ABB Relion 670 Series Applications Manual page 391

1MRK 511 358-UUS A
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.
At the permissive overreaching scheme, 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, when applied, the
send signal CS shall not be prolonged. So 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 186: 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 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.
Application manual
A
CS
A
A
tSendMin to zero in this case.
B
TRIP = OR + CR OR
B B B ,
IEC09000014-1-en.vsd
Section 14
Scheme communication
tCoord to zero.
OR
A
+ T2
B
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