Undervoltage Protection - ABB REU 610 Technical Reference Manual

1MRS755972
5.1.4.3.
Voltage Relay
Technical Reference Manual - ANSI Version

Undervoltage protection

The undervoltage protection can be based on either conventional voltage
measurement or the calculated positive phase-sequence voltage.
The low-set undervoltage element 27P-1 is based on conventional voltage
measurement. The low-set element can also be used for alarm purposes.
The high-set undervoltage element 27P-2 can be set to be based on either:
Conventional voltage measurement (27P-2 mode selected) or
*
Calculated positive phase-sequence voltage (27D mode selected).
*
The selection between these modes is made either by using HMI or parameter
S7, the default setting being conventional measurement. Element 27D (PPS)
and 47 (NPS) cannot be used at the same time.
The undervoltage elements can be set to be blocked when one of the
measured voltages fall below 0.15 × U
after the set resetting time. This feature can be used to avoid unnecessary
pickups and trips during, for example, an auto-reclose sequence. In addition,
the tripping of element 27P-1 can be set to be blocked by the element 27P-2
pickup. The selection is made in SGF4.
Element 27P-2 can be set out of operation in SGF3/2. This state is indicated
by dashes on the LCD and by 999 when the set pickup value is read via serial
communication.
It is possible to block the tripping of an undervoltage element by
applying a digital input signal to the relay.
Undervoltage protection based on conventional voltage
measurement
Both the low-set and the high-set undervoltage element can independently be
set to pickup and trip when one of the three voltages or all the voltages fall
below the set pickup value. By default, the low-set undervoltage element
operates when one of the three voltages fall below the set pickup value and
the high-set undervoltage element operates when all the voltages fall below
the set pickup value. The selection is made in SGF4/7 and SGF4/8.
When the phase-to-phase voltage values fall below the set pickup value of the
low-set element, 27P-1, the element generates a pickup signal after a ~ 80 ms'
pickup time. When the set operate time at definite-time characteristic or the
calculated operate time at IDMT characteristic elapses, the element generates
a trip signal.
(VT). The blocked element is reset
n
REU 610
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