hysteresis area, the START condition must be fulfilled again and it is not sufficient
for the signal to only return back to the hysteresis area.
The total time delay consists of the set value for time delay plus the
minimum operate time of the start function (80-90 ms).
On the RESTORE output of SAPTUF a 100ms pulse is issued, after a time delay
corresponding to the setting of tRestore, when the measured frequency returns to
the level corresponding to the setting RestoreFreq, after an issue of the TRIP
output signal. If tRestore is se to 0.000 s the restore functionality is disabled, and
no output will be given.
10.1.6.3 Voltage dependent time delay
M13354-19 v5
Since the fundamental frequency in a power system is the same all over the system,
except some deviations during power oscillations, another criterion is needed to
decide, where to take actions, based on low frequency. In many applications the
voltage level is very suitable, and in most cases is load shedding preferable in areas
with low voltage. Therefore, a voltage dependent time delay has been introduced,
to make sure that load shedding, or other actions, take place at the right location. At
constant voltage, U, the voltage dependent time delay is calculated according to
equation
53. At non-constant voltage, the actual time delay is integrated in a
similar way as for the inverse time characteristic for the undervoltage and
overvoltage functions.
( )
Exponent
U UMin
t tMax tMin tMin
UNom UMin
-
= × - +
-
é ù
ê ú
ë û
EQUATION1182 V1 EN-US
(Equation 53)
where:
t is the voltage dependent time delay (at constant voltage),
U is the measured voltage
Exponent is a setting,
UMin, UNom are voltage settings corresponding to
tMax, tMin are time settings.
The inverse time characteristics are shown in figure 127, for:
UMin
= 90%
UNom = 100%
tMax = 1.0 s
tMin = 0.0 s
Exponent = 0, 1, 2, 3 and 4
Section 10 1MRK 505 394-UEN A
Frequency protection
270 Line differential protection RED650 2.2 IEC
Technical manual
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