Harmonics

Discussion in 'Homework Help' started by Cerkit, Oct 16, 2012.

  1. Cerkit

    Thread Starter Active Member

    Jan 4, 2009
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    3
    Hi. If possible I would like a more intuitive explanation to how harmonics are generated regarding electrical power. Everywhere I read they just mention non linear loads, distortions or simply that harmonics of the fundamental ie 50Hz exist. To me this does not explain what happens at electron level which generates harmonics. I can visualize the fundamental so basically electrons oscillating back and forth a 50 times a second but how are the harmonics generated?

    Thanks.
     
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,962
    1,097
    The harmonic will be generated if load current has shape different from sinusoidal.
    For example exam current shape for a bridge rectifier circuit.
    [​IMG]

    [​IMG]
    V1=10Vp≈7.07sk
    I_V1≈0.177Ask

    And FET harmonics analysis
    [​IMG]
     
  3. Cerkit

    Thread Starter Active Member

    Jan 4, 2009
    275
    3
    Thank you for your response. I guess in many ways this is the same as what I mentioned earlier, I understand the load being non linear ( ie containing various impedance rather than just pure resistive) and this results in a distorted current waveform, how does that result in harmonics? I can't make the connection :/
     
  4. vk6zgo

    Active Member

    Jul 21, 2012
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    Any waveshape other than a pure sinewave (or cosine wave)may be regarded as a sinusoid at the repetition frequency of the waveform,plus a number of sinusoids at multiples of that frequency.

    Every time you put a sinewave through a non-linear circuit such that the waveshape changes,these multiples of the "fundamental" frequency are created.

    There is a classic graphical construction of a square wave from a fundamental & multiple harmonics which appears in most books on the subject.
    You should be able to find it on the Internet.

    Pure impedances do not cause harmonics,devices like rectifiers,saturable reactors & commutators,etc,which have a non-linear "transfer characteristic"are needed to do this.
     
  5. MrChips

    Moderator

    Oct 2, 2009
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    What vk6zgo is trying to tell you, only sine waves have a single frequency.
    Once you distort the sine wave into any other shape, you will generate other frequencies.
     
  6. vk6zgo

    Active Member

    Jul 21, 2012
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  7. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Here is a simple graphic that shows how a fundamental sine wave and its second harmonic, when summed, create second harmonic distortion.
     
  8. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    Switching regulators cause harmonics when they are used with 50Hz transformers. It is usually a mix of frequencies. If you draw some 2 Amps, a large transformer will make a buzzing noise.

    http://www.youtube.com/watch?v=5Q6VJdksp7A

    It is kind of specific noise, depends on the circuit.
     
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