ABB Relion 670 Series Applications Manual page 392

Section 14
Scheme communication
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
14.1.2.4 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 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
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.
14.1.3 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
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.
14.1.3.1 Blocking scheme
Set Operation
SchemeType
Set
tCoord
Set
tSendMin
Set
Set Unblock
tSecurity
Set
386
tCoord should be set to 10-30 ms dependant on type of communication
tCoord timer are based on maximal recommended transmission
= Enabled
Blocking
=
25 ms (10 ms + maximal transmission time)
= 0 s
= Disabled
NoRestart if Unblocking scheme with no alarm for loss of guard is
(Set to
to be used.
Restart if Unblocking scheme with alarm for loss of guard is to be
Set to
used)
= 0.035 s
1MRK 511 358-UUS A
tSecurity to 35 ms.
Application manual
M16866-71 v3
IP15021-1 v1
M13869-4 v4
M13869-8 v4