ABB Relion 670 Series Applications Manual page 448

Section 16
Scheme communication
IEC99000043 V3 EN-US
Figure 227: Current distribution for a fault close to B side when all breakers are closed
When the breaker B1 opens for clearing the fault, the fault current through B2 bay will invert. If
the communication signal has not reset at the same time as the distance protection function
used in the teleprotection scheme has switched on to forward direction, we will have an
unwanted operation of breaker B2 at B side.
IEC99000044 V3 EN-US
Figure 228: 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
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.
16.2.2.2 Weak-end infeed logic
Permissive communication schemes can only operate when the protection in the remote IED
can detect the fault. The detection requires a sufficient minimum fault current, normally >20%
of I . The fault current can be too low due to an open breaker or low short-circuit power of the
r
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 additionally 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.
When used 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
442
L1
A1 B1
L2
A2 B2
IEC9900043-2.vsd
L1
A1 B1
L2
A2 B2
IEC99000044-2.vsd
tDelayRev time has been elapsed. To achieve this the reverse zone on the
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