Undervoltage Unit - ABB REU 523 Technical Reference Manual

REU 523
4.1.3.3.
14
Combined Overvoltage and Undervoltage Relay
Technical Reference Manual
The low-set and high-set stages of the overvoltage unit may be given a definite-time
or an inverse definite minimum time (IDMT) characteristic. When the IDMT
characteristic is chosen, two time/current curve groups called A and B are available.
The high-set stage can be deselected from operation by setting a bit in one of the
software switchgroups. When the stage is disabled, "---" is shown on the LCD and
"999" in communication via the SPA bus indicating deselection of the protection
stage.

Undervoltage unit

When one or several of the measured voltages fall below the set start value of the
low-set stage U< and the preset start time of ~ 80 ms elapses, the undervoltage unit
begins delivering a start signal. Further, when the set operate time for the low-set
stage at definite-time operation or the calculated operate time at inverse-time
operation passes, the undervoltage unit operates.
When the conventional operation mode is selected for the high-set undervoltage
stage and one or all of the measured voltages, depending on the set operation criteria,
fall below the set start value of the high-set stage U<<, the undervoltage unit begins
delivering a start signal after a preset ~ 50 ms start time.
When the positive-phase-sequence protection mode is selected for the high-set
undervoltage stage and the calculated positive-phase-sequence voltage U1s falls
below the set start value of the high-set stage U<<, the undervoltage unit begins
delivering a start signal after a preset ~ 50 ms start time. When the set operate time
at definite-time operation or the calculated operate time at inverse-time operation for
the high-set stage elapses, the undervoltage unit operates.
The low-set and high-set stages of the undervoltage unit may be given a definite-
time or an inverse definite minimum time (IDMT) characteristic. When the IDMT
characteristic is chosen, one time/current curve group called C is available.
Starting and operation of the low-set and high-set undervoltage stages can be
internally blocked when the measured value falls below 0.2 x U
selected in one of the software switchgroups.
The high-set stage can be deselected from operation by setting a bit in one of the
software switchgroups. When the stage is disabled, "---" is shown on the LCD and
"999" in communication via the SPA bus indicating deselection of the protection
stage.
The operation of stage U< can be blocked by the start of the stage U<<. The selection
is made with a switch in one of the software switchgroups.
1MRS 750942-MUM
. This function is
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