ABB Relion REC670 Applications Manual page 350

Section 14
Scheme communication
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
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.
OR
B
IEC09000013 V1 EN-US
Figure 172: 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 gives
instantaneous trip of the protected object. The overreaching zone used in the teleprotection
scheme must be activated at the same time as the received signal is present. The scheme can
be used for all line lengths.
In permissive overreaching schemes, the communication channel plays an essential roll to
obtain fast tripping at both ends. Failure of the communication channel may affect the
selectivity and delay tripping at one end at least, for faults anywhere along the protected
circuit.
Teleprotection operating in permissive overreaching scheme must beside the general
requirement of fast and secure operation also consider requirement on dependability.
Inadequate security can cause unwanted tripping for external faults. Inadequate speed or
dependability can cause delayed tripping for internal faults or even unwanted operations.
This scheme may use virtually any communication media that is not adversely affected by
electrical interference from fault generated noise or by electrical phenomena, such as
lightning, that cause faults. Communication media that uses metallic path are particularly
subjected to this type of interference, therefore, they must be properly shielded or otherwise
designed to provide an adequate communication signal during power system faults.
344
tSendMin reset timer. The recommended setting of tSendMin is
A
UR
B
CS
B
TRIP: UR, OR+CR
UR
A
CS
A
B
IEC09000013-1-en.vsd
1MRK 511 358-UEN A
OR
A
M16866-41 v3
Application manual