Operation Principle - ABB RELION REX640 Technical Manual

Section 4
Protection functions
4.3.1.5
556
in this document. The configuration can be written to the protection relay once the
mismatch is corrected.

Operation principle

The function can be enabled and disabled with the Operation setting. The
corresponding parameter values are "on" and "off".
The function can also be set into test mode by setting the Operation setting to "test/
blocked".
The operation of the line differential protection and related measurements, stabilized
and instantaneous stages can be described using a module diagram.
I_LOC_A
I_LOC_B
I3P
I_LOC_C
I_REM_A
I_REM_B
I3P (remote)
I_REM_C
BLOCK_LS
ENA_MULT_HS
BLOCK
GUID-616C5AE6-546E-43CB-B2A0-500F0A149470 V2 EN
Figure 302: Functional module diagram. I_LOC_x stands for current of the local
end and I_REM_x for phase currents of the remote ends.
Stabilized low stage
In the stabilized low stage, the higher the load current is, the higher the differential
current required for tripping is. This happens on normal operation or during external
faults. When an internal fault occurs, the currents on both sides of the protected object
flow towards the fault and cause the stabilizing current to be considerably lower. This
makes the operation more sensitive during internal faults. The low stage includes a
timer delay functionality.
The characteristic of the low stage taking the apparent differential current into account
is influenced by various factors:
• Small tapped loads within the protection zone
• Current transformer errors
• Current transformer saturation
• Small asymmetry of the communication channel go and return paths
Inrush
detector
From remote
Stabilized
end
low stage
Differential
calculation
Transformer vector
group matching
Instantane
ous high
Zero-sequence
stage
component elimination
Fail safe
function
1MRS759142 C
OPERATE
START
STR_LS_LOC
Direct
intertrip
OPR_LS_LOC
OPR_HS_LOC
From
STR_LS_REM
remote end
OPR_LS_REM
OPR_HS_REM
BLKD2H_LOC
BLKD2H_REM
PRO_ACTIVE
REX640
Technical Manual