But the problem of harmonics will be solved as soon as EN 61000-3-2 takes effect!

Answer by Stefan Fassbinder

In a legal sense the EN 61000-3-2 became effective on January 1, 2001. Unfortunately this does not mean that it does also take substantial effect in a technical sense, while the basic idea was really a very proficient appoach – to solve the problem of harmonics dissipation right at the point of origin. Mind that the source of harmonics is generally the power consuming device and that therefore harmonics dissipate »upstream« from there, opposed to the direction of energy flow! End consumer device industry, however, fearing additional design difficulties and production costs, offered heavy resistance so that in the end the threshold values were fixed so high and so many peepholes were included that a nameworthy mitigation of harmonics dissipation into the networks cannot be expected even when all old machines will have been replaced with compliant models.

For instance, on a 1995 computer with common SMPS technique an bare of any mitigation technique a THD (total harmonic distortion) of 73.7% was measured in the input current. The 1999 successor model was already designed according to EN 61000-3-2 and had a slightly reduced THD of 67.9%. That was enough for a pass.

When replacing the screen with a new modern 2002 flat screen it could be read in the manual that this flat screen also matched EN 61000-3-2, while it is a question of linguistics rather than of technology whether this statement is true. After all only PCs and single-phase peripherals ranging from 75 W to 600 W input rating are covered, while modern flat screens only have about 25 W input. The measured value was 78.1% THD but as the device falls out of the range of validity it can with some justification be said it matches the EN 61000-3-2.

20/12/2006

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