ABB RELION 670 SERIES Applications Manual page 772

Section 16
Scheme communication
766
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
Figure 375: 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).
The WEI function can be extended to trip also the breaker in the weak side. The trip is
achieved when one or more phase voltages are low during an echo function.
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 protection at the remote
B1
B2
IEC14000003-1-en.vsd
Line distance protection REL670 2.2 ANSI
1MRK 506 369-UUS -
Application manual