High field effects on the electrical aging of polyethylene and of polypropylene

In this paper, we show that the electrical aging equation for polyethylene and polypropylene under high fields (above 100 kV/mm) require and additional term, which is the strain energy (sometimes called the electromechanical energy). This term becomes significant at high fields when the electromechanical stress thus generated compress the tested sample. From a practical point of view, this means that life could be a bit longer than expected at very high fields. Examples with the two above polymers are shown along with the corresponding calculated activation volume and the strained activation volume. The stress at which the strain energy becomes significant can also be calculated from the mechanical properties of the polymer. This makes the aging equation a little bit more complicated than we expected but it is still possible to relate the fast breakdown measurements with long lasting endurance tests.