ABB RELION REX640 Technical Manual page 1277

1MRS759142 F
Level detector
Level detector sends an enabling signal to Weak-end trip logic when the residual
voltage is above the
Echo logic
Echo logic returns the received carrier signal with the ECHO output when it receives
a carrier receive signal (CR) if no fault has been detected by the forward and reverse
directional residual overcurrent functions and the duration of CR is longer than
the coordination time delay (the setting
signal is also given as the CR output.
The ECHO and CR outputs can be blocked by activating the BLOCK input. The FF,
BLK_WEI1 and BLK_WEI2 inputs can be used to block the ECHO output. The FF
input is usually connected to the functional output of the fuse failure function, and
the BLK_WEI1 input is typically connected to the start signals of the forward and
reverse directional residual overcurrent functions in the terminal. The BLK_WEI2
signal has an in-built 200 ms drop-off delay and is usually connected to all the fault
detection functions in the terminal except the residual overvoltage function.
Weak-end trip logic
Weak-end trip logic is activated if it receives an enable signal from Level detector
and ECHO output of Echo logic is activated. Then a general trip signal OPR_WEI is
activated. The activation of the CB_OPEN input blocks the tripping.
The OPR_WEI output can be blocked by activating the BLOCK input.
5.13.6 Application
Current reversal logic
When the overreaching permissive communication schemes are used in parallel
feeder applications, the current reversal can result in unselective tripping. Such a
condition can occur in the healthy feeder when the fault is cleared in the faulty
feeder. The tripping of the healthy parallel feeder can lead to losing the connection
between the two buses. To avoid this situation, the current reversal logic (transient
blocking logic) can be used.
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.
REX640
Technical Manual
Residual voltage Val setting.
When the WEI logic is enabled at both feeder ends, a spurious signal
can be looped round by Echo logic. To avoid a continuous lockup of the
system, the duration of the echoed signal is limited to 200 ms.
Protection related functions
Wei Crd time ). The received carrier receive
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