ABB Relion 670 Series Applications Manual page 444

Section 16
Scheme communication
Since the received communication signal is combined with the output from an overreaching
zone, there is less concern about a false signal causing an incorrect trip. Therefore set the
tCoord to zero.
timer
Failure of the communication channel does not affect the selectivity, but delays tripping at one
end(s) for certain fault locations.
OR
B
IEC09000013 V2 EN-US
Figure 225: Principle of Permissive underreaching scheme
UR: Underreaching
OR: Overreaching
CR: Communication signal received
CS: Communication signal send
Permissive overreaching scheme
In a permissive overreaching scheme there is an overreaching zone that issues the send signal.
At the remote end the received signal together with the start of an overreaching zone will give
an instantaneous trip. 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 the tripping at one end at least, for faults anywhere along the protected
circuit.
Teleprotection, operating in permissive overreaching scheme, must consider besides the
general requirement of fast and secure operation also consider requirement on the
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. Communication media that uses metallic paths 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.
The send signal (CS) might be issued in parallel both from an overreaching zone and an
underreaching, independent tripping zone. The CS signal from the overreaching zone must not
be prolonged while the CS signal from zone 1 can be prolonged.
To secure correct operations of current reversal logic in case of parallel lines the send signal CS
shall not be prolonged. Set the
There is no need to delay the trip at receipt of the signal, so set the timer
438
A
UR
B
CS
B
TRIP: UR or OR+CR
tSendMin to zero in this case.
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UR
A
CS
A
B
IEC09000013-2-en.vsd
1MRK 511 401-UEN Rev. K
OR
A
M16866-41 v4
tCoord to zero.
Bay control REC670
Application manual