As for polymeric cable insulations used in nuclear power plants, acceleration aging is used both for type tests and for aging estimation. In order to explain both degradation phenomena, which occur under the test conditions and under actual operation environments, numerical calculation programs are needed. The present paper refines such program to fit to so-called reversed sequential acceleration that applies radiation followed by thermal aging. The advantage of the calculation is to provide correlation map of several parameters such as the dose rate, radiation exposure time, heating temperature, and heating time. The program also judges the feasibility for acceleration aging by estimating the homogeneity of degradation inside the bulk. The correlation between radiation and heating is numerically investigated by changing dose rate and heating time, and the result shows complex three-dimensional surface. Two kinds of featured dose-rate dependencies are obtained for the cases that the target degradation is achieved only by the radiation or heating. These characteristics show an intersection on the dose rate dependency, which results in providing a key factor to divide the role and contribution against the target degradation. The paper also discusses the effect of heating temperature on such a time-based relation between radiation and heating time.

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Thin-films of gold-metalized polypropylene submitted to DC and AC electric fields in conditions where electrical discharges in ambient are avoided emit light in the visible part of the optical domain. The origin of the light is discussed with the help of light intensity vs. voltage characteristics and spectral analysis. Two components of the light with different features have been unraveled being due to an interfacial phenomenon and to the polymer itself. The first one is attributed to the formation of surface plasmons excited at the metal/dielectric interfaces by charge injection/extraction. These coherent collective excitations of the electron gas at the metal surface decay by emitting a typical optical signature in the red part of the visible domain. The second component of the electroluminescence spectrum is attributed to the formation of excitonic states in polypropylene excited upon charge recombination or hot electron effects. A strong evidence is provided by the spectral shape analysis which shows the spectrum exhibits identical features with the cathodo-luminescence spectrum of the material. This main component of the emission spectrum under AC field would also be involved in the emission under DC stress, the latter being so weak preventing a spectral analysis. These excitonic states provide a route for a series of reactions associated with chemical degradation of the polymer during its ageing under high field. Finally, it is shown that similar excited species are generated in polyethylene as well pointing towards a generic origin of these excited states in polyolefins.

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The authors examined the possibility of terahertz (THz) absorption spectroscopy whether it can be used as a tool to estimate the content of talc in ethylene-propylene-diene copolymer (EPDM), an important factor determining the electrical insulation properties of EPDM-insulated power cables. For this purpose, absorption spectra were measured in a frequency range from 0.3 to 10.0 THz for EPDM sheets containing different contents of talc, a disk-shaped sample made of talc powder, and a similar disk-shaped sample made of a mixture of talc and high-density polyethylene. As a result, the whole absorption in the frequency range from 0.3 to 10.0 THz is increased by the addition of talc into EPDM sheets. More specifically, it has become clear that talc in EPDM induces absorption peaks at 3.05, 4.8, 5.1, 5.3, 6.9, and 7.8 THz. The integrated absorption coefficients calculated for these absorption peaks show a good linearity with respect to the content of talc. Therefore, by watching the increments of these absorption peaks, the content of talc can be quantitatively estimated.

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Surface potential decay (SPD) crossover of LDPE (low density polyethylene) is investigated by a dynamic model combining charging, surface charge accumulation, and charge transport processes. The charge continuity and Poisson's equation are solved by a highly stable and fifth order accurate finite difference weighted essentially non-oscillatory method and boundary element method, respectively. The simulations are performed at various charging times and various recombination coefficients. The simulation results show that the SPD crossover properties are influenced by charging times and recombination coefficients. The time for the occurrence of SPD crossover decreases with an increase in charging time, whereas it increases with an increase in recombination coefficient. It is demonstrated that the variation of charging times and recombination coefficients changes the distributions of charge densities and electric field in the bulk of LDPE. The differences of the distributions of charge densities and electric field affect the decay rates of surface potentials, which will determine the SPD crossover properties.

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A proper and controlled filler dispersion is the goal of each compound, and nanodielectrics are not an exception for this purpose. A method to avoid agglomeration and ensure a standard dimension of interface region is presented in this work. Graphene oxide has been dispersed into a thermoplastic polymer starting from standardized building-blocks made of polymeric matrix with a single controlled nano-interface of graphene oxide inside. Electrical properties, such as space charge accumulation, permittivity and conductivity, of the nanodielectric have been deeply investigated and a hypothesis on charge carrier motion inside it is proposed.

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In this paper, we propose a new simple device for visualizing bioactive molecules with a fine spatial resolution by using a membrane in which a specific enzyme is immobilized. The layer produces fluorescence after association with a specific substance. The layer, on which a biological tissue is to be mounted, is deposited on a quartz substrate that is used as a light guide to introduce UV light to the layer. Substance release is observed by a CCD camera from the opposite side of the substrate. In order to shorten the experiment time, we had automated the optical device. The paper also describes the reduction of background fluorescence by means of image processing technique. Images were acquired by employing two UV-LEDs with slightly different angle. Image processing was performed to separate background and target fluorescence by means of independent component analysis. Finally the release of GABA(γ-aminobutyric acid) and glutamate from specific layers in rat cerebellum was successfully observed. It is expected that, using this method, both real-time transmitter release and its response to medicine can be observed.

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This paper deals with discharge characteristics in the oil/pressboard composite insulation system under application of lightning impulse voltage. Large oil gaps in power transformer are often subdivided by insulating barriers into small ones. We observed partial discharge at an oil gap across the barrier without puncturing it in a test sample and also evaluated the voltage required for the phenomenon. As a result, we conclude that the discharge occurred in the oil gap due to the electric field enhancement along with discharge propagation.

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To reduce the insulation faults in GIS, it is still important to develop a new material for the epoxy spacer with high thermal and insulating properties. In this paper, six kinds of materials were prepared with different concentrations of 12-21 µm micro-alumina, 30 nm nano-alumina and 10 nm nano-titania fillers, i.e. neat epoxy, micro composite, two kinds of nano-composites, and two types of nano-micro-mixture-composites. Their thermal behavior, dielectric strength, dielectric spectrum were measured and analyzed. It is concluded that nano-filler addition can increase glass transition temperature and breakdown strength.

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