80 Questions
What is the safe limit for induction due to low frequency induction due to short circuit fault?
430V
Who issues the NOC after reviewing the induced voltage figures?
GM (S&T) of the concerned Railways
What happens if the induced voltage figures are within safe limits?
NOC is issued by the Railways
Who compiles all BSNL details in the PTCC route approval process?
Railway Authority
What is the purpose of calculating induced voltage figures in the PTCC route approval process?
To identify potential hazards and take protection measures
Who forwards the proposal for PTCC route approval to the concerned DET?
Power Utility/State Electricity Board
What happens if the induced voltage figures are not within safe limits?
Re-engineering is proposed
Who marks the railway telecom details in the PTCC route approval process?
Railway Authority
What should be ensured before giving final clearance for energization of power lines?
Provision of protective measures is completed wherever necessary
Who is responsible for depositing the expenditure for provision of protective measures?
The agency which carries out erection of the new power lines
What is the primary reason for examining induced voltages under normal conditions?
To ensure telecom circuit safety
What is the purpose of EPR counters in telephone plants?
To define hazard zone for telephone plants
What should be checked during inspections at stations?
Availability of protective measures
What is the prescribed safe limit of induced voltage on telecom circuits?
430V
What is the purpose of connecting the third electrode of a GD tube to the earth?
To virtually earth the telecom line during induced voltage exceedance
What is the safe limit of EPR at locations of telephone exchanges for high reliability power lines?
430 V
How is the number of GD tubes required for protection calculated?
Induced Voltage / 300
Who heads the PTCC monitoring cell?
CCE/Dy.CSTE(Tele)
What is the purpose of the PTCC manual?
To describe method for carrying out low frequency induction test
What happens to the telecom line when the induced voltage exceeds the pre-determined value of 250V?
The telecom line is virtually earthed
What is the safe limit of EPR at locations of cables (metal sheathed) for high reliability power lines?
650 V
How are GD tubes installed when the number of required tubes is more than three?
Two tubes at each end of the paralleling section and the rest in between at equal intervals
Why is it necessary to ensure that the earth connection to the GD tube has very low resistance?
To reduce the voltage across the tube
Where should GD tubes be installed on the telecom lines?
On all telecom wires in the paralleling section
What is the maximum acceptable limit of induced voltage due to power parallelism in railway block and communication circuits?
2000V
What is the recommended replacement for the existing DC blocking condenser in the telephone circuits?
A one rated for 1000V DC
What is the primary purpose of GD tubes in railway control and other overhead circuits?
To provide protection against hazardous potentials
What is the recommended approach to check for interference to signaling circuits?
By checking the AC immunity of the signaling equipment
What is the recommended action to be taken when induced voltages exceed the acceptable limit of 2000V?
Treat the case as a re-engineering case and consult with the Railway Board
What is the primary purpose of the safety protocols in telecom circuits?
To prevent electrical shock to personnel
What is the recommended approach to determine the required number of GD tubes for a particular circuit?
By calculating the induced voltage due to power parallelism
What is the primary purpose of the DC blocking condenser in the telephone circuits?
To block the DC voltage in the circuits
What is the primary purpose of calculating induced voltage figures in the PTCC route approval process?
To identify potential hazards due to low frequency induction
Who is responsible for marking the telecom details in the PTCC route approval process?
Railway Authority
What is the outcome if the induced voltage figures are within safe limits?
NOC is issued by the Railways
Who compiles the telecom details of BSNL in the PTCC route approval process?
Concerned Engineer of Telecom Circle, BSNL
What is the role of the Director (PTCC) in the PTCC route approval process?
To review the proposal for PTCC route approval
Who forwards the proposal for PTCC route approval to the Concerned DET, PTCC?
Power Utility/SEB
What is the consequence of induced voltage figures not being within safe limits?
Re-engineering of the power transmission line is proposed
Who is responsible for issuing the PTCC route approval?
Concerned DET, PTCC
What is the maximum induced voltage that a Single Line Ball Token/ Tablet Token Block Instrument can withstand without special precautions?
430 V
What modification is required for Diado Single Line Tokenless Block Instruments to withstand induced voltages up to 650V AC?
Replacing line condensers with higher voltage rating
What type of block instrument is only suitable for use in non-AC electrified sections?
Push Button Type Single Line Tokenless Block Instrument
What is the voltage rating of the replaced line condensers in Diado Single Line Tokenless Block Instruments?
1000 V
What is the purpose of interposing a polarized relay in the line circuit of Diado Single Line Tokenless Block Instruments?
To feed the existing line relay from local battery
What is the maximum induced voltage that a Diado Single Line Tokenless Block Instrument can withstand without modification?
74 V
What type of relay is used in Neale’s token or SGE double line block instrument?
A-3 position polarized relay
Where can the guidelines for protective measures against induced voltages be found?
Appendix XVII to Chapter I of PTCC manual
What happens to the telecom line when the induced voltage exceeds the pre-determined value of 250V?
The telecom line is virtually earthed
What is the purpose of connecting the third electrode of a GD tube to the earth?
To restrict the voltage across the tube to safer values
How is the number of GD tubes required for protection calculated?
Induced Voltage / 300
Why is it necessary to ensure that the earth connection to the GD tube has very low resistance?
To restrict the voltage across the tube to safer values
Where should GD tubes be installed on the telecom lines?
In all the above-mentioned locations
What is the primary purpose of GD tubes in railway control and other overhead circuits?
To protect the equipment and personnel from hazardous potentials
How are GD tubes installed when the number of required tubes is more than three?
Two GD tubes are installed at each end and the rest in between at equal intervals
What is the purpose of examining induced voltages under normal conditions?
To protect the equipment and personnel from hazardous potentials
What is the formula to calculate the induced voltage on a telecommunication line during an earth fault on the power line?
V = MxI
What is the unit of Mutual Coupling (M) between the Power line and telecom line?
Ohms
Which of the following factors affects the value of Mutual Coupling (M)?
Distance between power and telecom lines
What is the purpose of calculating the induced voltage in the PTCC route approval process?
To mitigate the effects of low frequency induction
Who is responsible for calculating the induced voltage in the PTCC route approval process?
Concerned DET
What is the significance of the distance between power and telecom lines in the calculation of induced voltage?
It affects the value of Mutual Coupling (M)
What is the primary purpose of the Railway Telecom Manual?
To provide guidelines for PTCC route approval
What is the consequence of not considering the induced voltage in the PTCC route approval process?
Risk of low frequency induction hazards
What is the maximum acceptable limit of induced voltage due to power parallelism in railway block and communication circuits?
2000V
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?
DC blocking condenser with a 1000V rated one
Who is responsible for providing the interference voltage to signaling circuits?
Railways
What should be checked with reference to the AC immunity of the signaling equipment?
Point machines and all of the above
What is the recommended approach to check for interference to signaling circuits?
By checking the AC immunity of the signaling equipment
What should be done in cases of induced voltages above the maximum acceptable limit of 2000V?
Treat them as re-engineering cases
What should be provided invariably on railway control and other overhead circuits?
GD tubes
Where should the voltage limit for safe working be referred to?
OEM manual
What is the primary purpose of calculating induced voltage figures in the PTCC route approval process?
To identify the need for re-engineering of the power line route
Who is responsible for forwarding the proposal for PTCC route approval to the concerned DET?
Power Utility/SEB
What is the safe limit for induction due to low frequency induction due to short circuit fault?
430V
What happens if the induced voltage figures are not within safe limits?
Re-engineering of the power line route is proposed
Who marks the railway telecom details in the PTCC route approval process?
Railway Authority
What is the purpose of marking the telecom details in the PTCC route approval process?
To ensure the safe operation of power lines up to 132 KV
Who is responsible for issuing the PTCC route approval?
Concerned DET of the Central PTCC
What is the outcome if the induced voltage figures are within safe limits?
NOC is issued by the Railways
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
This quiz covers the safety measures to protect equipment and personnel from hazardous potentials in telecom circuits, specifically in cases of short circuit faults.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
