Radio Relay Station Protection Arrangements
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Questions and Answers

How should the earth termination be constructed?

  • In a different manner from the tower ground ring
  • Using a different type of conductor
  • In the same manner as the tower ground ring (correct)
  • With a separate external ground ring

    • What is the diameter of the bare tinned copper conductor used to connect the tower ground ring to the external ground ring?

  • 4mm
  • 8mm
  • 10mm
  • 6mm (correct)

    • How many places should the tower ground ring be connected to the external ground ring?

  • Three places
  • Two places (correct)
  • One place
  • Four places

    • How should the waveguide run be connected to the tower metal structure?

    <p>At the top and the bottom</p> Signup and view all the answers

    What should be connected to the internal ground ring according to section 23.31.4?

    <p>All of the above and other incidental metal objects</p> Signup and view all the answers

    How should each rack/equipment be earthed?

    <p>Through a separate earth connection to the internal ground ring</p> Signup and view all the answers

    How should the internal ground ring be bonded to the external ground?

    <p>At four corners of the building</p> Signup and view all the answers

    What type of wire should be used for connections to the internal ground ring?

    <p>6mm dia copper clad steel wire</p> Signup and view all the answers

    What is the primary purpose of the lightning protection arrangement across the DC supply voltage?

    <p>To protect the equipment from power surges</p> Signup and view all the answers

    Who is responsible for ensuring that the complete protection arrangement is installed satisfactorily?

    <p>ASTE/DSTE/Sr.DSTE</p> Signup and view all the answers

    How often should the earth resistance of the installation be checked?

    <p>Twice a year</p> Signup and view all the answers

    What is the purpose of the log book maintained in the station?

    <p>To record the measurement and inspection of the installation</p> Signup and view all the answers

    What is the formula for calculating earth resistance of the rod/pipe electrodes when 25 < L/d < 100?

    <p>R = 0.75 o/L</p> Signup and view all the answers

    What is the value of 'o' assumed in the calculation of earth resistance?

    <p>40 Ohm.M</p> Signup and view all the answers

    What is the calculated value of R when L = 2.5M and d = 38 mm?

    <p>12 ohms</p> Signup and view all the answers

    What is the purpose of checking the earth connections of all installations two months in advance of every monsoon season?

    <p>To take remedial measures in advance of the monsoon season</p> Signup and view all the answers

    What is the approximate value of IKL in the context of Surat-W.Rly along the West coast?

    <p>34</p> Signup and view all the answers

    What is the degree of isolation of the structure in Uruli (Central Railway)?

    <p>Exceeds double the height of the surrounding structures</p> Signup and view all the answers

    What is the type of terrain in Surat-W.Rly along the West coast?

    <p>Flat</p> Signup and view all the answers

    What is the height of the tower in Uruli (Central Railway)?

    <p>50m</p> Signup and view all the answers

    What is the Risk Index in the context of tower 90m?

    <p>84</p> Signup and view all the answers

    What is the type of construction in Surat-W.Rly along the West coast?

    <p>RCC building without metal roofs</p> Signup and view all the answers

    What is the value of IKL in the context of Uruli (Central Railway)?

    <p>21</p> Signup and view all the answers

    What is the Risk Index in the context of Surat-W.Rly along the West coast?

    <p>58</p> Signup and view all the answers

    Which city has the highest number of thunderstorm days?

    <p>Dibrugarh</p> Signup and view all the answers

    Which of the following cities has the lowest number of thunderstorm days?

    <p>Azamgarh</p> Signup and view all the answers

    What is the number of thunderstorm days in Jaipur?

    <p>39</p> Signup and view all the answers

    Which city has the same number of thunderstorm days as Udaipur?

    <p>Neemuch</p> Signup and view all the answers

    What is the number of thunderstorm days in Shillong?

    <p>75</p> Signup and view all the answers

    Which city has the same number of thunderstorm days as Hazaribagh?

    <p>Daltonganj</p> Signup and view all the answers

    What is the number of thunderstorm days in Madras?

    <p>47</p> Signup and view all the answers

    Which city has the same number of thunderstorm days as Varanasi?

    <p>Allahabad</p> Signup and view all the answers

    At what interval should earth electrodes be installed around the tower foundation?

    <p>4 Meter</p> Signup and view all the answers

    What is the minimum depth below the ground level for burying the bare tinned copper conductor?

    <p>2.5M</p> Signup and view all the answers

    How should the bare tinned copper conductor be connected to the electrodes?

    <p>Soldered / Clamped / Welded</p> Signup and view all the answers

    What is the purpose of the single earth system in telecom installations?

    <p>To reduce the possibility of side flash</p> Signup and view all the answers

    What type of conductor is used for the internal ground ring?

    <p>38 mm sq. bare tinned copper conductor</p> Signup and view all the answers

    At what distance from the tower foundation should the bare tinned copper conductor be buried?

    <p>0.5M</p> Signup and view all the answers

    What is the minimum internal diameter of a pipe that can be used as an earth electrode?

    <p>38mm</p> Signup and view all the answers

    How many copper wires are used to connect each leg of the tower to the tower ground ring?

    <p>2</p> Signup and view all the answers

    What is the purpose of driving the electrode inclined by about 30 degrees to the vertical when rock is encountered?

    <p>To improve the contact between the electrode and the earth</p> Signup and view all the answers

    What is the minimum separation between multiple electrodes?

    <p>4 M</p> Signup and view all the answers

    What is the external ground ring used for in telecom installations?

    <p>Earthing system surrounding the plinth of the building</p> Signup and view all the answers

    What is the purpose of artificially treating the soil with salt and charcoal?

    <p>To decrease the earth resistance</p> Signup and view all the answers

    What is the minimum depth up to which the electrode should be driven?

    <p>2.5 M</p> Signup and view all the answers

    What is the top of the electrode typically kept above the ground?

    <p>30 cm</p> Signup and view all the answers

    What is the diameter of the earth pit formed for artificial treatment of soil?

    <p>600 mm</p> Signup and view all the answers

    What is the material used for the copper rod electrode?

    <p>Tinned copper</p> Signup and view all the answers

    If the desired earth resistance is 1 ohm, and the resistance of a single electrode is 12 ohms, how many electrodes are required to achieve the desired resistance?

    <p>18</p> Signup and view all the answers

    What is the typical distance interval between electrodes installed in parallel?

    <p>3-4 M</p> Signup and view all the answers

    What is the order of soil resistivity in the Kakarepar, Surat region?

    <p>6-23 ohm-meter</p> Signup and view all the answers

    What is the underlying bedrock in the Narmada Valley region?

    <p>Sand stones, shale, and limestones</p> Signup and view all the answers

    What should be the diameter of the copper conductor used to connect the waveguide portion inside the building to the tower ground?

    <p>6mm</p> Signup and view all the answers

    What is the formula to calculate the earth resistance of a single electrode?

    <p>R(d) = (1.5/N) x R</p> Signup and view all the answers

    What is the purpose of the external ground ring in the protection arrangement of radio relay stations?

    <p>To provide a path to ground for lightning strikes</p> Signup and view all the answers

    Why are multiple electrodes required to achieve a desired earth resistance?

    <p>To reduce the earth resistance</p> Signup and view all the answers

    What is the primary purpose of installing multiple electrodes?

    <p>To reduce the earth resistance</p> Signup and view all the answers

    What should be connected to the internal ground ring according to the protection arrangement?

    <p>All incidental metal objects, conduits, and battery trays</p> Signup and view all the answers

    How should the tower ground ring be connected to the external ground ring?

    <p>With 6mm dia bare tinned copper conductor</p> Signup and view all the answers

    What is the type of soil in the Taptee Valley region?

    <p>Alluvium</p> Signup and view all the answers

    What is the purpose of the internal ground ring in the protection arrangement of radio relay stations?

    <p>To provide a common ground point for all equipment</p> Signup and view all the answers

    How should the external metallic sheath of RE coaxial cable be earthed?

    <p>In the same manner as the waveguide</p> Signup and view all the answers

    What should be connected to the tower metal structure at the top and the bottom?

    <p>The waveguide run</p> Signup and view all the answers

    How should the internal ground ring be bonded to the external ground ring?

    <p>With 6mm dia copper wire</p> Signup and view all the answers

    What is the minimum depth required for filling the pit with layers of salt and charcoal?

    <p>20 cm</p> Signup and view all the answers

    What is the purpose of spraying water on the excavated earth after filling the pit?

    <p>To ensure good electrical contact</p> Signup and view all the answers

    What type of material is used for the bonds in lightning protection systems?

    <p>Mild steel</p> Signup and view all the answers

    Why should joints be avoided in lightning conductors and underground earth conductors?

    <p>To minimize electrical impedance for surge current</p> Signup and view all the answers

    What is the purpose of the testing point in lightning protection systems?

    <p>To facilitate isolation of the two sections</p> Signup and view all the answers

    How often should the earth electrode be cleaned?

    <p>At least once in two years</p> Signup and view all the answers

    What should be used to protect joints of bimetallic elements from corrosion?

    <p>Loaded grease or M-seal compounds</p> Signup and view all the answers

    What is the purpose of using layers of common salt and charcoal in the pit?

    <p>To reduce the resistance of the earth</p> Signup and view all the answers

    What is the purpose of the external ground ring in a radio relay station?

    <p>To provide a common ground point for all equipment</p> Signup and view all the answers

    How is the waveguide run connected to the tower metal structure?

    <p>At the top and bottom with a 6mm dia copper conductor</p> Signup and view all the answers

    What type of wire is used to connect the tower ground ring to the external ground ring?

    <p>6mm dia copper wire</p> Signup and view all the answers

    What is the purpose of the internal ground ring in a radio relay station?

    <p>To provide a common ground point for all equipment and racks</p> Signup and view all the answers

    How is the earth termination constructed in a radio relay station?

    <p>In the same manner as the tower ground ring</p> Signup and view all the answers

    Study Notes

    Protection Arrangements for Radio Relay Stations

    • For stations with a risk index of 80 or more, the protection arrangement should consist of a tower ground ring, external ground ring, and internal ground ring.
    • The tower ground ring should be connected to the external ground ring with 6mm dia bare tinned copper conductor laid in underground trenches at two places.

    Earth Termination and Internal Ground Ring

    • The waveguide run should be connected to the tower metal structure at the top and bottom, and the waveguide portion inside the building should be connected to the tower ground by 6mm dia copper wire.
    • The external metallic sheath of RE coaxial cable should be earthed in the same manner as the waveguide.
    • The following should be connected to the internal ground ring:
      • Battery charger positive terminal, earth terminals of microwave/UHF/train radio/Optical fibre equipments, and Multiplexing equipments.
      • Earth terminal of lightning ARRESTER & MOVRs provided in the DC circuits.
      • All conduits, battery trays, battery chargers, cable trays, and jumper wire cable trays.
      • All incidental metal objects such as ducts, distribution frame, metal door frames, etc.
    • Each rack/equipment should have a separate earth connection to the internal ground ring.

    Bonding and Lightning Protection

    • The internal ground ring should be bonded to the external ground at four corners of the building with 6mm copper wire.
    • Lightning protection arrangement should be provided across DC supply voltage at the power distribution board.

    Inspection and Testing

    • 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.
    • Routine inspection of the installation, particularly the earth resistance, should be taken twice a year by the SE/SSE in charge of the station.
    • Earth connections of all installations should be checked thoroughly two months in advance of every monsoon season, and remedial measures should be taken well in advance of monsoon.
    • A log book should be kept to record the details of the measurement and inspection.

    Calculation of Earth Resistance

    • The approximate earth resistance of the rod/pipe electrodes can be calculated using the given formulae, which depend on the length and diameter of the electrode and the resistivity of the earth.

    Risk Index Calculation

    • The risk index is calculated based on the usage of the structure, type of construction, contents, degree of isolation, type of terrain, and height of the structure.
    • Examples of risk index calculations are provided for different locations, including Peddagutta, Ongole, New Delhi, Surat, and Uruli.

    ISO Xeraunic Data

    • The ISO Xeraunic data provides information on the number of thunderstorm days for various locations across India.

    Earthing Systems for Telecom Applications

    • The tower ground ring is an earthing system used at the foot of towers for telecom applications, consisting of earth electrodes and an underground tinned bare copper conductor.
    • Earth electrodes are installed at an interval of about 4 meters surrounding the tower foundation, with a bare tinned copper conductor of 38 sq.mm buried at least 2.5 meters below the ground level and at a distance of 0.5 meters from the tower foundation.
    • The conductor is soldered/clamped/welded to the electrodes to provide a good electrical connection.
    • Each leg or two diagonal legs of the tower are connected to the tower ground ring with 2 nos. of 6mm dia copper wire.

    External Ground Ring

    • The external ground ring is an earthing system surrounding the plinth of the building, housing telecom equipment, constructed in the same manner as the tower ground ring.

    Internal Ground Ring

    • The internal ground ring is an earthing arrangement inside the equipment room, consisting of an earth bus bar (25 mm x 5mm copper flat or 38mm sq. bare tinned copper conductor) installed surrounding the equipment room 0.5 meters below the ceiling or 0.5 meters above the floor level.

    Single Earth System

    • The telecom installations use a single earth system, where different earth connections from equipment, towers, DC power supply, metallic structures, etc. are interconnected to each other through low resistance earthing conductors.
    • This method is recommended to keep all points to be earthed at approximately the same potential level to reduce the possibility of side flash and subsequent damages.

    Installation of Electrodes

    • Electrodes have a spike at one end and a clamp at the other end for connecting earth lead.
    • Electrodes are directly driven into the earth up to a depth of at least 2.5 meters.
    • In cases where rock is encountered at a depth less than 2.5 meters, the electrode is driven inclined by about 30 degrees to the vertical.
    • In hard soil, a hole for the electrode may be drilled by an earth auger or by manual trenching.

    Use of Multiple Electrodes

    • In cases where a single electrode is not sufficient to provide the desired earth resistance, more than one electrode is used.
    • The separation of electrodes is about 4 meters.

    Calculation of the Number of Electrodes

    • Approximate calculation of the number of electrodes required to get the desired value of earth resistance can be made using the guidelines given in Annexure-A.

    Artificial Treatment of Soil

    • In soils of high resistivity, even multiple earth electrodes may not provide the 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 are formed by excavation, and the electrode is placed at the center of the pit.

    Protection Arrangements for Radio Relay Stations with High Risk Index

    • Protection arrangements for stations with a risk index of 80 or more include a tower ground ring, external ground ring, and internal ground ring.
    • The tower ground ring is connected at two places to the external ground ring with 6mm dia bare tinned copper conductor laid in underground trenches.
    • The waveguide run is connected to the tower metal structure at the top and the bottom, and the waveguide portion inside the building is connected to the tower ground by 6mm dia copper wire.
    • The external metallic sheath of RE coaxial cable is earthed in the same manner as in the case of the waveguide.

    Bonding and Joints

    • Bonds made of mild steel clamps with galvanized nuts and bolts are used to connect the lightning protection system with other metallic structures.
    • Joints are avoided in lightning conductors and underground earth conductors, and when necessary, they are crimped, riveted, welded, or soldered to ensure minimum electrical impedance for the surge current.
    • All joints of bimetallic elements are protected from corrosion by covering the joint with loaded grease or M-seal compounds.

    Testing Point

    • A clamp between earth termination at the electrodes and the down conductors is provided to facilitate isolation of the two sections and measurement of earth resistance.
    • This joint, known as the testing point, is made of mild steel with galvanized nuts and bolts.

    Tower Ground Ring

    • Consists of earth electrodes and underground tinned bare copper conductor
    • Earth electrodes installed at an interval of about 4 meters surrounding the tower foundation
    • Bare tinned copper conductor of 38 sq.mm buried at least 2.5M below ground level and 0.5M from tower foundation
    • Conductor soldered/clamped/welded to electrodes for good electrical connection
    • Each leg or two diagonal legs of the tower connected to tower ground ring with 2 nos. of 6mm dia copper wire

    External Ground Ring

    • Earthing system surrounding the plinth of the building housing telecom equipment
    • Constructed in the same manner as tower ground ring

    Internal Ground Ring

    • Earthing arrangement inside the equipment room
    • Consists 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

    Single Earth System

    • Telecom installations use single earth system to interconnect earth connections from equipments, towers, DC power supply, metallic structures, etc.
    • Recommended to keep all points to be earthed at approximately the same potential level to reduce the possibility of side flash and subsequent damages

    Installation of Electrode

    • Electrodes have a spike at one end and a clamp at the other end for connecting earth lead
    • Electrodes directly driven into the earth up to a depth of at least 2.5 M
    • In cases where rock is encountered, electrodes driven inclined by about 30 degrees to the vertical

    Use of Multiple Electrodes

    • More than one electrode used in cases where a single electrode is not sufficient to provide desired earth resistance
    • Separation of electrodes shall be about 4 M

    Artificial Treatment of Soil

    • In soils of high resistivity, soil should be artificially treated with salt and charcoal in appropriate proportion
    • Earth pits of 600 mm dia and 2.5 M depth formed by excavation and the electrode placed at the centre of the pit

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