LS Industrial Systems Metasol Series, Технический каталог, Страница: 53 / 156

52
Technical catalog for Susol & Metasol ACB
Technical catalog for Susol & Metasol ACB
D
THD (Total Harmonic Distortion), TDD (Total Demand Distortion) for P, S Type
THD =
U
U
2
k
√
Σ
∝
k =2
rms
TDD =
U
U
2
k
√
Σ
∝
k =2
Peak Demand
K-Factor =
U
K
2
U
2
k
√
Σ
∝
k =2
rms
THD =
U
U
2
k
√
Σ
∝
k =2
1
1. THD Definition
1) THD is a single value which expresses the total harmonic distortion.
2) THD value measured is getting higher when total harmonics increases. THD value comes into ‘0’ under no
harmonics state.
3) The THD has two formulas. One is the ratio of a harmonics value to the fundamental wave and the other is
the ratio of a harmonics value to the RMS value.
4) S type calculates THD by the ratio of a harmonics value to the fundamental wave.
5) THD is calculated on each phase of voltage and current.
6) For 3P4W, THD is calculated from phase-to-phase voltage and for 3P3W, THD is calculated from line voltage.
2. TDD Definition
1) TDD is a different way to show the total harmonic distortion of current.
2) The value of THD is supposed to be very high when non-linear loads are used such as computer under the
circumstance of almost no load. Actually, a harmonics value is much lower comparing to normal condition, but
when load current is relatively low at some point, it has no meaning as an index.
3) TDD is an index to show the total harmonic distortion to solve the problem described above. As TDD is the
total harmonics distortion of Peak Demand current, it is available to show the harmonics distortion regardless
of the load current at some point.
2. K-Factor Definition
1) The K-Factor is an index that indicates harmonics for the temperature rise of transformer. It is defined by
standard ANSI/IEEE C57.110.
2) In other words, the 3 rd harmonics and 7 th harmonics have the different temperature rise of transformer. 7 th
harmonics generates much higher heat than 3 rd harmonics.
3) Heat capacity becomes the standard ratings for transformer capacity and the ratings does not include the
harmonics (fundamental frequency). But, load current actually includes various harmonics which heats the
transformer much higher than fundamental frequency. Therefore, 100% of transformer capacity will not be
used when it includes harmonics.
4) K-Factor indicates as ‘1’ without harmonics. As mentioned previously, even under the harmonics which
has the same value, harmonics with higher degree has a higher K-Factor. Namely, the K-Factor of
7
th harmonic is much higher than K-Factor of 3 rd harmonic under the same value.
Apply on S T
ype