Room temperature vulcanized (RTV) silicone rubber is extensively used in power system due to its hydrophobicity and hydrophobicity transfer ability. Temperature has been proven to markedly affect the performance of silicone rubbers. This research investigated the degradation of RTV silicone rubber under temperature cycling treatment. Hydrophobicity and its transfer ability, hardness, functional groups, microscopic appearance, and thermal stability were analyzed using the static contact angle method, a Shore A durometer, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetry (TG), respectively. Some significant conclusions were drawn. After the temperature was cycled between −25 °C and 70 °C, the hydrophobicity changed modestly, but its transfer ability changed remarkably, which may result from the competition between the formation of more channels for the transfer of low molecular weight (LMW) silicone fluid and the reduction of LMW silicone fluid in the bulk. A hardness analysis and FTIR analysis demonstrated that further cross-linking reactions occurred during the treatment. SEM images showed the changes in roughness of the RTV silicone rubber surfaces. TG analysis also demonstrated the degradation of RTV silicone rubber by presenting evidence that the content of organic materials decreased during the temperature cycling treatment.

The outdoor ultra-high voltage (UHV) dry-type air-core smoothing reactors (DASR) of High Voltage Direct Current systems are equipped with a rain cover and an acoustic enclosure. To study the convective heat transfer between the DASR and the surrounding air, this paper presents a coupled model of the temperature and fluid field based on the structural features and cooling manner. The resistive losses of encapsulations calculated by finite element method (FEM) were used as heat sources in the thermal analysis. The steady fluid and thermal field of the 3-D reactor model were solved by the finite volume method (FVM), and the temperature distribution characteristics of the reactor were obtained. Subsequently, the axial and radial temperature distributions of encapsulation were investigated separately. Finally, an optical fiber temperature measurement scheme was used for an UHV DASR under natural convection conditions. Comparative analysis showed that the simulation results are in good agreement with the experimental data, which verifies the rationality and accuracy of the numerical calculation. These results can serve as a reference for the optimal design and maintenance of UHV DASRs.

The spark discharge in the soil is a key factor that affects the impulse characteristics of grounding devices under the lightning current. However, since soil is inhomogeneous medium consisted with humid‐air, ionic liquid, and soil particles, the developing process of the soil sparkover is very complicated. In this study, the polyester‐based sensitive films are used to observe the morphology features of the soil sparkover in the plate electrodes. According to the observed images, the spark discharge in the soil can be divided into partial discharge and arc discharge. The change of instantaneous resistance can be explained by the three stages of soil ionisation/deionisation. Moreover, the distinct images of the sparkover around the rod electrode buried horizontally in the grounding pool are obtained by the proposed method. The distribution of discharge points, developing process, and feature of the soil sparkover are analysed.

HVDC Deep-well grounding electrode covers a small area, which effectively alleviates the problem of difficulty in selecting the site of grounding electrode. Due to the small number of electrodes, each sub-electrode has to bear tens of times the current of conventional electrodes. In order to reduce the current density on the electrode, it is usually necessary to use long vertical electrodes to extend into low resistivity layers’ hundreds of meters underground. Because it involves a wide range of underground depths, it is particularly important to accurately evaluate the distribution of resistivity at the electrode site for calculating the electrical parameters of deep-well grounding electrodes. In this paper, four-point method (FP), controllable source audio magnetotelluric method (CSAMT) and magnetotelluric method (MT) are proposed to analyze the conductivity structure of the shallow layer, deep layer and the vicinity of the electrode, and the earth resistivity model of deep-well grounding electrode is obtained. By comparing the on-site grounding resistance measurements of practical engineering application, it is found that the absolute error of the earth resistivity model obtained in this paper is 0.064Ω when calculating the grounding resistance of the deep-well grounding electrode. Engineering examples show that the exploration method in this paper has strong adaptability to the site, and the earth resistivity modeling method has good reliability.

Transmission tower grounding safety is a critical element that significantly impacts the reliability and sustainability of power grids. Tower grounding resistance is a significant grounding characteristic parameter. In order to accurately measure the grounding resistance of towers using the clamp meter method in both single-tower and multi-tower parallel scenarios, this paper establishes theoretical calculation models for measuring tower grounding resistance using the clamp meter method. Considering the interaction between the artificial grounding device and the tower foundation, this paper models and simulates transmission towers and lightning shield wires, analyzing the influencing factors on the grounding resistance measurement results using the clamp meter method in both single- and multi-tower parallel scenarios. The results show that for single towers, the clamp meter measurement results increase with decreasing foundation root spacing and increasing length of the artificial device’s extension lines, but the changes are relatively small. In multi-tower grounding scenarios, due to the shunting effect of the parallel branches formed by the towers and lightning shield wires, the value is smaller than in single-tower grounding scenarios. Changing the number of parallel towers and the type of lightning shield wire produces little effect on the measurement results. However, changes in soil resistivity have the most significant impact. Therefore, correction formulas for the impact of soil resistivity on clamp meter measurements are proposed and then verified by applying them to field tests.