Podcast
Questions and Answers
What voltage levels can be received from the supply authorities at traction substations?
What voltage levels can be received from the supply authorities at traction substations?
How is the 25KV power supply for traction derived?
How is the 25KV power supply for traction derived?
What is the purpose of the 25KV feeder breaker?
What is the purpose of the 25KV feeder breaker?
How are adjacent substations fed in terms of electrical phases?
How are adjacent substations fed in terms of electrical phases?
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What is the function of interruptors in the OHE supply system?
What is the function of interruptors in the OHE supply system?
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What does the backup protection for the 25KV transformer breaker serve to do?
What does the backup protection for the 25KV transformer breaker serve to do?
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In the event of a total shutdown of a sub-station, how can power be extended from adjacent substations?
In the event of a total shutdown of a sub-station, how can power be extended from adjacent substations?
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What is the main function of the pantoflash over relay?
What is the main function of the pantoflash over relay?
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What condition removes the need for a pantoflash over relay?
What condition removes the need for a pantoflash over relay?
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What is the adjustable time setting range for the auto-reclosing relay?
What is the adjustable time setting range for the auto-reclosing relay?
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Which relay is used for detection and clearance of high resistance earth faults of the OHE?
Which relay is used for detection and clearance of high resistance earth faults of the OHE?
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What additional protection mechanism is provided by the purchaser in case of undervoltage?
What additional protection mechanism is provided by the purchaser in case of undervoltage?
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What is the primary benefit of the single shot auto reclosing scheme for 25kV feeder circuit breakers?
What is the primary benefit of the single shot auto reclosing scheme for 25kV feeder circuit breakers?
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Which event can trigger the inter-tripping of feeder circuit breakers?
Which event can trigger the inter-tripping of feeder circuit breakers?
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What issue can occur due to wrong phase coupling at the overlap of a failed sub-station?
What issue can occur due to wrong phase coupling at the overlap of a failed sub-station?
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How does the single shot auto reclosing scheme protect the OHE system?
How does the single shot auto reclosing scheme protect the OHE system?
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What equipment is used to achieve inter-tripping during a fault scenario?
What equipment is used to achieve inter-tripping during a fault scenario?
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What is the consequence of a pantograph passing over a failed sub-station during wrong phase coupling?
What is the consequence of a pantograph passing over a failed sub-station during wrong phase coupling?
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Why is it essential to minimize arc damage to OHE during sub-station failures?
Why is it essential to minimize arc damage to OHE during sub-station failures?
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What role do bridging interruptors play during an emergency feed condition?
What role do bridging interruptors play during an emergency feed condition?
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What does the term 'auto reclosing' refer to in electrical systems?
What does the term 'auto reclosing' refer to in electrical systems?
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What is the value of loop impedance for a single track OHE with RC?
What is the value of loop impedance for a single track OHE with RC?
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Which standard specification relates to static protective relays?
Which standard specification relates to static protective relays?
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Which type of alarms require a hand-reset as specified?
Which type of alarms require a hand-reset as specified?
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What is the primary purpose of the draw-out (plug-in) relays specified?
What is the primary purpose of the draw-out (plug-in) relays specified?
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What additional feature is specified for relays to ensure proper function?
What additional feature is specified for relays to ensure proper function?
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Which of the following values corresponds to the loop impedance for double track OHE?
Which of the following values corresponds to the loop impedance for double track OHE?
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Which of these components specifically requires a manual reset service?
Which of these components specifically requires a manual reset service?
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What is the impedance value for double track OHE with RC?
What is the impedance value for double track OHE with RC?
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Which circuit function has flag type operation indicators?
Which circuit function has flag type operation indicators?
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What is the specified finish for the covers of the relays?
What is the specified finish for the covers of the relays?
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What is the rated continuous current for the current coil mentioned?
What is the rated continuous current for the current coil mentioned?
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What is the overload capability of the current coil for the specified duration?
What is the overload capability of the current coil for the specified duration?
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What is the designed continuous service voltage for the auxiliary relay coils?
What is the designed continuous service voltage for the auxiliary relay coils?
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How much fluctuation in voltage can the auxiliary relay coils satisfactorily operate under?
How much fluctuation in voltage can the auxiliary relay coils satisfactorily operate under?
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What type of contact is specified for the relays?
What type of contact is specified for the relays?
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Which of the following relay types includes a bias setting of 40%?
Which of the following relay types includes a bias setting of 40%?
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What protective feature should be included with the metal case of the relays?
What protective feature should be included with the metal case of the relays?
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What is the burden rating for the auxiliary relay that the output of the relays should operate?
What is the burden rating for the auxiliary relay that the output of the relays should operate?
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Which of the following settings is included in the IDMT overcurrent relay (CDG-26)?
Which of the following settings is included in the IDMT overcurrent relay (CDG-26)?
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What is the voltage class of the relays according to the specifications?
What is the voltage class of the relays according to the specifications?
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What is the maximum acceptable operating time for the earth leakage relays specified?
What is the maximum acceptable operating time for the earth leakage relays specified?
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Which feature is essential to prevent operation due to magnetisation current when charging the transformer?
Which feature is essential to prevent operation due to magnetisation current when charging the transformer?
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What is the adjustable current setting range for the relays described?
What is the adjustable current setting range for the relays described?
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Which of the following must the relays not operate for?
Which of the following must the relays not operate for?
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What is the minimum operating current bias setting required for the relays to suit the tapping range?
What is the minimum operating current bias setting required for the relays to suit the tapping range?
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What is the role of the transformer in the power supply system for traction?
What is the role of the transformer in the power supply system for traction?
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What happens to the OHE supply during a fault condition?
What happens to the OHE supply during a fault condition?
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How is the earthing of the transformer secondary side accomplished in the traction system?
How is the earthing of the transformer secondary side accomplished in the traction system?
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What is the primary function of the neutral section in the OHE system?
What is the primary function of the neutral section in the OHE system?
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What does the backup protection for the 25KV transformer breaker primarily ensure?
What does the backup protection for the 25KV transformer breaker primarily ensure?
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What mechanism is used to switch on or off the OHE supply?
What mechanism is used to switch on or off the OHE supply?
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During an emergency shutdown of a sub-station, how is power maintained from adjacent stations?
During an emergency shutdown of a sub-station, how is power maintained from adjacent stations?
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What primary function does a booster transformer serve in relation to the 25KV traction overhead equipment?
What primary function does a booster transformer serve in relation to the 25KV traction overhead equipment?
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Which relays are specifically included in the protection scheme for the transformer in the traction sub-station?
Which relays are specifically included in the protection scheme for the transformer in the traction sub-station?
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What is the typical leakage impedance of a booster transformer as mentioned in the content?
What is the typical leakage impedance of a booster transformer as mentioned in the content?
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In the context of overhead equipment protection, which type of relay is used to prevent issues caused by wrong phase coupling?
In the context of overhead equipment protection, which type of relay is used to prevent issues caused by wrong phase coupling?
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How far apart are the booster transformers typically spaced on the electrified track?
How far apart are the booster transformers typically spaced on the electrified track?
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Which relay is not mentioned as part of the transformer protection in the traction sub-station?
Which relay is not mentioned as part of the transformer protection in the traction sub-station?
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What is the capacity rating of the booster transformer used in the electrified track system?
What is the capacity rating of the booster transformer used in the electrified track system?
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Which of the following is a feature of the IDMT overcurrent relay on the HV side?
Which of the following is a feature of the IDMT overcurrent relay on the HV side?
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What is the significance of spacing booster transformers apart by 2.66 km?
What is the significance of spacing booster transformers apart by 2.66 km?
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What is the loop impedance value for a single track OHE with RC at a phase angle of 700?
What is the loop impedance value for a single track OHE with RC at a phase angle of 700?
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Which standard specification corresponds to electrical relays for power system protection?
Which standard specification corresponds to electrical relays for power system protection?
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Which of the following relay types requires a hand-reset as specified in the document?
Which of the following relay types requires a hand-reset as specified in the document?
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What type of cover finish is specified for the relays?
What type of cover finish is specified for the relays?
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In what scenario must the relay’s current terminals automatically short when drawn out?
In what scenario must the relay’s current terminals automatically short when drawn out?
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Which of the following impedance values corresponds to the double track OHE?
Which of the following impedance values corresponds to the double track OHE?
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What is the status of the auxiliary unit in differential relays according to the specifications?
What is the status of the auxiliary unit in differential relays according to the specifications?
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Which of these indications must all protective relays have according to the specifications?
Which of these indications must all protective relays have according to the specifications?
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Which impedance value applies to double track OHE with RC?
Which impedance value applies to double track OHE with RC?
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What feature is critical for test initialization in the relays as per the specifications?
What feature is critical for test initialization in the relays as per the specifications?
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What type of directional protection does the MHO type relay (YCG-14) provide?
What type of directional protection does the MHO type relay (YCG-14) provide?
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Which setting range is applicable for the instantaneous high set over current relay on the 25KV side?
Which setting range is applicable for the instantaneous high set over current relay on the 25KV side?
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What relay is used for alarm annunciation control?
What relay is used for alarm annunciation control?
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What is the primary purpose of the high-speed master trip relay (VAJH-13)?
What is the primary purpose of the high-speed master trip relay (VAJH-13)?
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For the auxiliary relay used for contact multiplication of the directional distance protection relay (YCG-14), what is the designation?
For the auxiliary relay used for contact multiplication of the directional distance protection relay (YCG-14), what is the designation?
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What feature is NOT provided by the Buchholz relay regarding oil temperature?
What feature is NOT provided by the Buchholz relay regarding oil temperature?
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What is the forward offset percentage of the MHO relay for wrong phase coupling protection (YCG-14)?
What is the forward offset percentage of the MHO relay for wrong phase coupling protection (YCG-14)?
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Which type of timer relay is specified for an auto-reclosing scheme?
Which type of timer relay is specified for an auto-reclosing scheme?
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Which relay is mentioned as providing DC supervision for transformer low voltage circuit breakers?
Which relay is mentioned as providing DC supervision for transformer low voltage circuit breakers?
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What is the protection scheme implemented for internal faults in transformers?
What is the protection scheme implemented for internal faults in transformers?
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Study Notes
Power Supply System
- Power is received from utility grids at 132kV, 110kV, or 66kV.
- Supply is either at individual or single points, then transmitted via 132/110/66kV lines.
- 25kV traction power is derived through single-phase transformers.
- Primary winding connects to two phases of incoming three-phase or two-phase lines.
- Secondary side connects one terminal to OHE and the other to the running track rail.
- Each transformer has associated breakers on both the 132/110/66kV and 25kV sides.
- Feeder breakers for OHE lines.
- Adjacent sub-stations receive power from different phases.
- Neutral/dead sections (SP) are provided on 25kV OHE for fault location and maintenance.
- OHE supply is switched on/off by interrupters that don't open on fault.
- Fault clearing by feeder circuit breakers.
- Power supply extends to neutral sections on either side.
- In emergencies, adjacent sub-stations can bridge the neutral section.
Booster Transformers
- Installed in series with overhead equipment to reduce inductive interference with communication circuits.
- Primary winding connected to 25kV overhead equipment.
- Secondary winding in series with return conductor close to 25kV overhead equipment.
- 100kVA rating forces traction return current to flow through return conductor.
- Leakage impedance about 0.15 ohms each, spaced 2.66km apart.
Protective Relays at Traction Sub-Station
- Relays are on control panels to protect the transformer, sub-station, and feeder.
-
Transformer Protection:
- Differential relays.
- IDMT overcurrent relays for primary and secondary sides (instantaneous element).
- Instantaneous earth leakage relays for primary and secondary sides.
- High-speed inter-tripping relays.
- Auxiliary relays (Buchholz, oil temp, low oil).
-
Overhead Equipment Protection:
- Admittance type directional distance relays.
- Admittance type relays for wrong phase coupling.
- Instantaneous overcurrent relays.
- Pantograph flashover relays.
- Delta I relays for high-resistance faults.
Auto-Reclosing of Feeder Circuit Breakers
- Single-shot auto-reclosing scheme for 25kV feeder circuit breakers facilitates automatic reclosure after a pre-set time delay.
- Transient faults allow for quick restoration of supply to OHE.
- Prevents continued arcing during pantograph overlap.
Inter-Tripping of Feeder Circuit Breakers
- If a traction sub-station fails, supply is extended from adjacent sub-stations.
- Wrong phase coupling may occur during emergency leading to 25kV breaker tripping.
Governing Specifications
- Electrical relays for power system protection (IS:3231).
- Static protective relays (IS:8686).
- Electrical indicating instruments (IS:1248).
- Control cable (IS:694).
- Interposing current transformers (IS:2705).
Relays
- Draw-out/plug-in switchboard type, back-connected, semi-flush mounting.
- Dust-tight covers, dull black enamel.
- Secondary injection test blocks.
- Self-reset, except some types (e.g., low oil level, winding temp).
Static Type Relays
- Electro-mechanical relays manufactured by English Electric (GEC-ALSTHOM) used in 25kV sub-stations.
Transformation Protection
- Transformer percentage-based differential relays (DDT-12).
- IDMT overcurrent relays (CDG-26, CAG-13).
- Combined with CAC-13 instantaneous high-set overcurrent (132kV side).
- Restricted earth relays (CAG-14).
OHE Protection
- MHO type directional distance protection relays (YCG-14)
- Instantaneous high-set overcurrent relays (CAG-17)
- Auxiliary relays for supervision of various components.
Scheme of Protection for 25KV Overhead Equipment
- Overhead equipment protected from short circuits and overloads by feeder circuit breakers.
- Tracks on one side of sub-station are fed by a single feeder breaker.
- Detect short circuits within zone of overhead equipment fed by feeder breaker.
- Operate with minimal delay in opening the circuit breakers.
- Prevents short circuits especially remote from the station.
- Automatic reclosing of feeder circuit breakers.
- Detection and isolation of flashovers causing by pantograph overlap.
- Detection and isolation of high-resistance OHE ground faults.
Other Protective Devices
- Low oil level alarm.
- Buchholz relay with alarm and trip.
- Oil temp indicator with alarm and trip.
- Winding temp indicator with alarm and trip.
Earth Leakage Protection
- Backup protection for internal earth faults within the transformer using high-speed,sensitive earth leakage relays.
- Relays connected to separate current transformers on primary and secondary sides.
- Adjustable from 20% to 40% of 5 Amps in equal steps.
- Operates in 10ms.
Overcurrent Protection
- Protection against overcurrent in the transformer using non-directional overcurrent relays with inverse definite minimum time lag characteristics.
Specifics of Operation:
- Various specific types of relays, including time multiplier, current settings, and operating times are detailed in the specifications.
Additional Notes:
- Standards (e.g., IS) are mentioned for relay and component specifications.
- Many specific relay types (e.g., IDMT, MHO, differential) are detailed, including settings and operating parameters.
- Complete protection schemes are described, indicating where relays operate in conjunction (e.g., inter-tripping).
- Transformer characteristics, including ratings to ensure appropriate relay/circuit breaker operation, are detailed.
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Description
Test your knowledge on power supply systems, including voltage levels, transformer configurations, and operational procedures. This quiz covers the essential components and functions involved in transmitting power through OHE and various substations. Gain insights into fault management and emergency protocols within the power supply framework.
