Huidong Tian

Dielectric properties of graphene-filled epoxy nanocomposite with enhanced thermal conductivity

The development of advanced dielectric materials with high thermal conductivity is of crucial importance in modern electronic and power equipment systems. Herein, multilayer graphene nanosheets/epoxy nanocomposites with enhanced thermal conductivity were fabricated by solution blended processes. It was found that the incorporation of graphene nanosheets had little impact on thermogravimetric properties of epoxy composite but had a certain effect on glass transition temperature (Tg), which increased by 4.63 °C with the incorporation of 0.1 wt.% graphene nanosheets. The incorporation of graphene nanosheets also increased dielectric constant and loss as well as DC conductivity in different ranges. At 25 C and 50 Hz, in contrast with the neat epoxy composite, dielectric constant increased by 36.87 % with incorporation of 0.5 wt.% graphene nanosheets. The thermal conductivity and diffusivity increased by 34.59 % and 24.37 % respectively with the incorporation of 0.5 wt.% graphene nanosheets. The incorporation of uniformly dispersed graphene nanosheets into polymer matrix as thermal conductive fillers paves a way to expand the application of polymer materials in electronic packaging fields.

Influence of key structure parameters on electrical field distribution of tri-post insulator used in UHV

Gas insulated metal enclosed line (GIL) has been widely applied in power transmission system due to its high safety and reliability level. Because of its cost saving production and excellent mechanical property, tri-post insulator is the key structure of insulation in GIL. Therefore, the safe operation of tri-post insulator determines the insulation strength level of GIL. Tri-post insulators have the characteristic structure with post zone and sphere zone. The thickness and width of sphere zone, conical degree and radius of post zone, depth and radius of metal insert have great influence on electrical field strength. High electrical field are mainly distributed on surfaces of insulator and metal inserts. Over-high partial electrical field may cause the partial discharge or insulation failure. This paper has researched how these parameters impact the field strength, and adjusted the parameters listed above to lower the maximum field value, which is vital for insulation structure design and production.

Properties of interface between epoxy resin layers cured at different times

Interfacial materials have been used as transition layers between the conductor metal and the insulation composite in some high voltage power equipment. Epoxy resin composite is one of the most important materials used as the interfacial coating, then an interface between epoxy coating and epoxy insulation composite is formed. Therefore the influence of the epoxy-epoxy interface should be studied. The interface samples are formed by an epoxy resin layer cured on the epoxy resin which has cured with the same procedure. Compared with the sample without the interface, the existence of this interface makes the mechanical properties have different extent reduction. The tensile strength decreases 28.4%. The bending strength decreases 39.5%. The impact strength decreases 39.2%. The results of mechanical strength testes indicates that epoxy resin on both sides of the interface should link through chemical bonds, and the interface may form a “weak crosslinking” area. This interface has little influence on the thermal performance. And in the measurement range, the relative permittivity and dielectric loss show little change too. The existence of this interface formed by curing does not affect the application of the thermal and AC systems.

Influence of moisture and temperature on the frequency domain spectroscopy characteristics of transformer oil

Transformer oil is an important liquid dielectric of oil-immersed transformers. Moisture and temperature bring a great harm on the transformer insulation. This research was carried out to find the influence of moisture and temperature on the frequency domain spectroscopy (FDS) characteristics of transformer oil. As a non-destructive diagnostic technique, FDS technique possesses characteristics of strong anti-interference ability and abundant information, which is very suitable for the measurement on spot. This paper focuses on the research of the relationship between moisture, temperature and dielectric properties of transformer oil with the help of IDAX300 measurement system. Oil samples of different moisture level, 8ppm, 20ppm, 27ppm and 42ppm, have been measured at different temperatures, 29°C, 40°C, 60°C and 80°C. Results shows that the relative permittivity, in low-frequency areas, increase rapidly with moisture content and temperature. The DC conductivity calculated from dissipation factor increases exponentially both with the increase of moisture content and temperature. This relationship can be described as a fitting formula. This finding can be used for the online diagnosis of transformer oil moisture content.