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Sci.Electronics.Basics -> harmonics in power
There are 8 messages in this thread.
You are currently looking at messages 1 to 8.
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i was unable to understand what these harmonics are?
plz help me regarding this
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Author: EeyoreDate: 07:28 27-03-08
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dileepkumarladi@gmail.com wrote:
> i was unable to understand what these harmonics are?
When an electrical circuit does not draw a current from the supply
that's equivalent to a resistive load, the current flow is
non-sinusoidal.
Non-sinusoidal waveforms may be considered as a series of harmonics of
the fundamental frequency (see Fourier).
That's where these harmonics come from.
Graham
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Author: Ian MacmillanDate: 08:48 27-03-08
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"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:47EB84F4.D6EE485A@hotmail.com...
>
>
> dileepkumarladi@gmail.com wrote:
>
> > i was unable to understand what these harmonics are?
>
> When an electrical circuit does not draw a current from the supply
> that's equivalent to a resistive load, the current flow is
> non-sinusoidal.
>
> Non-sinusoidal waveforms may be considered as a series of harmonics of
> the fundamental frequency (see Fourier).
>
> That's where these harmonics come from.
>
> Graham
>
Non-resistive loads such as capacitors by themselves do not create
harmonics.
As any waveform can be synthesised by adding harmonics of various amplitudes
and phases, it follows that anything that causes a waveform to depart from a
perfect sinewave will create harmonics, that is multiples of the fundamental
frequency - 50 or 60 Hz.
A common example is the rectifier with a capacitive input filter, which
draws a pulse from the supply at each voltage peak. If you put a scope on
the mains you can see the blip caused by thousands of TV sets and computers
all charging their filter capacitors together.
All the best
Ian Macmillan
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Author: John FieldsDate: 09:08 27-03-08
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On Thu, 27 Mar 2008 11:28:52 +0000, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:
>
>
>dileepkumarladi@gmail.com wrote:
>
>> i was unable to understand what these harmonics are?
>
>When an electrical circuit does not draw a current from the supply
>that's equivalent to a resistive load, the current flow is
>non-sinusoidal.
---
That's not true, since if the load is linear, but reactive, and the
voltage across it is sinusoidal, the current waveform through the load
will also be sinusoidal. Voltage and current will be out of phase
with each other, but no harmonics will be generated.
---
>Non-sinusoidal waveforms may be considered as a series of harmonics of
>the fundamental frequency (see Fourier).
---
But, if the load is linear, the current and voltage waveforms will be
sinusoidal.
---
>That's where these harmonics come from.
---
Yup.
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On Mar 27, 6:08 am, John Fields <jfie...@austininstruments.com> wrote:
> On Thu, 27 Mar 2008 11:28:52 +0000, Eeyore
>
> <rabbitsfriendsandrelati...@hotmail.com> wrote:
>
> >dileepkumarl...@gmail.com wrote:
>
> >> i was unable to understand what these harmonics are?
>
> >When an electrical circuit does not draw a current from the supply
> >that's equivalent to a resistive load, the current flow is
> >non-sinusoidal.
>
> ---
> That's not true, since if the load is linear, but reactive, and the
> voltage across it is sinusoidal, the current waveform through the load
> will also be sinusoidal. Voltage and current will be out of phase
> with each other, but no harmonics will be generated.
> ---
>
> >Non-sinusoidal waveforms may be considered as a series of harmonics of
> >the fundamental frequency (see Fourier).
>
> ---
> But, if the load is linear, the current and voltage waveforms will be
> sinusoidal.
> ---
>
> >That's where these harmonics come from.
>
> ---
> Yup.
Same story with subharmonics?
Michael
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Author: EeyoreDate: 20:30 27-03-08
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mrdarrett@gmail.com wrote:
> John Fields <jfie...@austininstruments.com> wrote:
> > Eeyore wrote:
> > >dileepkumarl...@gmail.com wrote:
> >
> > >> i was unable to understand what these harmonics are?
> >
> > >When an electrical circuit does not draw a current from the supply
> > >that's equivalent to a resistive load, the current flow is
> > >non-sinusoidal.
> >
> > ---
> > That's not true, since if the load is linear, but reactive, and the
> > voltage across it is sinusoidal, the current waveform through the load
> > will also be sinusoidal. Voltage and current will be out of phase
> > with each other, but no harmonics will be generated.
> > ---
> >
> > >Non-sinusoidal waveforms may be considered as a series of harmonics of
> > >the fundamental frequency (see Fourier).
> >
> > ---
> > But, if the load is linear, the current and voltage waveforms will be
> > sinusoidal.
> > ---
> >
> > >That's where these harmonics come from.
> >
> > ---
> > Yup.
>
> Same story with subharmonics?
I'm not familiar with any in this context.
Graham
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On Mar 27, 5:30 pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:
> mrdarr...@gmail.com wrote:
> > John Fields <jfie...@austininstruments.com> wrote:
> > > Eeyore wrote:
> > > >dileepkumarl...@gmail.com wrote:
>
> > > >> i was unable to understand what these harmonics are?
>
> > > >When an electrical circuit does not draw a current from the supply
> > > >that's equivalent to a resistive load, the current flow is
> > > >non-sinusoidal.
>
> > > ---
> > > That's not true, since if the load is linear, but reactive, and the
> > > voltage across it is sinusoidal, the current waveform through the load
> > > will also be sinusoidal. Voltage and current will be out of phase
> > > with each other, but no harmonics will be generated.
> > > ---
>
> > > >Non-sinusoidal waveforms may be considered as a series of harmonics
of
> > > >the fundamental frequency (see Fourier).
>
> > > ---
> > > But, if the load is linear, the current and voltage waveforms will be
> > > sinusoidal.
> > > ---
>
> > > >That's where these harmonics come from.
>
> > > ---
> > > Yup.
>
> > Same story with subharmonics?
>
> I'm not familiar with any in this context.
>
> Graham
So if I've got a 50 kHz switcher, I don't have to worry about anything
at 25 kHz, or 12.5 kHz?
MD
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Author: whit3rdDate: 21:56 28-03-08
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On Mar 28, 8:18=A0am, mrdarr...@gmail.com wrote:
> So if I've got a 50 kHz switcher, I don't have to worry about anything
> at 25 kHz, or 12.5 kHz?
Worry is definitely called for, because instead of a simple
50 kHz switch, you have a SWITCHING POWER SUPPLY WITH LOAD AND
FEEDBACK. Either modulation of the load, or modulation in
the feedback control, can cause subharmonics.
Most good switching supplies will not generate subharmonics
in the absence of load requirement, but that's because the
switching frequency was chosen to be easy to filter (and lower
frequencies aren't as easy). If your load can be modulated
by an applied signal, the switching supply will cheerfully sing the
aria from Rigoletto...
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