5.3.6. Undervoltage (U<; 27)
The undervoltage function is used for undervoltage alarms. The undervoltage function is based on a
line-to-line fundamental frequency or on a line-to-neutral fundamental frequency. If the supervision is
based on line-to-line voltage, the undervoltage function is not affected by an earth fault in isolated or
compensated networks. The undervoltage function stage has two blocking instances: internal blocking
that is based on voltage measurement, and low voltage or external blocking that takes place during, for
example, a voltage transformer fuse failure. The setting group selection controls the operating
characteristics of the function during normal operation, i.e. the user can change parameters while the
station is running.
The output of the function is the ALARM signal. The setting parameters are static inputs for the
function which can only be changed by the user in the setup phase of the function. The undervoltage
function uses a total of eight (8) separate setting groups which can be selected from one common
source.
The operational logic consists of the following:
input magnitude selection
input magnitude processing
threshold comparator
two block signal check
output processing.
The inputs for the function are the following:
operating mode selections
setting parameters
digital inputs and logic signals
measured and pre-processed voltage magnitudes.
The function's output ALARM signal can be used for direct I/O controlling and also for user logic
programming. The function registers its operation into the last twelve (12) time stamped registers and
also generates general time stamped ON/OFF events to the common event buffer from the output
signal. The time stamp resolution is 1 ms. The function also provides a resettable cumulative
counter for ALARM events.
Measured input
The function block uses analog voltage measurements and always uses peak-to-peak measurement
from samples. The monitored magnitude is equal to RMS values.
Table. 5.3.6. - 65. Analog magnitudes used by the U< function.
Signal
Description
Time base
U
1
RMS
Fundamental RMS measurement of voltage U
1
/V
5 ms
U
2
RMS
Fundamental RMS measurement of voltage U
2
/V
5 ms
U
3
RMS
Fundamental RMS measurement of voltage U
3
/V
5 ms
AQ-E215
Instruction manual
Version: 2.01
© Arcteq Relays Ltd
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