频率对聚乙烯电树起始的影响特性研究

为研究电压频率对聚乙烯电树起始特性的影响,用冰水淬火冷却高密度聚乙烯试验50Hz～90kHz交流电压下的电树起始特性。试验发现电树起始电压值在50Hz～1kHz间变化不大,>5kHz时电树起始电压为先增后减;在试验频率范围内共存在7种电树形态,电树形态种类随频率提高而增多,每种电树形态对材料的绝缘破坏程度不尽相同,7种电树形态的起始电压存在较大差异。最后对高频电压对电子加速过程的影响及高频所引起的材料疲劳效应加剧的试验结果展开了讨论。

Influence of Frequency on Electrical Tree Initiation in Polyethylene

Treeing degradation in dielectric polymers often leads to insulation failures in electrical equipment. In order to make out the breakdown failures, the tree initiation characteristics of ice- water quenched HDPE under AC voltage in frequencies ranging from 50 Hz to 90 kHz are studied. It is found that the tree initiation voltages (TIV) change a little when the frequency is from 50 Hz to 1 kHz. When the frequency is higher than 1 kHz,the TIV increases with the increase of frequency before reaching a maximum TIV. While the TIV decreases at first then increases at frequency >10 kHz. There are 7 categories of tree shapes, including branch- like, trunk- like, bosk- like, direct breakdown, bosk- trunk, bosk- breakdown and branch- trunk, appeared in the experiment. The categories of tree shapes manifold with the frequency increasing. The TIV of different categories are different apparently. The breakdown shape shows the highest TIV while the branch- like one shows the lowest TIV. The damage degrees to insulation material are different for different categories. It is also found that as the frequency increases, the dispersion of TIV increases remarkably. Though the polymer shows higher average TIV values as the frequency is larger than 1 kHz, the larger dispersion in higher frequency region indicates that the application of polymer insulators in medium or high frequency area would bring a higher breakdown risk as one can find from the frequent insulation failures in high frequency machines. The influence of frequency on electron accelerating process and fatigue effect aggravation in material under high frequency are considered as main causes of the experiment results.