Zhikang Yuan

Moisture induced local heating of overhead line composite insulators

There has been a growing concern over recent years regarding the phenomenon of local heating of composite insulators. In this paper, the influences of humidity, contamination and local electric field on the temperature and dielectric properties of field-aged insulators were studied experimentally. Aging of the silicone rubber (SIR) material on the weathershed surface, rather than resistive current flow from contamination, was found to be the major cause of local heating observed by thermography. The aged SIR material exhibited strong dielectric loss under high localized AC electric field and high relative humidity. A hypothesis was developed to mitigate the moisture induced local heating on composite insulators.

TSC characteristics of composite insulators in 2000h salt fog ageing test

With the increase of composite insulators operating years in the grid, the ageing of the silicone rubber materials become a hot research topic. Artificial ageing tests are wildly used methods to assess the long-term operating performance of composite insulators in short time. Salt fog ageing test is an effective method of artificial accelerated ageing test. The 2000h salt fog ageing test for composite insulators was carried out in this paper. Silicone rubber sample was cut from umbrella skirt for thermal stimulation current (TSC) test. Test results showed that with the increase of salt fog aging time, the peak current and trap charge of silicone rubber materials increased, while trap level showed a trend of decline at the early stage of aging, and a rising trend in the later stage of aging. It can be inferred that the charged particles bombardment produced by corona discharge may be the main cause of the change of the surface trap charge and the trap level of the silicone rubber materials.

Vapor-liquid equilibria of (CF 3 I + CO 2 ) at the temperature of 243.150K

It has become an imperative case on seeking the substitute of SF₆ for its severe greenhouse effect in recent years, not only for scientists but also the electricity sectors. CF₃I, as a substitute gas for SF₆ with lower Global Warming Potential (GWP), has been investigated. The use of pure CF₃I in gas insulated switchgear (GIS) and gas insulated metal enclosed transmission line (GIL) is difficult because CF₃I has a high dew temperature. We have therefore mixed CF₃I with CO₂. In this paper, an apparatus was used to get the vapor-liquid equilibrium data for (CF₃I + CO₂) system at 243.150 K. All of the experimental data were correlated with the Peng-Robinson (PR) EoS using the classical van der Waals (vdW) mixing rule (PR-vdW model). The results show the changing rule for the vapor pressure and its corresponding mole fraction of (CF₃I + CO₂) gas mixtures to suit the operation environment in GIS/GIL and supply an accurate basis for the application of (CF₃I + CO₂) gas mixtures in electric equipment.

Analysis on FRP rod of composite insulators by XPS

Composite insulators are widely used in transmission lines. Performance degradation of material is more and more urgent with operation time increases. In China Southern Power Grid, some composite insulators in-service suffer partial abnormal temperature rise which has been a serious potential hazard to operation of transmission lines. In this paper, a 500 kV AC composite insulator with partial abnormal temperature rise, was analyzed. By dissecting these insulators, FRP rod corrosion with varying degrees were found along the string. After that, chemical compositions on FRP rod corrosion surface were examined by XPS (X-Ray Photoelectron Spectroscopy). Test results showed that the basic elements, carbon, nitrogen and oxygen changes according to certain rules and the chain number of Si-O increases when corrosion degree aggravate. Analysis on change of chemical element reveals that the FRP rod corrosion of the composite insulators with partial abnormal temperature rise is mainly due to oxidation.