underreaching function is connected to the CSUR input. The duration of the CSUR
input signal can be prolonged by the
Carrier Min Dur
setting to ensure a sufficient
duration of the CS_PRM signal.
In case of parallel feeders, when the external current reversal logic
(RCRWPSCH) is enabled, the CS_PRM signal is not prolonged and the
value of
Carrier Min Dur
is set to zero to secure correct operation.
In the permissive overreach scheme, the received signal CR_PRM or CRL, if
the unblocking function is enabled, is used to allow the overreaching residual
overcurrent function DEFLPDEF to trip (activation of the OPERATE output) after the
settable pick-up delay
Coordination time
. The start signal from the overreaching
zone is connected to the CACC input.
The CS_PRM signal is also generated if the CR_PRM signal is received and the local
carrier acceleration signal CACC is active.
Activating the BLOCK input totally blocks the permissive overreach scheme. The
CS_PRM and OPERATE outputs can be blocked by the BLK_CS_OPR input.
~ ~
DEFH_START
CB_A
CB_B
Z2_START
DEFL_START
TRIP_CB_A
TRIP_CB_B
Bus A
Figure 713: Simplified functional diagram of the permissive overreach scheme
Directional comparison blocking scheme DCB
The directional comparison blocking scheme is enabled with
Scheme type
=
"Blocking".
In the blocking scheme, the START signal from the reverse-looking residual
overcurrent function DEFLPDEF set to operate for the reverse direction earth fault,
is connected to the CSBLK input to create a CS_BLOCKING signal. The starting of
the reverse-looking function indicates that the fault is located outside the protected
feeder. The duration of the CSBLK input signal can be prolonged with the
Carrier Min
Dur
setting to ensure a sufficient duration of the CS_BLOCKING signal.
The blocking scheme is mainly used to allow the forward-looking overreaching
residual overcurrent function to trip (activation of the OPERATE output) after the
1MRS759142 F
Protection related functions
REX640
Technical Manual
1255
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