ABB RELION RET670, Applications Manual

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The send signal (CS) might be issued in parallel both from an overreaching zone and
an underreaching, independent tripping zone. The CS signal from the overreaching
zone must not be prolonged while the CS signal from zone 1 can be prolonged.
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 385: 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 CR_GUARD, which must always be present,
even when no CR signal is received. The absence of the CR_GUARD 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.
1MRK 504 163-UUS A
Section 16
Scheme communication
Transformer protection RET670 2.2 ANSI 817
Application manual