Application - ABB RELION REX640 Technical Manual

Section 5
Protection related functions
5.13.6
1180
• If Wei mode = "Off", the WEI logic is disabled.
• If Wei mode = "Echo", the WEI logic is enabled without Level detector.
• If Wei mode = "Echo and Operate", the WEI logic is enabled with Level detector.
Level detector
Level detector sends an enabling signal to Weak-end trip logic when the residual
voltage is above the Residual voltage Val setting.
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 Wei Crd time). The received carrier receive signal
is also given as the CR output.
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.
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.

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.
1MRS759142 C
REX640
Technical Manual