Liu Yingyan

Electric field and electromagnetic environment analyses of a 500 kV composite cross arm

In order to further utilize the transmission line cooridor, meanwhile, achieve a relatively friendly electromagnetic environment, composite cross arm is developed and employed in the transmission system. The electric field distribution as well as the electromagentic environment of composite cross arm deserves a detailed and in-depth study to verify its performance. In this research, the three-dimension (3D) finite element method (FEM) was employed to calculate the electric field distribution of composite cross arm. The electromagnetic environment was characterized by electric field intensity on the ground, radio interference and audible noise and these parameters were investigated and analysed. Calculation results indicated that by using proper metal hardware, composite cross arm could obtain a relatively suitable distribution of electric field and potential. The electromagnetic environment calculation results demonstrated that composite cross arm could meet the standard design requirement. Furthermore, some suggestions were made based on this research to achieve an optimization use of composite cross arm.

Effective Equivalent Salt Deposit Density of polluted silicone rubber insulators in wetting process

The pollution flashover characteristics of insulators are tightly related to the salt dissolving out of pollution layer which makes contribution to surface conductivity of insulators in wetting process. For hydrophobic pollution layer on silicone rubber (SR) insulator, both the process of salt dissolving out and the process of salt running off are more complicated in wetting process. The concept of Effective Equivalent Salt Deposit Density (EESDD) is used to characterize the effective salt in wetting process, which is defined as the amount of salt dissolved in water on insulator surface minus the amount of salt ran off from insulator. Actual measurements indicate that EESDD of SR insulators increases in initial half of the wetting period and decreases in ending half of the wetting period. Hydrophobicity of pollution layer, NSDD, polluted manner all have significant influence on EESDD in wetting process. The wetting process of SR specimen keeps 6-9 times as long as that of glass specimen. For naturally polluted SR insulators, maximum percent of EESDD is about 15% of the total ESDD, which is another reason why SR insulators have higher pollution flashover voltage.

Study on the model selection of water diffusion into silicone rubber by NMR and gravimetric technique

Moisture plays a major role in the aging phenomena of high temperature vulcanizing (HTV) silicone rubber material, which is always used as high voltage composite insulator sheds and sheath. In order to obtain an appropriate model to describe the process of water molecule diffusion into silicone rubber, the solid state nuclear magnetic resonance (NMR) was conducted to investigate the existence state of water molecule in silicone rubber. The gravimetric method was also employed to obtain the weight gain curves caused by the water molecule diffusion. The study showed that water molecules had two different state in silicone rubber, one was “free” state and the other one was “bound” state. By combining the results of NMR analysis and gravimetric method analysis, we suggested that the water molecules diffusion into silicone rubber could be explained quantitatively by a Non-Fick diffusion model, Langmuir diffusion model, instead of the classical Fick diffusion model. Furthermore, the water distribution curves in the silicone rubber were also predicted by solving the Fick diffusion equation and the Langmuir diffusion equation, the difference between these two kinds of water distribution curves had been distinguished and analyzed in depth.

Adhesion force measurement of electrical insulating materials by atomic force microscopy

For long-term operating outdoor insulation, contamination accumulation has become an increasingly serious problem. In this paper, atomic force microscopy was used to measure the adhesion force of glass, silicon rubber, porcelain, stalinite samples. Test results showed that adhesion force of silicon rubber was the largest, approximately larger than the other three samples by one or two orders of magnitude. Furthermore, silicon rubber surface exhibited a long-range attractive force and multiple points contact, probably due to the electrostatic interaction and surface roughness. It might be a theoretical proof which accounts for the different contamination accumulation between composite insulator and porcelain or glass insulator.

The dielectric loss mechanism of biological material during low temperature freezing

The dielectric loss property of some biological materials has been studied during freezing. Generally, biological materials have very high permittivity at room temperature and low frequency because of their high water content. During low temperature freezing, the permittivity changes suddenly from 10/sup 6/ to 10/sup 2/ with a large proportion of water changing into ice. At the same time, the dielectric loss tangent (tg/spl delta/) increases and a peak appears. The temperature appearing peak is dependent on the composition of material and the content of water. The variation rate of permittivity and dielectric loss tangent with temperature can show the dimensions and quantity of the ice crystals in materials. Therefore, the relationship between dielectric spectrum and phase change, or dielectric spectrum and the metabolic rate of cells may be established, by means of studying the dielectric polarization and loss phenomena of biological materials in the course of the phase change at low temperature.

Optimum design on anti-corona coating of high voltage generator coil ends

In order to solve the problem of the optimum design of silicon carbide (SiC) anti-corona structures, a new object function of anti-corona optimization is presented. Genetic algorithms are successfully applied to optimize the anti-corona structure of high voltage generator coil ends. The calculation results show the efficacy of the genetic algorithms.

Liquids permeation into HTV silicone rubber under AC/DC electric field

As shed and sheath materials, high temperature vulcanization (HTV) silicone rubber suffers from various types of environmental stresses in actual use. Liquids permeation, as a kind of silicone rubber aging factor, has been investigated by many researchers. However, most of the studies are conducted under the condition of no electric field. Since that composite insulators, especially the high voltage (HV) side, are under high electric field, it is worthy of attention on liquids permeation under AC/DC voltages. In this study, we utilized a new-designed liquids permeation test unit under AC/DC electric field to measure the weight of HTV silicone rubber specimens during the test process. Deionized water, as well as basic fuchsine ethanol solutions were used to verify the effects of electric field on liquids permeation. Besides, the influence of ATH content on the liquids permeation was involved.