Why do we use only Sinusoidal Wave in AC supply why not the Square,Triangle or Sawtoo

Discussion in 'General Electronics Chat' started by 3thuram, Apr 1, 2009.

  1. 3thuram

    Thread Starter New Member

    Apr 1, 2009
    Why do we use only Sinusoidal Wave in AC supply why not the Square,Triangle or Sawtooth etc
  2. leftyretro

    Active Member

    Nov 25, 2008
    Because AC generators generate sine wave outputs.
  3. Ratch

    New Member

    Mar 20, 2007

    It has special properties, one of which is the following. No other periodic wave will pass through a linear network containing energy storage elements, (capacitors and inductors) and leave with the same frequency and shape except for phase and amplitude changes. All those other waves you mentioned will not have the same output shape as the input shape. That is because the derivative and integral of a sinusoidal wave are the same except for phase differences.

  4. mik3

    Senior Member

    Feb 4, 2008
    I agree with Ratch and find it quite interesting why this happens. The think with derivatives is just mathematics. Does anyone knows a more physical reason?
  5. kubeek


    Sep 20, 2005
    The more physical reason (and historical too), as leftyretro already said, is the mechanical AC generator. Because it always provided sinus voltage, and it always will (try making a mechanical swatooth-voltage power generator with reasonable efficiency:)), we will always have the AC power in form of sinus waves.

    Sinus also happens to be the most natural periodic function, as it is in many things from simple weight-on-spring which oscillates in sinus rythm.
  6. mik3

    Senior Member

    Feb 4, 2008
    Yes but this is a coincidence with the properties of sine waves Ratch said.
  7. Nanophotonics

    Active Member

    Apr 2, 2009
    We can say that a sinusoidal waveform is rather analog (continuous) and not discrete (in steps).
    It also depends on the types of application you might want to use the signal as the other waveforms might cause undesirable distortions. In some applications, you might find the distortion desirable, for example, in non-linear applications of operational amplifiers, the comparator or Schmitt trigger give a distorted (non-linear) output waveform, yet it is desirable in this case.
    Non-sinusoidal waveforms also contain harmonics which need to be filtered most of the time, otherwise, it might lead to noise and affect circuit performance.

  8. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    And imagine the system losses (wasted energy) that would be encountered ....
  9. donatosd


    Mar 31, 2009
    I agree.. it all comes down from the mathematics. Only phase and amplitude changes will occur. Signal integrity will remain intact.
  10. Wendy


    Mar 24, 2008
    Not to mention rotating mechanics involves rotating wheels, which is the root of a sine wave. Any time a wheel is rotating there is a sine function present.
  11. steveb

    Senior Member

    Jul 3, 2008
    I think the mathematic argument is more compelling than the practical explanation with motors. Motors do produce nearly sinusoidal output, but they also have significant harmonic distortion. Much work has gone into reducing harmonic distortion in motors. As far as lab equipment, the same can be said. It takes good design work to reduce harmonic distortion. Hewlett and Packard were launched with their novel idea to generate ultra-pure RF sine waves.
  12. Nanophotonics

    Active Member

    Apr 2, 2009
    Strictly speaking, every signal is analog, only the time they take to change from one value to another is different. Even a square wave, if you view it on a very very small time period, the change is analog over time, but it does it so fast, that you can consider it as an instantaneous change from a certain value to another. No discrete waveform is absolutely perfect in that sense, but you virtually consider it discrete over infinite accuracy.
  13. SgtWookie


    Jul 17, 2007
    A pure sine wave consists of only the fundamental frequency.
    Both triangle waves and square waves consist of the fundamental frequency and odd harmonics.
    Sawtooth waves consist of the fundamental frequency and both odd/even harmonics.

    Power transformers are optimized for the fundamental frequency of the waveform; 50Hz or 60Hz, depending upon where you live. They would filter out the higher harmonics.

    Wikipedia has some good animated gif images that show the effects of adding in the various harmonics to the fundamental frequency to produce the various waveforms.
  14. m4yh3m

    AAC Fanatic!

    Apr 28, 2004

    is why we typically use Sine waves in AC power. No additional equipment is needed to "modify" it to a sine shape; unlike the square, triangle, and sawtooth -- which need additional processing to generate their signature shapes. As designed by nature, nothing exists that generates a square, triangle, or sawtooth design. Cost is also reason why we keep the Sine wave. It's been perfect for decades. Imagine trying to redesign electronics for use with triangle waves. I won't, but you can feel free to :)
  15. studiot

    AAC Fanatic!

    Nov 9, 2007
    The original question is actually very reasonable, but Mik did ask for a physical justification as well, which has yet to be provided.

    It has already been pointed out that early generators could only generate sine waves as shaped windings were not available.

    Remember, however that the earliest generators were DC. This of course is generated as a sine wave with alternate half cycles inverted.

    Remember also that reactive elements respond to rate of change of current or voltage.

    For a square wave the rate of change is zero most of the time.

    For a sine wave there are only two points on the wave that have zero rate of change. For all the rest of the cycle some 'driving force' is available

    This is the physical basis why square waves are not used for power transmission.

    However exactly this characteristic is good for signal transmission.

    Ramp waveforms have unequal half cycles, which leads to magnetisation of inductive components. So these are only used for special purposes, eg flyback.

    Triangular waveforms have some advantages over sine waves, but their extra generating difficulty easily outweighs these.
  16. steveb

    Senior Member

    Jul 3, 2008
    Can we interpret your answer to mean that the physical explanation, at least for power generation and transmission, is that the sine wave is the most energy efficient?
  17. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    It can also be shown (though I've misplaced the rigorus proof I once had....if anyone has this, please post!) that for a given peak voltage the sine wave has the most possible energy content (for a bandwidth limited system).

  18. studiot

    AAC Fanatic!

    Nov 9, 2007
    Well yes and no.

    Yes for application to linear circuits. For example the RMS of a triangular wave is Vmax/√3, not Vmax/√2 as with a sine wave.

    Not necessarily for non linear elements such as transistors where operation in the linear region is less efficient than switched rapidly into full saturation, due to resistive dissapation. For example static invertors are usually square wave driven.

    It also depends upon what you mean by the most efficient, which is limited by the maximum power transfer theorem.
    We do however often arange for circuit impedance to favour certain parts of the circuit. For example to get as near to 100% transfer out of our power transformer as possible. We don't care if the power transformer impedance doesn't match the mains very well.

    I'll try to dig out Eric's proof.
  19. studiot

    AAC Fanatic!

    Nov 9, 2007
    I really ought to mention that the RMS voltage for a square wave is Vmax = V so a square wave actually packs more energy in than any other waveform.

    But you also want to get it out again. this is what I assume Steve means by efficiency.