8.1.2.4
Voltage instability mitigation
M13851-59 v3
This setting is very much dependent on the power system characteristics, and thorough
studies have to be made to find the suitable levels.
8.1.2.5
Backup protection for power system faults
M13851-62 v3
The setting must be below the lowest occurring "normal" voltage and above the highest
occurring voltage during the fault conditions under consideration.
8.1.2.6
Settings for two step undervoltage protection
M13851-65 v14
The following settings can be done for Two step undervoltage protection UV2PTUV:
ConnType: Sets whether the measurement shall be phase-to-earth fundamental value, phase-
to-phase fundamental value, phase-to-earth RMS value or phase-to-phase RMS value.
Operation: Off or On.
UBase (given in GlobalBaseSel): Base voltage phase-to-phase in primary kV. This voltage is
used as reference for voltage setting. UV2PTUV will operate if the voltage becomes lower than
the set percentage of
UBase. This setting is used when ConnType is set to PhPh DFT or PhPh
RMS. Therefore, always set UBase as rated primary phase-to-phase voltage of the protected
object. For more information, refer to the
Technical manual.
The setting parameters described below are identical for the two steps (
n = 1 or 2). Therefore,
the setting parameters are described only once.
Characteristicn: This parameter gives the type of time delay to be used. The setting can be
Definite time, Inverse Curve A, Inverse Curve B, Prog. inv. curve. The selection is dependent on
the protection application.
OpModen: This parameter describes how many of the three measured voltages should be
below the set level to give operation for step n. The setting can be
1 out of 3, 2 out of 3 or 3 out
of 3. In most applications, it is sufficient that one phase voltage is low to give operation. If
UV2PTUV shall be insensitive for single phase-to-earth faults,
2 out of 3 can be chosen. In
subtransmission and transmission networks the undervoltage function is mainly a system
supervision function and 3 out of 3 is selected.
Un<: Set operate undervoltage operation value for step n, given as % of the parameter UBase.
The setting is highly dependent on the protection application. It is essential to consider the
minimum voltage at non-faulted situations. Normally, this non-faulted voltage is larger than
90% of the nominal voltage.
tn: time delay of step n, given in s. This setting is dependent on the protection application. In
many applications the protection function shall not directly trip when there is a short circuit or
earth faults in the system. The time delay must be coordinated to the other short circuit
protections.
tResetn: Reset time for step n if definite time delay is used, given in s. The default value is 25
ms.
tnMin: Minimum operation time for inverse time characteristic for step n, given in s. When
using inverse time characteristic for the undervoltage function during very low voltages can
give a short operation time. This might lead to unselective tripping. By setting
t1Min longer
than the operation time for other protections, such unselective tripping can be avoided.
ResetTypeCrvn: This parameter for inverse time characteristic can be set to Instantaneous,
Frozen time, Linearly decreased. The default setting is Instantaneous.
Section 8
1MRK 505 370-UEN D
Voltage protection
208
Busbar protection REB670
Application manual
Summary of Contents for REB670 Series
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