This study investigates the characteristics of electrical trees in silicone rubber (SiR) samples after soaking in silicone grease (SG) for various times and exposed to switching impulses. The results show that the tree initiation probability increases from 60 to 100 % after SG soaking for 340 h when the impulse amplitude is 38 kV and the tree fractal dimension increases from 1.16 to 1.45. A similar trend is observed under negative impulse. It is suggested that SG soaking leads to a higher tree initiation probability and a larger tree fractal dimension. In addition, isothermal surface potential decay measurements are employed to obtain the trap parameters of SiR samples. Equilibrium swelling procedures are used to test the crosslinking density. The energy level and density of deep trap both decrease with SG soaking time, which is beneficial for the transport of charge carriers injected from the needle tip and further results in more severe scission of SiR molecular chains. Moreover, the expansion of free volume originating from the broken physical crosslinking structure allows more violent impact ionization of charges to occur, which can also aggravate the scission of SiR molecular chains. Therefore, the decreased tree resistance can be found in SiR after SG soaking. Furthermore, the polarity effects can be observed during the tree initiation and propagation process, which are mainly rooted in the different distribution of hole­type and electron-type traps.

中文翻译：

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硅橡胶中的电树：硅脂和开关脉冲的作用

本研究调查了在硅脂 (SG) 中浸泡不同时间并暴露于开关脉冲后硅橡胶 (SiR) 样品中电树的特性。结果表明，当脉冲幅度为38 kV，树木分形维数从1.16增加到1.45时，SG浸泡340 h后树木启动概率从60％增加到100％。在负面冲动下观察到类似的趋势。这表明SG浸泡导致更高的树木启动概率和更大的树木分形维数。此外，采用等温表面电位衰减测量来获得 SiR 样品的陷阱参数。平衡溶胀程序用于测试交联密度。深陷阱的能级和密度都随着 SG 浸泡时间的增加而降低，这有利于从针尖注入的电荷载流子的传输，并进一步导致更严重的 SiR 分子链断裂。此外，由于物理交联结构的断裂导致自由体积的扩大，使得电荷发生更剧烈的碰撞电离，这也会加剧 SiR 分子链的断裂。因此，SG 浸泡后在 SiR 中可以发现树木抗性降低。此外，在树的萌生和传播过程中可以观察到极性效应，这主要源于空穴型和电子型陷阱的不同分布。源于物理交联结构断裂的自由体积的膨胀允许发生更剧烈的电荷碰撞电离，这也会加剧 SiR 分子链的断裂。因此，SG 浸泡后在 SiR 中可以发现树木抗性降低。此外，在树的萌生和传播过程中可以观察到极性效应，这主要源于空穴型和电子型陷阱的不同分布。源于物理交联结构断裂的自由体积的膨胀允许发生更剧烈的电荷碰撞电离，这也会加剧 SiR 分子链的断裂。因此，SG 浸泡后在 SiR 中可以发现树木抗性降低。此外，在树的萌生和传播过程中可以观察到极性效应，这主要源于空穴型和电子型陷阱的不同分布。