ABB Relion 670 Series Technical Reference Manual page 559

1MRK505222-UUS C
9.1.2.3
Technical reference manual
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, V, the voltage dependent time delay is calculated according to equation 147.
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
é - ù
V VMin
(
= ×
t t MaxTripDelay t MinTripDelay _
ê ú
ë û
-
VNom VMin
EQUATION1559 V1 EN
where:
t
V
Exponent
VMin, VNom
t_MaxTripDelay, t_MinTripDelay are time settings.
The inverse time characteristics are shown in figure 281, for:
VMin = 90%
= 100%
t_MaxTrip = 1.0 s
Delay
t_MinTripD = 0.0 s
elay
Exponent = 0, 1, 2, 3 and 4
)
- +
_ t MinTripDelay _
is the voltage dependent time delay (at constant voltage),
is the measured voltage
is a setting,
are voltage settings corresponding to
Section 9
Frequency protection
(Equation 147)
553