Electrification box causes wall resonance
The most likely culprit of this unexpected result was probably due to cavity resonance. The metal box tested formed a resonant cavity, where standing waves in the field were formed between opposite sides when the dimension between the sides of the box was a multiple of. Here, the capacitor bank and the grid inductance (transformer) are in parallel as seen from the harmonic source (the load). In my consulting work, I have noticed that radiated emission (RE) and radiated immunity (RI) have become much more pervasive issues for most of my clients. There are several reasons for this, which include the shift to more compact design, more portable products, as well as the fact that noise. Everything looks solid — until something inside the metal box starts misbehaving at a specific frequency, and nobody can explain why. It's one of the most underdiagnosed failure modes in EMC engineering, and it hits small RF shielded. Ferroresonance is a non-linear resonance phenomenon that can affect power networks. Considering the simplified circuit represented on Figure L29 (no PFC capacitors connected): The voltage distortion V h at the busbar level results from two different factors: voltage distortion U h present on the supply network due to non-linear loads outside of the considered circuit (incoming.
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