CET PMC-592, User Manual, Page: 98 / 177

97
CET Electric Technology
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Uan/Ubn/Ucn HD31 (WYE)
Uab/Ubc/Uca HD31 (Delta)
Uan/Ubn/Ucn HD31 (WYE)
Uab/Ubc/Uca HD31 (Delta)
Harmonics-Current
Ia/Ib/Ic THD Ia/Ib/Ic THD
Ia/Ib/Ic TEHD Ia/Ib/Ic TEHD
Ia/Ib/Ic TOHD Ia/Ib/Ic TOHD
Ia/Ib/Ic TDD Ia/Ib/Ic TDD
Ia/Ib/Ic TEDD Ia/Ib/Ic TEDD
Ia/Ib/Ic TODD Ia/Ib/Ic TODD
Ia/Ib/Ic K-Factor Ia/Ib/Ic K-Factor
Ia/Ib/Ic Crest-Factor Ia/Ib/Ic Crest-Factor
Ia/Ib/Ic HD02 Ia/Ib/Ic HD02
… …
Ia/Ib/Ic HD31 Ia/Ib/Ic HD31
Table 4-21 Harmonics Measurements
Total Demand Distortion (TDD)
TDD the ratio of the root mean square (rms) of the harmonic current to the root mean square value of
the rated or maximum demand fundamental current, expressed as a percent.
TDD of the current I is calculated by the formula below:
where
I
L
= maximum demand of fundamental current which calculated via FFT (Fast Fourier
Transform)
h = harmonic order (1, 2, 3, 4, etc.)
I
h
= rms load current at the harmonic order h
K-Factor and Crest Factor
K-factor is defined as the weighted sum of the harmonic load currents according to their effects on
transformer heating, as derived from ANSI/IEEE C57.110. A K-Factor of 1.0 indicates a linear load (no
harmonics). The higher the K-Factor , the greater the harmonic heating effects.
The calculation method of K-Factor is listed below:
) (
) (
K
2
h h
1 h
2
h h
1 h
max
max
h
h
I
h I
Factor






 
I
h
= h
th
Harmonic Current in RMS
h
max
= Highest harmonic order
h = Harmonic order
Crest Factor is defined as the Peak to Average Ratio (PAR) , and its calculation is listed below:
x
x
rms
peak
C

|X|
peak
= Peak amplitude of the waveform
X
rms
= RMS value
The following screen captures display the Crest Factor and TDD parameters on the Web Interface and
optional HMI.