Application - ABB RELION REX640 Technical Manual

Section 5
Protection related functions
5.12.6
1172
Level detector
Both phase-to-earth and phase-to-phase voltages are monitored. The undervoltage
criteria are applied to the phase-to-phase voltages with the PPV level for Wei setting
and to the phase-to-earth voltages with the PhV level for Wei. Level detector sends an
enable signal for a phase to Weak-end trip logic when one or more voltages are below
the corresponding settings. Level detector blocks the enable signal if all three-phase
voltages are above the set value more than 100 ms. This is to avoid sending an
unnecessary operate signal if the breaker is already open.
Echo logic
Echo logic returns the received carrier signal with the ECHO output when it receives a
CR signal if no fault has been detected by the forward- and reverse-looking zones and
the duration of CR is longer than the coordination time delay (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 within the terminal. The BLK_WEI2 signal
has an in-built 200 ms drop-off delay. The BLK_WEI2 input is usually connected to
all the fault detection functions within 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
In parallel feeder applications, when the overreaching permissive communication
schemes are used, unselective tripping may result due to the current reversal. 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 may 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