ABB Relion 670 series, Technical Reference Manual

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13.3.2.2 Weak-end infeed logic
The weak-end infeed logic (WEI) function sends back (echoes) the received signal
under the condition that no fault has been detected on the weak-end by different fault
detection elements (distance protection in forward and reverse direction).
The WEI function returns the received signal, see figure 396 , when:
• No active signal present on the input BLOCK.
• The functional input CRL is active. This input is usually connected to the CRL
output on the scheme communication logic ZCPSCH (85).
• The WEI function is not blocked by the active signal connected to the WEIBLK1
functional input or to theLOVBZ functional input. The later is usually configured
to the BLOCK functional output of the fuse-failure function.
• No active signal has been present for at least 200 ms on the WEIBLK2 functional
input. An OR combination of all fault detection functions (not undervoltage) as
present within the IED is usually used for this purpose.
WEIBLK1
CRL
WEIBLKn
ECHO
ECHO - cont.
OR
AND
AND
BLOCK
WTSZ
200ms
0
0
0-tWEI
0
200ms
50 ms
0
en06000324_ansi.vsd
ANSI06000324 V1 EN
Figure 396: Echo of a received signal by the WEI function
When an echo function is used in both IEDs (should generally be avoided), a spurious
signal can be looped round by the echo logics. To avoid a continuous lock-up of the
system, the duration of the echoed signal is limited to 200 ms.
An undervoltage criteria is used as an additional tripping criteria, when the tripping of
the local breaker is selected, setting
WEI = Echo&Trip, together with the WEI function
and ECHO signal has been issued by the echo logic, see figure 397 .
1MRK505222-UUS C
Section 13
Scheme communication
805
Technical reference manual