ABB RELION RET670 Applications Manual page 193

1MRK 504 163-UUS A
Transformer protection RET670 2.2 ANSI
Application manual
PU 3I0 : Level of high zero sequence current detection given in % of IBase. This
setting should be based on fault calculations to find the zero sequence current in case
of a fault at the point on the protected line giving the smallest fault current to the
protection. The zero sequence current shall be calculated for different types of faults
(single phase-to-groundand phase to phase to ground) at different switching states in
the network.
t3I0: Time delay of zero sequence overcurrent criterion. Default value 0.0 s is
recommended
Setting for low voltage criterion subfunction are described below.
OperationUV: Enabled/Disabled, is set Enabled for detection of faults by means of
low phase-to-ground or phase-to-phase voltage
V_Ph-N: Level of low phase-ground voltage detection, given in % of VBase. This
setting should be based on fault calculations to find the phase-ground voltage decrease
in case of a fault at the most remote point where the differential protection shall be
active. The phase-ground voltages shall be calculated for different types of faults
(single phase-to-ground and phase to phase to ground) at different switching states in
the network. The setting must be higher than the lowest phase-ground voltage during
non-faulted operation.
V_Ph-Ph: Level of low phase-phase voltage detection, given in % of VBase. This
setting should be based on fault calculations to find the phase-phase voltage decrease
in case of a fault at the most remote point where the differential protection shall be
active. The phase-phase voltages shall be calculated for different types of faults (single
phase to ground and phase to phase to ground) at different switching states in the
network. The setting must be higher than the lowest phase-phase voltage during non-
faulted operation.
tUV: Time delay of undervoltage criterion. Default value 0.0 s is recommended
Settings for low current criterion subfunction are described below.
Operation37: Enabled/Disabled, is set Enabled when tripping is preferred at
energizing of the line if differential does not behave correctly.
PU_37: Level of low phase current detection given in % of IBase. This setting shall
detect open line ends and be below normal minimum load.
tUC: Time delay of undercurrent criterion. Default value is recommended to verify that
the line is open.
Section 7
Differential protection
187