Level
detector
CR
CB_OPEN
ECHO
OPR_WEI
CR
Weak end
trip logic
Echo
logic
BLK_WEI1
BLK_WEI2
FF
BLOCK
U3P
U_AB
U_B
U_C
U_A
U_BC
U_CA
Figure 718: Functional module diagram of weak-end infeed logic
The WEI logic is enabled using the
Wei mode
setting.
• 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
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.
Protection related functions
1MRS759142 F
1268 REX640
Technical Manual
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