Transformer Basics and Mechanical Arrangement
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Transformer Basics and Mechanical Arrangement

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Questions and Answers

What is a primary risk associated with porcelain bushings in transformers?

  • Risk of oil leakage (correct)
  • Enhanced thermal conductivity
  • Improved mechanical stability
  • Increased electrical efficiency

    • Which factor significantly contributes to the likelihood of transformer failures?

  • Usage of high-quality bushings
  • Upgraded insulation materials
  • Regular maintenance procedures
  • Aging of transformers (correct)

    • What is a characteristic weakness of porcelain bushings?

  • Low pressure tolerance
  • Weak bending strength (correct)
  • High thermal expansion
  • Poor electrical insulation

    • What maintenance is necessary for porcelain bushings?

    <p>Cleaning and washing</p> Signup and view all the answers

    How do bushings affect the overall reliability of transformers?

    <p>They are major initiators of transformer failures.</p> Signup and view all the answers

    According to failure statistics, what is the annual failure risk of large power transformers?

    <p>1%</p> Signup and view all the answers

    What is the recommended mounting orientation for porcelain bushings?

    <p>Vertical mounting is critical.</p> Signup and view all the answers

    What type of management strategy can improve transformer reliability?

    <p>Proactive bushing fleet management</p> Signup and view all the answers

    What happens to the current in the primary coil when a load is connected to the secondary winding of a transformer?

    <p>It increases.</p> Signup and view all the answers

    Which of the following accurately describes the differences between unloaded and loaded transformers?

    <p>Loaded transformers experience increased primary current.</p> Signup and view all the answers

    What primarily determines short-circuit voltage in a transformer?

    <p>The construction of the core and coil position.</p> Signup and view all the answers

    How is short-circuit current defined in relation to the secondary side of a transformer?

    <p>Current that flows during a short circuit at nominal primary voltage.</p> Signup and view all the answers

    What effect do high stray fluxes have on short-circuit voltage?

    <p>They lead to higher short-circuit voltage.</p> Signup and view all the answers

    What may occur as a result of a short-circuit current being significantly higher than the rated current?

    <p>The transformer may be destroyed within a short time.</p> Signup and view all the answers

    What characterizes a short-circuit proof transformer?

    <p>Designed specifically to handle short-circuit conditions.</p> Signup and view all the answers

    In which direction do the currents flow in the primary and secondary windings when the primary current flows right-handed?

    <p>The secondary current flows left-handed.</p> Signup and view all the answers

    Which type of winding involves a high number of turns with relatively low currents?

    <p>Disc Winding</p> Signup and view all the answers

    What is a primary advantage of using axial spacers in helical windings?

    <p>Enhanced cooling properties</p> Signup and view all the answers

    Which type of insulation is commonly used with conductors in transformer windings?

    <p>Enamel insulation</p> Signup and view all the answers

    What disadvantage is associated with multi-layer windings?

    <p>Limited cooling efficiency</p> Signup and view all the answers

    In which winding type is the term 'interleaving' most relevant?

    <p>Disc Winding</p> Signup and view all the answers

    Which winding configuration generally serves as a regulating winding in transformers?

    <p>Single Loop Layer Winding</p> Signup and view all the answers

    What material is NOT commonly used for covering transformer windings?

    <p>Copper foil</p> Signup and view all the answers

    Which conductor type provides advantages of both cooling and low insulation requirements?

    <p>Transposed cable</p> Signup and view all the answers

    Which characteristic is associated with low voltage main windings in power transformers?

    <p>Low number of turns with high current</p> Signup and view all the answers

    What type of conductor covering may be used in conjunction with individual paper covering?

    <p>Common netting tape</p> Signup and view all the answers

    What is the primary function of the Buchholz protection device in transformers?

    <p>To serve as a sensitive fault detector that operates independently of transformer configuration</p> Signup and view all the answers

    Which component of the Buchholz protection detects fluid movement?

    <p>Pivoted vane</p> Signup and view all the answers

    What triggers the movement of the piston in the pressure relay of the tap changer oil compartment?

    <p>A sudden increase in pressure exceeding spring counter force</p> Signup and view all the answers

    What is the purpose of a frangible disk in a transformer?

    <p>To relieve pressure and prevent explosive ruptures</p> Signup and view all the answers

    What does the oil level monitor in a transformer typically include?

    <p>Two contacts for maximum and minimum oil level alarms</p> Signup and view all the answers

    What is the primary function of the capillary-type top-oil thermometer in transformers?

    <p>To measure the top-oil temperature and indicate it via electrical contacts</p> Signup and view all the answers

    How does the oil conservator's incline affect the performance of transformers?

    <p>It allows for reliable operation by facilitating fluid movement.</p> Signup and view all the answers

    Which of the following is NOT a function of the microswitch inside the pressure relay?

    <p>Automatically shutting down the transformer during faults</p> Signup and view all the answers

    What is the primary function of the tank in a transformer?

    <p>To provide structural support for the CCA while facilitating cooling.</p> Signup and view all the answers

    Which voltage class predominantly utilizes vacuum drying for transformers?

    <p>Voltage class above 33 KV.</p> Signup and view all the answers

    What ensures that excessive pressure does not cause damage in a transformer tank?

    <p>Incorporation of a conservator for oil expansion and contraction.</p> Signup and view all the answers

    What is the purpose of terminal identifications on the bushings?

    <p>To facilitate proper connection and maintenance.</p> Signup and view all the answers

    During the final assembly of a transformer, what is inspected?

    <p>Clearances inside the tank and the positioning of the CCA.</p> Signup and view all the answers

    What type of insulation is used for primary and secondary terminations?

    <p>Porcelain or epoxy cast insulation.</p> Signup and view all the answers

    What is typically the first step in the installation process of a transformer?

    <p>Initial inspection and testing of the transformer.</p> Signup and view all the answers

    What feature is included to allow for oil filling, sampling, and draining?

    <p>Valves fitted on the transformer tank.</p> Signup and view all the answers

    Study Notes

    Transformer Basics

    • An unloaded transformer has no load connected to the secondary winding. The iron losses are greater than the copper losses.
    • A loaded transformer has a consumer connected to the secondary winding, drawing electrical energy. The secondary current opposes the primary current.
    • Short-circuit voltage in a transformer is determined by the core construction and winding positions. High stray fluxes result in a high short-circuit voltage.
    • Short-circuit current is the current flowing during a short circuit on the secondary side. It's significantly higher than the rated current, posing a risk of damage.
    • Higher short-circuit current corresponds to a lower short-circuit voltage.

    Transformer Mechanical Arrangement

    • Transposed cable, individual epoxy & enamel covering, common paper or netting tape covering are used for transformer windings.
    • Triple conductor, twin conductor, flat conductor and paper insulation are used for transformer windings.
    • Different winding types include:
      • Layor Winding: Tertiary Winding, Regulating Winding
      • Single Layer Winding: MV and LV Main Winding
      • Multi-Layer Winding: LV Main Winding
      • Helical Winding: MV and LV Main Winding
      • Disc Winding: HV Main Winding
    • Regulating Winding: A winding used to adjust the output voltage.
    • Bushings are insulated components used to pass electrical conductors through transformer tanks.

    Increasing Transformer Reliability

    • Manage the bushing fleet throughout its lifetime to reduce the risk of failures and minimize downtime.
    • Aging of transformers increases the hazard rate.
    • Transformer insulation failures, followed by winding and winding exit lead failures, are major contributors to transformer failures.
    • Anticipate aging trends within an installed transformer fleet.

    ### HV Bushings Life Management Importance

    • Bushings are vital components of power transformers. They're a major cause of transformer failures, contributing to a 1% yearly failure rate.
    • Buchholz protection is a fast and sensitive fault detector, independent of windings and tap changer positions.

    Protective Devices

    • Transformers with on-tank tap changers often have pressure protection for the separate tap changer compartment.
    • Pressure relief devices, such as frangible disks, prevent explosive ruptures and fires by relieving pressure during internal faults..
    • Oil level monitors use contacts to signal high or low oil levels.
    • Top-oil thermometers measure top-oil temperature and can have multiple contacts for different temperature thresholds.

    Transformer Manufacturing Process

    • The tank, made of mild steel, is the transformer enclosure holding the core and coil assembly (CCA).
    • The tank must be leak-proof and withstand pressure.
    • Final assembly includes:
      • Inserting the CCA into the tank.
      • Bringing terminations out through bushings.
      • Adding safety devices, such as Buchholz relay, pressure relief valve, and temperature monitoring instruments.
      • Providing a conservator for oil expansion and contraction.
    • Testing and inspection are vital before transformer installation. Initial inspection includes checking the transformer upon receiving it from the factory.

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    Description

    This quiz covers the fundamental concepts of transformers, including unloaded and loaded conditions, short-circuit voltages and currents, as well as the mechanical arrangements used in transformer windings. Test your understanding of these key topics related to transformer operation and construction.

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