ABB RELION REX640 Technical Manual page 1187

1MRS759142 C
REX640
Technical Manual
In the current reversal condition, the relays Relay A1, Relay A2, Relay B1 and Relay
B2 can be equipped with the scheme communication logic RESCPSCH and the
permissive overreach scheme can be enabled.
A fault occurs at Feeder 1 close to bus B. Relay A2 at the healthy feeder 2 recognizes
the fault in the forward direction and sends a CS signal to Relay B2 according to the
PUTT scheme. Relay B2 does not recognize the fault in the forward direction and
hence does not send a permissive signal to Relay A2.
GUID-E0CB19A7-9435-4594-9F6E-7096603E2BCA V1 EN
Figure 637: Fault occurs at one of the parallel lines. CS=carrier signal sending,
CR=carrier signal receiving
The faulty feeder (Feeder 1) is not simultaneously tripped at both ends and, for
example, the circuit breaker closer to the fault at Relay B1 may be tripped faster than
the breaker at bus A. As a result, when the breaker at Relay B1 opens, the direction of
the fault current at the healthy feeder (Feeder 2) is reversed.
GUID-D2A85D10-C2F2-40E9-B6B7-158938F7D39D V1 EN
Figure 638: Circuit breaker at Relay B1 opens and creates a current reversal
condition. CS=carrier signal sending, CR=carrier signal receiving.
Relay A2 still sends the CS signal because of the reset time delay of the forward
direction residual overcurrent function of Relay A2. When Relay B2 starts to
recognize the fault in the forward direction, Relay B2 can malfunction and trip the
breaker of the healthy feeder.
Protection related functions
Section 5
1181