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# Design guide

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K9AE33000
DD210679
PD202028
PD202029
2
Schneider Electric
Design guide
Design guide
Harmonic currents
Harmonic currents are caused by non-linear loads connected to distribution
systems, i.e. by loads that draw current with a waveform different that that of the
voltage that supplies them.
The most common non-linear loads are equipment including rectifiers, fluorescent
lighting and computer hardware.
In installations with a distributed neutral, non-linear loads may cause significant
overloads in the neutral conductor due to the presence of third-order harmonics.
Harmonic order
The order is the ratio
between the harmonic
frequency fn and the
fundamental frequency
(generally the power
frequency, 50 or 60 Hz):
n = fn / f1
By definition, the
fundamental f1 is order 1
(H1).
Third-order harmonics (H3)
have a frequency of 150 Hz
(when f1 = 50 Hz).
The presence of third-order harmonics depends on the applications involved.
It is necessary to carry out an in-depth study on each non-linear load to determine
the level of H3:
ih3 (%) = 100 x i3 / i1
i3 = rms current of H3
i1 = rms current of the fundamental
Assuming that H3 is preponderant among harmonics, the THD is close to the value
of H3 (ih3(%)).
There are two decisive factors:
the types of connected devices:
disturbing loads: fluorescent lighting, computer hardware, rectifiers, arc furnaces,
etc.,
non-disturbing loads: heating, motors, pumps, etc.,
the ratio between the two types of disturbing loads.
b
b
b
v
v
b
Workshops
UPSs, fluorescent lighting) and non-
heating).
Low probability of harmonics
THD 15%.
Offices
UPSs, fluorescent lighting).
High probability of harmonics
15 % < THD 33%.
Origin of harmonic currents
Estimating THD (total harmonic
distortion)
Canalis KTA

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Summary :

## K9AE33000 DD210679 PD202028 PD202029 2 Schneider Electric Design guide Design guide Harmonic currents Harmonic currents are caused by non-linear loads connected to distribution systems, i.e. There are two decisive factors: the types of connected devices: disturbing loads: fluorescent lighting, computer hardware, rectifiers, arc furnaces, etc., non-disturbing loads: heating, motors, pumps, etc., the ratio between the two types of disturbing loads.

Tags : harmonic,harmonics,disturbing,thd,fluorescent,lighting,frequency,nonlinear,order,current,thirdorder,fundamental,currents
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