ABB Relion 670 Series Applications Manual page 443

1MRK 511 401-UEN Rev. K
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 224: Principle of delta blocking scheme
OR:
CR:
CS:
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.
The underreaching zones at the local and remote end(s) must overlap in reach to prevent a gap
between the protection zones where faults would not be detected. If the underreaching zone
do not meet the required sensitivity due to for instance fault infeed from the remote end, a
blocking or permissive overreaching scheme should be considered.
The received signal (CR) must be received when the overreaching zone is activated to achieve
an instantaneous trip. In some cases, due to the fault current distribution, the overreaching
zone can operate only after the fault has been cleared at the terminal nearest to the fault.
There is a certain risk that in case of a trip from an independent tripping zone, the zone issuing
the send signal (CS) resets before the overreaching zone has started at the remote terminal.
To assure a sufficient duration of the received signal (CR), the send signal (CS) can be
prolonged by a
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
tSendMin reset timer. The recommended setting of tSendMin is 100 ms.
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Scheme communication
B
TRIP = OR + tCoord+ CR
B B
IEC11000252-1-en.vsd
Section 16
M16866-33 v4
M16866-53 v4
437