Siemens siprotec 7SA6, Manual

Page: 337 / 876

Functions
6-147
7SA6 Manual
C53000-G1176-C156-2
In Figure 6-83 the operation scheme is shown.
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 6-83 Operation scheme of the directional blocking method
Sequence Figure 6-84 shows the logic diagram of the blocking scheme for one line end.
The stage to be blocked must be set to
Forward
(
3I0... DIRECTION
); also refer
to Sub-section 6.7.2 under margin heading „Teleprotection with Earth Fault Protec-
tion“.
The occurrence of erroneous signals resulting from transients during clearance of ex-
ternal faults or from direction reversal resulting during the clearance of faults on par-
allel lines, is neutralized by the “Transient Blocking”. It prolongs the blocking signal by
the transient blocking time
TrBlk BlockTime
(address
3210
), if it has been present
for the minimum duration equal to the waiting time
TrBlk Wait Time
(address
3209
).
It lies in the nature of the blocking scheme that earth faults with single sided infeed can
be rapidly cleared without any special measures, as the non feeding end does not gen-
erate a blocking signal.
On three terminal lines, the transmit signal is sent to both opposite line ends. The re-
ceive 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
Line
Config.
(address
3202
) the device is informed as to whether it has one or two op-
posite line ends.
A B
EF/
FD
trip
rec.
&
d
dt
40 ms
T
S
&
≥
1
transm.
(u,i)
3I0 Min
Telep.
(A)
T
V
EF/
FD
trip
rec.
&
d
dt
40 ms
T
S
&
≥
1
transm.
(u,i)
(B)
T
V
E/F.
forwd.
E/F.
forwd.
3I0 Min
Telep.
EF/FD = Pickup by any E/F stage