ABB Relion 670 Series Applications Manual page 388

Section 14
Scheme communication
14.1.2.1 Blocking schemes
In blocking scheme a reverse looking zone is used to send a block signal to 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
be set longer than the maximal transmission time of the channel. A security margin of at least 10
ms should be considered.
The timer
Z rev
A
OR
B
IEC09000015 V2 EN-US
Figure 183: Principle of blocking scheme
OR:
CR:
CS:
Z rev : Reverse zone
A
14.1.2.2 Delta blocking scheme
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 pickup 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
382
tSendMin for prolonging the send signal is proposed to set to zero.
A
CS
Z rev
A
A
Overreaching
Communication signal received
Communication signal send
tCoord has elapsed. The setting of tCoord must
B
TRIP = OR + tCoord+ CR
B B
IEC09000015_2_en.vsd
1MRK 511 358-UUS A
M16866-24 v4
GUID-D699D2D8-6479-4B40-8B09-7B24CA86C24B v1
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