2.8 Teleprotection for earth fault overcurrent protection (optional)
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7SA522 Manual
C53000-G1176-C155-3
Figure 2-81 Unblock logic
2.8.4 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 may be sent directly after fault incep-
tion (jump detector above dotted line), and stopped immediately, as soon as the dis-
tance protection detects a fault in the forward direction, alternatively the signal is only
sent when the distance protection detects the fault in the reverse direction. 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 transmitted across the protected feeder by means of power line carrier (PLC)
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