[SI-LIST] physics behind EMI powerline filters


Hello Group,

I have a "long-time" question, that the thread "square-wave harmonics" reme=
mbered me.

I'll put a case, and ask the question after.

This is the case:

- When trying to minimize the conducted emissions from a electrical equipme=
nt / circuit, one of the things to do is to put a EMI filter at the power e=
ntrance. This filter can be from a manufacturer (ready filter) or you can m=
ake one (with common mode inductors, capacitors, inductors).

This are the questions (they arearelated, i.e., complete each other):

- What, physically speaking, happens to the EMI energy that leaves the equi=
pment when I add a filter??? When there is no filter, I understand that the=
 energy goes to the mains?? Does the filter reflect the EMI energy, keeping=
 it "arrested" inside the equipment?

- Thinking under the light of the principle of energy conservation, what ha=
ppens to the EMI energy when I add a filter?? It cannot be lost...

- ... And, supposing that the energy keeps arrested inside the equipment, i=
sn't it worse for radiated emissions?? i.e., it can increase the level of r=
adiated emissions??

Thanks in advance for your attention.

Regards,

Muriel Bittencourt de Liz
Ph.D. Student
Interest Areas: EMC for power electronics, RF measures, EM interference
Federal University at Santa Catarina State
Florian=F3polis, Santa Catarina, Brazil


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