Cloud-to-Ground IR d) Lightning between Cloud and ground is only considered which may ruin the S&T equipments partially or completely. IRISET 55 Telecom Hand Book Earthing & Surge Protection System 6. Lightning strike can be a. direct strike on equipment room b. indirect strike due to galvanic coupling, inductive coupling and capacitive coupling 7. There are different lightning zones outside and inside the building. 8. LPZ 0A-0B refers to outside the building ET 9. LPZ 1, 2 & 3 refers to inside the building 10. There are two types of protection systems IS a. External protection (Class-A protection) b. Internal or Surge protection (Class-B, C & D renamed as Type I,II & III protection) 11. Class-A protection system : (External) IR a. It consists of air termination(air rods or mesh) on top of building connected to Earth through a Down conductor b. Surroundings outside the building fall in LPZ 0 c. 50% of lightning energy is transferred to ground d. Balance 50% enters building through Power/Telecom cables, Metal-Water conduits etc. e. Lightning conductor can be – Single/Multiple spike/Dome, but single rod suffice f. Lightning conductor shall not touch the structure 12. Type-I i.e., class B protection system (Internal) a. First stage protection before the eqpt at mains distribution panel b. Spark-gap technology – Operates on arc chopping principle c. Lightning currents handled 10/350 micro sec. pulses d. SPD provided between each P-N and N-E e. 100 kA amplitude between N-E since Earth is at higher potential during lightning f. 50 kA amplitude between R/Y/B & N IRISET 56 Telecom Hand Book  Earthing & Surge Protection System 13. Type-II i.e., class-C protection system a. Comprises of fast acting Metal Oxide Variable Resistor (MOVR) to provide surge protection with low Let Through Voltage b. Provided between P-N c. Surge rating taken care : 50 kA, 8/20 µs pulse d. Shall be a single compact device 14. Type-III i.e., Class-D protection system a. All external data/signaling (AC/DC) lines connected to electronic equipment at either end should be protected by Class-D device b. Comprises of MOVRs/Gas Discharge(GDs) or its combinations c. One set each provided at both end of the cable i.e. equipment room and field location 15. All SPDs shall have some of following features for showing its functionality : i. LED Indication (shows red) when device failed ii. Flap indication (thermal disconnection of device when it starts having heavy current due to ageing / handling several surges  ET iii. Potential Free Contact for remote monitoring iv. Counter for showing no. of impulse encountered Any SPD can withstand maximum of 15 – 20 impulses beyond which SPD will get deteriorated IS 16. Following are Parameters of SPD: Parameter Sym Meaning Nominal voltage U0 Power supply system for which SPD is meant IR Rated voltage UC Maximum continuous operating V (connected to SPD) Temporary over UT Voltage which can be withstood by SPD for voltage specific dur(5 or 200m sec Voltage protection UP Limiting V across terminals of SPD under level surge condition Voltage withstand UW Insulation withstand level(4-level 1.5/2/4/6KV) Impulse current Iimp Peak value of 10/350µsec current that can be handled (Class-A rating) Nominal discharge In 15imp of 8/20µsec can be withstood-used for current Class B rating Follow-up current If I delivered by D/S system which is extinguished by SPD Response time Tr Activation (closure) time IRISET 57 Telecom Hand Book Earthing & Surge Protection System 17. The standards/specifications for provision of SPDs are a) IEC ( International electro-technic commission) b) VDE (German Standards) c) RDSO (RDSO / SPN /TC / 98 / 2011 Rev. 0) 8.2 Relevant IEC standards for SPDs ET 8.3 Lightning Safety Tips for Indoors & Outdoors IS  "If thunder roars, go indoors".  Do not stand under the trees (side flash may occur)  Do not touch any metallic object (touch voltage)  Drop to your knees with your feet closed and bend forward putting IR your hands on your knees. Do not lie flat on the ground.(step voltage)  Disconnect electronic gadgets from source of power supply  No contact with plumbing. Bathroom fixtures can conduct electricity.  Keep in mind that you must not be the tallest point in an area, so do not go to open field/park.  Large enclosed steel frame structures is much safer than smaller or open structures. 8.4 General Precautions to be followed for SPD’s  SPD and protected equipment should be apart minimum by 3 feet  Protected & Unprotected wiring should occupy separate conduit feed (Clean and Dirty cables)  Proper grounding is required and should be of Low Impedence  Earthing be provided near to eqpt & length of cable shall be minimum  Class B&C type devices shall be of same manufacturer and pluggable type for easy replacement IRISET 58 Telecom Hand Book  Earthing & Surge Protection System 8.5 Earthing  RDSO/SPN/197/2008 covers specifications of earthing system for S&T installations  Fundamentals of Earthing: Earth is not a good conductor but still we resort to earthing because earth is ideal equi-potential surface. But, if area of path for current is large enough, resistance can be quite low and earth can be a good conductor. Earth Resistance should be as low as possible. 8.6 Earthing is very much important but least bothered by maintenance staff normally 1. It provides low impedance path to fault current 2. Reduces shock hazards to personnel 3. Provides protection from lightning and controls electrical noise 4. Less system downtime since fewer eqpt failures 8.7 Location of Earth ET 1. Low lying areas close to the building or eqpt 2. Close to water bodies but not well drained. 3. Dry sand, lime stone, granite and stony ground should be avoided. IS 4. Should not be installed on high bank or made up soil Earth are of three types: a. Plate earthing, b. Pipe earthing and c. Maintenance free earthing IR Pipe electrode: electrode to earth resistance (R) is R = þ L / A Where L is length of electrode, A area of pipe, þ is soil resistivity 8.8 Characteristics of EARTH ELECTRODE It should have excellent electrical conductivity fr withstanding high fault I Low resistance (to ensure lightning will flow thru ground in preference to other path) High corrosion Res(CU coating is used which is less likely to corrode) Material used of high tensile low carbon steel & caters for (UL)orlatest The minimum copper bonding thickness shall be 250 microns and Should be Robust and reliable 8.9 Factors which influence earth resistance of an electrode Composition of soil-Clay is having least resistivity(2000 - 6000Ω/cm³) Temperature and Moisture content of the soil IRISET 59 Telecom Hand Book Earthing & Surge Protection System 8.10 Methods of reducing Earth Resistance: Electrode to earth resistance depends on soil resistivity, which has to be reduced to a considerable value, the simplest way to do so is a. By adding salt, charcoal and sand mixture to the pit b. By screening fillings in the immediate vicinity of electrode c. Size, shape, increasing depth & spacing of electrodes. d. Go for maintenance free earth e. For 10Ω-m soil resistivity reaches 100Ω-m in 3 yrs. Earth Treatment is required every 3 yrs Further to reduce Earth Resistance, Ring Earth to be adopted by having parallel ground electrodes and connecting them in parallel to have low resistance path to earth. It comprises of a. Equipotential bonding of earth electrodes forming ring outside buildng b. Provision of equi-potential bus-bar or ring inside equipment room ET c. Joining the external and internal rings. Distance between