Weak-End Infeed Logic - ABB REC670 Applications Manual

Section 15
Scheme communication
15.2.2.2
442
L1
A1
L2
A2
IEC99000044 V3 EN-US
Figure 194: 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 I
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 IED. The echo signal would block the operation of the distance
B1
B2
IEC99000044-2.vsd
. The fault current can be too low due to an open
r
1MRK 511 401-UEN A
M13895-16 v7
Bay control REC670 2.2 IEC
Application manual