Weak-End Infeed Logic - ABB RELION RET670 Applications Manual

1MRK 504 163-UUS A
16.3.2.2
Transformer protection RET670 2.2 ANSI
Application manual
CLOSED
Strong
source
A:1
A
CLOSED
A:2
ANSI99000044 V1 EN-US
Figure 388: Current distribution for a fault close to B side when breaker B1 has
opened
To handle this the send signal CS or CSLn from B2 is held back until the reverse zone
IRVLn has reset and the tDelayRev time has been elapsed. To achieve this the reverse
zone on the distance protection shall be connected to input IRV and the output IRVL
shall be connected to input BLKCS on the communication function block ZCPSCH.
The function can be blocked by activating the input IRVBLK or the general BLOCK
input.

Weak-end infeed logic

Permissive communication schemes can basically operate only when the protection in
the remote IED can detect the fault. The detection requires a sufficient minimum fault
current, normally >20% of . The fault current can be too low due to an open breaker or
low short-circuit power of the source. To overcome these conditions, weak-end infeed
(WEI) echo logic is used. The fault current can also be initially too low due to the fault
current distribution. Here, the fault current increases when the breaker opens at the
strong terminal, and a sequential tripping is achieved. This requires a detection of the
fault by an independent tripping zone 1. To avoid sequential tripping as described, and
when zone 1 is not available, weak-end infeed tripping logic is used. The weak end
infeed function only works together with permissive overreach communication
schemes as the carrier send signal must cover the complete line length.
The 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).
Also, the WEI function can be extended to trip the breaker in the weak side. The trip is
achieved when one or more phase voltages are low during an echo function.
In case of single-pole tripping, the phase voltages are used as phase selectors together
with the received signal CRLn.
Together with the blocking teleprotection scheme some limitations apply:
• Only the trip part of the function can be used together with the blocking scheme. It
is not possible to use the echo function to send the echo signal to the remote line
FAULT OPEN
LINE 1
B:1
B
CLOSED
LINE 2
B:2
en99000044_ansi.vsd
Section 16
Scheme communication
Weak
source
M13895-16 v7
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