Permanent Magnetic Generators in Gas Turbine Engines
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Questions and Answers

What is the advantage of permanent magnetic generators over brushed generators?

  • They do not require power to be supplied to the field
  • They are more efficient at high altitudes
  • They have a longer lifespan due to fewer moving parts
  • All of the above (correct)

    • How can permanent magnetic generators operate?

  • Neither voltage mode nor current mode
  • In both voltage mode and current mode (correct)
  • Only in voltage mode (open circuit)
  • Only in current mode (closed circuit)

    • What are the crucial components that permanent magnetic generators provide power to?

  • Ignition exciter and FADECs (correct)
  • Fuel pumps and hydraulic systems
  • Landing gear and braking systems
  • Environmental control systems and avionics

    • What type of alternators are used in large jet-powered aircraft?

    <p>Brushless alternators</p> Signup and view all the answers

    How does a brushless alternator induce current into the field coil?

    <p>Through an exciter</p> Signup and view all the answers

    What are the three separate fields in a brushless alternator?

    <p>Permanent magnetic field, exciter field, and main output field</p> Signup and view all the answers

    Which phase has a maximum voltage induced in the right-hand schematic?

    <p>Phase B</p> Signup and view all the answers

    What does a 90° rotation of the rotor correspond to in the right-hand schematic?

    <p>One quarter of a cycle</p> Signup and view all the answers

    How are the voltages induced in phase A and phase B related in the waveform picture?

    <p>90° out of phase</p> Signup and view all the answers

    What is the configuration of a two-phase, three-wire alternator?

    <p>Three connections brought out from the stator</p> Signup and view all the answers

    What effect does connecting one end of B1 to one end of A2 have on the output voltages?

    <p>Increases output voltage</p> Signup and view all the answers

    What is the result of adding the instantaneous values of phase A and phase B?

    <p>Voltage C</p> Signup and view all the answers

    What is the phase difference between the voltages induced in any two phases of a three-phase alternator?

    <p>120°</p> Signup and view all the answers

    In a two-phase alternator, what is the output voltage at C in relation to the voltage of either phase A or B?

    <p>1.414 times higher</p> Signup and view all the answers

    Which type of alternator is seldom seen in actual use?

    <p>Two-phase alternator</p> Signup and view all the answers

    What is the advantage of a two-phase alternator over a single-phase alternator?

    <p>Multiple output connections</p> Signup and view all the answers

    How are the voltages generated across each phase of a three-phase alternator represented in a schematic diagram?

    <p>As a single winding</p> Signup and view all the answers

    What is the phase relationship between the voltage waveforms generated across each phase of a three-phase alternator?

    <p>Phase-displaced by 120°</p> Signup and view all the answers

    What type of waveform is commonly associated with alternating current?

    <p>Sine wave</p> Signup and view all the answers

    In which direction does direct current (DC) flow?

    <p>Only in one direction</p> Signup and view all the answers

    What eliminates the need to carry current to a rotating assembly through brushes?

    <p>Permanent magnet</p> Signup and view all the answers

    What type of waveform is a representation of induced EMF for a single coil rotated through a uniform magnetic field?

    <p>Sinusoidal sine wave</p> Signup and view all the answers

    How does an alternating current (AC) flow compared to direct current (DC)?

    <p>First in one direction, then in the opposite direction</p> Signup and view all the answers

    What produces a greater force to drive electrons when cutting lines of flux quickly?

    <p>Conductor moving quickly across the face of the magnetic field</p> Signup and view all the answers

    What is the purpose of a Constant Speed Drive unit in an aircraft?

    <p>To regulate the rotational speed of the AC generator</p> Signup and view all the answers

    What determines the displacement of the axial-piston variable-displacement hydraulic pump in a Constant Speed Drive unit?

    <p>The rotational speed of the AC generator</p> Signup and view all the answers

    In an aircraft, how does a Constant Speed Drive unit help to maintain a uniform frequency between multiple generators?

    <p>By ensuring all generators are driven at the same RPM</p> Signup and view all the answers

    Which term is commonly used for hydraulic transmissions found on gas turbine engines' accessory drives?

    <p>Constant Speed Drive (CSD)</p> Signup and view all the answers

    What type of modern aircraft generator is integrated with a Constant Speed Drive unit into a single unit known as IDG?

    <p>Integrated Drive Generator</p> Signup and view all the answers

    How does an Integrated Drive Generator (IDG) contribute to maintaining a constant AC frequency output in modern jet aircraft?

    <p>By combining the functions of a generator and a CSD into a single unit</p> Signup and view all the answers

    Study Notes

    Permanent Magnetic Generators vs. Brushed Generators

    • Permanent magnetic generators offer higher efficiency due to the absence of brushes, reducing wear and maintenance needs.
    • They operate using permanent magnets which create a magnetic field, allowing for simpler designs than brushed generators.

    Operation of Permanent Magnetic Generators

    • These generators utilize the principle of electromagnetic induction, where movement through a magnetic field generates electricity.
    • Permanent magnets are crucial components, eliminating dependency on external power sources for excitation.

    Power Supply of Permanent Magnetic Generators

    • They primarily power aviation electrical systems, sensors, and control systems in aircraft.
    • Support for auxiliary power units (APUs) and other ancillary equipment ensures continuous operation.

    Alternators in Jet-Powered Aircraft

    • Large jet-powered aircraft typically use brushless alternators, known for reliability and reduced maintenance.
    • Brushless alternators enhance operational safety by eliminating brush wear.

    Inducing Current in Brushless Alternators

    • A brushless alternator induces current using a rotating magnetic field produced by permanent magnets or a rotor.
    • It utilizes a rotating DC generator to produce AC voltage through electromagnetic induction.

    Configuration of Brushless Alternators

    • A brushless alternator has three separate fields arranged to ensure balanced output.
    • The fields include the main rotor field, the exciter field, and the output field.

    Voltage Induction in Right-Hand Schematic

    • Phase A has a maximum voltage induced in the right-hand schematic during specific rotor positions.
    • A 90° rotation of the rotor corresponds to a transition point between maximum and minimum induced voltages.

    Voltage Relationship in Phase A and Phase B

    • In the waveform picture, voltages induced in phase A and phase B are out of phase, representing the sinusoidal nature of AC.
    • The combined output forms a resultant voltage that can be harnessed for electrical systems.

    Configuration of Two-Phase, Three-Wire Alternator

    • This configuration allows the sharing of a common return path, optimizing the wiring and simplifying the circuit design.
    • Connecting B1 to A2 can influence the output voltage balance and phase relationship.

    Results of Adding Phase A and Phase B Instantaneous Values

    • The addition of instantaneous values can produce a resultant voltage that serves various electrical loads effectively.
    • This provides a continuous power supply to multiple aircraft systems.

    Phase Difference in Three-Phase Alternators

    • The phase difference between voltages induced in any two phases of a three-phase alternator is typically 120°.
    • This spacing ensures a balanced load and consistent power delivery.

    Output Voltage of Phase C in Two-Phase Alternator

    • The output voltage at phase C is directly related to the combined outputs of either phase A or B.
    • This configuration assists in maximizing power output.

    Less Common Alternator Types

    • Various alternator designs exist, but certain configurations, such as some two-phase designs, are seldom seen in practical applications.

    Advantages of Two-Phase Over Single-Phase Alternators

    • Two-phase alternators offer improved power delivery and reduced ripple compared to single-phase alternators.
    • Enhanced efficiency translates to better performance in aircraft systems.

    Schematic Representation of Three-Phase Alternator Voltages

    • Voltages across each phase are depicted in a schematic diagram as sine waves, emphasizing their phase relationship.
    • The phase relationship is crucial for synchronized operations and load balancing in generators.

    Waveforms Associated with AC and DC

    • Alternating current (AC) is commonly represented by sinusoidal waveforms.
    • Direct current (DC) flows consistently in one direction, providing stable output for various applications.

    Elimination of Brushes and Current Carrying

    • Designs like brushless alternators eliminate the need for brushes, enhancing longevity and reliability in electrically driven systems.

    Induced EMF Representation

    • The induced EMF for a single coil rotating within a magnetic field is illustrated as a sinusoidal waveform, showcasing varying potential differences.

    Comparison of AC and DC Flow

    • AC current alternates its direction, resulting in periodic changes, while DC flows uniformly in a single direction.
    • This distinction affects their applications in electrical systems.

    Factors Affecting Electromagnetic Force

    • A greater force driving electrons is produced by rapidly cutting through magnetic flux lines, enhancing energy generation efficiency.

    Constant Speed Drive (CSD) Unit Purpose

    • The CSD unit maintains consistent generator speed, achieving reliable electrical output across varying engine speeds.
    • It ensures synchronized performance among multiple power generators.

    Axial-Piston Variable-Displacement Pump Determinants

    • Displacement is determined by the control mechanisms within the pump, regulating hydraulic flow based on operational needs.

    CSD in Aircraft Frequency Management

    • The CSD unit’s design allows for uniform frequency maintenance, ensuring compatibility between engine speeds and electrical demands.
    • This reliability reduces the risk of electrical failure during flight.

    Hydraulic Transmissions in Gas Turbine Engines

    • Hydraulic transmissions found in gas turbine engines' accessory drives are commonly referred to as Constant Speed Drives.

    Integrated Drive Generator (IDG) Specification

    • IDGs combine the generator and CSD into a single, efficient unit known for reliability and consistent output in modern aircraft.

    Contribution of IDG to AC Frequency Control

    • The IDG maintains a steady AC frequency output, ensuring electrical systems function properly without fluctuation, essential for aircraft operations.

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    Description

    Learn about the key features and applications of permanent magnetic generators in gas turbine engines. Explore how PMGs can operate in voltage mode or current mode depending on the conditioning electronics downstream.

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