Voltage Dependent Time Delay - ABB Relion 670 Series Technical Reference Manual

Section 8
Frequency protection
8.1.1.3
258
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 equation 61. 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 TimeDlyOperate. 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, TimeDlyReset, 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 output of SAPTUF a 100ms pulse is issued, after a time delay
corresponding to the setting of TimeDlyRestore, when the measured frequency
returns to the level corresponding to the setting RestoreFreq.

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 61. 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
U UMin
(
= ×
t tMax tMin
ê ú
ë - û
UNom UMin
EQUATION1182 V1 EN
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 131, for:
)
- +
tMin
1MRK 505 208-UEN B
131
(Equation 61)
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