ABB Relion 670 Series Applications Manual page 226

Section 8
Voltage protection
8.1.2.4 Voltage instability mitigation
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
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
The following settings can be done for Two step undervoltage protection UV2PTUV (27):
ConnType: Sets whether the measurement shall be phase-to-ground fundamental value, phase-to-phase
fundamental value, phase-to-ground RMS value or phase-to-phase RMS value.
Operation: Disabled or Enabled.
VBase (given in GlobalBaseSel): Base voltage phase-to-phase in primary kV. This voltage is used as
reference for voltage setting. UV2PTUV (27) will operate if the voltage becomes lower than the set
percentage of VBase. This setting is used when ConnType is set to PhPh DFT or PhPh RMS. Therefore,
always set VBase 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 (27) shall be
insensitive for single phase-to-ground 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.
Pickupn: Set pickup undervoltage operation value for step n, given as % of the parameter VBase. 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 ground 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.
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1MRK 505 370-UUS Rev. K
M13851-59 v3
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M13851-65 v15
Busbar protection REB670
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