Methods of quality characterization of foil-based capacitors

The quality of aluminium foil-based capacitors is sensitive to various technological parameters within the production process. There are a few methods of their quality assessment that can identify defects inside the wound foil structures, poor metal contacts or bad packing. These methods are often applied at the end of production to monitor the quality of the final products. Only a small fraction of the produced capacitors is checked by a long-lasting procedure of extensive and repeatable charging and discharging. This procedure makes it plausible that some capacitors can fulfil the assumed quality requirements but will deteriorate soon and can cause serious economic losses when used in equipment. Therefore, it is recommended to identify the most informative methods of capacitor quality assessment. This paper investigates the problem by presenting measurement results of the third harmonic index, dielectric loss and acoustic emission in type WXPC capacitors which are widely applied to reduce electromagnetic interference caused by domestic electric equipment.