Trip signal issuing requires that the underfrequency condition continues for at least the user set
time delay
tDelay
. If the PICKUP 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
PICKUP output is reset, after that the defined reset time has elapsed. Here it should be noted that
after leaving the hysteresis area, the PICKUP 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 (81) 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
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, V, the voltage dependent time delay is calculated according to
equation
199. 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
V VMin
t t MaxTripDelay t MinTripDelay t MinTripDelay
VNom VMin
-
= × - +
-
é ù
ê ú
ë û
EQUATION1559 V1 EN-US (Equation 199)
where:
t is the voltage dependent time delay (at constant voltage),
V is the measured voltage
Exponent is a setting,
VMin, VNom are voltage settings corresponding to
t_MaxTripDelay, t_MinTripDelay are time settings.
The inverse time characteristics are shown in figure 362, for:
VMin = 90%
= 100%
t_MaxTrip
Delay
= 1.0 s
t_MinTrip
Delay
= 0.0 s
Exponent = 0, 1, 2, 3 and 4
Section 10 1MRK 502 066-UUS B
Frequency protection
668
Technical manual
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