Permissive Schemes - ABB REC670 Applications Manual

Section 15
Scheme communication
15.1.2.3
468
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 tSendMin for prolonging the send signal is proposed to set to zero.
DeltaBasedDetection (deltaA)
OR
B
deltaA
IEC11000252 V1 EN-US
Figure 190: Principle of delta blocking scheme
OR: Overreaching
CR: Communication signal received
CS: Communication signal send
deltaA: Delta based fault inception detection on A side that gets inhibited for forward faults

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.
A
CS
1MRK 511 401-UUS A
B
TRIP = OR + tCoord+ CR
B B
IEC11000252-1-en.vsd
M16866-33 v4
Bay control REC670 2.2 ANSI
Application manual