ABB RED650 Applications Manual page 287

1MRK 505 393-UEN B
Line differential protection RED650 2.2 IEC
Application manual
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IEC09000013 V2 EN-US
Figure 120: 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.
Scheme communication
UR
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CS
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UR
B
CS
B
TRIP: UR or OR+CR
Section 13
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IEC09000013-2-en.vsd
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