ABB RELION REX640 Technical Manual page 1268

Protection and control

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Protection related functions

Figure 718: Functional module diagram of weak-end infeed logic

The WEI logic is enabled using the

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

and to the phase-to-earth voltages with the

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 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

time ). The received carrier receive 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 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.

Wei mode = "Off", the WEI logic is disabled.

Wei mode = "Echo", the WEI logic is enabled without Level detector.

Wei mode = "Echo and Operate", the WEI logic is enabled with Level detector.

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.

Wei mode setting.

PhV level for Wei . Level detector sends

1MRS759142 F

PPV level for Wei setting

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