ABB REC670 Applications Manual page 476

Section 15
Scheme communication
470
A
OR
B
IEC09000013 V2 EN-US
Figure 191: 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.
UR
A
CS
A
UR
B
CS
B
TRIP: UR or OR+CR
1MRK 511 401-UUS A
OR
A
B
IEC09000013-2-en.vsd
M16866-41 v4
Bay control REC670 2.2 ANSI
Application manual