Harmonic Distortions
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Harmonic Distortion
Harmonic distortion is a means for measuring nonlinear distortion. Nonlinear distortion is a form of signal processing error that creates signals at frequencies that are not necessarily present in the input.
Consider these facts:
A Concise Report on the Effects of Harmonic Distortion
1. The adverse effects of harmonics on electrical power systems are well known. International standards exist to help manage the injection of harmonic currents into the power system.
2. A pure sine wave consists of a single
fundamental frequency. Most waves are
complex and can be broken down into
a series of harmonics. For instance, the
3rd harmonic of the fundamental
frequency 60 Hz is 180 Hz. The opposite
end of the scale from a pure sine wave
is a square wave, which contains all the
odd harmonics of a fundamental
frequency starting with the 3rd harmonic
and extending to infinity.
3. Harmonic distortion is a measure of
the ratio between the fundamental
and the harmonics that are present in
a waveshape.
4. Distortion is caused by non-linear loads
drawing non-sinusoidal currents.
5. Non-linear loads include such office
equipment as computers (draw 3rd
and 5th harmonics); lighting (ballasts
produce 3rd and 5th), transformers
(3rd component), power converters
(variable speed drives, UPS, electronic
ballasts produce 3rd, 5th, 7th and 11th),
commercial appliances such as photocopiers
and printers.
6. The harmonic currents in a distribution
system have the following undesirable
effects:
a. Significant effects on the performance
of computer power supplies.
b. Heating of magnetic devices, which
can cause premature insulation failure
and breakdown.
c. Triple harmonics produce higher
than expected neutral currents,
potentially resulting in insulation
damage and breakdown due to
temperature rise.
d. High neutral currents cause additional
voltage drops, reducing available
voltage and introducing even
more distortion at the load. The
resulting neutral-to-ground voltage
also causes parasitic ground
currents.
data lines.
h. Stray magnetic fields can introduce
annoying interference patterns in
VDTs.
i. Undesirable ground currents may
cause upstream GFI (Ground Fault
Interrupts)to trip, degrading power
availability.
Computer Loads
Computer power supplies are usually
designed to operate over a range of AC
input voltages. They produce a DC voltage
that is affected by the waveshape of the
AC waveform. Harmonic distortion has the
effect of actually reducing the computer
power supply’s operating voltage. That
variation is compounded by the normal
variation of 10%. The end result is that the
computer supply may malfunction, hiccup,
or fail to provide the required output logic
voltages, resulting in potential bit errors. A
further negative side-effect of effectively
lowering the computer’s operating voltage
range is the reduction of “hold-up” time,
essential for the ability of the power supply
to “ride through” power sags (caused
by other equipments’ startups). The result
is more potential bit errors.
The simple
fact is that the harmonic distortion prevalent
in the modern office has a direct
pathway to your computer power supplies,
and once there it can cause data loss and
other operating errors.
