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Re: A Practical Problem in E&M



Hi Raymond-
The question was, what was the mechanism that was causing
the fuses to blow?
When you write:"it isn't so much the harmonics", I think that
you are missing the change in the frequency content of the clipped
waveform (idealize it as a square wave) and the original sinusoidal
waveform. The square wave may be thought of as a Fourier synthesis
of the original sinusoid and an infinite set of harmonics. It is the
harmonics that blow the fuse, because the transformer iron core makes
the inductive reactance decrease at high frequencies.
The "clipped waveform" is roughly a square wave". If it contains "high
voltage spikes", then it hasn't been clipped. Again, it's the harmonics
that make up the square wave. Your transistor radio experiment, for which
I thank you, demonstrates the the harmonics are non-neglible even at
radio frequencies. There are no "transients", in the strict sense of the
word, because we are dealing with a steady-state situation.
Regards,
Jack
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Jack: As I understand it the cause of fuse and power supply problems
with SCR/Triac dimmers (cheap ones such as household dimmers) is
extremely fast, high voltage spikes created by the clipped waveform.
It isn't so much the harmonics but that the resultant output voltage
is almost a square wave. The fast change from a sinusoidal increase in
voltage to a flat, horizontal slope waveform creates these transients.
Just take a transistor radio and place it next to a household dimmer
that is has been turned to some level between max and zero. The RF
interference is caused by both the square wave harmonics and
especially the transients.
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