HT instruments VEGA78 - Manual (Page 117)

VEGA78
EN - 115
LEGEND:
1. Fundamental
2. Third Harmonic
3. Distorted
Waveform
Effect of the sum of 2 multiple frequencies
The EN50160 standard recommends to stop the index in the expression (1) corresponding
to the 40
th harmonic. A fundamental element to detect the presence of harmonics is THD
defined as:
100 %
1
40
2
2
x
V
V
THDV
h
h

 
This index takes all the harmonics into account. The higher it is, the more distorted the
waveform results.
10.2.2. Limit values for harmonic voltage
EN50160 standard fixes the limits for the harmonic voltages, which can be introduced into
the network by the power supplier. In normal conditions, during any period in a week, 95%
of the RMS values of each harmonic voltage, mediated on 10 minutes, shall be lower 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 40
th
order) must be lower than or
equal to 8%.
ODD HARMONICS EVEN HARMONICS
Not multiple of 3 Multiple of 3
Order h Relative voltage %Max
Order h Relative voltage % Max Order h Relative voltage % Max
5 6 3 5 2 2
7 5 9 1,5 4 1
11 3,5 15 0,5 6..24 0,5
13 3 21 0,5
17
2
19 1,5
23 1,5
25 1,5
Table 13: Reference values for harmonics voltage in compliance to EN50160
These limits, theoretically applicable only for the suppliers of electric energy, provide
anyway a series of reference values within which the harmonics introduced into the
network by the users must be contained.