Functions
2.7 Teleprotection for Distance Protection (optional)
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
203
2.7.9
Blocking Scheme
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 or immediately after
occurrence of a fault (jump detector via dotted line in Figure 2-95). 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 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 function scheme is shown in Figure 2-95.
Faults inside the overreaching zone Z1B, which is set to approximately 120% of the line length, will initiate trip-
ping unless a blocking signal is 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 pos-
sible differences in the pickup times 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 2-95
Function diagram of the blocking scheme
