ABB RELION RET670 Applications Manual page 836

Section 16
Scheme communication
830
L1
A1
L2
A2
IEC14000002 V1 EN-US
Figure 389: 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.
L1
A1
L2
A2
IEC14000003 V1 EN-US
Figure 390: Current distribution for a fault close to B side when breaker B1 is
opened
To handle this, the send signal CS or CSLx from B2 is held back until the reverse zone
IRVLx has reset and the tDelayRev time has elapsed. To achieve this, the reverse zone
on the distance protection shall be connected to input IRVLx and the output IRVOPLx
shall be connected to input BLKCS on the communication function block ZCPSCH.
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 Ir. 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
in 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 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).
B1
B2
IEC14000002-1-en.vsd
B1
B2
IEC14000003-1-en.vsd
Transformer protection RET670 2.2 ANSI
1MRK 504 163-UUS A
Application manual