Synchronous Generator Construction
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Questions and Answers

What is the primary function of a synchronous generator?

  • Regulate frequency of the electrical output
  • Convert AC power into mechanical power
  • Store electric energy as mechanical energy
  • Convert mechanical power into AC electric power (correct)

    • What component of the synchronous generator carries the armature winding?

  • Slip rings
  • Rotor
  • Exciter
  • Stator (correct)

    • Which type of rotor construction in alternators projects from its base?

  • Cylindrical rotor
  • Permanent magnet rotor
  • Salient pole rotor (correct)
  • Induction rotor

    • What material is commonly used for the stator core to reduce hysteresis and eddy-current losses?

    <p>High-grade silicon steel</p> Signup and view all the answers

    Which statement is true regarding the armature winding of a synchronous generator?

    <p>The winding of each phase is distributed over several slots.</p> Signup and view all the answers

    Which component supplies the direct current to the rotor field winding in a synchronous generator?

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

    How is the output of a synchronous generator typically taken?

    <p>From the stator</p> Signup and view all the answers

    What does the term 'synchronous speed' refer to in the context of synchronous generators?

    <p>The speed necessary to produce AC power of the desired frequency</p> Signup and view all the answers

    What is the main function of a dynamometer when it acts as a generator?

    <p>It returns some mechanical power back to the electrical supply system.</p> Signup and view all the answers

    How is efficiency calculated in the context of machines acting as motors and generators?

    <p>Efficiency = (Output Power - Absorbed Power) / Output Power</p> Signup and view all the answers

    What is a primary advantage of DC machines in electric vehicles?

    <p>Excellent torque-speed ratios.</p> Signup and view all the answers

    What is one reason for connecting alternators in parallel?

    <p>To ensure continuity of service during maintenance.</p> Signup and view all the answers

    Which condition is NOT necessary for paralleling alternators?

    <p>The terminal voltage must be greater than busbar voltages.</p> Signup and view all the answers

    How do parallel operations of alternators contribute to operational economy?

    <p>They reduce operating costs and energy generation costs.</p> Signup and view all the answers

    Which application is NOT typically associated with DC machines?

    <p>High-voltage transmission lines</p> Signup and view all the answers

    What is the role of testing DC machines?

    <p>To ensure optimal performance and reliability.</p> Signup and view all the answers

    In the context of parallel operation, what is the term for an alternator that is being connected to an existing system?

    <p>Incoming alternator</p> Signup and view all the answers

    Which characteristic makes DC machines favorable for industrial applications?

    <p>Exact speed and torque feedback.</p> Signup and view all the answers

    What is a key benefit of having several alternators operate in parallel?

    <p>Facilitates load growth without disruptions.</p> Signup and view all the answers

    What happens to power supply if an alternator in parallel fails?

    <p>The remaining alternators take over the load.</p> Signup and view all the answers

    What essential information does testing provide about DC machines?

    <p>It helps identify and correct performance issues early.</p> Signup and view all the answers

    What does regenerative braking exploit in machines?

    <p>The conversion of mechanical power back to electrical power.</p> Signup and view all the answers

    Which factor does NOT influence the choice of testing methodologies for machines?

    <p>External market conditions.</p> Signup and view all the answers

    What distinguishes a salient pole rotor from a cylindrical rotor?

    <p>Cylindrical rotors have no physical poles visible.</p> Signup and view all the answers

    What is a characteristic feature of cylindrical rotors compared to salient pole rotors?

    <p>They provide noiseless operation at high speeds.</p> Signup and view all the answers

    Which principle does an alternator operate on?

    <p>Electromagnetic induction.</p> Signup and view all the answers

    What happens to the generated EMF when the rotor field winding is energized?

    <p>It induces an alternating voltage in the armature conductors.</p> Signup and view all the answers

    What is the formula to calculate the frequency of generated EMF in an alternator?

    <p>f = NsP / 60</p> Signup and view all the answers

    For what speed range is the salient pole rotor typically used?

    <p>From 120 to 400 RPM.</p> Signup and view all the answers

    What is one of the main disadvantages of using a salient pole rotor at high speeds?

    <p>Increased windage loss and noise.</p> Signup and view all the answers

    How is efficiency calculated using the direct method?

    <p>Efficiency = 100% × (Output Power / Input Power).</p> Signup and view all the answers

    What type of losses are included in the indirect method of determining efficiency?

    <p>Copper losses, iron losses, and mechanical losses.</p> Signup and view all the answers

    What defines the efficiency of a DC machine?

    <p>The ratio of output power to input power with losses included.</p> Signup and view all the answers

    What characteristic of cylindrical rotors contributes to better dynamic balancing?

    <p>They consist of solid forgings.</p> Signup and view all the answers

    What type of alternators are cylindrical rotors primarily used in?

    <p>High-speed alternators driven by steam turbines.</p> Signup and view all the answers

    What results from the energizing of the rotor field winding in an alternator?

    <p>Alternating magnetic poles are formed.</p> Signup and view all the answers

    Why is a large diameter typical for low speed alternators using salient pole rotors?

    <p>To allow more space for efficient windings.</p> Signup and view all the answers

    In which operation mode are iron losses measured in a DC machine?

    <p>With rated voltage applied and rotor stationary.</p> Signup and view all the answers

    Study Notes

    Synchronous Generator Construction

    • Synchronous generators convert mechanical power into AC electric power using electromagnetic induction.
    • They are also known as alternators or AC generators.
    • Synchronous generators can be single-phase or poly-phase (usually 3-phase).

    Stator Construction

    • The stator is the stationary part of the alternator.
    • It contains the armature winding where voltage is generated.
    • The stator frame is made of cast iron for small machines and welded steel for larger machines.
    • The stator core is made of laminated high-grade silicon steel to reduce hysteresis and eddy-current losses.
    • Slots are cut into the stator core to hold the 3-phase armature winding, which is typically star connected.
    • The armature winding is distributed over several slots to create a sinusoidal space distribution of EMF.

    Rotor Construction

    • The rotor is the rotating part of the alternator.
    • It carries the field winding, which is supplied with direct current through slip rings by a separate DC source (exciter).
    • There are two types of rotor constructions: salient-pole and cylindrical.

    Salient Pole Rotor

    • The rotor has poles projecting out from its surface.
    • Each field pole winding is connected in series with opposite polarities.
    • Used in low and medium speed alternators (120-400 RPM), for example, those driven by diesel engines or water turbines.
    • Advantages: simpler construction, suitable for low speeds, large diameter, short axial length.
    • Disadvantages: weaker mechanical strength, high windage loss, noisy at higher speeds.

    Cylindrical Rotor

    • The rotor is solid and cylindrical, with slots cut into its outer periphery to hold the distributed field windings.
    • The unslotted portion forms the pole faces.
    • Used in high-speed alternators (1500-3000 RPM), for example, those driven by steam turbines.
    • Advantages: greater mechanical strength, more accurate balancing, noiseless operation at high speeds, better EMF waveform.
    • Disadvantages: more complex construction, smaller diameter, longer axial length.

    Working Principle and Operation

    • Alternators operate on the principle of electromagnetic induction: when the flux linking a conductor changes, an EMF is induced.
    • When the rotor's field winding is energized, it creates a rotating magnetic field.
    • As the rotor rotates, the armature conductors on the stator are cut by the magnetic field.
    • This induces an alternating EMF in the armature conductors.
    • The direction of the generated EMF can be determined by Fleming's right-hand rule.
    • The frequency of the generated EMF is determined by the synchronous speed (Ns) and the number of rotor poles (P): f = NsP / 120.
    • The magnitude of the generated voltage depends on the rotor speed and the DC field excitation current.

    Efficiency Determination

    • Efficiency is the ratio of output power to input power, expressed as a percentage.
    • Direct method: Measures input and output power directly.
    • Indirect method: Measures losses separately (copper, iron, mechanical) and calculates efficiency using the principle of conservation of energy.
    • Regenerative method: Uses the dynamometer principle, where the machine acts as a generator and feeds some of the mechanical power back into the electrical system.

    Parallel Operation of Alternators - Synchronization

    • Parallel operation of alternators is crucial for interconnected power systems, providing reliability, economy, and load sharing.

    • Conditions for Synchronization:

      • Identical phase sequence.
      • Voltages in phase.
      • Equal voltage magnitudes.
      • Equal frequencies.

    • Synchronization process: Connecting an incoming alternator to a running alternator or busbar while ensuring these conditions are met.

    • Benefits:

      • Improved reliability.
      • Increased efficiency.
      • Ability to handle larger loads.
      • Load growth management.
      • Economic benefits.

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    Description

    This quiz covers the key components and construction of synchronous generators, also known as alternators. It explores the roles of the stator and rotor in converting mechanical power into AC electric power. Dive into the materials and design aspects that contribute to their efficiency and functionality.

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