Cumulative Damage Threshold Bands of LDPE and its Role in DC Lifetime Model Determination

Combining the inverse power law model with Miner's cumulative damage theory allows the description of complex insulation material failure processes as a straightforward mathematical analysis. The size of the cumulative damage threshold band determines the length of the material's voltage withstand time, which is ideal for use in life estimation of power equipment. While most researches focus on examining the voltage endurance coefficient of insulating materials, it is the often-overlooked cumulative damage threshold that is even the decisive factor. In this paper, step stress test, constant stress test and intermittent damage test were carried out using cable insulation LDPE samples under DC conditions. A simple method based on intergroup variance minimization is proposed to achieve the cumulative damage threshold band and voltage withstand coefficient, and the accuracy of the algorithm is verified according to the constant stress method. More importantly, subjecting new samples to voltage shocks and resting them to re-apply electrical damage directly confirms that the cumulative damage threshold is a key determinant of dielectric lifetime.