harmonics in power

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

Same story with subharmonics?

Michael

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