Unblocking With Z1B - Siemens siprotec 7SA6 User Manual

Functions
6.4.1.6

Unblocking with Z1B

Principle
6-86
The unblocking method uses a permissive release principle. It differs from the
permissive overreach transfer scheme (Sub-section 6.4.1.4) in that tripping is possible
also when no release signal is received from the opposite line end. It is accordingly
mainly used on long lines, if the signal is transmitted via the protected line with power
line carrier (PLC), and the attenuation of the transmitted signals at the fault location
can be so severe that the reception at the other line end cannot be guaranteed in all
cases. Here, a special unblocking logic takes effect.
Figure 6-51 shows the operation scheme.
Two signal frequencies which are keyed by the transmit output of the 7SA6 are
required for the transmission. If the transmission device has a channel monitoring,
then the monitoring frequency f
frequency) f . When the protection recognizes a fault inside the overreaching zone
U
Z1B, it initiates the transmission of the unblock frequency f
state or during a fault outside Z1B, or in the reverse direction, the monitoring frequency
f is transmitted.
0
If the unblock frequency f
signal is routed to the trip logic. Accordingly, it is a prerequisite for fast tripping, that
the fault is recognized inside Z1B in the forward direction at both line ends. The
distance protection is set such that the overreaching zone Z1B reaches beyond the
opposite station (approximately 120 % of line length). On three terminal lines Z1B
must be set to definitely reach beyond the longer line section even when intermediate
infeed via the tee point is present. The first zone is set in accordance with the usual
grading scheme, i.e. approximately 80 % of the line length; on three terminal lines at
least beyond the tee point.
The transmit signal can be prolonged by T
3URORQJ). The extension of the transmit signal is only effective when the protection
has already issued a trip command. This ensures release of the opposite line end even
when the short circuit has been switched off rapidly by the independent zone Z1.
A
Z1B(B)
Z1B
T1B
T
(A)
& S
&
≥1
Z1 or
further
zones
Unblock-
logic
f –
Off frequency (monitoring frequency)
0
f –
Unblock frequency (send frequency)
U
Figure 6-51 Operation scheme of the unblocking method with Z1B
is keyed over to the working frequency f
0
is faultlessly received from the opposite end, a release
U
(settable under address  6HQG
S
Z1(B)
f
U
≥1
transm.
f
0
trip
U
rec.
B
(unblocking
U
. During the quiescent
U
Z1(A)
B
f
U
≥1
transm.
T
f
S
0 &
&
≥1
trip
U
Unblock-
rec.
B
logic
U –
Unblocking signal
B –
Blocking signal
C53000-G1176-C133-1
Z1B(A)
Z1B
T1B
(B)
Z1 or
further
zones
7SA6 Manual