Temperature and Electric Field Distribution Characteristics of a DC-GIL Basin-Type Spacer with 3D Modelling and Simulation

The temperature properties of real-type direct-current gas-insulated transmission lines (DC-GIL) with a basin-type spacer were investigated by the finite element method in this paper. A horizontally installed model was established and the temperature distribution was obtained with a 3D model. The specific heat capacity and thermal conductivity of the spacer were measured and applied in the simulation. The results show that the temperature of the convex surface was slightly higher than that of the concave surface. With an increase in the SF6 pressure, the temperature of the spacer decreased, which can be attributed to the improvement of convection due to increases in the heat capacity per unit volume. With an increase in the ambient temperature, the temperature of the spacer increased linearly. The temperature difference between the inner and outer parts of the spacer increased with increases in the load current. Besides, an obvious increase in the surface electric field strength appeared under the influence of the thermal gradient compared to the results without the thermal gradient. Thus, special attention should be paid to the insulation properties of the spacer considering the influence of temperature distribution. This study evaluates both the thermal and insulation characteristics of the GIL along with the spacer under various conditions.

Terahertz Metamaterial Modulator Based on Phase Change Material VO2

In this paper, a new type of terahertz (THz) metamaterial (MM) modulator has been presented with bifunctional properties based on vanadium dioxide (VO2). The design consists of a VO2 resonator, polyimide substrate, frequency selective surface (FSS) layer, and VO2 film. Based on the metal-insulator transition (MIT) of VO2, this structure integrated with VO2 material can achieve the dynamic modulation on both transmission and reflection waves at 2.5 THz by varying the electrical conductivity value of VO2. Meanwhile, it also exhibits adjustable absorption performance across the whole band from 0.5–7 THz. At the lower conductivity (σ = 25 S/m), this structure can act as a bandpass FSS, and, at the high conductivity (σ = 2 × 105 S/m), it behaves like a wideband absorber covering 2.52–6.06 THz with absorption A > 0.9, which realizes asymmetric transmission. The surface electric field distributions are illustrated to provide some insight into the physical mechanism of dynamic modulation. From the simulated results, it can be observed that this design has the capability of controlling tunable manipulation on both transmission/reflection responses at a wide frequency band. This proposed design may pave a novel pathway towards thermal imaging, terahertz detection, active modulators, etc.

The Research of GIS Discharge Influence Based on Particle Properties in Installation Environment

In order to explore the influence of atmospheric free particles that exit during GIS installation on the stable operation of GIS, the size, shape and inner properties of the particles contained in the air are analyzed. And based on 500kV GIS equipment, the GIS gas chamber model and the model of free particles were established. By using the finite element simulation software, the surface electric field distribution when the free particles remain on the insulator surface is solved. The results show that the electric field distribution of particles which exist along the surface of insulator is directly related to the relative permittivity of the material of the particles themselves, and the intensity of the electric field along the surface increases with the increase of the relative permittivity. with the fact that the relative permittivity of air particles is almost below 20, as a result, the existence of 10µm grade non-metallic free particles will not cause flashover discharge. But, when a small number of Fe3O4 particles which size over 1mm or when them accumulate regularly, it will lead to flashover discharge. Therefore, the suspended atmospheric particles in the installation environment have little impact on the stable operation of GIS. When considering the installation environmental conditions, the installation can be carried out on a clear, windless day which can save costs.