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The electrical-tree degradation inside XLPE cable is a serious threat to the cables under operation. In this paper, the DCIC (direct current integrated charge) method was employed to evaluate the electrical tree inside XLPE insulation. During the preparation of cable samples, the tree inception voltage of ~8 kV was tested. Then 1, 5 and 10 needle electrodes were inserted into cable samples for the tree generation. After the preparation of samples, AC voltage of 10 kV was applied onto the needle electrodes for electrical tree growth. The treeing time was set to 0, 20, 40 and 60 min for the DCIC test. During the DCIC test, a DC voltage of 2 kV was applied on the conductor, and the integral capacitor was connected between the copper shield of cable and ground. From the experiment result, it can be found that with the increase of treeing time, the charging coefficient increases obviously if there are 5 and 10 electrical trees in the cable, this is maybe caused by the occurrence of polarization. The conduction current coefficient changes obviously before and after needles insertion. The information in DCIC curve can be used to analyze electrical tree degradation and mechanical damage in cables at the same time. This nondestructive testing method proposed in this paper will improve the testing efficiency and speed.

The cross-linked polyethylene insulation of power cables under multiple stresses will age and deteriorate, and eventually cause insulation failure, which threatens the reliability of transmission lines. In this contribution, based on Direct Current Integrated Charge method, the performances of XLPE under thermal aging are investigated. The results show that the charge minimally injects into the unaged XLPE insulation, and the charge injected behavior intensifies with the thermal aging time. Thermal aging treatment results in greater relative permittivity, volumetric conductivity, and absorbed charge of XLPE insulation. The permittivity of the aged XLPE insulation gradually increases by 18.24%, whereas the conductivity rises by 14.48 times, and the absorption charge shoots up by 18.03 times. It is conducted that the enhancement in charge injection and the acceleration of charge accumulation reflects the cable insulation thermal aging intensified.

Nanodielectrics have been one of the research hotspots in electrical insulation, since the concept was proposed in 1994. Numerous studies have shown that nanocomposites had better electrical, thermal and mechanical performances than microcomposites and undoped polymers. Especially, their excellent electrical properties, including low conductivity, high breakdown strength as well as suppressed space charge accumulation, make it possible to be the new generation of insulating materials, for instance, polyethlene-based nanocomposites for HVDC cables. These profound properties are thought to be ascribed to the great number of polymer-filler interfacial regions, ascribed to the high specific surface area of nanofillers. Graphene nanoplatelets, as a unique nano-scaled filler with a thickness of only an atomic layer, has an enormous specific surface area up to 2630 m2/g, which can significantly increase the polymer-filler interfacial regions in theory and advantage to exploit the further potentials of insulating nanodielectrics for HVDC cable application.

High temperature vulcanized (HTV) silicone rubber (SiR), due to its excellent electrical insulation, elasticity and temperature resistance, is used in cable accessories for HVDC cables. The space charge, generated under dc stress in SiR, would distort the local electric field, furtherly influencing the characteristics of partial discharge and accelerating the insulation aging. This paper tried to modify the space charge behaviors of HTV SiR composites by incorporating silicon carbide (SiC) particles into the polymer matrix. The effects of the SiC particle content on the field-dependent conductivity and the space charge behaviors of HTV SiR were studied. The results indicated that the conductivity of SiR/SiC composites was a nonlinear function of electric field when the content exceeds 30 wt%. With the increase of filler content, the threshold field for nonlinear conductivity decreased and the nonlinear coefficient increased. Meanwhile, the amount of space charges was dramatically reduced. It is suggested that the SiR/SiC composites with nonlinear conductivity can improve the dc conductivity under high electric field, thus suppressing the accumulation of space charge.

A time-domain discontinuous Galerkin method is presented to analyze transient scattering from perfect electrically conducting (PEC) objects. As mono-polar RWG functions are chosen for spatial functions, it is possible to analyze complex structures with either conformai or non-conformal discretization. Numerical results are included to demonstrate the accuracy and efficiency of this method.

The corona discharge has been realized close to point electrode under both negative and positive high voltage in normal liquid helium (LHe) at 4.2 K. The experiments have been carried out at constant temperature and for different pressures in a wide range. An intensity of the visible light emitted from the zone closed to tip was enough for its spectroscopic analysis. The shift and width of the spectra observed were measured as a function of the applied pressure. It is shown that the spectra belong to excited atoms inside of empty cavity in LHe. The significant ldquored satellitesrdquo were observed in the spectra of positive corona.

We report a Si/SiGe-based vertical-illuminated photodiode at 830 nm wavelength. Wide 3-dB bandwidth (>10 GHz), high responsivity (1.38 A/W), and high output current (2.35 mA) under avalanche operation can be achieved simultaneously without using silicon-on-insulator (SOI) substrate.

Although directional measurements of brightness temperature has made by a number of satellite- based and airborne sensors for a long time, interpretation of such measurements is a difficult task due to the fact that surface radiometric temperatures are resulted from energy balances in multi-scales from leaf and soil to the top of canopy or pixel. In this paper, a non-isothermal Monte-Carlo method based algorithm was proposed to model the angular emission from vegetative canopy and scale radiometric temperatures of foliage and soil to the top of canopy. This approach allows an accurate simulation of multi-reflection between foliage layers, foliage layer and soil surface, and foliage layers and sky, as well as the non-isothermal condition within canopy and between canopy layers and soil surface. Field measurements of directional thermal infrared radiation, which were collected in the Shunyi remote sensing campaign in Shunyi, Beijing in 2001 was used to preliminarily validate this non-isothermal Monte-Carlo algorithm. A reasonable agreement was archived from this validation.