2 Functions
186
7SA522 Manual
C53000-G1176-C155-3
and the attenuation of the transmitted signal at the fault location may be so severe that
reception at the other line cannot necessarily be guaranteed.
The scheme functionality is shown in Figure 2-82.
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 pick up time delays of
the devices at both line ends and due to the signal transmission 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 2-82 Operation scheme of the directional blocking method
Sequence Figure 2-83 shows the logic diagram of the blocking scheme for one line end.
The stage to be blocked must be set to )RUZDUG (,',5(&7,21); refer also
to Subsection 2.7 at the margin heading “Teleprotection with Earth Fault Protection”.
On two terminal lines, the signal transmission may be phase segregated. Send and
receive circuits in this case are built up for each phase. On three terminal lines, the
transmit signal is sent to both opposite line ends. The receive signal is then combined
with a logical OR gate as no blocking signal must be received from any line end during
an internal fault. With the setting parameter /LQH&RQILJ (address ) the
device is informed as to whether it has one or two opposite line ends.
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