ABB Relion 670 Series Applications Manual page 414

Section 15
Scheme communication
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 194: Principle of blocking scheme
OR:
CR:
CS:
Z rev : Reverse zone
A
15.1.2.2 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
is inhibited by a forward directed distance (or directional current or directional ground fault)
element.
408
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
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tCoord has elapsed. The setting of tCoord must
B
TRIP = OR + tCoord+ CR
B B
IEC09000015_2_en.vsd
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