ABB RELION REX640 Technical Manual page 1022

Section 4
Protection functions
1016
Timer 2
The Timer 2 characteristics are according to Definite Time (DT) .When the operation
timer has reached the value of Alarm delay time, the ALARM output is activated.
If a drop-off situation happens, the timer is reset.
The Timer 2 module is internally blocked for one second after the
capacitor bank is connected by detecting the rising edge of the
CB_CLOSED signal. The CB_CLOSED signal is True when the CB
position is closed.
Under current detector
The Under current detector module can be enabled by setting Enable under current to
"Enable" and disabled by setting it to "Disable". The Under current detector module
is also disabled when CB_CLOSED is FALSE, that is, when circuit breaker is open.
The fundamental frequency component of phase currents is compared to the setting
Start value Un Cur. If all the three-phase currents are below the setting Start value Un
Cur, the Under current detector module enables the Timer 3 module.
Timer 3
Once activated, the Timer 3 module activates the ST_UN_I output. The operation is
based on DT characteristics. When the operation timer has reached the value of Un
Cur delay time, the OPR_UN_I output is activated.
If the undercurrent situation disappears, the operation timer is reset. The
ST_DUR_UN_I output indicates the percentage ratio of the undercurrent start
situation and the set operation time in the Timer 3 module and is available in the
monitored data view.
The OPR_UN_I output is of pulse type and remains TRUE for 150 ms. After that,
ST_DUR_UN_I and OPR_UN_I are deactivated and ST_DUR_UN_I is reset.
If the circuit breaker closed status signal is not detected, the constant
value TRUE has to be connected to CB_CLOSED input to enable the
undercurrent detector.
If the circuit breaker status signal is not connected to CB_CLOSED
input, the OPR_UN_I output is activated even if the circuit breaker is
open and undercurrent is detected.
1MRS759142 C
REX640
Technical Manual