Alternator Construction and Principles
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Questions and Answers

What happens to the terminal voltage of a DC shunt generator when the load increases?

  • The voltage remains constant regardless of load.
  • The terminal voltage increases create a larger inductive reactance.
  • The terminal voltage drops due to armature reaction and resistance. (correct)
  • The terminal voltage rises due to increased load.

    • Which of the following statements correctly explains the effect of the distribution factor on electrical winding?

  • Distributing the winding reduces mechanical strength.
  • Distributing the winding shapes the voltage wave closer to a sinusoidal function. (correct)
  • Distributing the winding increases the overall resistance.
  • Distributing the winding leads to unbalanced voltage throughout the system.

    • What is the consequence of a lower lagging power factor in an electrical circuit?

  • It causes a significant voltage rise in the system.
  • It has no effect on voltage levels in the circuit.
  • It results in an increase in the amount of current flowing.
  • It leads to a higher voltage drop across the circuit. (correct)

    • Before an AC generator can deliver electrical load, which condition must be satisfied?

    <p>It must be brought up to synchronous speed by its prime mover.</p> Signup and view all the answers

    In a pure resistance circuit, how do current and voltage behave?

    <p>They are in phase with each other.</p> Signup and view all the answers

    What occurs to the flux in a DC shunt generator when under load?

    <p>The flux diminishes as a result of armature reaction.</p> Signup and view all the answers

    What is the relationship between current and voltage in a pure reactance circuit?

    <p>The current lags the voltage by 90 degrees.</p> Signup and view all the answers

    How does a lower leading power factor affect voltage in a circuit?

    <p>It leads to a voltage rise.</p> Signup and view all the answers

    What does the pitch factor (Kp) represent in an electrical machine?

    <p>The reduction in electromotive force (emf)</p> Signup and view all the answers

    In concentrated winding, what characterizes the emfs in the coils?

    <p>They are in phase</p> Signup and view all the answers

    How does capacitive load affect circuit current in relation to voltage?

    <p>Current leads voltage</p> Signup and view all the answers

    What is the primary effect of a distributed winding compared to concentrated winding?

    <p>Increased phase difference between emfs</p> Signup and view all the answers

    What does the distribution factor indicate in relation to generated voltage?

    <p>It must be multiplied to find generated voltage</p> Signup and view all the answers

    Which load type corresponds with a unity power factor?

    <p>Resistive load</p> Signup and view all the answers

    What happens to the terminal voltage behavior of alternators in the presence of a capacitive load?

    <p>It will rise</p> Signup and view all the answers

    What factors influence the terminal voltage behavior of alternators?

    <p>The magnitude of the load and actual overall power factor</p> Signup and view all the answers

    What is the primary condition for paralleling an alternator with an infinite bus-bar system?

    <p>The incoming alternator's terminal voltage must match the bus-bar's voltage.</p> Signup and view all the answers

    Which of the following statements about synchronous motors is correct?

    <p>They can develop a starting torque equal to their pull-out torque.</p> Signup and view all the answers

    What defines synchronous speed in an alternator?

    <p>The speed at which the rotating magnetic field rotates.</p> Signup and view all the answers

    What describes full-load torque in an induction motor?

    <p>Torque developed at its rated power output.</p> Signup and view all the answers

    Which of these is NOT a condition for paralleling an incoming alternator?

    <p>The armature winding must span 180 electrical degrees.</p> Signup and view all the answers

    Which method is used for speed control of induction motors?

    <p>Concatenation Method</p> Signup and view all the answers

    What does voltage regulation refer to in the context of alternators?

    <p>The percentage change in terminal voltage from no-load to full-load conditions.</p> Signup and view all the answers

    Which type of winding creates a rotating field at synchronous speed in synchronous motors?

    <p>Whole-coiled winding</p> Signup and view all the answers

    What is the purpose of slip in an induction motor?

    <p>To indicate the difference between actual rotor speed and synchronous speed.</p> Signup and view all the answers

    What is the primary principle behind an induction motor's operation?

    <p>Magnetic induction and Lenz's Law.</p> Signup and view all the answers

    What characterizes the power factor operation in synchronous motors?

    <p>They can operate under a wide range of power factors.</p> Signup and view all the answers

    What must be true about the phase of the incoming alternator voltage during synchronization?

    <p>It must be in phase with the bus-bar's voltage.</p> Signup and view all the answers

    Which of the following statements accurately describes dynamic braking?

    <p>It involves disconnecting the AC source quickly.</p> Signup and view all the answers

    Which method of starting involves interchanging two stator leads?

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

    What is the purpose of slip rings in a wound-rotor induction motor?

    <p>To provide an electrical connection to the rotor windings.</p> Signup and view all the answers

    What characterizes a squirrel-cage rotor?

    <p>It consists of bars short-circuited at both ends.</p> Signup and view all the answers

    What is the primary characteristic of a synchronous motor in terms of speed?

    <p>Runs at synchronous speed, which is constant</p> Signup and view all the answers

    Which type of rotor is typically used in lower-speed applications?

    <p>Salient Pole Rotor</p> Signup and view all the answers

    Why is a synchronous motor described as 'not self-starting'?

    <p>It needs to synchronize with the supply after reaching synchronous speed</p> Signup and view all the answers

    What is the function of the d.c. source in a synchronous motor once the rotor reaches synchronous speed?

    <p>It creates poles that attract the stator poles</p> Signup and view all the answers

    What kind of applications are synchronous motors preferred for?

    <p>Driving high-power loads at low speeds</p> Signup and view all the answers

    What determines the synchronous speed of a motor?

    <p>The frequency of the AC power supply and the number of poles</p> Signup and view all the answers

    Which rotor construction is made by forcing molten conducting material into slots?

    <p>Squirrel Cage Rotor</p> Signup and view all the answers

    What type of rotor is primarily used for speed control or high starting torque needs?

    <p>Wound Rotor</p> Signup and view all the answers

    What is the synchronous speed in an induction motor primarily determined by?

    <p>Supply frequency and number of poles in stator winding</p> Signup and view all the answers

    During the plugging period in an induction motor, what happens to the motor speed?

    <p>The speed decreases as it works against the load</p> Signup and view all the answers

    What is the primary purpose of a transformer?

    <p>To transform electric power from one circuit to another at the same frequency</p> Signup and view all the answers

    What effect does applying reverse torque to an induction motor have?

    <p>It decreases the motor's speed</p> Signup and view all the answers

    What components are essential in the construction of a transformer?

    <p>Two coils with mutual inductance and a laminated steel core</p> Signup and view all the answers

    How does a transformer adjust voltage?

    <p>By using the turns ratio of its coils</p> Signup and view all the answers

    What characteristic about electricity in power lines makes transformers necessary?

    <p>It can exceed 300,000 volts, which is too high for direct use</p> Signup and view all the answers

    What is a wound-rotor motor distinguished by?

    <p>The rotor has insulated windings connected to slip rings</p> Signup and view all the answers

    Study Notes

    Alternators

    • Alternators are primary energy sources
    • Operate on electromagnetic induction principles
    • Constant speed operation is crucial
    • Rotor windings generate a magnetic field
    • Stator windings receive induced voltage

    Alternator Construction

    • Rotor: Large electromagnet with field windings, supplied with DC through slip rings
    • Stator: Laminated steel with slots for armature windings.
    • Slip rings: Metal rings for DC connection to the field windings
    • Brushes: Graphite brushes on slip rings to deliver DC current

    Advantages of Stationary Armature

    • Bracing is easier (high centrifugal forces)
    • Insulation is simpler (higher voltages)
    • Voltage output is easier (no brush drop)
    • Field exciter (low voltage, safely transferred)

    Armature Windings

    • Symmetrically distributed in slots (3-phase)
    • Identical windings, spaced 120 electrical degrees apart
    • Full-pitch or fractional-pitch coils, affecting voltage waveform
    • Half-coiled: Twice as many turns, half as many coils (same phase voltage)
    • Whole-coiled: Half as many turns, twice as many coils(same phase voltage)

    Frequency of Alternators

    • Frequency is directly related to rotational speed
    • Synchronous generators synchronize frequency with rotational speed

    Losses in Alternators

    • Rotational: Friction, windage, ventilation, hysteresis, eddy currents
    • Electrical: Field winding, armature winding, brush contact
    • Stray losses: Eddy currents (armature copper conductors)

    Load and Power Factor

    • Load changes affect voltage regulation (drop or rise)
    • Lagging power factor: Greater voltage drop
    • Leading power factor: Greater voltage rise

    Additional Topics

    • Salient pole rotors: Used for low-speed machines with many poles
    • Non-salient pole (Cylindrical) rotors: Used for high-speed machines (turbine generators)

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    Description

    This quiz covers the fundamental principles and construction of alternators, including their operation based on electromagnetic induction. Explore the components like rotors, stators, and understand the advantages of stationary armatures. Test your knowledge on armature windings and their configurations.

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