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16.6.2. Limit values for harmonics
EN-50160 fixes the limits for the harmonic voltages, which can be introduced into the
network by the power supplier. In normal conditions, during whatever period of a week,
95% if the RMS value of each harmonic voltage, mediated on 10 minutes, will have to be
less than or equal to the values stated in the following table.
The total harmonic distortion (THD) of the supply voltage (including all the harmonics up to
th
40
order) must be less than or equal to 8%.
Not multiple of 3
Order h
Relative voltage % Max
5
6
7
5
11
3,5
13
3
17
2
19
1,5
23
1,5
25
1,5
These limits, theoretically applicable only for the supplier of electric energy, provide
however a series of reference values within which the harmonics introduced into the
network by the users must be contained.
16.6.3. Presence of harmonics: causes
Any apparatus that alters the sine wave or uses only a part of such a wave causes
distortions to the sine wave and therefore harmonics.
All current signals result in some way virtually distorted. The most common situation is the
harmonic distortion caused by non-linear loads such as electric household appliances,
personal computers or speed control units for motors. Harmonic distortion causes
significant currents at frequencies that are odd multiples of the fundamental frequency.
Harmonic currents affect considerably the neutral wire of electric installations.
In most countries, the mains power is three-phase 50/60Hz with delta primary and star
secondary transformers. The secondary generally provides 230V AC from phase to neutral
Odd harmonics
Multiple of 3
Order h
Relative voltage % Max
3
5
9
1,5
15
0,5
21
0,5
MULTITEST2000
Even harmonics
Relative voltage %Max
Order h
2
2
4
1
6..24
0,5
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