ABB Relion 670 Series Technical Reference Manual page 174

Section 5
Differential protection
168
The zero sequence current criterion can be blocked by activating the BLK3I0 input signal.
Low voltage criterion
Low voltage criterion is mainly for detection of the three phase faults occurring on
weak side with pre fault no load condition. The low voltage criterion takes the voltage
phase values, voltage phase-to-phase values and remote startup signals as inputs. The
logic for low voltage criterion is shown below:
V3P (UPhN)
V_Ph-N
V3P (UPhPh)
V_Ph-Ph<
(Recived)
REMSTEP
BLKUV
BLOCK
ANSI09000779 V2 EN
Figure 69: Low voltage criterion logic diagram
Voltage phase value is compared with the pickup value of voltage phase and voltage
phase-to-phase value is compared with the pickup value of voltage phase-to-phase. If
any of the phase voltage and phase-to-phase voltages is below the set voltage levels for
some time duration (tUV) then the low voltage PICKUP signal becomes activated after
receiving the remote startup signal. Low voltage criterion can be blocked by activating
BLKUV input signal.
If there are more than one remote IED, all the startup signals of the remote ends are
logically OR to obtain the REMSTEP signal from the remote side as input.
Low current criterion
The current in each phase is compared to the set current level. If all currents are below
setting PU_37, the STUC output is activated after the set delay tUC.
a
a<b
b
OR
a
a<b
b
OR
1MRK505222-UUS C
tUV
27 PU
AND
t
ANSI09000779-2-en.vsd
Technical reference manual