高频下电树老化引起的高密度聚乙烯击穿现象

为了分析高频下电树老化引起的高密度聚乙烯击穿现象,实验研究了冰水淬火高密度聚乙烯(HDPE)薄膜在频率50 Hz~90 kHz范围内的交流电压作用下电树老化引起的破坏现象及电树生长过程中的电树形态特性的变化。观测高频下树老化引起击穿过程中电弧运动发现:不同频率下HDPE薄膜中电树生长过程中存在树枝、树干、丛状和击穿型4种基本电树形态;在高频下不同电树形态存在形态转换的关系,且随着频率和电压的升高,相同条件下电树老化引起的击穿破坏概率大大增加。试验结果表明,在较高频率下树的形态易向击穿型发展。最后从高频电压对材料极化过程的影响及高频所引起的材料疲劳效应、热效应加剧角度出发,对在高频下电树老化易于引发击穿的特性展开了深入的讨论,解释了高频或中频电气设备易发生绝缘老化破坏的现象。

Breakdown Phenomena Caused by Electrical Tree Degradation in High Density Polyethylene Under High Frequency Voltage

The shape change of electrical tree propagating in ice-water quenched high-density polyethylene(HDPE) film under AC voltage of different frequency ranging from 50 Hz to 90 kHz as well as the breakdown phenomena caused by the treeing degradation under high frequency condition were studied.The electrical treeing aging experiment is carried out at room temperature.The shape change of electrical tree and the arcing process during the experiment is observed via a digital micro-observing system.It is found that the arcing process can be obviously observed under a high frequency voltage compared with that under low frequency voltage.It is also found that under different frequency voltages the electrical tree initiation shape is different.Most of the electrical trees are branch-shape tree under lower frequency voltage.When the frequency is higher than 5 kHz,trunk-shape tree and bosk-like tree appears.Once the frequency is higher than 50 kHz,breakdown tree can be found out.It is shown that the tree shape conversion is influenced by the frequency.The electrical tree usually has a simple shape and rarely changes under low frequency voltage in one hour or more.However,under a high frequency voltage,the electrical tree shape changes more frequently and has a large probability to breakdown.The influence of frequency on material polarization process,fatigue and thermo effect is considered as the main causes of the experiment results.The more serious destruction caused by high frequency electrical treeing degradation can well explain the reason of insulation premature inactivation in mid-frequency or high-frequency electrical equipment.