Hitachi Relion 670 Series Applications Manual page 287

1MRK506375-UEN Rev. N
duration of the received signal (CR), the send signal (CS) can be prolonged by a tSendMin reset
timer. The recommended setting of tSendMin is 100 ms.
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 timer tCoord to
zero.
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 137:
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 tSendMin to zero in this case.
There is no need to delay the trip at receipt of the signal, so set the timer tCoord to zero.
Railway application RER670
Application manual
A
UR
B
CS
B
TRIP: UR or OR+CR
Principle of Permissive underreaching scheme
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UR
A
CS
A
B
IEC09000013-2-en.vsd
Section 13
Scheme communication
OR
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M16866-41 v4
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