Analysis of polarity effect of electrical tree in silicone rubber under impulse voltage

作者： GOZ Electric 时间：2024-09-07 09:35:59 阅读：16

There is a polarity effect in the initiation and growth process of SiR electrical dendrites under impulse voltage, which is mainly manifested in that SiR electrical dendrites are easier to initiate and grow under positive impulse voltage than under negative impulse voltage. The polarity effect under impulse voltage is closely related to the behavior of space charge, and the distribution of space charge is affected by traps. When an impulse voltage is applied to the needle electrode, the injected charge will be captured by a deep trap near the needle tip. Since the time interval between the two impulse voltages during the experiment is 30s, which is much shorter than the dissipation time of the space charge (about a few hours), this part of the trapped charge will form a charge shielding layer around the needle tip, weakening the electric field strength at the needle tip, as shown in Figure 1, thereby inhibiting the growth of electrical dendrites.

Figure 1

The influence law and mechanism of the swelling effect caused by silicone grease under impulse voltage on the electrical tree characteristics of SiR are analyzed. At the same time, the differences in the electrical tree characteristics of SiR under different polarity impulse voltages are compared and analyzed. The following conclusions are obtained:

(1) Under the action of impulse voltage, the swelling effect of SiR caused by silicone grease leads to a decrease in its resistance to electrical tree aging. With the increase of swelling time, the probability of SiR tree formation gradually increases, and the fractal dimension of electrical tree increases. Compared with negative polarity impulse voltage, SiR electrical tree is easier to initiate and grow under positive polarity impulse voltage.

(2) The swelling effect causes the physical cross-linking structure of SiR to be destroyed. The destruction of the physical cross-linking structure increases the free volume of SiR, reduces the deep trap density, enhances the charge transport process, intensifies the collision ionization process, and intensifies the degree of molecular chain breakage, which in turn leads to a decrease in the resistance to electrical tree characteristics of SiR.

(3) Under the action of impulse voltage, the polarity effect of SiR electrical trees is mainly caused by the difference in the distribution of hole-type and electron-type traps. The electron-type deep trap density in SiR (5.82×10^21 m^-3) is higher than the hole-type deep trap density (5.13×10^21 m^-3). A higher density of electrons will be captured around the needle tip, and the charge shielding layer formed will have a stronger weakening effect on the electric field at the needle tip, which makes it more difficult for SiR electrical trees to initiate and grow under negative voltage.