Permissive Schemes - ABB REL650 Applications Manual

Section 12
Scheme communication
12.1.2.2
394
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
Figure 192: 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 scheme permission to trip is sent from local end to remote end(s), that is
protection at local end have 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 is detected a fault in forward direction.
Either end may send a permissive (or command) signal to trip to the other end(s), and the
teleprotection equipment need to be able to receive while transmitting.
A general requirement on permissive schemes is that it shall be fast and secure.
Depending on if the sending signal(s) is issued by underreaching or overreaching zone, it
is divided into 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.
A
CS
1MRK 506 334-UUS A
B
TRIP = OR + tCoord+ CR
B B
IEC11000252-1-en.vsd
Application manual