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Homework Help: Alternative Current AC-sinus

  1. Feb 17, 2012 #1
    why we use a sinusoidal voltage source and no others (square, saw waves ...)? :uhh:
  2. jcsd
  3. Feb 17, 2012 #2
    For instance, because of harmonics higher of the fundamental present in sharp waves: this declines effectiveness of powered equipment, increases audio and electrical noise, and introduces huge problems of electromagnetic compatibility.
  4. Feb 17, 2012 #3
    Because that's what gets naturally produced by alternators.
    Also, because that's the best wave to have it transformed between different voltage levels using transformers.
    Also, because that's the best wave for AC motors, which are superior than DC motors.
  5. Feb 17, 2012 #4
    i need more explaination !
  6. Feb 17, 2012 #5
    Other wave shapes are used where appropriate.
    Transformers, capacitors and inductors produce effects that depend on 'rate of change' and sine waves produce cos waves in these cases.... the 'shape' of the wave remains the same.
  7. Feb 17, 2012 #6
    As 'I am learning' pointed out, sine waves are just what you get when you generate electricity via some mechanical means. You could convert them into square waves or triangle waves afterward, but sine waves are what you start out with when you spin an electric motor (generator) using steam or wind or water or whatever to get electricity. A sine wave is just a mathematical description of any smoothly repeating oscillation with respect to time.
  8. Feb 17, 2012 #7
    For detailed explanation you need to study about the working of Transformers. But to put it shortly, as technician pointed out, if you put in sinusoidal wave into transformer, you get sinusoidal wave out. It won't happen for other cases. So, if you need to keep on transforming voltage levels using transformers, and if you need to preserve your wave shape (if you don't want to, then why would you desire for particular wave shape anyway? ), then your best option is to use sinusoidal waves.
    Also, I am in the thought that Transformers would have minimal loss when using sinusoidal waves (because higher order harmonics in other wave shapes will create huge hysteresis and eddy losses? ), and ditto for other electromagnetic machines.
  9. Feb 17, 2012 #8
    thank you all,

    after your explanations, i tried to summarize the advantages of sine as follows:

    - At power generation, the sine shape is naturally generated by alternative motor (synchronous),that more advantageous than DC Motor,

    - in transmission: sine is the most appropriate to vary by a transformer and with less waste and harmony,

    - Distribution: the sine signal are avoided during an abrupt voltage variation (this is not the case for other forms: square ...).

    is that it's just my abstract ??
  10. Feb 17, 2012 #9


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    Pretty close.

    Like said....a generator naturally makes a sin wave.....and a motor naturally excepts a sin wave. So...certainly convenient.

    Transformers love ths sin wave....and being able to raise or lower voltage saves millions and millions of dollars during distribution.

    Those two right there are HUGE.
  11. Feb 17, 2012 #10


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    As a side note. Most power inverters, that is the device that converts 12VDC to 120VAC, in your car do NOT produce a sine wave. That is why some devices have troubles with them.
  12. Feb 17, 2012 #11


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    That may be true....but keep in mind that the alternator in your car produces AC...then goes thru a full wave rectifier to produce DC.....the juice your battery and car devices run off of.

    But if you are saying an inverter does not make a perfect wave from DC to AC...I certainly agree...whether it's a car or not.
  13. Feb 18, 2012 #12
    By using square waveforms over a reactive load (i.e. transformer, RC networks and so on) there are a lot of unwanted effects related to its harmonics, as shown by an analysis of the development of Fourier of such signals, then eddy currents, high extra voltages, lower efficiency. For these reasons all high-quality DC/AC converters have quite robust integrators at their outputs to minimize all signals other than the sine wave, the pure signal.
    Last edited by a moderator: Feb 18, 2012
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