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Measured input values
Function block uses analog current measurement values. Function block always utilizes FFT
measurement of whole harmonic specter of 32 components from each measured current channel
which from the THD is calculated either as amplitude or power ratio THD. -20ms averaged value of the
selected magnitude is used for pre-fault data registering.
Table. 5.6.7. - 240. Analogic magnitudes used by the THD function.
Signal
Description
Time base
IL1FFT
Fundamental RMS measurement of phase L1/A current
5 ms
IL2FFT
Fundamental RMS measurement of phase L2/B current
5 ms
IL3FFT
Fundamental RMS measurement of phase L3/C current
5 ms
I01FFT
Fundamental RMS measurement of residual I01 current
5 ms
I02FFT
Fundamental RMS measurement of residual I02 current
5 ms
Selection of the THD calculation method is made with a setting parameter commonly for all of the
measurement channels.
General settings
The following general settings de ne the general behavior of the function. These settings are static i.e.
it is not possible change them with setting group switching.
Table. 5.6.7. - 241. General settings of the function
Name
Description
Range
Step
Default
Measurement
magnitude
De nes which available measured magnitude of THD is used by
the function.
1:Amplitude
2:Powers
-
1:Amplitude
Pick-up characteristics
Pick-up and activation of the THD function alarm is controlled by
IsetPh, IsetI01
and
IsetI02 pick-up
setting parameters, which de nes the maximum allowed measured current THD before action from the
function. In order to have alarm signals activated from the function, the corresponding pick-up element
needs to be activated by the
Enable PH, Enable I01
and
Enable I02
setting parameters. Each pick-up
element can be activated individually. The function constantly calculates the ratio in between of the
setting values and measured magnitude (Im) per all three phases. Reset ratio of 97 % is inbuilt in the
function and is always related to the settingvalue. The setting value is common for all measured phases
and single-, dual- or all phases Im exceed of the Iset value will cause pick-up operation of the function.
Table. 5.6.7. - 242. Pick-up characteristics setting
Name
Range
Step
Default
Description
Enable
PH
On
Off
-
Off
Enable of the THD alarm function from phase currents.
Enable
I01
On
Off
-
Off
Enable of the THD alarm function from residual current input I01.
Enable
I02
On
Off
-
Off
Enable of the THD alarm function from residual current input I02.
IsetPh
0.10 …
200.00% 0.01% 20.00%
Pick-up setting for THD alarm element from the phase currents. The measured THD
value has to be over this setting on at least one of the measured phases to activate
the alarm signal.
AQ-F255
Instruction manual
Version: 2.00
295
© Arcteq Relays Ltd