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2 Functions
2.7.9
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 may be sent directly after fault incep-
tion (jump detector above dotted line in Figure 2-79), and stopped immediately, as
soon as the distance protection detects a fault in the forward direction, alternatively the
signal is only sent when the distance protection detects the fault in the reverse direc-
tion. It is stopped immediately as soon as the distance protection detects a 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 transmitted 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 cannot necessarily be guaranteed.
The scheme functionality is shown in Figure 2-79.
Faults inside the overreaching zone Z1B, which is set to approximately 120% of the
line length, will initiate tripping if a blocking signal is not received from the other line
end. On three terminal lines, Z1B must be set to reliably reach beyond the longer line
section, even if there is an additional infeed via the tee point. Due to possible differ-
ences in the pickup times of the devices at both line ends and due to the signal trans-
mission time delay, the tripping must be somewhat delayed by T
To avoid signal race conditions, a transmit signal can be prolonged by the settable time
T
Figure 2-79
192
once it has been initiated.
S
Function diagram of the blocking scheme
in this case.
V
7SD5 Manual
C53000-G1176-C169-1
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