Influence of Different Step Time and Step Voltage on the Calculation of Endurance Coefficient in Polypropylene AC Step-Stress Tests

Polypropylene is considered to be one of the new power cable insulation materials due to its excellent insulating and thermal properties, and numerous of studies on its insulating properties have been published recently. The endurance coefficient plays a vital important role in assessing the performance of polypropylene insulation under long-term electrical stress ageing and the step-stress method is usually adopted to calculate the endurance coefficient of insulation. Nowadays, step stress tests are mainly implemented by changing the step voltage and the method has a large time consumption at longer step times. In this paper, the AC breakdown field strength of polypropylene is obtained by AC breakdown test to provide a reference for step stress test. The polypropylene endurance coefficient is calculated by different methods of varying the step time and the step voltage. It is found that the method of varying the step voltage could also calculate the endurance coefficient of polypropylene and the result is similar to that obtained by varying the step time. At the same time, it is also found that the large step voltage may cause the sample breakdown during the pressurization process, resulting in data distortion, so the step voltage should be selected reasonably when choose the method of changing the step voltage.