Undervoltage Unit - ABB REU 523 Technical Reference Manual

1MRS 750942-MUM
4.1.4.3.
Combined Overvoltage and Undervoltage Relay
Technical Reference Manual

Undervoltage unit

When the voltage values fall below the set start value of low-set stage U<, the
undervoltage unit will start to deliver a start signal after a ~ 80 ms' start time. When
the set operate time at definite-time characteristic or the calculated operate time at
IDMT characteristic elapses, the undervoltage unit will deliver a trip signal.
The high-set undervoltage stage, U<<, can be set to start and trip either based on
conventional undervoltage measurement or on the calculated
positive-phase-sequence voltage, U
automatically deseclect the other.
When the conventional protection mode has been selected and the voltage values fall
below the set start value of the high-set stage, the undervoltage unit will start to
deliver a start signal after a ~ 50 ms' start time.
When the positive-phase-sequence protection mode has been selected and the
calculated positive-phase-sequence voltage value, U
of the high-set stage, the undervoltage unit will start to deliver a start signal after a
~ 50 ms' start time. When the set operate time at definite-time characteristic or the
calculated operate time at IDMT characteristic elapses, the undervoltage unit will
deliver a trip signal.
The start and the tripping of an undervoltage stage can be set to be internally blocked
when the measured value falls below 0.2 x U
In addition, the tripping of stage U< can be set to be blocked by the start of stage
U<<. The tripping of an undervoltage stage can also be blocked by applying an
external binary input signal to the relay.
The high-set stage can be set out of operation. This state will be indicated by dashes
on the LCD and by "999" when the set start value is read via serial communication.
. Selecting either of these two will
1s
, falls below the set start value
1s
with a switch of switchgroup SGF2.
n
REU 523
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