Regarding corona discharges

 What is corona discharge?
 Strongly oscillating electrical field around the electrode from high-frequency waves and high-voltage separate air molecules. The generated ions and atoms and the electrons already existing in the air accelerate and contact other molecules. The impacted molecules separate and increase the number of electrons and ions. The space where corona discharges occur generates light. This atmosphere promotes chemical reactions that breakdown insulating film. The higher the frequency, the quicker the insulation is damaged. This is why the best course is to design products such that corona discharges do not occur.


The dangers of corona discharges
When corona discharges occur, the higher the frequency, the shorter the product life. For example, even a product that can withstand corona discharges at 50 Hz for 100 years will breakdown after 1 month with corona discharges at 50 kHz. (1/1,000)
If insulation is damaged, flashovers occur and cause products defects. However, conventional insulation testers cannot detect corona discharges. Since the product operates normally at the factory, defects are not found until the product is on the market.
High-frequency components increase due to inverter control, which increases danger. The CORONA-i XT series is valuable for controlling accidents caused by such corona discharge


Corona discharges and dielectric breakdowns
Of late years the thoughts of eco-measures increased, and an electric appliance, parts to use by a high frequency, high voltage with it increased. It is a corona discharge (partial electric discharge) phenomenon to have to be careful when handle a high frequency, high voltage.
The corona discharge is the phenomenon that cannot discover easily in the conventional withstand pressure examination and insulation examination.
In corona discharges, electrons are pulled by positive poles and accelerate to very high speed. They hit air molecules repeatedly and knock out their electrons, causing ionization. This has the side effect of generating ozone (O3).
Ozone gas is a strong oxidizer and gradually oxidizes and breaks down insulators. Furthermore, high speed electrons and ions collide with the insulators and wear away at their surfaces.
Finally, corona generates heat and the combination of these side effects gradually breaks down the insulators. Eventually, dielectric breakdowns and flashovers occur.
However, corona discharges are unusually weak electrical discharges. Furthermore, the operating waveform of most circuits is normal. As a result, no abnormalities appear and the products pass inspection.
While the energy of corona discharges is only several Pico coulombs per cycle, deterioration can build up over several months.





 
The blue sine waveform is a drive voltage waveform
(No abnormality can be found from this waveform)
 
Corona discharge waveform overlaps
the purple waveform
 
The green waveform is a
corona discharge detection pulse

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