Voltage and Current Distortion Quiz
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Questions and Answers

What are the most common sources of harmonics?

  • Ground fault circuit interrupters (GFCIs) and circuit breakers
  • Instrument and relay transformers
  • Lightning and voltage sags
  • Power electronic loads such as adjustable speed drives (ASDs) and switching power supplies (correct)
  • What is the effect of harmonics on instrument and relay transformer accuracy?

  • Affects accuracy (correct)
  • Increases efficiency
  • No effect
  • Improves accuracy
  • What type of loads use diodes, silicon controlled rectifiers (SCRs), power transistors, and other electronic switches?

  • Linear loads
  • Electronic loads (correct)
  • Non-linear loads
  • Electrical loads
  • What is the consequence of harmonic voltages and currents on ground fault circuit interrupters (GFCIs)?

    <p>Causes false tripping</p> Signup and view all the answers

    What is the nature of harmonics?

    <p>Steady-state, periodic phenomena</p> Signup and view all the answers

    What is the ratio of in Individual Harmonic Distortion (IHD)?

    <p>The ratio of RMS value of individual harmonic to the RMS value of the fundamental component</p> Signup and view all the answers

    What is the Total Harmonic Distortion (THD) calculated up to?

    <p>50th order</p> Signup and view all the answers

    What is the suffix used to denote current distortion parameters?

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

    What is the peak factor of a sinusoidal wave?

    <p>1.41</p> Signup and view all the answers

    Which of the following is NOT a source of harmonic currents and voltages?

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

    Study Notes

    Harmonics in Power Systems

    • Power systems operate at frequencies of 50 or 60Hz, but certain loads produce currents and voltages with frequencies that are integer multiples of the fundamental frequency, known as power system harmonics.

    Sources of Harmonics

    • The most common sources of harmonics are power electronic loads, such as:
      • Adjustable speed drives (ASDs)
      • Switching power supplies
    • Other sources include:
      • Magnetic core equipment (e.g. transformers, electric motors, generators)
      • Conventional equipment (e.g. arc furnaces, arc welders, high-pressure discharge lamps)
      • Electronic and power electronic equipment

    Characteristics of Harmonics

    • Harmonics are steady-state, periodic phenomena that produce continuous distortion of voltage and current waveforms.
    • Harmonics can cause:
      • Malfunction or loss of efficiency in computers, communication equipment, and other power systems
      • False tripping of ground fault circuit interrupters (GFCIs)
      • Nuisance tripping of circuit breakers
      • Instrument and relay transformer accuracy issues

    Quantities Describing Voltage and Current Distortion

    Individual Harmonic Distortion (IHD)

    • The ratio of the RMS value of an individual harmonic to the RMS value of the fundamental component.

    Total Harmonic Distortion (THD)

    • The ratio of the RMS value of the sum of all harmonic components to the RMS value of the fundamental component.
    • Often limited to 50 or 25 harmonics, depending on the risk of resonance.

    Peak Factor

    • The ratio of the peak value to the RMS value of a periodic waveform.
    • A value other than 1.41 indicates waveform distortion.

    Crest Factor

    • The ratio of the RMS value to the average value of a waveform.
    • Crest factor indicates waveform distortion.

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    Description

    Test your knowledge of Individual Harmonic Distortion (IHD) and Total Harmonic Distortion (THD) in voltage and current waveforms.

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