ABB REL650 Applications Manual page 401

1MRK 506 334-UUS A
Application manual
The underreaching zones at local and remote end(s) must overlap in reach to prevent a gap
between the protection zones where faults would not be detected. If the underreaching
zone do not meet required sensitivity due to for instance fault infeed from remote end
blocking or permissive overreaching scheme should be considered.
The received signal (CR) must be received when the overreaching zone is still activated
to achieve an instantaneous trip. In some cases, due to the fault current distribution, the
overreaching zone can operate only after the fault has been cleared at the terminal nearest
to the fault. There is a certain risk that in case of a trip from an independent tripping zone,
the zone issuing the send signal (CS) resets before the overreaching zone has operated at
the remote terminal. To assure a sufficient duration of the received signal (CR), the send
signal (CS), can be prolonged by a tSendMin reset timer. The recommended setting of
tSendMin is 100 ms.
Since the received communication signal is combined with the output from an
overreaching zone, there is less concern about false signal causing an incorrect trip.
Therefore set the timer tCoord to zero.
Failure of the communication channel does not affect the selectivity, but delays tripping
at one end(s) for certain fault locations.
A
OR
B
IEC09000013 V1 EN
Figure 193: Principle of Permissive underreaching scheme
UR: Underreaching
OR: Overreaching
CR: Communication signal received
CS: Communication signal send
Permissive overreaching scheme
In permissive overreaching scheme there is an overreaching zone that issues the send
signal. At remote end the received signal together with activating of an overreaching zone
Scheme communication
UR
A
CS
A
UR
B
CS
B
TRIP: UR, OR+CR
Section 12
OR
A
B
IEC09000013-1-en.vsd
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