ABB RELION REX640 Technical Manual page 1609

1MRS759142 C
REX640
Technical Manual
The operation of CHMHAI can be described with a module diagram. All the modules
in the diagram are explained in the next sections.
I3P
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Figure 828: Functional module diagram
Distortion measurement
The Distortion measurement module measures harmonics up to the 11
The filter used for harmonics includes a spectrum of frequencies near each harmonic
frequency. FFT for one period is used. The resulting frequency spectrum is wider than
in a harmonic subgroup. An anti-aliasing filter is used.
Total harmonic distortion
The total harmonic distortion THD is calculated from the measured harmonic
components with the formula
2
n
I
h
 
THD
=
∑
 
I
1
h 2  
=
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I
th
h harmonic component
h
I
Fundamental frequency current (1
1
n Number of harmonics
Power quality measurement functions
I_A
Distortion Total
I_B
measure- harmonic
I_C
ment distortion
Total
demand
distortion
Harmonic
calculation
st
harmonic)
Section 10
SMNTHD_A
SMNTHD_B
SMNTHD_C
SMNTDD_A
SMNTDD_B
SMNTDD_C
SMNDC_A
SMNDC_B
SMNDC_C
SMNH01_A
SMNH01_B
SMNH01_C
SMNH02_A
SMNH02_B
SMNH02_C
...until hmax
th
harmonic.
(Equation 351)
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