What are harmonics?
Harmonics are on a power system,
an electrical distribution
system.
Well, harmonics, the way
that we look at these,
they're really just a
multiple of a given frequency.
So, for example, in
the United States,
we talk about 60 hertz as being
our fundamental frequency.
So, the first harmonic of
the fundamental, that's
going to be 60 hertz.
And a second harmonic
would be 2 times 60 hertz.
That would be 120 hertz.
Third harmonic
would be 180 hertz.
And so on, and so on.
And if you're in a
country or an area
with a 50-hertz
power system, this
would just be
translated to 50 hertz.
The first harmonic
would be 50 hertz.
Second harmonic
would be 100 hertz.
And so on, and so on.
And so the math
of what harmonics
are, just a multiple of a
given frequency, that's easy.
But what really are harmonics?
And how do they get
into the power system?
Well, this graph
right here shows
that the top
waveform, that would
be the 60-hertz characteristic.
And then just below it,
I show the fifth harmonic
as being 49 or 49%.
So, if we have 100%
of 60-hertz component,
and 49% of a fifth
harmonic component,
if you go to the waveform
on the very bottom,
those are the two waveforms
superimposed on each other.
And that waveform on the bottom
actually shows the 60 hertz,
but then superimposed on
top of it is the 300 hertz,
or the fifth harmonic waveform.
Almost like a carrier wave.
And so you have a really
heavily distorted waveform.
The next illustration
I want to show you
is the seventh harmonic.
You see the 60-hertz
characteristic up at the top.
And then where I have the
label "Seventh Harmonic,"
that's listed as 49%.
And 49% was just kind
of random on my part.
And down at the bottom,
if you take the 60 hertz
and add it to the
seventh harmonic,
you have some pretty
significant distortion as well.
The waveform on
the bottom actually
shows the seventh harmonic
superimposed on top
of the 60-hertz waveform.
And then this continues.
We could look at, for
example, an 11th harmonic.
And the 11th harmonic, you see
that the 11th harmonic waveform
is also superimposed.
And it continues.
You could have a 13th harmonic.
And it doesn't just have to be
the ones that I'm showing here.
There are other harmonics
that could be out there.
If we have what's called
a six-pulse waveform,
a six-pulse waveform has a
lot of different harmonics
that make it up.
And a six-pulse waveform
is created based
on certain types of loads.
Like certain types of drives,
certain types of rectifiers,
can result in the current,
the actual input current,
looking as if it's pulsed in
six separate pulses instead
of a clean sine wave.
So, this diagram, if you
look down at the bottom,
that is actually a
six-pulse waveform.
And that six-pulse
waveform, that's
what you and I would see.
But the power system
treats this as
if it's individual sine waves
of different frequencies
and different magnitudes,
that, when added together,
result in this
six-pulse wave form.
So, if you begin at the top,
that's the 60-hertz component.
I set that at 100%.
And then the fifth
harmonic is 18%.
And then there's a seventh
harmonic component, 11th
and 13th harmonic.
And you see there is a vertical
line connecting all of these.
And so what happens, if you
go down that vertical line
and you graphically
add the magnitude,
at any point in time,
you'll get the magnitude
of that same point on
the six-pulse waveform.
So, some of you may
remember, or maybe,
through selective amnesia, chose
to forget, Fourier analysis.
That's really what
this is based on.
That you're taking a periodic
or repeating wave form.
And you resolve it into
individual components
of sine waves of
different frequencies
and different magnitudes
that, when added together,
create the waveform that we
have, the six-pulse waveform.
And the way that most harmonics
get into the power system
is the load.
It's a characteristic
of the load.
If you have a load that's
distorting, or pulsing,
or otherwise changing the
characteristic of a current,
that current can be
rich in harmonics.
