voltage level causes a short time delay. For the definite time delay, the setting
tDelay
sets the time delay.
For the voltage dependent time delay the measured voltage level and the settings
UNom
,
UMin
,
Exponent
,
tMax
and
tMin
set the time delay according to figure
and
. The setting
TimerOperation
is used to decide what type of time delay to
apply.
Trip signal issuing requires that the underfrequency condition continues for at least
the user set time delay
tDelay
. If the START condition, with respect to the measured
frequency ceases during this user set delay time, and is not fulfilled again within a user
defined reset time,
tReset
, the START output is reset, after that the defined reset time
has elapsed. Here it should be noted that after leaving the 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.
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
.
10.1.7.3
Voltage dependent time delay
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
. 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
(Equation 135)
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
, for:
Section 10
1MRK502052-UEN B
Frequency protection
546
Technical manual
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