To secure correct operations of current reversal logic in case of parallel lines the
send signal CS shall not be prolonged. Set the tSendMin to zero in this case.
There is no need to delay the trip at receipt of the signal, so set the timer tCoord to
zero.
A B
OR
A
OR
B
OR
A
CS
A
TRIP
B
= OR
B
+ CR
B ,
OR
B
+ T2
IEC09000014-1-en.vsd
IEC09000014 V1 EN-US
Figure 121: Principle of Permissive overreaching scheme
OR: Overreaching
CR: Communication signal received
CS: Communication signal send
T2: Timer step 2
Unblocking scheme
M16866-67 v5
Metallic communication paths adversely affected by fault generated noise may not
be suitable for conventional permissive schemes that rely on a signal transmitted
during a protected line fault. With power line carrier for example, the
communication signal may be attenuated by the fault, especially when the fault is
close to the line end, thereby disabling the communication channel.
To overcome the lower dependability in permissive schemes, an unblocking
function can be used. Use this function at older, less reliable, power-line carrier
(PLC) communication, where the signal has to be sent through the primary fault.
The unblocking function uses a guard signal CRG, which must always be present,
even when no CR signal is received. The absence of the CRG signal during the
security time is used as a CR signal. This also enables a permissive scheme to
operate when the line fault blocks the signal transmission. Set the tSecurity to 35
ms.
13.1.2.4 Intertrip scheme
M16866-71 v4
In some power system applications, there is a need to trip the remote end breaker
immediately from local protections. This applies for instance when transformers or
reactors are connected to the system without circuit-breakers or for remote tripping
following operation of breaker failure protection.
Section 13 1MRK 505 393-UEN B
Scheme communication
282 Line differential protection RED650 2.2 IEC
Application manual
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