ABB RELION RET670, Applications Manual

Page: 621 / 1016

10.1.3.5 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.
10.1.3.6 Settings for two step undervoltage protection
M13851-65 v14
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
1MRK 504 163-UUS A
Section 10
Voltage protection
Transformer protection RET670 2.2 ANSI 615
Application manual