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MI 2792A PowerQ4 Plus
Theory and internal operation
3. Current integration period CUR.IP
counter measures energy during recording over current time interval.
5.1.8 Harmonics and interharmonics
Standard compliance: IEC 61000-4-30 Class A (Section 5.7)
IEC
Calculation called fast Fourier transformation (FFT) is used to translate AD converted input signal to sinusoidal components. The following equation describes relation between input signal and its frequency presentation.
Voltage harmonics and THD
U
FFT
Uhn t
1 2 3 4 5 6 50 n
10 periods
I
Current harmonics and THD
Ihn
FFT
t
1 2 3 4 5 6 50 n
10 periods
Figure 5.4: Current and voltage harmonics u
(
t
)
c
0
512
k
1
c k
sin
k
10
2
f
1
t
k
f c
1
– frequency of signal fundamental (in example: 50 Hz)
0
– DC component
(17) k – ordinal number (order of the spectral line) related to the frequency basis
f
C
1
1
T
N
T
N
– is the width (or duration) of the time window (T
N
= N*T
1
; T
1
=1/f
1
). Time window is that time span of a time function over which the Fourier transformation is performed. c k
– is the amplitude of the component with frequency
– is the phase of the component c k
– is the RMS value of component c k
f
Ck
k
10
f
1
k
U c,k
Phase voltage and current harmonics are calculated as RMS value of harmonic subgroup (sg): square root of the sum of the squares of the RMS value of a harmonic and the two spectral components immediately adjacent to it.
106
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