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High Frequency Distortion in Power Grids due
to Electronic Equipment
Anders Larsson
Luleå University of Technology
Outline of the presentation
• Background and motivation of the work
• Waveform distortion
– Low-frequency distortion (harmonics)
– High-frequency distortion
• Results and analysing methods of measurements
– Measurement on fluorescent tube power by a
high frequency ballast
– Measurement on multiple fluorescent lamps
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– Long term measurement at different locations
Background and motivation
of the work
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• New technology has changed our lifestyle, we use more
electronic product in our life than ever
• Electronic equipment is often served by a regulated
power supply
• New technology has made it possible to build more
energy efficient power supplies
• Often are this type of power supplies nonlinear
• This new technology has brought new distortions
phenomena to the power grid
• New measurement technology has made it easier and
cheaper to measure
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Some questions brought up in the beginning of
the project
• What types of signals can be found in this frequency range?
• How do we observe these types of signals?
• What happens when a large number of equipments are connected
together?
• How does these signals propagate in the LV net work?
• Can these signals lead to a barrier to the introduction of other
equipments such as PLC, home care equipments, alarms, audio
equipments etc?
• Can high frequency distortion lead to deterioration of other
equipments?
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Waveform distortion
Low frequency distortion
(harmonics)
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Current drawn by a 100W incandescent lamp
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How do we analyze waveform distortion?
• If the current is not sinusoidal it contains
other frequencies than the fundamental at 50
or 60 Hz
• One way to analyze the signal is to use the
Discreet Fourier Transform (DFT) to transfers
the signal from the time- to the frequencydomain
• There are two reasons to transform the
signal; to quantify the waveform distortion and
to determent the propagation of the signal
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Harmonic content of the current
drawn by the incandescent lamp
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Current drawn by a Computer
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Harmonic content of the Current
drawn by a Computer
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Current drawn by a HFFluorescent Light
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Current drawn by a HFFluorescent Light
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High frequency distortion
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• Almost all new electronic equipments has SMPS that
uses switching technology in the frequency range from
about 20 to 80 kHz
• The product standards covering harmonic set limits up to
about 2 or 3 kHz
• Radio disturbances standards mainly sets limits from
150 kHz and up
• High frequency distortion is in this case
defined from 2 kHz up to about 1 MHz
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Sources
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Switch Mode Power Supplies
HF-ballasts
Active Power Factor Correction
Power Line Communications
Other loads containing power electronics
e.g. converters, dimmers etc.
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Fluorescent lamps powered
by high frequency ballast
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Annex B in IEC 61000-4-7
Gb 
b 100Hz
C
b 90Hz
2
f
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Spectrogram of the filtered voltage in the range between 2 and 150 kHz with 0.5 ms time resolution, 50%
overlap and 1kHz frequency separation.
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Multiple lamps
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• Some examples of
measurement at different
locations
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Some conclusion
• The lamp adds extra high frequency components
• The high frequency components are often synchronized with the
fundamental frequency
• One lamp generate high frequency notches which repeats
synchronized with the power system frequency
• Published papers describing “zero-crossing distortion” generated
by the APFC circuit reminds of “high frequency notches”
• High frequency notches increases with the number of lamps but
the increase seems not to be linear. The STFT shows that these
signals is found in the lower frequency range
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• The DFT gives some information about the content of high
frequency distortion but the time-domain information is “lost”
• The STFT seems like a suitable analysing method but in this case
when many of the high frequency components are synchronized
with the fundamental it is impossible to get an good frequency
resolution in the lower frequency range
• There are large deviations between different locations and quite
surprisingly the highest amplitudes were found at the resident
• There is an change of in amplitude of the high frequency distortion
over time. Some frequencies seems to be attenuated by loads
coming on while other frequencies is generated by the loads
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Thanks for your attention
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