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“An Update on Flicker" With
trilingual summary
From the earliest use of electric distribution systems to serve
incandescent lighting, utility customers have been bothered by
"flicker"--the periodic dimming and brightening of electric lamps
caused by fluctuations in system voltage. Typical causes of such
variations are the switching on and off of other loads. Arcing
devices such as welders and furnaces are particularly troublesome.
Both the perception of flicker and the annoyance
it may cause are determined largely by the disturbance frequency. A
higher repetition rate tends to increase observer reaction. Many
experimental studies during the 20th century resulted in publication
of graphs (flicker curves) relating the voltage disturbance
rate to the threshold of observer perception--and objection to--the
consequent light variation. Those reactions are subject to wide
variation among individuals.
Most studies involved the simplest form of voltage
disturbance: a rectangular dip in voltage, applied to incandescent
lamps. Since then, the advent of electronic dimmers, fluorescent
lighting with electronic ballasts, and newer technologies such as the
metal halide lamp, have greatly changed the relationship between
voltage fluctuation (which often involves non-rectangular wave
shapes) and the visible effects.
That has led to development of more sophisticated
standards to predict, measure, and evaluate flicker, such as IEC
61000-3. The relationship between voltage and light variations in
those standards was developed for specific incandescent lamps. Also,
only rectangular voltage dips were considered. To account for other
waveforms, and for the duration of individual disturbances, the IEC
has developed shape factor curves to modify the measurement
standards.
To govern the measurement process itself, the IEC
(in standard 61000-4-15) calls for use of an electronic
flickermeter incorporating a mathematical model of the typical
human eye-to-brain response to light
variation. Based on that, the meter produces a numerical index of
flicker severity. The IEC document has now been incorporated into an
IEEE standard (No. 1453). Some commercially available power quality
analyzers now provide that meter capability.
Although use of the flickermeter is considered a
much more scientific approach to evaluation of expected human
response to light fluctuations, the fact remains that no two
individuals will exhibit identical reactions.
From “An
Update on Flicker"
to be published in the
Electrical Apparatus March 2007 issue
. Visit our online webstore to
order
copies. © 2007
Barks Publications, Inc. All Rights Reserved.
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