High energy density capacitor is a key device in power supply source in Electromagnetic Gun (EMG) system. In order to increase the reliability of the power source equipment, the lifetime of capacitors must be lengthened. The increasing of the capacitor's lifetime is mainly beneficial from its self-healing capability. Nevertheless the self-healing is the main reason for the capacitance loss of metallized film capacitors, and it might finally lead to the failure of a capacitor. Firstly, the research results show that the self-healing energy is the crucial factor which influences the self-healing process. Secondly, the paper analyzes the capacitance loss mechanism of metalized film capacitor, including the effect of electrode structure and interlayer air. And then, the corresponding methods of increasing the lifetime of the metalized film capacitors are proposed. At last, based on parameter optimization of electrode pattern construction and practical techniques, a dry-type compact metalized film capacitor with energy density of 2.0 MJ/m3 is designed and tested with a lifetime over 500 shots. And the impregnated metalized film capacitor can be expected to achieve a lifetime of 1000 shots. And the second type design with 1.5 MJ/m3 design with discharge current magnitudes up to 100 kA have already been testified in an Electromagnetic Gun (EMG) system application.
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