Amprobe DM-4 Power-Quality-Recorder - Manual (Page 50)

A fundamental element to detect the presence of harmonics is Thd defined as:
This index takes all the harmonics into account. The higher it is, the more
distorted the waveform gets.
15.2.2 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 40th order) must be less than or equal to 8%.
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.
49
DM-4 Power Quality Recorder
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