ABB REL670 2.2 IEC, Applications Manual

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on a received CR signal for a fast trip, so its dependability is lower than that of a
blocking scheme.
16.1.2.1 Blocking schemes
M16866-24 v5
In a blocking scheme a reverse looking zone is used to send a block signal to the
remote end to block an overreaching zone.
Since the scheme is sending the blocking signal during conditions where the
protected line is healthy, it is common to use the line itself as communication
media (PLC). The scheme can be used on all line lengths.
The blocking scheme is very dependable because it will operate for faults
anywhere on the protected line if the communication channel is out of service. On
the other hand, it is less secure than permissive schemes because it will trip for
external faults within the reach of the tripping function if the communication
channel is out of service.
Inadequate speed or dependability can cause spurious tripping for external faults.
Inadequate security can cause delayed tripping for internal faults.
To secure that the send signal will arrive before the zone used in the
communication scheme will trip, the trip is released first after the time delay
tCoord has elapsed. The setting of tCoord must be set longer than the maximal
transmission time of the channel. A security margin of at least 10 ms should be
considered.
The timer tSendMin for prolonging the send signal is proposed to set to zero.
A B
OR
B
Z rev
A
Z rev
A
CS
A
TRIP
B
= OR
B
+ tCoord + CR
IEC09000015_2_en.vsd
IEC09000015 V2 EN-US
Figure 365: Principle of blocking scheme
OR: Overreaching
CR: Communication signal received
CS: Communication signal send
Z rev
A
: Reverse zone
Section 16
1MRK 506 369-UEN B
Scheme communication
702 Line distance protection REL670 2.2 IEC
Application manual