ABB Relion 670 series, Applications Manual

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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 374: Principle of blocking scheme
OR: Overreaching
CR: Communication signal received
CS: Communication signal send
Z rev
A
: Reverse zone
15.1.2.2 Delta blocking scheme
GUID-D699D2D8-6479-4B40-8B09-7B24CA86C24B v1
In the delta blocking scheme a fault inception detection element using delta based quantities
of voltage and current will send a block signal to the remote end to block an overreaching
zone.
The delta based start is very fast and if the transmission channel is fast then there is no need
for delaying the operation of remote distance element. If the fault is in forward direction, the
sending is inhibited by a forward directed distance (or directional current or directional earth
fault) element.
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. Conversely, 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.
Section 15 1MRK 505 343-UEN B
Scheme communication
600
Application manual