Measures For Weak Or Zero Infeed - Siemens siprotec 7SA522 User Manual

Functions
6.6.1.5

Measures for Weak or Zero Infeed

Echo Function
6-120
case of permissive schemes, this is achieved by blocking of the transmit and receive
circuit.
Figure 6-71 shows the principle of the transient blocking for a directional comparison
and directional unblocking scheme.
If a fault in the reverse direction is detected within the waiting time 7U%ON :DLW 7LPH
(address  ) following fault detection, the transmit circuit and the trip release are
inhibited. This blocking is maintained for the duration of the transient blocking time
7U%ON %ORFN7LPH (address ) also after the reset of the blocking criterion.
In the case of the blocking scheme, the transient blocking prolongs the received block-
ing signal as shown in the logic diagram Figure 6-70.
EF Telep. off
1313 >EF TeleprotBLK
EF Pickup
&
EF forward
Figure 6-71 Transient blocking for a
schemes
On lines where there is only a single sided infeed or where the star-point is only
earthed behind one line end, the line end without zero sequence current cannot gen-
erate a permissive signal, as fault detection does not take place there. With the com-
parison schemes, using a permissive signal, fast tripping could not even be achieved
at the line end with strong infeed without special measures, as the end with weak in-
feed does not transmit a permissive release signal.
To achieve rapid tripping at both line ends under these conditions, the device has a
special supplement for lines with weak zero sequence infeed.
To enable even the line end with the weak infeed to trip, 7SA522 provides a weak in-
feed tripping supplement. As this is a separate protection function with a dedicated trip
command, it is described in a separate section (6.7).
Figure 6-72 shows the method of operation of the echo function. It may be switched in
address  )&7 :HDN ,QIHHG (Weak Infeed MODE) to be activated ((&+2
RQO\) or to be deactivated (2))). By means of this "switch" the weak infeed tripping
function can also be activated ((&+2 DQG 75,3, refer also to Section 6.7). This set-
ting is common to the teleprotection function for the distance protection and for the
earth fault protection.
The received signal at the line end that has no earth current is returned to the other
line end as an "echo" by the echo function. The received echo signal at the other line
end enables the release of the trip command.
The detection of the weak infeed condition and accordingly the requirement for an
echo are combined in a central AND gate. The earth fault protection must neither be
switched off nor blocked, as it would otherwise always produce an echo due to the
missing fault detection.
≥1
"!( U…7yxÃXhv‡ÃUv€r
T
T
"!  U…7yxÃ7y‚pxUv€r
directional comparison and directional unblocking
&
1386
EF TeleTransBlk
transient
blocking
Figure 6-66
or 6-68
7SA522 Manual
C53000-G1176-C119-2