ABB Relion 670 Series Applications Manual page 445

1MRK 511 401-UEN Rev. K
OR
B
OR
IEC09000014 V1 EN-US
Figure 226: Principle of Permissive overreaching scheme
OR: Overreaching
CR: Communication signal received
CS: Communication signal send
T2: Timer step 2
Unblocking scheme
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
ms.
16.1.2.4 Intertrip scheme
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.
In an intertrip scheme, the send signal is initiated by an underreaching zone or from an
external protection (transformer or reactor protection). At the remote end, the received
signals initiate a trip without any further protection criteria. To limit the risk for an unwanted
trip due to the spurious sending of signals, the timer
dependant on the type of communication channel.
The general requirement for teleprotection equipment operating in intertripping applications
is that it should be very secure and very dependable, since both inadequate security and
dependability may cause unwanted operation. In some applications the equipment shall be
able to receive while transmitting, and commands may be transmitted over longer time period
than for other teleprotection systems.
Bay control REC670
Application manual
A
CS
A
A
© Copyright 2017 Hitachi Power Grids. All rights reserved
B
TRIP = OR + CR OR + T2
B B B , B
IEC09000014-1-en.vsd
tCoord should be set to 10-30 ms
Section 16
Scheme communication
OR
A
M16866-67 v5
tSecurity to 35
M16866-71 v4
439