Telecom Circuits Safety Measures
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Questions and Answers

What is the safe limit for induction due to low frequency induction due to short circuit fault?

  • 450V
  • 300V
  • 430V (correct)
  • 390V

    • Who issues the NOC after reviewing the induced voltage figures?

  • Concered DET
  • GM (S&T) of the concerned Railways (correct)
  • Central PTCC
  • Power Utility/State Electricity Board

    • What happens if the induced voltage figures are within safe limits?

  • Re-engineering is proposed
  • PTCC Route Approval is issued by the concerned DET
  • The process is terminated
  • NOC is issued by the Railways (correct)

    • Who compiles all BSNL details in the PTCC route approval process?

    <p>Railway Authority</p> Signup and view all the answers

    What is the purpose of calculating induced voltage figures in the PTCC route approval process?

    <p>To identify potential hazards and take protection measures</p> Signup and view all the answers

    Who forwards the proposal for PTCC route approval to the concerned DET?

    <p>Power Utility/State Electricity Board</p> Signup and view all the answers

    What happens if the induced voltage figures are not within safe limits?

    <p>Re-engineering is proposed</p> Signup and view all the answers

    Who marks the railway telecom details in the PTCC route approval process?

    <p>Railway Authority</p> Signup and view all the answers

    What should be ensured before giving final clearance for energization of power lines?

    <p>Provision of protective measures is completed wherever necessary</p> Signup and view all the answers

    Who is responsible for depositing the expenditure for provision of protective measures?

    <p>The agency which carries out erection of the new power lines</p> Signup and view all the answers

    What is the primary reason for examining induced voltages under normal conditions?

    <p>To ensure telecom circuit safety</p> Signup and view all the answers

    What is the purpose of EPR counters in telephone plants?

    <p>To define hazard zone for telephone plants</p> Signup and view all the answers

    What should be checked during inspections at stations?

    <p>Availability of protective measures</p> Signup and view all the answers

    What is the prescribed safe limit of induced voltage on telecom circuits?

    <p>430V</p> Signup and view all the answers

    What is the purpose of connecting the third electrode of a GD tube to the earth?

    <p>To virtually earth the telecom line during induced voltage exceedance</p> Signup and view all the answers

    What is the safe limit of EPR at locations of telephone exchanges for high reliability power lines?

    <p>430 V</p> Signup and view all the answers

    How is the number of GD tubes required for protection calculated?

    <p>Induced Voltage / 300</p> Signup and view all the answers

    Who heads the PTCC monitoring cell?

    <p>CCE/Dy.CSTE(Tele)</p> Signup and view all the answers

    What is the purpose of the PTCC manual?

    <p>To describe method for carrying out low frequency induction test</p> Signup and view all the answers

    What happens to the telecom line when the induced voltage exceeds the pre-determined value of 250V?

    <p>The telecom line is virtually earthed</p> Signup and view all the answers

    What is the safe limit of EPR at locations of cables (metal sheathed) for high reliability power lines?

    <p>650 V</p> Signup and view all the answers

    How are GD tubes installed when the number of required tubes is more than three?

    <p>Two tubes at each end of the paralleling section and the rest in between at equal intervals</p> Signup and view all the answers

    Why is it necessary to ensure that the earth connection to the GD tube has very low resistance?

    <p>To reduce the voltage across the tube</p> Signup and view all the answers

    Where should GD tubes be installed on the telecom lines?

    <p>On all telecom wires in the paralleling section</p> Signup and view all the answers

    What is the maximum acceptable limit of induced voltage due to power parallelism in railway block and communication circuits?

    <p>2000V</p> Signup and view all the answers

    What is the recommended replacement for the existing DC blocking condenser in the telephone circuits?

    <p>A one rated for 1000V DC</p> Signup and view all the answers

    What is the primary purpose of GD tubes in railway control and other overhead circuits?

    <p>To provide protection against hazardous potentials</p> Signup and view all the answers

    What is the recommended approach to check for interference to signaling circuits?

    <p>By checking the AC immunity of the signaling equipment</p> Signup and view all the answers

    What is the recommended action to be taken when induced voltages exceed the acceptable limit of 2000V?

    <p>Treat the case as a re-engineering case and consult with the Railway Board</p> Signup and view all the answers

    What is the primary purpose of the safety protocols in telecom circuits?

    <p>To prevent electrical shock to personnel</p> Signup and view all the answers

    What is the recommended approach to determine the required number of GD tubes for a particular circuit?

    <p>By calculating the induced voltage due to power parallelism</p> Signup and view all the answers

    What is the primary purpose of the DC blocking condenser in the telephone circuits?

    <p>To block the DC voltage in the circuits</p> Signup and view all the answers

    What is the primary purpose of calculating induced voltage figures in the PTCC route approval process?

    <p>To identify potential hazards due to low frequency induction</p> Signup and view all the answers

    Who is responsible for marking the telecom details in the PTCC route approval process?

    <p>Railway Authority</p> Signup and view all the answers

    What is the outcome if the induced voltage figures are within safe limits?

    <p>NOC is issued by the Railways</p> Signup and view all the answers

    Who compiles the telecom details of BSNL in the PTCC route approval process?

    <p>Concerned Engineer of Telecom Circle, BSNL</p> Signup and view all the answers

    What is the role of the Director (PTCC) in the PTCC route approval process?

    <p>To review the proposal for PTCC route approval</p> Signup and view all the answers

    Who forwards the proposal for PTCC route approval to the Concerned DET, PTCC?

    <p>Power Utility/SEB</p> Signup and view all the answers

    What is the consequence of induced voltage figures not being within safe limits?

    <p>Re-engineering of the power transmission line is proposed</p> Signup and view all the answers

    Who is responsible for issuing the PTCC route approval?

    <p>Concerned DET, PTCC</p> Signup and view all the answers

    What is the maximum induced voltage that a Single Line Ball Token/ Tablet Token Block Instrument can withstand without special precautions?

    <p>430 V</p> Signup and view all the answers

    What modification is required for Diado Single Line Tokenless Block Instruments to withstand induced voltages up to 650V AC?

    <p>Replacing line condensers with higher voltage rating</p> Signup and view all the answers

    What type of block instrument is only suitable for use in non-AC electrified sections?

    <p>Push Button Type Single Line Tokenless Block Instrument</p> Signup and view all the answers

    What is the voltage rating of the replaced line condensers in Diado Single Line Tokenless Block Instruments?

    <p>1000 V</p> Signup and view all the answers

    What is the purpose of interposing a polarized relay in the line circuit of Diado Single Line Tokenless Block Instruments?

    <p>To feed the existing line relay from local battery</p> Signup and view all the answers

    What is the maximum induced voltage that a Diado Single Line Tokenless Block Instrument can withstand without modification?

    <p>74 V</p> Signup and view all the answers

    What type of relay is used in Neale’s token or SGE double line block instrument?

    <p>A-3 position polarized relay</p> Signup and view all the answers

    Where can the guidelines for protective measures against induced voltages be found?

    <p>Appendix XVII to Chapter I of PTCC manual</p> Signup and view all the answers

    What happens to the telecom line when the induced voltage exceeds the pre-determined value of 250V?

    <p>The telecom line is virtually earthed</p> Signup and view all the answers

    What is the purpose of connecting the third electrode of a GD tube to the earth?

    <p>To restrict the voltage across the tube to safer values</p> Signup and view all the answers

    How is the number of GD tubes required for protection calculated?

    <p>Induced Voltage / 300</p> Signup and view all the answers

    Why is it necessary to ensure that the earth connection to the GD tube has very low resistance?

    <p>To restrict the voltage across the tube to safer values</p> Signup and view all the answers

    Where should GD tubes be installed on the telecom lines?

    <p>In all the above-mentioned locations</p> Signup and view all the answers

    What is the primary purpose of GD tubes in railway control and other overhead circuits?

    <p>To protect the equipment and personnel from hazardous potentials</p> Signup and view all the answers

    How are GD tubes installed when the number of required tubes is more than three?

    <p>Two GD tubes are installed at each end and the rest in between at equal intervals</p> Signup and view all the answers

    What is the purpose of examining induced voltages under normal conditions?

    <p>To protect the equipment and personnel from hazardous potentials</p> Signup and view all the answers

    What is the formula to calculate the induced voltage on a telecommunication line during an earth fault on the power line?

    <p>V = MxI</p> Signup and view all the answers

    What is the unit of Mutual Coupling (M) between the Power line and telecom line?

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

    Which of the following factors affects the value of Mutual Coupling (M)?

    <p>Distance between power and telecom lines</p> Signup and view all the answers

    What is the purpose of calculating the induced voltage in the PTCC route approval process?

    <p>To mitigate the effects of low frequency induction</p> Signup and view all the answers

    Who is responsible for calculating the induced voltage in the PTCC route approval process?

    <p>Concerned DET</p> Signup and view all the answers

    What is the significance of the distance between power and telecom lines in the calculation of induced voltage?

    <p>It affects the value of Mutual Coupling (M)</p> Signup and view all the answers

    What is the primary purpose of the Railway Telecom Manual?

    <p>To provide guidelines for PTCC route approval</p> Signup and view all the answers

    What is the consequence of not considering the induced voltage in the PTCC route approval process?

    <p>Risk of low frequency induction hazards</p> Signup and view all the answers

    What is the maximum acceptable limit of induced voltage due to power parallelism in railway block and communication circuits?

    <p>2000V</p> Signup and view all the answers

    What should be replaced in the telephone circuits to ensure safe operation in block circuits subjected to maximum induction 650V r.m.s. 50 cycles AC?

    <p>DC blocking condenser with a 1000V rated one</p> Signup and view all the answers

    Who is responsible for providing the interference voltage to signaling circuits?

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

    What should be checked with reference to the AC immunity of the signaling equipment?

    <p>Point machines and all of the above</p> Signup and view all the answers

    What is the recommended approach to check for interference to signaling circuits?

    <p>By checking the AC immunity of the signaling equipment</p> Signup and view all the answers

    What should be done in cases of induced voltages above the maximum acceptable limit of 2000V?

    <p>Treat them as re-engineering cases</p> Signup and view all the answers

    What should be provided invariably on railway control and other overhead circuits?

    <p>GD tubes</p> Signup and view all the answers

    Where should the voltage limit for safe working be referred to?

    <p>OEM manual</p> Signup and view all the answers

    What is the primary purpose of calculating induced voltage figures in the PTCC route approval process?

    <p>To identify the need for re-engineering of the power line route</p> Signup and view all the answers

    Who is responsible for forwarding the proposal for PTCC route approval to the concerned DET?

    <p>Power Utility/SEB</p> Signup and view all the answers

    What is the safe limit for induction due to low frequency induction due to short circuit fault?

    <p>430V</p> Signup and view all the answers

    What happens if the induced voltage figures are not within safe limits?

    <p>Re-engineering of the power line route is proposed</p> Signup and view all the answers

    Who marks the railway telecom details in the PTCC route approval process?

    <p>Railway Authority</p> Signup and view all the answers

    What is the purpose of marking the telecom details in the PTCC route approval process?

    <p>To ensure the safe operation of power lines up to 132 KV</p> Signup and view all the answers

    Who is responsible for issuing the PTCC route approval?

    <p>Concerned DET of the Central PTCC</p> Signup and view all the answers

    What is the outcome if the induced voltage figures are within safe limits?

    <p>NOC is issued by the Railways</p> Signup and view all the answers

    Study Notes

    Protection from Induced Voltages

    • Induced voltages in telecom circuits need to be examined, especially in cases of short circuit faults.
    • If induced voltage exceeds 430V, protection measures must be taken to prevent hazardous potentials.

    Gas Discharge (GD) Tubes

    • GD tubes are used to protect telecom circuits from induced voltages.
    • Two electrodes are connected to the telecom wires, and the third electrode is connected to earth through an earth cap.
    • Under normal conditions, the telecom line is insulated, but when induced voltage exceeds 250V, the gap breaks down, and the telecom line is virtually earthed.

    Installation of GD Tubes

    • The number of GD tubes required for protection is calculated by dividing the induced voltage by a constant (300).
    • If the result is a fraction, it is rounded off to the next integer value.
    • GD tubes are installed in the following manner:
      • 3 tubes: 2 at the ends of the telecom lines and 1 in the middle.
      • More than 3 tubes: 2 at each end and the rest at equal intervals in between.

    PTCC Route Approval Process

    • For power lines up to 132 KV:
      • Proposal for PTCC route approval is forwarded by Power Utility/SEB to GM (S&T) of the concerned Railways.
      • Calculation of induced voltage figures and forwarding to GM (S&T) of the concerned Railways for issuing NOC.
    • For power lines above 132 KV:
      • Proposal for PTCC route approval is forwarded by Power Utility/SEB to Director (PTCC), CEA.
      • Calculation of induced voltage figures and forwarding to GM (S&T) of the concerned Railways for issuing NOC.

    Safe Limits and Protective Measures

    • Safe limit for induction due to low frequency induction is 430V.
    • Maximum acceptable limit of induced voltage due to power parallelism is up to 2000V on railway block and communication circuits.
    • Cases exceeding these limits are treated as re-engineering cases.
    • Railway control/block and all other circuits are normally working on OFC/Quad and require GD tubes for protection.

    Interference to Signaling Circuits

    • Interference to signaling circuits shall be checked with reference to the AC immunity of the signaling equipment.
    • Interference voltages to signaling circuits are not provided by PTCC and will have to be done by the Railways in specific cases.

    Maintenance and Expenditure

    • Divisions shall ensure that protective measures are maintained properly.
    • Expenditure for provision of protective measures shall be deposited by the agency which carries out the erection of new power lines.

    Induced Voltage Calculations

    • Induced voltage calculations are calculated differently depending on the voltage level of the power line:
      • Above 11 kV and up to 33 kV: Single Circuit (SC)
      • 33 kV Double Circuit (DC)
      • Above 132 kV: Central Electricity Authority, New Delhi (CEA, New Delhi)

    Method to Calculate Induced Voltage

    • Induced voltage (V) is calculated using the formula: V = M x I
    • Where M is the Mutual Coupling in Ohms between the power line and telecom line, and I is the Earth Fault Current in Amps

    Factors Affecting Mutual Coupling (M)

    • Distance between power and telecom lines
    • Length of parallelism
    • Fundamental frequency of the power supply
    • Soil resistivity of the area

    Protective Measures

    • Longitudinal induced voltages under normal conditions are examined in specific cases
    • If induced voltage exceeds 430V, protection measures are necessary to prevent hazardous potentials
    • One common protection measure is the use of three-electrode Gas Discharge (GD) tubes

    Installation of GD Tubes

    • Number of GD tubes required: Induced Voltage / Constant (300)
    • GD tubes are installed:
      • Two at each end of the paralleling section of the telecom lines
      • One in the middle of the two
      • Additional tubes fitted in between at equal intervals if necessary

    Block Instruments

    • SINGLE LINE BALL TOKEN/ TABLET TOKEN BLOCK INSTRUMENT:
      • No special precaution necessary for induced voltage up to 430V
      • Metallic return and GD tubes required for induced voltage above 430V
    • DOUBLE LINE BLOCK INSTRUMENT: Same as SINGLE LINE BALL TOKEN/ TABLET TOKEN BLOCK INSTRUMENT
    • KYOSAN TOKENLESS PUSH BUTTON: 650V AC with modification
    • DIADO SINGLE LINE TOKENLESS BLOCK INSTRUMENTS:
      • Can safely stand induction up to 74V 50 cycles AC induced voltage
      • Modification required for induced voltage up to 650V AC

    Maximum Acceptable Limit of Induced Voltage

    • Up to 2000V on railway block and communication circuits
    • Cases above this limit should be treated as re-engineering cases and consulted with the Railway Board

    Protective Measures for Railway Control/Block and Other Circuits

    • Normally working on Optical Fiber Cable (OFC)/Quad
    • Railway control and other overhead circuits should be provided with GD tubes

    Interference to Signaling Circuits

    • Checked with reference to the A.C. immunity of signaling equipment
    • Interference voltages not provided by PTCC, but should be done by the Railways in specific cases where interference is suspected

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    Description

    This quiz covers the safety measures to protect equipment and personnel from hazardous potentials in telecom circuits, specifically in cases of short circuit faults.

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