ABB Relion REC670, Applications Manual

Page: 473 / 658

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 189: 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 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.
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.
Inadequate speed or dependability can cause spurious tripping for external faults.
Inadequate security can cause delayed tripping for internal faults.
1MRK 511 401-UUS A
Section 15
Scheme communication
Bay control REC670 2.2 ANSI 467
Application manual