PQA819 - PQA820
EN – 24
12.2.1. Limit values for harmonics
EN50160 guideline prescribes the limits for the Harmonic voltages the Supplier may put in
network.
In normal operating conditions, at any time in a week, 95% of the efficient values of
each harmonic voltage, averaged to 10 minutes, must be lower than or equal to the
values indicated in the following Table 6
The total harmonic distortion (THD) of supply voltage (including all harmonics up to the
40th 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 6: Maximum values of voltage harmonics in compliance with EN50160
These limits, which theoretically apply only to Electric Power Suppliers, anyway provide a
series of reference values within which also the harmonics put into network by users
should be kept.
12.2.2. Causes of the presence of harmonics
Any appliance altering the sinusoidal wave or simply using a part of such wave causes
distortions to the sinusoid, and hence harmonics
All current signals are therefore someway virtually distorted. The most common
distortion is the harmonic distortion caused by non-linear loads such as household
appliances, personal computers or motor speed adjusters. Harmonic distortion
generates significant currents at frequencies which are whole multiples of network
voltage. Harmonic currents have a remarkable effect on neutral conductors of
electrical systems
In most countries, the network voltage used is three-phase 50/60Hz, supplied by a
transformer with triangle-connected primary circuit and star-connected secondary
circuit. The secondary circuit generally generates 230V AC between phase and neutral
and 400V AC between phase and phase. Balancing loads for each phase has always
been a problem electrical system designers
Until approximately ten years ago, in a fully balanced system, the vector sum of the
currents in the neutral was zero or anyway quite low (given the difficulty of obtaining a
perfect balance). Connected devices were incandescent lights, small motors and other
devices that presented linear loads. The result was an essentially sinusoidal current in
each phase and a low current on the neutral at a frequency of 50/60Hz. “Modern”
devices such as TV sets, fluorescent lights, video machines and microwave ovens
normally draw current for only a fraction of each cycle, thus causing non-linear loads
and, consequently, non-linear currents
