Mechanical Stress Distribution inside Dry Capacitor Elements

Many power products are produced by winding paper, polymer film or metal foils around an electrically active or passive core, like cables, bushings and capacitor elements. The mechanical stress distribution inside the product has high impact on its final performance. The stress distribution will be determined by the selected materials, winding parameters, and the ambient temperature. In this work the stress distribution inside dry metallized film capacitor elements for HV applications has been investigated using multiple experimental methods: Parotester, Smith needle, Pressure sensors and X-ray computed tomography. The results showed that the tested methods were unable to provide exact values of the radial stress distribution inside the capacitor element. As a continuation, the nonlinear material properties of the biaxially oriented polypropylene capacitor film were characterized. This work indicated that the temperature and the initial film stress will have an effect on the resulting tightness of the capacitor element.