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.
A B
OR
B
DeltaBasedDetection (deltaA)
deltaA
CS TRIP
B
= OR
B
+ tCoord+ CR
IEC11000252-1-en.vsd
IEC11000252 V1 EN
Figure 368: 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
16.1.2.3 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.
Permissive underreaching scheme
Permissive underreaching scheme is not suitable to use on short line length due to
difficulties for distance protection measurement in general to distinguish between internal
and external faults in those applications.
Section 16 1MRK 506 369-UUS -
Scheme communication
750 Line distance protection REL670 2.2 ANSI
Application manual
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