MI 2792 PowerQ4 Plus
Theory and internal operation
105
2. Last integration period
LST.IP
counter measures energy during recording over
last interval. It is calculated at end of each interval.
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 and S (Section 5.7)
IEC
61000-4-7
Class
I
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.
FFT
Voltage harmonics and THD
10 periods
t
n
1 2 3 4 5 6
50
U
FFT
10 periods
t
n
1 2 3 4 5 6
50
I
Uhn
Ihn
Current harmonics and THD
Figure 5.4: Current and voltage harmonics
k
k
k
t
f
k
c
c
t
u
1
512
1
0
2
10
sin
)
(
(17)
f
1
– frequency of signal fundamental (in example: 50 Hz)
c
0
– DC component
k – ordinal number (order of the spectral line) related to the frequency basis
N
C
T
f
1
1
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
1
10
f
k
f
Ck
k
– is the phase of the component c
k
U
c,k
– is the RMS value of component c
k
