The applicability of functionally graded materials (FGM) for solid insulator of gas insulated switchgear (GIS) was investigated. First, a new fabrication method based on layer-by-layer casting technique was demonstrated to prepare FGM insulator possessing spatial distribution of dielectric constants. Then, electric field strength in the FGM spacer model was calculated and optimized by using finite element method (FEM). Three types of truncated cone spacers were fabricated according to the optimization results. Finally, surface flashover tests were performed under AC voltage and lightning impulse voltage applications. Results in both circumstances indicated an evident improvement of flashover voltage when FGM insulator was employed. As a result, we verified the fabrication technique and the applicability of FGM insulator for enhancement of insulation performance in GIS device.

Contamination flashover of insulators is one of the main threats to the safety of power systems, and regular cleaning of insulator surface pollution is an effective solution to this problem. In this paper, the laser cleaning of ceramic insulators is studied via simulations and experiments. The adhesion between a contamination layer and an insulator surface is estimated. A laser cleaning model for contaminated insulators is established, and a numerical analysis of the thermal stress field distribution characteristics of laser cleaning is carried out. Various factors that affect the thermal stress field distribution, including the laser power, laser scanning speed and thickness of the contamination layer, are also analysed. The optimal cleaning parameters for the best performance of laser cleaning are obtained through simulation and experiments. The result shows if the equivalent salt deposit density (ESDD) is 0.05 mg/cm 2 , and the nonsoluble deposit density (NSDD) is 0.25 mg/cm 2 , the best cleaning effect could be achieved when the laser power is 100 W and the scanning speed reached 6000 mm/s.

No abstract

No abstract

When a high-power very low frequency (VLF) communication system is in operation, the end of the antenna is in an alternating strong electric field environment. Due to dielectric loss, abnormal temperature rise may occur at the end of the antenna. To solve the problem, analysis on the electric field distribution and temperature rising effect at the end of the antenna is first carried out in this paper. The factors that affect the electric field distribution and temperature rising, including the amplitude and frequency of the excitation voltage, the diameter of the antenna conductor and the material properties of the outer sheath of the antenna, are studied in detail. A novel approach to improve the electric field distribution and to suppress temperature rising is proposed by designing a dielectric loss eliminator, and the effectiveness of the designed device is verified by simulation.