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1MRK 506 369-UEN B
10.1.3.6
Line distance protection REL670 2.2 IEC
Application manual
Settings for two step undervoltage protection
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.
Section 10
Voltage protection
M13851-65 v14
535
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