Gideon Analytical Laboratories received several failed 55 Amp (55BCF6- F8236B) and 75A (75BCF6-F8237B) TE Corcom EMI filters for failure analysis. These EMI filters used capacitors manufactured by Hua Jung Components (HJC). Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction. Most electronics contain an EMI filter, either as a separate device or embedded in circuit boards. Its function is to reduce high-frequency electronic noise that may cause interference with other devices. Regulatory standards exist in most countries that limit the amount of noise that can be emitted. All of the TE Corcom EMI filters were from the same vintage according to the outside label. The goal was to determine the cause of the failure.
Failure analysis ensued. The units were all taken apart to examine. In only one of the 75amp units did the capacitors to arc out to the ground (which was metal housing). In all of the other 55A and 75A units the capacitors arced out to the ground, and this sustained current burned out the internal cavity of the capacitors, which lasted long enough to short to the metal housing. Damage was severe for each input capacitor; the fire melted the insulation foil, the plastic housing, the epoxy encapsulation, and the polypropylene dielectric film. On the 55A capacitors, the wire coming from the schoopage metal was also burned. These capacitors also had cracks in the thermoset epoxy resin, which is caused by too much internal pressure. In the 75A unit, two of the four capacitors burned. The back two remained intact. These two were examined by removing the epoxy and the packaging. Something was wrong with the metal or delamination had occurred because they had lower than normal capacitance and separation from the schoopage metal. The foil was unrolled until the failure site was located. There was a hole in the polypropylene film. SEM-EDS analysis was performed at the failure site.
These several failed 55 Amp(55BCF6- F8236B) and 75A (75BCF6-F8237B) TE Corcom EMI filters were failing due to their Hua Jung Components (HJC) capacitors. There were significant problems with the capacitors. There was electrical arcing. There was cracking. There was also degassing and shrinking of the polypropylene film. The thermal issues created in the first input capacitor failure caused the other two to fail in the line to line input. The heat melts the PP causing a cavity and loss in capacitance. Several new filters were examined and several input capacitors (HJC 10uF) were out of specification. Whether you're a big company or small, product liability is one of the most important issues facing companies. This could lead to lawsuits, incurred damages or loss of life. Protect yourself.
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