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Note: The fastest possible
operation time is limited
according to this figure.
At slope settings less than 0.7 Hz/s, the fastest possible operation
time is limited according to Figure 3.29.
Figure 3.29 – Very sensitive slope settings
Inverse operation time characteristics
By setting the second delay parameter t
operational delay t, an inverse type of operation time characteristics
is achieved (Figure 3.30).
Figure 3.31 shows an example, where the frequency behavior is the
same as in the first figure, but the t
being equal with t. The operation time depends of the measured
average slope according the following equation.
Equation 3.4
⋅
s
t
=
SET
SET
t
TRIP
s
t
=
Resulting operation time (seconds).
TRIP
s
=
df/dt i.e. slope setting (hertz/seconds).
SET
t
=
Operation time setting t (seconds).
SET
s
=
Measured average frequency slope (hertz/seconds).
The minimum operation time is always limited by the setting
parameter t
. In the example of the fastest operation time, 0.15 s,
Min
is achieved when the slope is 2 Hz/s or more. The leftmost curve
in Figure 3.30 shows the inverse characteristics with the same
settings as in Figure 3.31.
Protection Functions
smaller than the
Min
setting is 0.15 s instead of
Min
where,
3-61
857-UM001A-EN-P – July 2009
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