Environmental Engineering Reference
In-Depth Information
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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