ABB RELION REX640 - Page 645

4.3.1.5 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.
Inrush
detector
From remote
end
Stabilized
low stage
Instantane
ous high
stage
Fail safe
function
BLOCK
BLOCK_LS
ENA_MULT_HS
OPERATE
START
STR_LS_LOC
STR_LS_REM
OPR_LS_LOC
OPR_LS_REM
OPR_HS_LOC
OPR_HS_REM
BLKD2H_LOC
BLKD2H_REM
PRO_ACTIVE
Direct
intertrip
From
remote end
Differential
calculation
Transformer vector
group matching
Zero-sequence
component elimination
I3P (remote)
I_LOC_A
I3P
I_LOC_B
I_LOC_C
I_REM_A
I_REM_B
I_REM_C
Figure 361: 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
• Small steady state line charging current
• In-zone transformer no load current
• Impact of tap changer positions
1MRS759142 F
Protection functions
REX640
Technical Manual
645