ABB REL650 series, Applications Manual

Page: 399 / 516

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
Figure 191: Principle of blocking scheme
OR: Overreaching
CR: Communication signal received
CS: Communication signal send
Z rev
A
: Reverse zone
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.
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 506 334-UUS A
Section 12
Scheme communication
393
Application manual