ABB RELION REX640 Technical Manual page 1179

1MRS759142 C
REX640
Technical Manual
Assume that Relay A1, Relay A2, Relay B1 and Relay B2 are equipped with
DSOCPSCH and the permissive overreach scheme is 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 within the overreaching zone Z2 and sends a CS signal to Relay B2
according to the POTT scheme. Relay B2 does not recognize the fault in the forward
direction and does not operate even though a permissive CR signal is received from
Relay A2. Moreover, Relay B2 does not send a permissive signal to Relay A2.
GUID-76F08FB3-232C-4CE7-901B-9E159A7883DE V1 EN
Figure 632: The fault occurs at one of the parallel lines.
The faulty feeder (Feeder 1) is not simultaneously tripped at both ends and it might
occur that, for example, the circuit breaker closer to the fault at Relay B1 is tripped
faster than the breaker at bus A due to the direct operation of the zone Z1 of Relay B1.
Thus, when the breaker at Relay B1 opens, the direction of the fault current at the
healthy feeder (Feeder 2) is reversed.
Protection related functions
Section 5
1173