Power Supply Installations Overview
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Questions and Answers

What is the primary function of sub-stations in the electric traction system?

  • To ensure continuous power supply. (correct)
  • To record passenger information.
  • To monitor train schedules.
  • To manage maintenance personnel.

    • What should be recorded in the inspection book at a sub-station?

  • Train departure times.
  • Weather conditions every hour.
  • Observations made by supervisory officials. (correct)
  • Daily passenger counts.

    • What is the maximum permissible temperature rise for the winding of a traction transformer at an ambient temperature of 45 degrees Celsius?

  • 40 degrees Celsius.
  • 55 degrees Celsius.
  • 65 degrees Celsius.
  • 50 degrees Celsius. (correct)

    • After how long can a traction transformer experience another 50% overload following continuous operation at maximum ambient temperature?

    <p>3 hours.</p> Signup and view all the answers

    Who is responsible for controlling switching operations at sub-stations?

    <p>Traction Power Controller.</p> Signup and view all the answers

    What is the overload capacity of traction transformers for a 100% overload?

    <p>5 minutes.</p> Signup and view all the answers

    Which part of the traction transformer has a maximum permissible temperature rise of 35 degrees Celsius?

    <p>Current carrying parts.</p> Signup and view all the answers

    What is a significant consequence of thermal and electrical stresses in oil-filled equipment?

    <p>Gas formation and lowering of flash point</p> Signup and view all the answers

    Which method is considered the most sensitive and efficient for detecting incipient faults in transformers?

    <p>Dissolved gas analysis (DGA)</p> Signup and view all the answers

    What happens to the condition of cellulosic insulation due to insufficient monitoring?

    <p>It suffers from reduced mechanical and dielectric strength</p> Signup and view all the answers

    Which action should be undertaken to prepare for the overhaul of a transformer?

    <p>Ensure spare gaskets of proper quality are available</p> Signup and view all the answers

    What is the recommended frequency for drawing oil samples for analysis in transformer condition monitoring?

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

    What aspect of oil is significantly affected by temperature rise in transformer operation?

    <p>Dielectric properties and flash point</p> Signup and view all the answers

    What should be done with bushings during the transformer overhaul process?

    <p>Carefully remove and protect them</p> Signup and view all the answers

    What can dissolved gases indicate in the context of transformer operation?

    <p>Incipient faults and deterioration</p> Signup and view all the answers

    In extreme cases, what can lower the flash point of the oil in transformers?

    <p>Gas formation due to electrical stress</p> Signup and view all the answers

    What is one main purpose of conducting gas chromatography on transformer oil?

    <p>To timely detect insulation deterioration</p> Signup and view all the answers

    What is the primary purpose of tap changers in Traction Transformers?

    <p>To adjust output voltage based on load conditions</p> Signup and view all the answers

    What voltage level must daily OHE voltage peaks remain below at the traction sub-station?

    <p>27.5 KV</p> Signup and view all the answers

    How often should a 24-hour record of voltages at neutral sections be taken?

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

    What specifications are adopted for EHV grade oil used in transformers?

    <p>IS-335 and IS-1866</p> Signup and view all the answers

    Which test can be conducted in PSI depots or sub-stations every six months?

    <p>Breakdown voltage (BDV) test</p> Signup and view all the answers

    What is the primary purpose of providing wedges in traction transformers?

    <p>To hold the windings tightly together against mechanical forces.</p> Signup and view all the answers

    What is the purpose of connecting a recording voltmeter at the traction sub-station?

    <p>To monitor voltage variations over time</p> Signup and view all the answers

    What condition may indicate a failure due to overheating in transformers?

    <p>Evidence of carbon deposits or flash marks on critical components.</p> Signup and view all the answers

    Which factor requires the CTFO/PSI to stay in contact with supply authorities?

    <p>To address changes in grid system connections</p> Signup and view all the answers

    What should be done regarding tools used during transformer maintenance?

    <p>All tools used must be listed out and accounted for to avoid hazards.</p> Signup and view all the answers

    What is a potential consequence of exceeding 27.5 KV at the traction sub-station?

    <p>Decreased lifespan of the transformer</p> Signup and view all the answers

    What is a characteristic feature of transformer failure due to lightning discharge?

    <p>Presence of flash marks on the end coil and nearby grounded parts.</p> Signup and view all the answers

    What is the primary characteristic monitored through the acidity test in transformer oil?

    <p>Degradation of insulation material</p> Signup and view all the answers

    What is recommended to counteract coil displacement in transformers?

    <p>Tighten the pressure screws and ensure wedges are fully home immediately.</p> Signup and view all the answers

    What should be noted if a transformer has been opened due to an internal fault?

    <p>Abnormalities such as carbon deposits and unusual odour</p> Signup and view all the answers

    What is the recommended location for replacing a burnt-out coil in a traction transformer?

    <p>In the manufacturer's works</p> Signup and view all the answers

    What cleaning measures should be taken inside the transformer tank?

    <p>Thoroughly clean and wash with fresh oil</p> Signup and view all the answers

    What is the best method to remove sludge from inaccessible places in a transformer?

    <p>Direct a thin jet of transformer oil under pressure</p> Signup and view all the answers

    Which of the following is NOT a recommended practice to protect the windings from moisture?

    <p>Ignore the moisture during service maintenance</p> Signup and view all the answers

    What should be done to the oil-tight gasket around the valve seat during maintenance?

    <p>Lightly polish the valve seat and renew the gasket</p> Signup and view all the answers

    How should debris and sludge be removed from transformer components?

    <p>With a wooden or fiber wedge to prevent damage</p> Signup and view all the answers

    What should you inspect if the coil assembly has been lifted after several years of service?

    <p>The amount of sludge formation present</p> Signup and view all the answers

    What is the first step in the maintenance process after opening a transformer?

    <p>Make a careful note of the internal conditions</p> Signup and view all the answers

    What is an important step after cleaning the transformer tank and before painting?

    <p>Ensure no rust or traces of oil remain</p> Signup and view all the answers

    What is the first action that should be taken to ensure the soundness of bonding and earthing connections?

    <p>Check physically the soundness of the connections.</p> Signup and view all the answers

    Which procedure is essential before checking the resistance of each group of earth electrodes?

    <p>Disconnect the group from the common earth system.</p> Signup and view all the answers

    What action should be taken if a battery is found to have excessive sediment accumulation?

    <p>Replace the battery with a new set.</p> Signup and view all the answers

    How often should the insulation resistance of motor windings be checked for motor-operated isolators?

    <p>Annually or as recommended during checks.</p> Signup and view all the answers

    What is the purpose of using a ‘Ductor’ in maintenance procedures for bus bars and connectors?

    <p>To measure the contact resistances of heavy current connections.</p> Signup and view all the answers

    What is the primary quality to be preserved during the purification of transformer oil?

    <p>Di-electric strength</p> Signup and view all the answers

    What occurs to the insulation resistance during the initial stages of the drying out process?

    <p>It drops to a low value due to heating</p> Signup and view all the answers

    At which point in the drying process should oil circulation be discontinued?

    <p>Upon completion of the drying out operation</p> Signup and view all the answers

    When does the insulation resistance rise above the leveling off point during the cooling process?

    <p>As oil cools after the drying out operation</p> Signup and view all the answers

    Which equipment specifications are referenced for purifying transformer oil?

    <p>RDSO’s Specification No.ETI/PSI/103</p> Signup and view all the answers

    What factors can cause moisture absorption in transformer oil?

    <p>Defective breathers and untreated make-up oil</p> Signup and view all the answers

    What temperature is associated with a low insulation resistance during the drying out process?

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

    What significant change occurs to the dielectric strength of cellulosic insulation over time?

    <p>It decreases due to mechanical stress.</p> Signup and view all the answers

    What method is utilized for condition monitoring of power transformers primarily based on gas analysis?

    <p>Dissolved gas analysis</p> Signup and view all the answers

    What happens to the flash point of transformer oil under extreme thermal stress?

    <p>It drops to between 50 degrees C and 80 degrees C.</p> Signup and view all the answers

    Why does the Buchholz relay fail to respond during the early stages of trouble in a transformer?

    <p>It requires a certain volume of gas to trigger.</p> Signup and view all the answers

    In what condition is it recommended to periodically undertake the overhaul of a transformer?

    <p>If it is faulty or at the end of 7-10 years.</p> Signup and view all the answers

    What is the primary purpose of gas chromatography in transformer condition monitoring?

    <p>To analyze the type and amount of dissolved gases.</p> Signup and view all the answers

    Which equipment condition requires immediate attention during transformer overhaul?

    <p>Excess sludge accumulation.</p> Signup and view all the answers

    What must be done with the oil before commencing maintenance work on a transformer?

    <p>It should be drained out.</p> Signup and view all the answers

    What is the first step when preparing for the removal of a transformer core during overhaul?

    <p>Ensure spare gaskets are available.</p> Signup and view all the answers

    What is the procedure for monitoring the condition of battery cells?

    <p>Check general conditions of all cells and measure specific gravity and voltage of the pilot cell, then for all cells if issues arise.</p> Signup and view all the answers

    Which action is required for bonding and earthing of electrical equipment?

    <p>Visually inspect all earth connections, ensuring duplicate earths are present for every equipment.</p> Signup and view all the answers

    During the inspection of insulators, what should specifically be looked for?

    <p>Cracks, chippings, and flashover marks, with replacement considered for badly chipped ones.</p> Signup and view all the answers

    What should be monitored regarding traction transformers?

    <p>The maximum oil temperature, silica-gel conditions, and gas collection in Buchholz relay.</p> Signup and view all the answers

    What must be done if the silica-gel in traction transformers appears pink?

    <p>Replace with dry gel and recondition the old silica-gel.</p> Signup and view all the answers

    What is the first step in checking oil levels in transformers and related equipment?

    <p>Inspect the oil level in the sight gauge glass and check for leaks.</p> Signup and view all the answers

    Regarding the operation of circuit breakers, what is a primary maintenance check?

    <p>Open the cover of the control box to inspect the operating mechanism.</p> Signup and view all the answers

    What should be done with minor chippings on insulators?

    <p>Apply a light coating of epoxy resin to prevent moisture ingress.</p> Signup and view all the answers

    In the context of traction transformers, which of the following is necessary for maintaining the silica-gel breather?

    <p>It must be monitored for color change and substituted when turning pink.</p> Signup and view all the answers

    How should checks be conducted for gas collection in Buchholz relays?

    <p>Gas collection must be checked continuously to ensure safety.</p> Signup and view all the answers

    What should be done if a battery is not in a fully charged condition?

    <p>Perform a boost charge and increase the trickle charging rate after investigation.</p> Signup and view all the answers

    What is a crucial aspect of maintaining the contact surfaces during maintenance?

    <p>Touch up the high spots on the contact surfaces to achieve a good fit.</p> Signup and view all the answers

    Which procedure must be followed for PTs during maintenance?

    <p>Check the fuse holders on the LV side to confirm their condition.</p> Signup and view all the answers

    During quarterly maintenance of batteries and battery chargers, what should be documented?

    <p>The specific gravity and cell voltage of every cell.</p> Signup and view all the answers

    What is the first step in maintaining booster transformers?

    <p>Replace or recondition the silica-gel breather, if necessary.</p> Signup and view all the answers

    When conducting inspections on auxiliary transformers, what value should be recorded alongside temperature?

    <p>Insulation resistance of the transformer winding.</p> Signup and view all the answers

    What maintenance step is specifically mentioned for the earth connections of booster transformers?

    <p>Check connections from the bottom to earth electrodes or rails.</p> Signup and view all the answers

    During maintenance checks of control and relay panels, what should be done with abnormal voltage or current readings?

    <p>Record them and take corrective action.</p> Signup and view all the answers

    What is a key maintenance action regarding silica-gel breathers in booster transformers?

    <p>Replace or recondition them as necessary.</p> Signup and view all the answers

    What should be checked for proper operation during the inspection of control and relay panels?

    <p>The state of all indicating and recording instruments.</p> Signup and view all the answers

    Study Notes

    2020 Introduction

    • This chapter is divided into four sections
    • Section 1 covers the organization and duties of Chief Traction Foreman (Power Supply Installations)
    • Section 2 details the operation of sub-stations
    • Section 3 covers guiding notes on maintenance of power supply equipment
    • Section 4 outlines a recommended maintenance schedule for power supply equipment

    Organization

    • Divisional set-up of senior subordinates under Sr. DEE/TRD is arranged in two patterns:
      • Territorial basis
      • Functional basis

    Operational and Maintenance

    • Sub-stations are vital for continuous power supply
    • Transmission lines and associated gear (transformers, switch gear, control, and relay panels) are duplicated in case of component failure
    • Centralized control by a single authority (Traction Power Controller) for switching operations

    Overload Capacity of Traction Transformers

    • Overload ratings typically include:
      • 50% overload for 15 minutes
      • 100% overload for 5 minutes
    • Temperature limitations are specified with ambient temperature (45°C)
      • Winding temperature: 50°C (by resistance method)
      • Oil temperature: 40°C (by thermometer)
      • Current-carrying parts temperature: 35°C (by thermometer)
    • Hotspot temperature limits: ≤100°C

    Inspection Book and Log Book at Sub Stations

    • Substations maintain "Inspection Books" for recorded observations by supervisors
    • Log books record traction transformer oil temperatures, ambient temperatures, currents, and voltages at set times
    • Investigate any unusual occurrences and implement corrective actions as required

    Duties of Chief Traction Foreman, Power Supply Installation

    • Supervises installation maintenance according to schedules, ensuring serviceability
    • Maintains coordination with Power Controller, Chief Foreman (OHE) to ensure power supply reliability
    • Keeps organization prepared for equipment breakdowns/failures
    • Oversees safety equipment (relays, bonding, earthing) function, properly trains staff, and enforces safety precautions
    • Deploys staff for refresher courses for deficient staff
    • Cares for special instruments and tools used for maintenance and operation
    • Keeps close watch on spare parts, initiating timely actions to replenish stocks
    • Ensures proper accounting of all tools and stores
    • Deploys staff to sub-stations and switching stations when remote equipment fails
    • Conducts monthly inspections with emphasis on safety
    • Provides timely updates to AEE/TRD and Sr. DEE/DEE(TRD) on developments
    • Carries out other duties as directed

    Protective Devices

    • Protective devices (alarms, trips, etc.) ensure safe operation with settings for extended use
    • Supervisory officials are notified for anomalies
    • Detailed reports are to be submitted to Sr. DEE/DEE(TrD)

    Testing of Transformer Oil

    • Performance and longevity of transformers are improved with use of EHV grade oil
    • Standard specifications (IS-335 and IS-1866) apply for new oil and oil in service, and these tests should be carried out regularly

    Oil Purification Plant

    • This plant aims to remove contaminants like water, deposits, dirt, sludge, dissolved moisture, and gases.
    • The main quality to preserve is dielectric strength
    • Removal of these contaminants is essential for safe operation.

    Insulation Resistance During Drying-Out

    • Temperature and insulation readings are recorded every two hours during the drying process
    • Plotting these values on a graph shows four distinct stages of the process
    • Stages depend on oil temperature and moisture removal, with resistance gradually increasing as moisture leaves

    Transformer Overhaul

    • Covered shops with facilities for core lifting are used to overhaul transformers
    • Equipment is thoroughly cleaned for internal faults, and component-by-component conditions are meticulously documented
    • Care must be taken to protect windings during overhaul

    Circuit Breakers and Interruptors

    • There are different types of circuit breakers: Minimum oil, SF6, Vacuum etc.
    • Manufacturers' instructions for maintenance are available for all these types, with additional, updated directives by RDSO.

    Battery Maintenance

    • Batteries must be in proper working order.
    • Condition assessment and maintenance for control, protection, and indication circuits is essential
    • Battery chargers should be appropriately sized
    • Periodic checks include specific gravity readings to ascertain the health and efficiency
    • Preventative steps for sulphation or over-charging are essential

    Protective Relays

    • Specialists conduct maintenance, repair, and test all protective relays; proper records are maintained
    • Strict authorization is required for any relay setting changes
    • A detailed register is required to show specifics of each relay and associated testing/maintenance info
    • This information is also to be shared with the Senior DEE/TRD

    Maintenance Schedules

    • Monthly, half yearly, and annual maintenance schedules are provided to ensure proper condition of equipment
    • These schedules should be adhered to, to prevent equipment failures and ensure safety and operational efficiency

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    Description

    This quiz covers key aspects of traction power supply installations, including the organization of Chief Traction Foreman duties, operational details of sub-stations, and maintenance guidelines. It also discusses essential components such as transformers, switch gear, and centralized control operations for efficient power management.

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