harmonics in power

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i was unable to understand what these harmonics are?
plz help me regarding this

 

[Eeyore]

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

 

[Ian Macmillan]

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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---
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.

Same story with subharmonics?

Michael

 

[Eeyore]

Same story with subharmonics?

I'm not familiar with any in this context.

Graham

 

[[email protected]]

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

 

[whit3rd]

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...