Siemens siprotec 7SA522 - Page 263

Functions
6-1157SA522 Manual
C53000-G1176-C119-2
Sequence Figure 6-66 shows the logic diagram of the directional comparison scheme for one line
end.
The directional comparison only functions for faults in the “forward” direction. Accord-
ingly the over current stage intended for operation in the direction comparison mode
must definitely be set to )RUZDUG (,',5(&7,21); refer also to Sub-section
6.5.2 under the margin heading “Teleprotection with Earth Fault Protection”.
On three terminal lines, the send signal is routed to both opposite line ends. The re-
ceive signals are then combined with a logical
AND gate, as all three line ends must
transmit a send signal during an internal fault. Via the setting parameter /LQH&RQ
ILJ (address ), the device is informed as to whether it has one or two opposite
line ends.
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” (refer to Sub-section 6.6.1.4).
On feeders with only a single-sided infeed or where the star-point is only earthed be-
hind one line end, the line end without zero sequence current cannot generate a per-
missive signal, as fault detection does not take place there. To ensure tripping by the
directional comparison even in this case the device contains a special function. This
“Weak Infeed Function” (echo function) is referred to in Sub-section 6.6.1.5. It is acti-
vated when a signal is received from the opposite line end — in the case of three ter-
minal lines from at least one of the opposite line ends — without the device having de-
tected a fault.
The circuit breaker can also be tripped at the line end with no or only weak infeed. This
“Weak-Infeed Tripping” is referred to in Section 6.7.
Figure 6-66 Logic diagram of the directional comparison scheme (one line end)
Two terminals
EF Telep. off
EF Pickup
&
EF forward

6HQG3URORQJ
T0
&
EF Enable Trip
Three terminals
Two terminals
Three terminals
„1“

/LQH&RQILJ
≥1
&
Trip command
&
Transient blocking
≥1
&
≥1
EF TeleprotOFF
≥1
&
≥1
Echo function
section 6.6.1.5
weak infeed trip
section 6.7
1313
>EF TeleprotBLK
1381
1318
>EF Rec.Ch1
1319
>EF Rec.Ch2
EF Tele SEND
1384