Chapter 23 - Protection of Telecom Equipments Against Lightning PDF

CHAPTER XXIII PROTECTION OF TELECOM EQUIPMENTS AGAINST LIGHTNING SECTION A INTRODUCTION 23.1 GENERAL Suitable protection arrangements shall be provided in telecom insta...

CHAPTER XXIII PROTECTION OF TELECOM EQUIPMENTS AGAINST LIGHTNING SECTION A INTRODUCTION 23.1 GENERAL Suitable protection arrangements shall be provided in telecom installations to protect the equipments from lightning and ensure safety of operational & maintenance staff. 23.2 PRINCIPLES OF PROTECTION: The protection system shall provide a very low impedance parallel path to the ground in such a manner that discharge current due to lightning is transmitted to the earth through this path, instead of passing through the equipment. SECTION B COMPONENTS OF PROTECTION SYSTEM & INSTALLATION 23.3 LIGHTNING ARRESTER: 23.3.1 The lightning arrester shall consist of lightning spike to the earth electrode. The material and the size of the conductor shall be as given below: MATERIAL SIZE G.I. WIRE 8mm dia G.I. STRIP 20mm x 3mm 23.3.2 The lightning conductors shall be drawn in most direct possible path avoiding bends, upturn or kinks. 23.4 EARTH TERMINATION: These are parts of the lightning protection system intended to distribute the discharge current into the general mass of the earth. The earth termination shall consists of suitable earth electrodes and underground conductors. 23.5 EARTH ELECTRODE: 23.5.1 Electrode Material & Size: Galvanised iron pipes or angles shall be used. In protected installations solid copper rod may also be used. 23.5.2 The size of the different types of electrodes shall be as under; Indian Railways Telecom Manual - 2021 Page 318  TYPE SIZE G.I. Pipe Length >=2.5M Internal Diameter >= 38mm G.I. ANGLE Length > = 2.5M Cross section: 50 mm x 50mmx5mm Copper Rod Length >= 2.5 M Diameter= 16mm 23.6 INSTALLATION OF THE ELECTRODE: The electrodes shall have a spike at one end and a clamp at the other end for connecting earth lead. The electrodes shall be directly driven in the earth up to a depth of atleast 2.5 M. Where rock is encountered at a depth less than 2.5M, the electrode shall be driven inclined by about 30 degrees to the vertical. In hard soil, hole for the electrode may be drilled by earth auger or by manual trenching. The top of the electrode shall be about 30 cm above the ground. After inserting the electrodes, the hole shall be filled with earth properly and water should be spread to ensure good contact between electrode and filling. 23.7 USE OF MULTIPLE ELECTRODES: In cases where a single electrode is not sufficient to provide the desired earth resistance, more than one electrode shall be used. The separation of the electrodes shall be about 4 M. 23.8 CALCULATION OF THE NUMBER OF ELECTRODES: Approximate calculation of the number of electrodes required to get desired value of earth resistance, can be made using the guidelines given in Annexure-A 23.9 ARTIFICIAL TREATMENT OF SOIL: In soils of high resistivity, even multiple earth electrode may not provide desired earth resistance. In such cases the soil should be artificially treated with salt and charcoal in appropriate proportion. Earth pits of 600 mm dia and 2.5 M depth shall be formed by excavation and the electrode shall be placed at the centre of the pit. The pit shall be filled alternatively with layers of common salt & charcoal, each layer of about 2.5cm thick, up to a depth of about 20 cm from the ground level. The pit shall be filled several times with water, which shall be allowed to be soaked in the ground. After this treatment, the pit shall be covered with excavated earth and water shall be sprayed to ensure good electrical contact. This earth electrode should be cleaned at least once in two years or whenever it is found that the resistance is above required value by excavating the earth and the process of filling with layers of salt and charcoal to keep the earth resistance to the required level. Indian Railways Telecom Manual - 2021 Page 319 23.10 BONDS: Bonds made of mild steel clamps with galvanised nuts & bolts shall be used to connect the lightning protection system with other metallic structures like metallic poles, water pipes etc. The bonds shall have more cross sectional area than the main lightning conductor and it shall be protected against corrosion. 23.11 JOINTS: 23.11.1 As far as possible joints shall be avoided in lightning conductors and underground earth conductors. 23.11.2 The joints shall be crimped, riveted, welded or soldered so as to ensure minimum electrical impedance for the surge current. 23.11.3 All joints of bimetallic elements shall be protected from corrosion by covering the joint with loaded grease or M-seal compounds. 23.12 TESTING POINT: A clamp between earth termination at the electrodes and the down conductors shall be provided to facilitate isolation of the two sections & measurement of earth resistance. This joint, known as testing point, shall be made of mild steel with galvanised nuts & bolts. 23.13 TOWER GROUND RING: This is the earthing system to be provided at the foot of towers used for telecom applications. This shall consist of earth electrodes and under ground tinned bare copper conductor forming the ground ring as shown in FIG-1 & 2. Earth electrodes shall be installed at an interval of about 4 Meter surrounding the tower foundation. Bare tinned copper conductor of 38 sq. mm shall be burried at least 2.5M below the ground level and at a distance of 0.5M from the tower foundation. The conductor shall be soldered /clamped /welded to the electrodes to provide good electrical connection. Each leg or two diagonal legs of the tower shall be connected to the tower ground ring with 2 nos. of 6mm dia copper wire. 23.14 EXTERNAL GROUND RING: The external ground ring is the earthing system surrounding the plinth of the building, housing telecom equipment. This shall be constructed in the same manner as tower ground ring. The layout is shown in Fig 1. 23.15 INTERNAL GROUND RING: Indian Railways Telecom Manual - 2021 Page 320  This is the earthing arrangement to be provided inside the equipment room. This shall consist of earth bus bar(25 mm x 5mm copper flat or 38mm sq. bare tinned copper conductor) installed surrounding the equipment room 0.5m below the ceiling or 0.5 M above the floor level. The layout is shown in Fig. 2. 23.16 SINGLE EARTH SYSTEM: The telecom installations shall use single earth system in which the different earth connections from equipments, towers, DC power supply, metallic structures etc. shall be interconnected to each other through low resistance earthing conductors. This method is recommended to keep all the points to be earthed at approximately same potential level in order to reduce the possibility of side flash & subsequent damages. SECTION C PROTECTION ARRANGEMENT AT AC MAINS SUPPLY 23.17 AC MAINS EARTHING SYSTEM: The A.C. mains earthing system shall be as per the rules and regulation issued by local power supply agency. 23.18 TERMINATION OF OVERHEAD POWER LINES: If mains supply is provided through overhead lines, the over head lines shall be terminated about 100M away from the building of sensitive telecom installation such as telephone exchange, radio relay or optical fibre installations. 23.19 CONNECTION FROM LOW VOLTAGE MAINS: Connection for low voltage mains shall be drawn through underground cable. The power cable sheath must be fully insulated from the earthing network of the telecom equipments. 23.20 SEPARATION BETWEEN MAINS EARTH & TELECOM EARTH The protective earth of telecom system shall not be connected to the earth of mains power supply system. A minimum distance of 10 M is desirable. 23.21 PROTECTION ARRANGEMENT ACROSS AC MAINS SUPPLY TO TELECOM INSTALLATIONS: Low voltage lightning discharger of nominal rating of 650V shall be provided across the 230 V mains power supply as shown in Fig 1 & 2. In case of high tension supply (11KV or above) are terminated near the telecom installation, suitable pole mounted high voltage arrester shall be provided. Indian Railways Telecom Manual - 2021 Page 321  SECTION D PROTECTION ARRANGEMENT ACROSS DC POWER SUPPLY 23.22 PROTECTION AT DC POWER SUPPLY: Suitable protection arrangement consisting of avalanche diode and L-C network shall be provided at the DC power supply point at the power distribution board and in heavy lightning prone areas, at the input terminals of the equipment. The rating of the diode shall be at least 20% above the nominal supply voltage. SECTION E PROTECTION OF UNDERGROUND CABLE 23.23 PROTECTION AT SUBSCRIBER PREMISES: In heavy lightning prone areas, the underground cable shall be terminated with line protector arrangement consisting of gas discharge (GD) tubes & MOVR. The specification of the protection arrangement is given in Annexure-B. 23.24 PROTECTION AT CABLE JUNCTION /TERMINATION BOXES: The metallic sheath or armour of the cable shall be earthed. In the cable termination/junction box, the sheath should be connected to the metallic body of the box which shall be earthed. In non metallic boxes a separate provision shall be made to earth the cable sheath. 23.25 PROTECTION AT TRANSMISSION/SWITCHING END: The metallic sheath shall be earthed and protective device as mentioned in Para 23.23 above shall be provided for each pair including unused pairs. 23.26 PROTECTION AT TRANSITION POINT BETWEEN OVERHEAD LINES & UNDERGROUND CABLE If the distance of the overhead lines drawn from the cable termination box exceeds 500 meters, protection arrangement consisting of GD tube & MOVR shall be provided for each pair of the conductor including unused pairs & the common earth point shall be connected to earth electrodes. SECTION F PROTECTION FOR CIRCUITS ON OVERHEAD WIRES Indian Railways Telecom Manual - 2021 Page 322 23.27 The protection arrangements similar to those of underground cable shall be provided. Every tenth pole of the overhead alignment shall be provided with earthed lightning arrestor to reduce the intensity of discharge current along the overhead line. SECTION G PROTECTION ARRANGEMENTS IN MICROWAVE, UHF & TRAIN RADIO STATIONS 23.28 PROTECTION ARRANGEMENTS FOR RADIO STATIONS The lightning surges in microwave, UHF & train radio stations may get entry into the equipment through any of the following paths- - Tower, waveguide or radio frequency coaxial cable - AC mains power supply - Over head telephones wires or underground telecommunications cables. Adequate protection arrangement shall be provided in each case to protect the equipment from damages. 23.29 RISK INDEX: The degree of protection required and the protection devices necessary to be installed shall be based on the RISK INDEX of the particular location. A method for calculation of the risk index is given in Annexure-C. 23.30 PROTECTION ARRANGEMENT OF RADIO TOWERS: 23.30.1 PROVISION OF TOWER GROUND RING: Tower ground ring as mentioned in para 23.13 shall be provided for all towers. 23.30.2 PROVISION OF LIGHTNING SPIKE: Lightning spike as mentioned in para 23.3 shall be provided for all towers, on the top of the tower. 23.30.3 PROTECTION FOR TOWERS SITUATED ON GROUND: In case of towers erected directly on ground the lower legs act as down conductors & no separate lightning conductor from lightning spike to earth is necessary. Each tower leg shall be connected to the tower ground ring by 2 no. of 14mm dia copper wire. 23.30.4 PROTECTION FOR TOWERS ON THE TOP OF BUILDING: The tower legs shall be connected to lightning conductors which shall be drawn along the building wall and connected to the earth Indian Railways Telecom Manual - 2021 Page 323  termination at ground. At least two number of such conductors shall be drawn. The earth termination shall be constructed in the same manner as the tower ground ring. 23.31 PROTECTION ARRANGEMENTS OF RADIO RELAY STATIONS WITH HIGH RISK INDEX: The protection arrangement as given in Fig-1 shall be taken for stations with risk index 80 or more. The arrangement shall consist of the following: (a) TOWER GROUND RING; (b) EXTERNAL GROUND RING; (c) INTERNAL GROUND RING; 23.31.1 The tower ground ring shall be connected at two places to the external ground ring with 6mm dia bare tinned copper conductor laid in underground trenches. 23.31.2 The waveguide run shall be connected to the tower metal structure at the top and the bottom. The waveguide portion inside the building shall be connected to the tower ground by 6mm dia copper wire. 23.31.3 The external metallic sheath of RE coaxial cable shall be earthed in the same manner as in case of waveguide. 23.31.4 Following shall be connected to the internal ground ring: (a) The battery charger positive terminal, earth terminals of microwave/UHF/train radio/Optical fibre equipments, Multiplexing equipments. (b) The earth terminal of lightning ARRESTER & MOVRs provided in the DC circuits. (c) All conduits, battery trays, battery chargers, cable trays, jumper wire cable trays. (d) All incidental metal objects such as ducts, distribution frame, metal door frames etc. For all these connections 4mm dia copper or 6mm dia copper clad steel wire shall be used. 23.31.5 Each rack /equipment shall have separate earth connection to the internal ground ring. 23.31.6 The internal ground ring is to be bonded to the external ground at 4 corners of the building with 6 mm copper wire. Indian Railways Telecom Manual - 2021 Page 324 23.32 PROTECTION SCHEME FOR RADIO STATIONS WITH LOW RISK INDEX: Protection arrangement as per Fig 2 shall be provided. 23.32.1 The protection arrangement shall consist of : (a) TOWER GROUND RING (b) INTERNAL GROUND RING The internal ground ring shall be connected to the tower ground ring by 6MM dia copper at minimum two places. 23.32.2 Following shall be connected to the internal ground ring (a) Battery charger positive. (b) Ground terminal of the microwave radio & multiplexing equipment. (c) Ground terminal of lighting arrestors across the charger. (d) Ground terminal of GD tube & MOVR. 23.32.3 The waveguide portion inside the building near the branching filter shall be connected to the tower ground ring with 6mm copper wire. The waveguide support ladder shall be connected to tower ring. 23.32.4 The waveguide shall be connected to tower structure at the top and the bottom. SECTION H PROTECTION ARRANGEMENT FOR TELEPHONE EXCHANGES 23.33 The protection system of telephone exchanges shall be similar to the radio relay station excepting that no tower earth is required. Suitable protection arrangement with fuse, GD tube and MOVR shall be provided. 23.33.1 EARTHING REQUIREMENT: External ground ring similar to the radio relay stations shall be provided for telephone exchanges. 23.33.2 Three stage system consisting of fuse, GD tube and MOVR shall be provided in the line side of the electronic telephone exchanges. However, for exchanges where above protections are inbuilt in the design of MFG and line cards, no separate protection is required. 23.33.3 Lighting protection arrangement as described in para 23.22 shall be provided across DC supply voltage at the power distribution board. 23.33.4 Metallic structures, chassis, racks etc. shall be connected to the external earth in the same manner as in radio relay stations. Indian Railways Telecom Manual - 2021 Page 325  SECTION I INSPECTION & TESTING 23.34 The complete protection arrangement should be inspected and tested by ASTE/DSTE/Sr.DSTE to ensure that the work has been completed in a satisfactory manner and the material and components used conform to the standard. 23.35 Routine inspection of the installation, particularly the earth resistance shall be taken twice a year by the SE/SSE incharge of the station and Earth connections of all installation should be checked thoroughly two months in advance of every monsoon season and remedial measures should be taken well in advance of monsoon. 23.36 A log book shall be kept in which details of the measurement and inspection should be recorded for scrutiny by higher officials. Indian Railways Telecom Manual - 2021 Page 326  ANNEXURE-A Para 23.8 CALCULATION OF EARTH RESISTANCE & NUMBER OF ELECTRODES The approximate earth resistance of the rod/pipe electrodes can be calculated by the following formulae. R = 0.75 X o/L if 25 < L/d < 100 = o/L if 100 < L/d < 600 = 1.2 o/L if 600 < L/d < 300 where, o = Resistivity of earth in Ohm.M L= Length of the electrode in M. d= Diameter of the electrode in M. Assuming a value of 'o'=40, L=2.5M , d = 38 mm the value of R comes out to be = 12 ohms. Thus with one electrode the earth resistance is 12 ohms. If the desired earth resistance is equal to R(d), the no. of electrodes required to achieve the above resistance can be approximately calculated by R(d) = (1.5/N) x R where, R= Resistance of single electrode N= No. of electrodes installed in parallel at a distance of 3 to 4 M interval. Thus to get earth resistance of 1 ohm the total no. of electrodes required N= 1.5 x 12= 18 The representative values of soil resistivity in various parts of India are given for ready reference. Representative values of soil resistivity in various parts of India S. Locality Type of soil Order of Remarks No. resistivity in ohm meter 1 2 3 4 5 1 Kakarepar, Surat Clayay black 6-23 Underlying bedrock Distt. Gujarat soil Deccan trap 2 Taptee Valley Alluviium 6-24 -do- 3 Narmada Valley Alluvium 4-11 Underlying bedrock-sand stones, shale and limestones, Deccan trap, Indian Railways Telecom Manual - 2021 Page 327  and geneises. 4 Purna Agricultural 3-6 Underlying bedrock Valley(Deogaon) Deccan trap. 5 Dhond, Bombay Alluvium 6-40 -do 6 Bijapur Distt. (a) black cotton 2-10 -do- Mysore State soil 10-50 (b) Moorm 7 Carimenapenta, Alluvium(Highly 2 Underlying bedrock Nellore Distt., clayey) geniuses. Andhra Pradesh. 8 Kartee (a) Alluvium 3-5 Underlying bedrock (b) Alluvium 9-21 sand-stone, trap or geniuses. 9 Delhi (a) Alluvium(dry, 75-170 -do- (a)Najafgarh sandy soil) (b) Loamy to 38-50 -do- Clayey soil) alluvium(Saline) 1.5-9 -do- (b)Chhatarpur Dry Soil 36-109 Underlying bedrock quartzites 10 Korba, M.P. (a) Moist Clay 2-3 Underlying bedrock (b) Alluvium soil 10-20 sand-stones or shale. 11 Cossipur, Calcutta. Alluvium 25(Approx) -------------- 12 Bhagalpur (a) Alluvium 9-14 Underlying bedrock Bihar (b) Top Soil 24-46 traps, sand -stones or gneisses. 13 Kerala(Trivendrum Leteritic Clay 2-5 Underlying bedrock Distt) leterite charnockite or ghanites. 14 Bharatpur Sandy, 6-14 ------ loam(saline) 15 Kalyadi, Mysore. Alluvium 60-150 Underlying bedrock gneisses. 16 Kolar Gold fields Sandy surface 45-185 -do- 17 Wajrakarur, Andhra Alluvium 50-150 -do- Pradesh 18 Koyna, Satara Lateritic 800- Underlying bed-rock Distt. 1200(dry) sand-laterite or trap. 19 Kutch-kandla (a) 4-50 Underlying bedrock Alluvium(clayey) sand-stone, shale or (b) trap. Alluvium(Sandy) 60-200 -do- 20 Villupuram Madras Clayey sands 11 Underlying bedrock- granite. 21 Ambaji, Alluvium 170 Underlying bedrock- Banaskantha, sand-stones and Gujarat. gneisses. Indian Railways Telecom Manual - 2021 Page 328 22 (a) Alluvium 2-5 Underlying bedrock sand-stones and gneisses. -do- (b) Lateritic soil 300 (approx) Note: The soil resistivities are subject to wide seasonal variation as they depend very much on the moisture content. Indian Railways Telecom Manual - 2021 Page 329  ANNEXURE – B Para23.23 PROTECTION ARRANGEMENT FOR SUBSCRIBERS LINES General Specification: i) Response Time - < 1 micro sec. ii) Protection level - ~ 22 V iii) Discharge current - > 10 KA iv) Insulation resistance - > 10 8 Ohms v) Capacitance - ~ 3 pf vi) Series resistance - 20 Ohms Specification of Gas Arrestor: (Discharge Tube ) i) DC spark over voltage - 300 - 500 V. ii) Impulse spark over voltage (1 KV/micro sec.) 800V iii) Nominal impulse discharge current - 10 KA (8/20 micro Sec. wave) iv) Insulation resistance at (100 VDC) - 10 10 Ohms v) Capacitance - 2.5 pf Specification of MOVR: i) Protection level voltage - 22 V ii) Surge current at (8/20 micro sec. wave) - upto 50 amps. iii) Average power dissipation - 0.02 W iv) Insulation resistance - > 100 M.Ohms. v) Capacitance - ~ 2 pf Indian Railways Telecom Manual - 2021 Page 330  ANNEXURE - C CALCULATION OF RISK INDEX BASED ON VARIOUS FACTORS AFFECTING RISK OF LIGHTNING AND CONSEQUENTIAL DAMAGE 1. Usage of Structure: If the structure is generally occupied by a large number of people, the consequential damage could be quite high. In case of radio relay installations, since they can be treated as places occupied by a limited number of people and having a tall outdoor metallic structure, the value of the index is 4. 2. Type of construction: A steel framed building is self-protecting against lightning while brick buildings require greater degree of protection. In case of Radio Relay installations:- i. For reinforced concrete building with any roof other than metal- index is 2. ii. For Brick, plain concrete or masonary with any roof other than metal or thatch - the index is 4. iii. Reinforced concrete with metal roof - 7 iv. Brick, plain concrete, masonary with metal roofing the index is - 8. 3. Contents or consequential effects: If the installation contains equipment, damage to which will seriously disrupt normal working, then such an installation requires a higher level of protection. In case of radio relay installations, the value of the index is 6. 4. Degree of Isolation: In closely built-up towns and cities, the lightning hazard is not as great as in the open country. For radio relay installations, the index value is i. For structures located in a large area of structures of trees of the same or greater height, for example in a large town or forest-2. ii. For structures located in an area with few other structures or trees of similar height-5. iii. For structures completely isolated or exceeding at least twice the height of surrounding structures or trees- 10. iv. or radio relay stations with no motorable approach roads to the top and attendant difficulties in transporting equipment and reaching the station after sun-set, an index value of 10 is to be added to the values at (i) to (iii) above, Indian Railways Telecom Manual - 2021 Page 331  v. For radio relay stations situated on rocky soil where it is difficult to get a good earth connection an index value of 10 is to be added to the values of (i) to (iv) above. 5. Type of Terrain: An installation in a hilly or mountainous area is more susceptible to damage than a building in plains and flat terrain. In case of radio-relay installations; i. Situated on flat terrain at any level - index value is 2. ii. Hill terrain - index value is 6. iii. Mountainous terrain between 500 m to 1000 m- index value is 8. iv. Mountainous terrain above 1000m - index value is 10. 6. Height of Structures: Taller structures are subject to greater hazards, than smaller structures and therefore lightning protection is more desirable in tall structures. In case of Radio Relay installations, since the height of the tower is the deciding factor, the following index values are to be adopted:- Height of Structures (Height of tower, or height of building + tower in meters where tower is mounted on the building) Exceeding Not Exceeding Value of Index - 10 meters 2 10 meters 15 meters 4 15 meters 20 meters 5 20 meters 20 meters 8 20 meters 30 meters 11 30 meters 35 meters 16 35 meters 40 meters 19 40 meters 45 meters 22 45 meters 55 meters 30 55 meters 60 meters 32 60 meters 70 meters 35 70 meters 80 meters 37 80 meters 90 meters 39 90 meters 100 meters 40 Structures higher than 55m require protection in all cases. 7. Lightning Prevalence: Isokaraunic level (IKL) refers to the number of thunders storm days in a year at a particular place: the map at Appendix B shows the Average IKL in different parts of the country”. The risk of lightning strike increases with the IKL but the severity of lightning storms , as distinguished from their frequency Indian Railways Telecom Manual - 2021 Page 332  of occurrence is much greater in some locations than in others. Hence the need for protection at certain places may not be in direct proportion to IKL. The value of the index as a function of IKL is as under:- Number of thunderstorms days per year Exceeding Not Exceeding Value of Index - 5 4 5 10 8 11 15 13 16 20 18 21 - 21 Examples of Index Figure Calculations: a) Secunderabad Station S.C.Rly(situated in crowded areas) Factor Category Risk Index 1 Usage of structure Occupied by limited number of 4 people 2 Types of construction RCC with tower on top 7 3 Contents of conse- Communication network of 6 quential effects. Indian Railways 4 Degree of Isolation Height exceeds twice the height 10 of surrounding structures. 5 Type of terrain Flat terrain 2 6 Height of structure 60m(Tower and Building) 32 7 IKL 28 21 Index Figure= 4+7+6+10+2+32+21-= 82 b) Peddagutta (situated on an isolated hill) S.C.Rly 1 Usage of structure Same as above (in a) 4 2 Type of construction RCC Building with tower on top 7 3 Contents Same as above (in a) 6 4 Degree of isolation On an isolated hill 10+10+10 5 Type of Terrain Mountainous terrain 8 between 500 to 1000m. 6 Height of structure 10-15m(Building tower) 4 7 IKL 43(Approx.) 21 Index figure = 80 c) Ongole - SC Rly ( along the East Coast) 1 Usage of Structure Same as above (in a) 4 2 Type of construction RCC building with other 2 than metallic roof 3 Contents Same as above (in a ) 6 4 Degree of Isolation Height exceeding twice the 10 surround structure Indian Railways Telecom Manual - 2021 Page 333  5 Type of Terrain Hill terrain 6 6 Height of structure Height of tower is 90m 39 7 IKL 25 21 Index figure: 88 d) New Delhi- N.Rly(situated in crowded area) 1 `Usage of structure Same as above (in a) 4 2 Type of construction RCC building with other 2 than metallic roof. 3 Contents Same as above (in a ) 6 4 Degree of Isolation Located in the midst of 2 structure of comparable height 5 Type of Terrain Flat terrain 2 6 Height of structure Height of tower(50m) 30 7 IKL 38 21 Index Figure: 67 e) Bilaspur- S.E.Railway 1 Usage of structure Same as above (in a ) 4 2 Type of construction RCC building without metal roofing 2 3 Contents Same as above (in a ) 6 4 Degree of Isolation Exceeds double the height 10 of structures surrounding 5 Type of terrain Flat terrain 2 6 Height of structure Ht. of tower 90m 39 7 IKL 34(approx) 21 Risk Index= 84 f) Surat- W.Rly(along the West coast) 1 Usage of structure Same as above (in a ) 4 2 Type of construction RCC building without metal roofs 2 3 Contents Same as above(in a ) 6 4 Degree of isolation Exceeds double the height of the 10 surrounding structures 5 Type of Terrain Flat 2 6 Height of structure Height of tower (50m) 30 7 IKL 4 Risk Index: 58 g) Uruli (Central Railway) 1 Usage of structure Same as above (in a ) 4 2 Type of construction: RCC building without metal proof 2 3 Contents Same as above (in a ) 6 4 Degree of Isolation exceeds double the height of 10+10 surrounding structures. 5 Type of Terrain Hill terrain 6 6 Height of structure 50m tower 30 7 IKL 21 Risk Index : 89 Indian Railways Telecom Manual - 2021 Page 334  ISO XERAUNIC DATA (Reproduced from IS 2309-1969) S.No. Name of Place Annual Thunderstrom days 1 Gilgit 7 2 Skardu 5 3 Gulmarg 53 4 Srinagar 54 5 Dras 3 6 Kargil 2 7 Leh 3 8 Jammu 26 9 Dharamshala 13 10 Amritsar 49 11. Pathankot 4 12. Mandi 46 13 Ludhiana 12 14 Simla 40 15 Patiala 26 16 Ambala 9 17 Hissar 27 18 Delhi 39 19 Bikaner 10 20 Phalodi 14 21 Sikar 17 22 Barmer 12 23 Jodhpur 23 24 Ajmer 26 25 Jaipur 39 26 Kankroli 36 27 Mount Abu 5 28 Udaipur 38 29 Neemuch 28 30 Kota 27 31 Jallawar 40 32 Mussorie 61 33 Roorkee 74 34 Najibabad 36 35 Mukteshwar 53 36 Meerut - 37 Bareilly 34 38 Aligarh 30 39 Agra 25 40 Mainpuri 23 41 Baharaich 31` 42 Gonda 22 43 Lucknow 18 44 Kanpur 26 45 Fatehpur 24 46 Jhansi 20 47 Allahabad 51 48 Varanasi 51 Indian Railways Telecom Manual - 2021 Page 335 49 Azamgarh 1 50 Gorakhpur 11 51 Kathmandu 74 52 Motihari 38 53 Darbhanga 10 54 Patna 33 55 Gaya 38 56 Daltonganj 73 57 Hazaribagh 73 58 Ranchi 34 59 Chaibasa 70 60 Jamshedpur 66 61 Purnea 52 62 Sabour 76 63 Dumka 63 64 Darjeeling 28 65 Jalpaiguri 68 66 Malda 59 67 Asansol 71 68 Burdwan 39 69 Khargpur 76 70 Calcutta 70 71 Sagar Island 41 72 Dhubri 8 73 Tejpur 27 74 Dibrugarh 98 75 Sibsagar 103 76 Shillong 75 77 Cherrapunji 49 78 Silchar 33 79 Kohima 34 80 Imphal 49 81 Deesa 7 82 Dwarka 5 83 Jamna Nagar 8 84 Rajkot 12 85 Ahmedabad 11 86 Dohad 17 87 Porbundar 3 88 Varaval 3 89 Bhavnagar 11 90 Baroda 8 91 Surat 4 92 Gwalior 53 93 Guna 33 94 Nowgong 59 95 Satna 41 96 Sagar 36 97 Bhopal 44 98 Jabalpur 50 99 Umaria 37 100 Ambikapur 29 101 Indore 34 102 Hoshangabad 37 103 Pachmarhi 30 Indian Railways Telecom Manual - 2021 Page 336 104 Seoni 51 105 Pendaiah 56 106 Raipur 34 107 Chindawara 27 108 Kanker 37 109 Jagdalpur 35 110 Balasore 81 111 Chandbali 75 112 Angul 81 113 Bhubaneshwar 46 114 Puri 33 115 Gopalpur 34 116 Jharsuguda 85 117 Sambalpur 67 118 Titlagarh 24 119 Rajgangpur 1 120 Dhahanu 1 121 Nasik 17 122 Maligaon 13 123 Akola 20 124 Amraoti 32 125 Nagpur 45 126 Gonda 10 127 Aurangabad 34 128 Bombay 16 129 Aligarh 12 130 Ahmadnagar 10 131 Parbhani 32 132 Pune 22 133 Mahabaleshwar 14 134 Ratnagiri 6 135 Sholapur 23 136 Miraj 25 137 Vengurla 39 138 Najibabad 36 139 Hanamkonda 43 140 Hyderabad 28 141 Khammam 26 142 Kalingapatnam 20 143 Vishakhapatnam 46 144 Rentichintala 42 145 Masulipatnam 20 146 Ongole 25 147 Kurnool 29 148 Anantapur 22 149 Nellore 18 150 Bidar 15 151 Gulbarga 34 152 Bijapur 9 153 Belgaum 31 154 Raichur 17 155 Gadag 21 156 Bellary 22 157 Karwar 27 158 Honawar 5 Indian Railways Telecom Manual - 2021 Page 337 159 Chikalthana 24 160 Mangalore 36 161 Hassan 26 162 Bangalore 46 163 Mysore 44 164 Kozhikode 39 165 166 Cochin 69 167 Allopey 51 168 Trivandrum 68 169 Vellore 25 170 Madras 47 171 Cotacamud 24 172 Salem 69 173 Cuddalore 37 174 Coimbatore 40 175 Tiruchirapalli 41 176 Nagapattinam 15 177 Kodikanal 82 178 Madurai 39 179 Pambam 5 180 Tuticorin 14 181 Cape Comorin 68 182 Port Blair 62 183 Car Nicobar 18 184 Minicoy 20 Indian Railways Telecom Manual - 2021 Page 338 Indian Railways Telecom Manual - 2021 Page 339  -x-x-x- Indian Railways Telecom Manual - 2021 Page 340