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Functions
2.9 Teleprotection for Earth Fault Protection (optional)
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
257
2.9.4 Directional Blocking Scheme
The following scheme is suited for conventional transmission media.
Principle
In the case of the blocking scheme, the transmission channel is used to send a block signal from one line end
to the other. The signal is sent as soon as the protection detects a fault in reverse direction, alternatively also
immediately after fault inception (jump detector via dotted line). It is stopped immediately as soon as the earth
fault protection detects an earth fault in forward direction. Tripping is possible with this scheme even if no signal
is received from the opposite line end. It is therefore mainly used for long lines when the signal must be trans-
mitted across the protected line by means of power line carrier (PLC) and the attenuation of the transmitted
signal at the fault location may be so severe that reception at the other line end cannot necessarily be guaran-
teed.
The scheme functionality is shown in Figure 2-124.
Earth faults in the forward direction cause tripping if a blocking signal is not received from the opposite line end.
Due to possible differences in the pickup times of the devices at both line ends and due to the signal transmis-
sion time delay, the tripping must be somewhat delayed by T
V
in this case.
To avoid signal race conditions, a transmit signal can be prolonged by the settable time T
S
once it has been
initiated.
Figure 2-124 Operation scheme of the directional blocking method
Sequence
Figure 2-125 shows the logic diagram of the blocking scheme for one line end.
The stage to be blocked must be set to Forward ( 3I0... DIRECTION ); refer also to Section 2.8 under margin
heading „Teleprotection with Earth Fault Protection“.
On two terminal lines, the signal transmission may be phase segregated. In this case, send and receive circuits
operate separately for each phase. On three terminal lines, the transmit signals are sent to both opposite line
ends. The receive signals are then combined with a logical OR gate as no blocking signal must be received
from any line end during an internal fault. With the parameter
Line Config. (address 3202 ) the device is
informed as to whether it has one or two opposite line ends.