Importance of Frequency Control in AC Power Systems
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Questions and Answers

What determines the frequency in an AC power system?

  • The operation of consumer appliances
  • The balance between generation and demand (correct)
  • The type of transformers and induction motors used
  • The amount of renewable energy sources used
  • Why would large frequency drops be damaging to transformers and induction motors?

  • Due to the high reactive power supplied by the generators
  • Due to the low magnetizing currents required for maintaining the flux
  • Due to the high magnetizing currents required for maintaining the flux (correct)
  • Due to the low reactive power supplied by the generators
  • What are turbine blades designed to avoid?

  • Excessive heat generation
  • Excessive wear and tear
  • Corrosion due to high frequency
  • Mechanical vibrations at their natural frequencies (correct)
  • Why may a 50 Hz steam turbine not be able to withstand frequency deviations greater than ±2.5 Hz?

    <p>Turbine blades are designed to operate within a narrow frequency band</p> Signup and view all the answers

    What is the operational range for system frequency, according to power quality considerations?

    <p>$49.5 Hz ≤ f(t) ≤ 50$</p> Signup and view all the answers

    Why must system frequency remain within its operational range?

    <p>To prevent damage to transformers and induction motors</p> Signup and view all the answers

    What is the primary purpose of automatic load shedding in the operation of turbo-generators under abnormal system operating conditions concerning frequency?

    <p>To reject just enough loads to lighten the remaining generation system from overload and restore the system frequency close to nominal</p> Signup and view all the answers

    Why does the reduction in frequency cause generator control systems to increase their input power?

    <p>To maintain the generation and demand balance</p> Signup and view all the answers

    Why does a reduction in frequency and an increase in power may result in an increase of the internal temperature of the turbine and generator windings?

    <p>Due to a decrease in cooling and an increase in power demand</p> Signup and view all the answers

    What is the purpose of primary frequency control after an underfrequency event?

    <p>Automatically adjust output of generators equipped with frequency sensors</p> Signup and view all the answers

    What is the purpose of secondary frequency control if the under-frequency event does not correct itself?

    <p>Automatically regulate generation through Automatic Generation Control (AGC)</p> Signup and view all the answers

    What is the maximum operating time of a 60 Hz steam turbine at full load when its frequency drops to 58.8 Hz?

    <p>$90$ minutes</p> Signup and view all the answers

    How do grid operators typically respond if the frequency starts to exceed 60/50 Hertz?

    <p>By reducing output from some generators</p> Signup and view all the answers

    Why are under-frequency events more serious compared to over-frequency events?

    <p>They are often unexpected and involve the loss of a large source of electricity</p> Signup and view all the answers

    What is done when under-frequency events occur?

    <p>Automatic load shedding is activated.</p> Signup and view all the answers

    What increases as a result of a reduction in frequency and an increase in power?

    <p>Internal temperature of the turbine and generator windings.</p> Signup and view all the answers

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