ABB Relion 670 Series Applications Manual page 415

1MRK 511 401-UUS F
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.
Since the blocking signal is initiated by the delta based detection which is very fast the time delay
tCoord can be set to zero seconds, except in cases where the transmission channel is slow.
The timer
DeltaBasedDetection (deltaA)
IEC11000252 V1 EN-US
Figure 195: Principle of delta blocking scheme
OR:
CR:
CS:
deltaA: Delta based fault inception detection on A side that gets inhibited for forward faults
15.1.2.3 Permissive schemes
In permissive schemes, the permission to trip is sent from the local end to the remote end(s),
when the protection at the local end has detected a fault on the protected object. The received
signal(s) is combined with an overreaching zone and gives an instantaneous trip if the received
signal is present during the time the chosen zone has detected a fault.
Either end may send a permissive (or command) signal to trip to the other end(s), and the
teleprotection equipment needs to be able to receive while transmitting.
A general requirement on permissive schemes is that it shall be fast and secure.
If the sending signal(s) is issued by underreaching or overreaching zone, it is divided into a
permissive underreach or permissive overreach scheme.
Bay control REC670
Application manual
tSendMin for prolonging the send signal is proposed to set to zero.
A
OR
B
CS
deltaA
Overreaching
Communication signal received
Communication signal send
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Scheme communication
B
TRIP = OR + tCoord+ CR
B B
IEC11000252-1-en.vsd
Section 15
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