频率对硅橡胶起树电压及电树枝形态的影响

Influence of Frequency on Tree Initiation Voltage and Electrical Tree Shape in Silicone Rubber

超高压预制式电缆附件用硅橡胶材料的电树枝化制约了电力电缆系统的长期安全稳定运行。为了解电压频率对硅橡胶电树枝特性的影响,在50 Hz^130 kHz这一较宽频率范围的交流电压作用下,试验研究了硅橡胶中电树枝的引发及生长特性。结果表明,随着频率的升高,起树电压呈现出明显的阶段性下降特点。硅橡胶电树枝起始后,经过一定时间的生长主要发展为3种形态:树枝状电树、松枝状电树和丛状电树。3种形态的出现几率受频率影响较大,低频下以树枝状电树和松枝状电树为主,而高频下则以丛状电树为主。经分析认为,高频下作用于针尖处频繁的机电应力导致了弹性材料硅橡胶起树电压的降低。同时高频下急剧增大的介质损耗产生的热量导致了电树枝对材料的强烈侵蚀。

To investigate the influence of frequency on the electrical tree characteristics and the damage mechanism of such insulation, the characteristics of electrical tree in silicone rubber under AC voltage of different frequency ranging from 50 Hz to 130 kHz were studied. The tree initiation voltage was measured at room temperature and the processes of electrical tree were observed via a digital micro observing system. From the experiments, it is found that the electrical tree in silicone rubber is greatly affected by the frequency of applied voltage. With the increase of frequency, tree initiation voltage of silicone rubber decreases. And the frequency can be separated into four stages, while tree initiation voltage appears different magnitude of decrease. There are 3 kinds of electrical tree during the experiments： branch tree, trunk tree and pine tree. The branch tree and pine tree are the primary shapes in the range of low frequency, while the bush tree is the primary shape in the range of HF. The dielectric spectroscopy of silicone rubber was also measured. At last, the influence of frequency on electrical tree in silicone rubber was analyzed. The repeated electro-mechanical stresses applied to the needle tip under high frequency may lead to the decrease of tree initiation voltage of silicone rubber. And with the increase of frequency, the serious erosion in silicone rubber by electrical tree may be caused by the great increase of dielectric losses.