ABB Relion 670 Series Applications Manual page 417

1MRK 511 401-UUS F
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
OR
B
OR
IEC09000014 V1 EN-US
Figure 197: Principle of Permissive overreaching scheme
OR: Overreaching
CR: Communication signal received
CS: Communication signal send
T2: Timer step 2
Unblocking scheme
Metallic communication paths adversely affected by fault generated noise may not be suitable for
conventional permissive schemes that rely on a signal transmitted during a protected line fault.
With power line carrier for example, the communication signal may be attenuated by the fault,
especially when the fault is close to the line end, thereby disabling the communication channel.
To overcome the lower dependability in permissive schemes, an unblocking function can be used.
Use this function at older, less reliable, power-line carrier (PLC) communication, where the signal
Bay control REC670
Application manual
tSendMin to zero in this case.
A
CS
A
A
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tCoord to zero.
B
TRIP = OR + CR OR + T2
B B B , B
IEC09000014-1-en.vsd
Section 15
Scheme communication
OR
A
M16866-67 v5
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