Advantages of Operating Generators in Parallel
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What is the main advantage of having multiple generators operating in parallel?

  • Reduced reliability of the power system
  • Increased efficiency of individual generators
  • Total power loss to the load in case of failure of one generator
  • Ability to operate at near full load and thus more efficiently (correct)

    • What is the condition required for paralleling generators?

  • The two generators must have the same phase sequence (correct)
  • The rms line currents of the two generators must be equal
  • The frequency of the two generators must be equal
  • The power factors of the two generators must be different

    • What is the purpose of the governor mechanism on a prime mover?

  • To increase the speed of the prime mover with increasing load
  • To make the decrease in speed linear with an increase in power demand (correct)
  • To reduce the power output of the prime mover
  • To increase the voltage output of the prime mover

    • What is the speed droop (SD) of a prime mover defined by?

    <p>The equation: SD = (nnl - nfl) / nfl</p> Signup and view all the answers

    What is the characteristic of a synchronous generator with increasing power demand?

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

    Why is it possible to operate only a fraction of the generators in parallel?

    <p>Because the generators can operate at partial load</p> Signup and view all the answers

    What is the consequence of the failure of one generator in a parallel system?

    <p>No power loss to the load</p> Signup and view all the answers

    What is the advantage of using multiple generators in parallel over a single large generator?

    <p>Ability to supply a bigger load</p> Signup and view all the answers

    What is the typical speed droop of most generator prime movers?

    <p>2 to 4 percent</p> Signup and view all the answers

    What is the relationship between the shaft speed and the resulting electrical frequency?

    <p>They are directly proportional</p> Signup and view all the answers

    What determines the terminal voltage of a synchronous generator when a lagging load is added?

    <p>Field current</p> Signup and view all the answers

    What is the characteristic of an infinite bus power system?

    <p>Its voltage and frequency are constant regardless of the load</p> Signup and view all the answers

    What controls the generator's operating frequency when operating alone?

    <p>Governor set points</p> Signup and view all the answers

    What is the purpose of a governor mechanism in a generator?

    <p>To control the operating frequency</p> Signup and view all the answers

    What is the relationship between the real power and the frequency of a generator?

    <p>They are directly proportional</p> Signup and view all the answers

    What is the advantage of connecting a generator to an infinite bus system?

    <p>It provides a stable voltage and frequency reference</p> Signup and view all the answers

    What is the formula for calculating electrical frequency in a synchronous generator?

    <p>fe = 120/P * nm</p> Signup and view all the answers

    Why are synchronous generators operated in parallel?

    <p>To increase the power output and reliability of the system</p> Signup and view all the answers

    What is the characteristic of a cylindrical-rotor synchronous generator?

    <p>It has a uniform air-gap</p> Signup and view all the answers

    What is the effect of increasing the mechanical speed of rotation of a synchronous generator?

    <p>The electrical frequency increases</p> Signup and view all the answers

    What is the typical rating of a hydrogenerator?

    <p>Up to 2000 MVA</p> Signup and view all the answers

    What is the purpose of a governor mechanism in a synchronous generator?

    <p>To regulate the mechanical speed of rotation</p> Signup and view all the answers

    What is the characteristic of a salient-pole synchronous generator?

    <p>It has a non-uniform air-gap</p> Signup and view all the answers

    What is the effect of increasing the number of poles in a synchronous generator?

    <p>The electrical frequency decreases</p> Signup and view all the answers

    What is the advantage of using a direct-conductor cooling system in a synchronous generator?

    <p>It improves the efficiency of the generator</p> Signup and view all the answers

    What is the term for a system where multiple generators are connected to a common bus?

    <p>Infinite bus system</p> Signup and view all the answers

    Study Notes

    Advantages of Operating Generators in Parallel

    • Several generators can supply a bigger load than one machine by itself.
    • Having many generators increases the reliability of the power system, as the failure of one of them does not cause a total power loss to the load.
    • Having many generators operating in parallel allows one or more of them to be removed for shutdown and preventive maintenance.
    • Operating multiple smaller generators in parallel allows for more efficient operation, as only the required number of generators need to operate near full load.

    Conditions Required for Paralleling

    • The rms line voltages of the two generators must be equal.
    • The two generators must have the same phase sequence.
    • The phase angles of the two a phases must be equal.
    • The frequency of the oncoming generator must be slightly higher than the frequency of the running system.

    Frequency-Power and Voltage-Reactive Power Characteristics of a Synchronous Generator

    • Prime movers tend to behave similarly, with speed decreasing as power drawn from them increases.
    • Governor mechanisms are used to make the decrease in speed linear with an increase in power demand.
    • The speed droop (SD) of a prime mover is defined by the equation SD = (n nl - n fl) / n nl.

    Synchronous Generator Types

    • Salient-pole synchronous generators have a non-uniform air-gap and are typically used for hydroelectric power generation.
    • Cylindrical-rotor synchronous generators have a uniform air-gap and are typically used for turbogeneration.

    Operation Principle

    • The rotor of the generator is driven by a prime-mover.
    • A dc current flowing in the rotor winding produces a rotating magnetic field within the machine.
    • The rotating magnetic field induces a three-phase voltage in the stator winding of the generator.

    Electrical Frequency

    • The electrical frequency produced is locked or synchronized to the mechanical speed of rotation of a synchronous generator: fe = (120 * P) / nm.

    Parallel Operation of AC Generators

    • Synchronous generators are operated in parallel to provide a larger total power output and to improve system reliability.
    • The relationship between frequency and power can be described quantitatively by the equation.
    • The relationship between reactive power Q and terminal voltage VT can be derived similarly.

    Operation of Generators in Parallel with Large Power Systems

    • An infinite bus is a power system so large that its voltage and frequency do not vary regardless of how much real and reactive power is drawn from or supplied to it.
    • The power frequency characteristic of such a system is shown in Figure.
    • When a generator is connected to an infinite bus in parallel, the generator's prime mover and field controls determine the operating frequency and terminal voltage.

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    Related Documents

    SG LEC 1-6 PDF - Synchronous Machine Lectures

    Description

    Discover the benefits of operating multiple generators in parallel, including increased reliability and efficiency. Learn how this setup can improve power supply and maintenance.

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