Siemens siprotec 7SA6 User Manual page 305

Sequence
7SA6 Manual
C53000-G1176-C133-1
Figure 6-72 shows the logic diagram of the directional comparison scheme for one line
end.
The directional comparison only functions for faults in the "forward" direction.
Accordingly the overcurrent 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
receive 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
&RQILJ (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
external faults or from direction reversal resulting during the clearance of faults on
parallel 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 system starpoint is only
earthed behind one line end, the line end without zero sequence current cannot
generate a permissive 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 activated when a signal is received from the opposite line end — in the
case of three terminal lines from at least one of the opposite line ends — without the
device having detected 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.
EF Telep. off
1313 >EF TeleprotBLK
Transient blocking
Trip command
EF forward
&
EF Pickup
"!! GvrÃ8‚svtÃ
1318 >EF Rec.Ch1
1319 >EF Rec.Ch2
„1"
Figure 6-72 Logic diagram of the directional comparison scheme (one line end)
≥1
≥1
&
"!" TrqÃQ…‚y‚tÃ
0 T
&
≥1
Two terminals
≥1
Three terminals
≥1
Two terminals
Three terminals
Functions
1381
EF TeleprotOFF
&
1384
EF Tele SEND
Echo function
&
section 6.6.1.5
&
EF Enable Trip
6-123