ABB RELION REX640 Technical Manual page 1180

Section 5
Protection related functions
1174
GUID-1D2CDD15-11FC-4F41-9B28-421C48078962 V1 EN
Figure 633: The circuit breaker at Relay B1 opens and creates a current reversal
condition
Relay A2 is still sending the CS signal because of the reset time delay of the forward
zone of Relay A2 when the overreaching zone of Relay B2 starts to recognize the fault
in the forward direction. Relay B2 can malfunction and trip the breaker of the healthy
feeder.
This problem can be solved by using the reverse-looking zone (Z3) to recognize the
fault in reverse direction and temporarily block the operation of DSOCPSCH due to
the current reversal condition. This is used in CRWPSCH.
Weak-end infeed logic
Avoid using the WEI function at both feeder ends. It can only be
enabled at the weak end.
The weak-end infeed logic should be used only in permissive schemes.
Setting guidelines for current reversal logic
Setting Reversal reset time: Set the Reversal reset time setting to the maximum reset
time of the communication channel. A minimum setting of 40 ms is recommended. A
long Reversal reset time setting increases the security against unwanted tripping, but
delays the fault clearing if the fault develops in one feeder and involves the other.
However, the probability of this type of fault is small.
Setting Reversal time: Set the start delay Reversal time setting to less than 80 percent
of the breaker operate time, but to a minimum of 20 ms.
1MRS759142 C
REX640
Technical Manual