Siemens siprotec 7SA522, User Manual

Page: 269 / 628

Functions
6-121
7SA522 Manual
C53000-G1176-C119-2
The essential condition for an echo is the absence of an earth current (current stage
,R0LQ7HOHSURW
) with the simultaneous reception signal from the teleprotection
scheme logic, as shown in the corresponding logic diagrams (Figure 6-66 or 6-68).
To prevent the generation of an echo signal after the line has been tripped and the
earth current stage
,R0LQ7HOHSURW
has reset, it is not possible to generate an
echo if a fault detection by the earth current stage had already been present (RS flip-
flop in Figure 6-72). In any event, the echo may be blocked at any time via the binary
input „
!()%ON(FKR
“.
If the conditions for an echo signal are met, a short delay
7ULS(FKR'(/$<
is ini-
tially activated. This delay is necessary to avoid transmission of the echo if the protec-
tion at the weak line end has a longer fault detection time during reverse faults or if it
picks up a little later due to unfavourable short-circuit current distribution. If however
the circuit breaker at the non-feeding line end is open, this delay of the echo signal is
not required. The echo delay time may then be bypassed. The circuit breaker switch-
ing state is provided by the central information control functions. (refer to Section
6.17).
The echo impulse is then transmitted (alarm output “
(&+26,*1$/
”), the duration of
which can be set with the parameter
7ULS(;7(16,21
.
After transmission of the echo impulse, the transmission of a new echo is prevented
for at least 20 ms. This prevents from repetition of an echo after the line has been
switched off.
The echo function is not required for the blocking scheme, and is therefore ineffective.
Figure 6-72 Logic diagram of the echo function for the earth fault protection with teleprotection
Note:
The “
(&+26,*1$/
” (F.No. 4246) must be separately assigned to the output relay
that is used for signal transmission, as it is not included in the transmit signal
“EF Tele SEND”.
20 0
T
EF Pickup
&
S
R
Q
from rec. logic
(Fig. 6-66 or 6-68)
EF OFF/BLOCK
I
E
3I
0
,R0LQ7HOHSURW
≥
1
&
>EF BlkEcho
ECHO only
OFF
ECHO and TRIP
„1“
≥
1
≥
1
7LPH'(/$<
0
T
7ULS(;7(16,21
&
Echo release by
the distance prot.
(ref. to Fig. 6-55
&
CB open (3pole)
≥
1
&
S
R
Q
ECHO SIGNAL
1324
ms
4246
)&7:HDN,QIHHG