Application; Current Reversal Logic; Weak-End Infeed Logic - ABB Relion REC670 Applications Manual

Section 14
Scheme communication
14.2.2

Application

14.2.2.1

Current reversal logic

If parallel lines are connected to common buses at both terminals, overreaching permissive
communication schemes can trip unselectable due to current reversal. The unwanted tripping
affects the healthy line when a fault is cleared on the parallel line. This lack of security results in
a total loss of interconnection between the two buses.
To avoid this kind of disturbances, a fault current reversal logic (transient blocking logic) can
be used.
The unwanted operations that might occur can be explained by looking into Figure
Figure 175. Initially the protection A2 at A side will detect a fault in forward direction and send
a communication signal to the protection B2 at remote end, which is measuring a fault in
reverse direction.
IEC99000043 V3 EN-US
Figure 174: 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 175: 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.
14.2.2.2

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
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
348
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
. The fault current can be too low due to an open breaker or low short-
r
1MRK 511 358-UEN A
IP15023-1 v1
M13895-4 v5
174 and
M13895-16 v6
Application manual