5.4.10. Undervoltage U< (27)
Undervoltage function (UV) is used for instant- and time delayed undervoltage protection for various
applications including feeder, lter and machine applications of utilities and industry. Each IED with
voltage protection module has four available instances of the function (U<, U<<, U<<<, U<<<<).
Function constantly measures phase voltage- or line to line voltage magnitudes. Undervoltage
protection is based to line- to line fundamental frequency component or line- to neutral fundamental
frequency component if so chosen. If protection is based to line- to line voltage, during earth fault in
isolated or compensated networks the undervoltage protection is not affected. Undervoltage protection
stage has two blocking instances, internal blocking based on voltage measurement and low voltage or
external blocking during for example VT fuse failure. Blocking signal and setting group selection
controls the operating characteristics of the function during normal operation.
Outputs of the function are Start Trip and Blocked signals. Setting parameters are static inputs for the
function which are changed only by user input in the setup phase of the function. Undervoltage
function utilizes total of eight separate setting groups which can be selected from one common source.
The function can operate on instant or time delayed mode. In time delayed mode the operation can be
selected for de nite time or IDMT.
The operational logic consists of input magnitude processing, input magnitude selection, threshold
comparator, two block signal check, time delay characteristics and output processing.
Inputs for the function are the operating mode selections, setting parameters and measured and pre-
processed voltage magnitudes and binary input signals. Function outputs START, TRIP and BLOCKED
signals which can be used for direct IO controlling and also for user logic programming. The function
registers its operation into 12 last time-stamped registers and also generates general time stamped
ON/OFF events to the common event buffer from each of the three output signal. In instant operating
mode the function outputs START and TRIP events simultaneously with equivalent time stamp. Time
stamp resolution is 1ms. Function provides also cumulative counters for START, TRIP and BLOCKED
events.
In the following gure is presented the simpli ed function block diagram of the UV function.
Figure. 5.4.10. - 50. Simpli ed function block diagram of the UV function.
Measured input values
Analog voltage measurement values are used by the function. Function block always utilizes peak-to-
peak measurement from samples and the monitored magnitudes are fundamental frequency RMS
values. -20 ms averaged value is used for the pre-fault data.
AQ-T257
Instruction manual
Version: 2.00
© Arcteq Relays Ltd
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