ABB REL650 series, Applications Manual

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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.
12.1.2.3 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 intertrip scheme, the send signal is initiated by an underreaching zone or from an
external protection (transformer or reactor protection). At remote end, the received signals
initiate a trip without any further protection criteria. To limit the risk for unwanted trip due
to spurious sending of signals, the timer
tCoord should be set to 10-30 ms dependant on
type of communication channel.
12.1.3 Setting guidelines
The parameters for the scheme communication logic function are set via the local HMI or
PCM600.
Configure the zones used for the CS send and for scheme communication tripping by
using the ACT configuration tool.
The recommended settings of tCoord timer are based on maximal recommended
transmission time for analogue channels according to IEC 60834-1. It is recommended to
coordinate the proposed settings with actual performance for the teleprotection equipment
to get optimized settings.
12.1.3.1 Blocking scheme
Set
Operation
=
Enabled
Set
SchemeType
=
Blocking
Set
tCoord
25 ms (10 ms + maximal transmission time)
Table continues on next page
1MRK 506 334-UUS A
Section 12
Scheme communication
397
Application manual