ABB Relion 670 series, Applications Manual

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L1
L2
L3
Earth
IED IED
L1
L2
L3
Station A Station B
IEC06000309_2_en.vsd
IEC06000309 V2 EN-US
Figure 378: Simultaneous faults on two parallel lines
By using phase-segregated channels for the communication scheme, the correct phase
information in the protection IED near the faults can be transferred to the other side
protection IED. A correct single-pole trip can be achieved on both lines and at both line IEDs.
ZC1PPSCH requires three individual channels between the protection IEDs on each line in both
directions. In case of single-phase faults, only one channel is activated at a time. But in case of
multi-phase faults, two or three channels are activated simultaneously.
The following descriptions of the schemes generally presents one of the three identical
phases.
When only one channel is available in each direction, use the optionally available
three phase communication scheme logic ZCPSCH . Note that this logic can
issue an unwanted three-pole trip at the described simultaneous faults close to
one line end.
15.2.2.1 Blocking scheme
SEMOD141790-25 v1
In blocking scheme a reverse looking zone is used to send a block signal to remote end to
block an overreaching zone. Since the scheme is sending the blocking signal during conditions
where the protected line is healthy, it is common to use the line itself as communication media
(PLC). The scheme can be used on all types of line length.
The blocking scheme is very dependable because it will operate for faults anywhere on the
protected line if the communication channel is out of service. Conversely, it is less secure than
permissive schemes because it will trip for external faults within the reach of the tripping
function if the communication channel is out of service. Inadequate speed or dependability
can cause spurious tripping for external faults. Inadequate security can cause delayed tripping
for internal faults. To secure that the carrier send signal will arrive before the zone used in the
communication scheme will trip, the trip is released first after the time delay
tCoord has
elapsed. The setting of
tCoord must be set longer than the maximum transmission time of the
channel. A security margin of at least 10 ms should be considered.
The timer tSendMin for prolonging the carrier send signal is proposed to set to zero in
blocking schemes.
1MRK 505 343-UEN B Section 15
Scheme communication
607
Application manual