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 (85) 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 (85). Note
that this logic can issue an unwanted three-pole trip at the described
simultaneous faults close to one line end.
16.2.2.1
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.
16.2.2.2
Permissive schemes
SEMOD141790-30 v2
In permissive scheme permission to trip is sent from local end to remote end(s) that is,
protection at local end have detected a fault on the protected object. The received
signal(s) is combined with an overreaching zone and gives an instantaneous trip if the
Section 16
1MRK 504 163-UUS A
Scheme communication
822
Transformer protection RET670 2.2 ANSI
Application manual
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