Spatial resolution of space charge distribution measurement using PEA (Pulsed electro-acoustic) method at high temperature was improved by applying a thin piezo-electric sensor film with a glass substrate. Partial discharge generation is one of problems to be solved in motor winding when the driving voltage of motor is elevated to downsize it. In the high-voltage drive of motors, the space charge accumulation in the thin insulating layer of the winding is said to affect the partial discharge generation. Therefore, it is necessary to evaluate the space charge accumulation in thin insulating materials of the winding. Especially, since high temperature characteristics of the partial discharge is said to be important, the measurement of the space charge distribution for the thin insulating layer is required at high temperature. However, the spatial resolution of the ordinary PEA measurement system was not enough to measure the space charge distribution in such thin insulating materials for windings, especially at high temperature. Therefore, the PEA measurement system was improved using a thin sensor film, which is available at a relatively high temperature, as a sensor of the PEA measurement system with a high heat-resistant glass substrate. In this report, a typical measurement result of the space charge distribution observed in 25 µm-thick polyimide sample at 80°C is introduced.
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Renewable energy-based power systems will experience a larger number of harmonics in voltages and currents due to the increased use of converters, hybrid lines, and non-linear loads in the future. These harmonics could lead to additional power and heat losses, increase operational expenses and affect the life expectancy of components. This study aims at analyzing the increased losses and temperature rise in a 25kVA oil-filled distribution transformer under well-defined harmonics. The data obtained are then used to calculate the power losses for odd and even harmonic contents and a comparison is made between the two cases. The results contribute to a better understanding of the power losses for different harmonic contents. A direct correlation between theoretical and experimental results is established, showing the negative impact of harmonics on power losses and the corresponding temperature rise in a distribution transformer.
The dissolved gas analysis (DGA) is one of the main diagnostic techniques for oil-filled electrical equipment. Though self-contained fluid filled (SCFF) cables have been maintained by DGA, some faults occurred on SCFF cable joints in Japan. Therefore, it is important to improve DGA for SCFF cables. In this viewpoint, the characteristics of decomposition gases by partial discharges in the insulation system for SCFF cables were experimentally investigated. The insulation layer of test samples was composed of sheets of oil-impregnated insulating paper and an oil gap that simulated a butt gap in SCFF cables. Partial discharges were generated in the oil gap in short or long periods, and the oil gap and light emission due to partial discharges were observed. In addition, after partial discharge generation, the insulating oil in the oil gap was taken and hydrogen and hydrocarbon gases in the insulating oil were detected by DGA. As the result, in the short period case, partial discharges occurred through insulating oil, and main decomposition gases were H-2 and C2H2. On the other hand, in the long period case, partial discharges occurred in bubbles, and main decomposition gases were H-2, CH4 and C2H6. It was estimated from this result that the difference of the main decomposition gases between two cases depended on whether partial discharges mainly occurred through insulating oil or in bubble.
Dielectrically graded insulation (DGI) is a potential approach in next-generation electric insulation systems due to its effective electric field (E-field) regulation, high insulation performance and reduced geometrical size. However, it is challenging to find a construction method of DGI with facile procedures, high accuracy, high flexibility, and good scalability. Fortunately, the rapid developing of additive manufacturing (also known as 3D printing) provides a novel approach – lattice material – for DGI construction. The lattice material is made of ordered, periodical cellular structure (unit cell), in which the feature size or topological structure of every unit cell can be tailored to build non-uniform, functionally graded objects. Since the dielectric properties of almost all the insulation materials is strongly related to its internal structure, it is reasonable to build FGM insulation by lattice materials. In this paper, the concept of lattice-material DGI (LM-DGI) is proposed, which is based on the description and analysis of research progress in DGI. Finite element simulation is then conducted on a 2D example to verify its effectiveness in E-field regulation. The results indicate that despite certain amount of fluctuation, the LM-DGI still has adequate performance in electric field regulation. Moreover, the distribution of electric field can be flexibly modified by changing the feature size (e.g. hole radius) of unit cells. We believe that LM-DGI is promising for facile, accurate and large-scale DGI insulations, making it ideal for industrial usage.
