MI 2883 Energy Master
Theory and internal operation
134
Total harmonic distortion is calculated as ratio of the RMS value of the harmonic
subgroups
to the RMS value of the subgroup associated with the fundamental:
Total voltage harmonic distortion:
2
40
2
1
n
p
n
p
p
U
h
U
h
U
THD
,
p: 1,2,3
(44)
Total current harmonic distortion:
2
40
2
1
n
p
n
p
Ip
h
I
h
I
THD
,
p: 1,2,3
(45)
Spectral component between two harmonic subgroups are used for interharmonics
assessment. Voltage and current interharmonic subgroup of n-th order is calculated
using RSS (root sum square) principle:
n
th
voltage interharmonic:
8
2
2
)
10
,(
k
k
n
C
n
p
U
ih
U
p: 1,2,3
(46)
n
th
current interharmonic:
8
2
2
)
10
,(
k
k
n
C
n
p
I
ih
I
p: 1,2,3
(47)
50
100
150
200
Uc,k
Uh
1
Uh
2
Uh
3
Uh
4
Freqency
Uih
1
Uih2
Uih3
Figure 5.7: Illustration of harmonics / interharmonics subgroup for 50 Hz supply
The K factor is a factor that is developed to indicate the amount of harmonics that the
load generates. The K rating is extremely useful when designing electric systems and
sizing components. It is calculated as:
K - factor:
50
1
2
50
1
2
)
(
n
n
p
n
n
p
p
h
I
n
h
I
K
,
p: 1,2,3
(48)
5.1.8 Signalling
Standard compliance: IEC 61000-4-30 Class S (Section 5.10)
