Figure. 5.6.5 - 208. Simplified function block diagram of the total harmonic distortion monitor function.
Measured input
The function block uses analog voltage measurement values. The function always uses FFT
measurement of the whole harmonic specter of 32 components from each measured voltage channel.
From these measurements the function calculates either the amplitude ratio or the power ratio. A -20
ms averaged value of the selected magnitude is used for pre-fault data registering.
Table. 5.6.5 - 306. Measurement inputs of the total harmonic distortion monitor function.
Signal
Description
Time base
UL1FFT
FFT measurement of phase L1 (A) voltage
5ms
UL2FFT
FFT measurement of phase L2 (B) voltage
5ms
UL3FFT
FFT measurement of phase L3 (C) voltage
5ms
The selection of the calculation method is made with a setting parameter (common for all measurement
channels).
General settings
The following general settings define the general behavior of the function. These settings are static i.e.
it is not possible to change them by editing the setting group.
Table. 5.6.5 - 307. General settings.
Name
Range
Default
Description
THD> LN mode
1: On
2: Blocked
3: Test
4: Test/
Blocked
5: Off
1: On
Set mode of THD block.
This parameter is visible only when
Allow setting of individual LN mode is
enabled in
General menu.
Measurement
magnitude
1:
Amplitude
2: Power
1:
Amplitude Defines which available measured magnitude the function uses.
A
AQ
Q-M257
-M257
Instruction manual
Version: 2.07
392
© Arcteq Relays Ltd
IM00021
Summary of Contents for AQ-M257
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