Environmental Engineering Reference
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generally the case when the ratio of apparent powers S kV / S rA > 500, where S rA is
the rated power of the wind park.
Flicker is the subjective impression from light density variation of incandescent
lamps. The maximum permissible values of voltage variations, their source, are a
function of the frequency of their appearance. The conformity level d =
U / U N is
defined in dependence of their variations per minute. The values most inconvenient
for the human eye are around 1000 changes per minute, corresponding to voltage
variations of 8 ... 10 Hz.
IEC 61000-3 describes the assessment of flicker values and their limitation. De-
fined are a short-time flicker strength P st and a long-term flicker strength P lt , based
on a 10 min and 2 hour time-interval average, respectively. Figure 7.11, taken from
IEC 61000-3-3, shows the curve for P st = 1 for rectangular, equidistant voltage vari-
ations; it corresponds to the limit d =
Δ
Δ
u lim . Variants of the curve apply to other
voltage variation waveforms.
Flicker disturbance factors A st and A lt are connected with the flicker strengths P st
and P lt by the definitions
A lt = ( P lt ) 3
A st = ( P st ) 3 .
;
In practice the P st value can be determined by using empirical equations, using
the flicker impression time t f measuring deviations by means of
F ) 3 , 2 , in s ,
t f = 2 , 3 s
·
(100
·
d
·
where
d is the maximum relative voltage change in % of rated voltage;
Fig. 7.11 Limiting curve of voltage variations per minute
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