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Questions and Answers
What is a primary risk associated with porcelain bushings in transformers?
What is a primary risk associated with porcelain bushings in transformers?
Which factor significantly contributes to the likelihood of transformer failures?
Which factor significantly contributes to the likelihood of transformer failures?
What is a characteristic weakness of porcelain bushings?
What is a characteristic weakness of porcelain bushings?
What maintenance is necessary for porcelain bushings?
What maintenance is necessary for porcelain bushings?
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How do bushings affect the overall reliability of transformers?
How do bushings affect the overall reliability of transformers?
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According to failure statistics, what is the annual failure risk of large power transformers?
According to failure statistics, what is the annual failure risk of large power transformers?
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What is the recommended mounting orientation for porcelain bushings?
What is the recommended mounting orientation for porcelain bushings?
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What type of management strategy can improve transformer reliability?
What type of management strategy can improve transformer reliability?
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What happens to the current in the primary coil when a load is connected to the secondary winding of a transformer?
What happens to the current in the primary coil when a load is connected to the secondary winding of a transformer?
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Which of the following accurately describes the differences between unloaded and loaded transformers?
Which of the following accurately describes the differences between unloaded and loaded transformers?
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What primarily determines short-circuit voltage in a transformer?
What primarily determines short-circuit voltage in a transformer?
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How is short-circuit current defined in relation to the secondary side of a transformer?
How is short-circuit current defined in relation to the secondary side of a transformer?
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What effect do high stray fluxes have on short-circuit voltage?
What effect do high stray fluxes have on short-circuit voltage?
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What may occur as a result of a short-circuit current being significantly higher than the rated current?
What may occur as a result of a short-circuit current being significantly higher than the rated current?
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What characterizes a short-circuit proof transformer?
What characterizes a short-circuit proof transformer?
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In which direction do the currents flow in the primary and secondary windings when the primary current flows right-handed?
In which direction do the currents flow in the primary and secondary windings when the primary current flows right-handed?
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Which type of winding involves a high number of turns with relatively low currents?
Which type of winding involves a high number of turns with relatively low currents?
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What is a primary advantage of using axial spacers in helical windings?
What is a primary advantage of using axial spacers in helical windings?
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Which type of insulation is commonly used with conductors in transformer windings?
Which type of insulation is commonly used with conductors in transformer windings?
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What disadvantage is associated with multi-layer windings?
What disadvantage is associated with multi-layer windings?
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In which winding type is the term 'interleaving' most relevant?
In which winding type is the term 'interleaving' most relevant?
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Which winding configuration generally serves as a regulating winding in transformers?
Which winding configuration generally serves as a regulating winding in transformers?
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What material is NOT commonly used for covering transformer windings?
What material is NOT commonly used for covering transformer windings?
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Which conductor type provides advantages of both cooling and low insulation requirements?
Which conductor type provides advantages of both cooling and low insulation requirements?
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Which characteristic is associated with low voltage main windings in power transformers?
Which characteristic is associated with low voltage main windings in power transformers?
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What type of conductor covering may be used in conjunction with individual paper covering?
What type of conductor covering may be used in conjunction with individual paper covering?
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What is the primary function of the Buchholz protection device in transformers?
What is the primary function of the Buchholz protection device in transformers?
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Which component of the Buchholz protection detects fluid movement?
Which component of the Buchholz protection detects fluid movement?
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What triggers the movement of the piston in the pressure relay of the tap changer oil compartment?
What triggers the movement of the piston in the pressure relay of the tap changer oil compartment?
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What is the purpose of a frangible disk in a transformer?
What is the purpose of a frangible disk in a transformer?
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What does the oil level monitor in a transformer typically include?
What does the oil level monitor in a transformer typically include?
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What is the primary function of the capillary-type top-oil thermometer in transformers?
What is the primary function of the capillary-type top-oil thermometer in transformers?
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How does the oil conservator's incline affect the performance of transformers?
How does the oil conservator's incline affect the performance of transformers?
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Which of the following is NOT a function of the microswitch inside the pressure relay?
Which of the following is NOT a function of the microswitch inside the pressure relay?
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What is the primary function of the tank in a transformer?
What is the primary function of the tank in a transformer?
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Which voltage class predominantly utilizes vacuum drying for transformers?
Which voltage class predominantly utilizes vacuum drying for transformers?
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What ensures that excessive pressure does not cause damage in a transformer tank?
What ensures that excessive pressure does not cause damage in a transformer tank?
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What is the purpose of terminal identifications on the bushings?
What is the purpose of terminal identifications on the bushings?
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During the final assembly of a transformer, what is inspected?
During the final assembly of a transformer, what is inspected?
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What type of insulation is used for primary and secondary terminations?
What type of insulation is used for primary and secondary terminations?
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What is typically the first step in the installation process of a transformer?
What is typically the first step in the installation process of a transformer?
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What feature is included to allow for oil filling, sampling, and draining?
What feature is included to allow for oil filling, sampling, and draining?
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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.
