Search

Penetration of wind power plants (WPPs) in the electric power system will complicate the system load flow analysis. Consequently, the traditional load flow algorithm can no longer be used to find the solution to the load flow problem of such a system. This paper proposes a doubly fed induction generator (DFIG)-based WPP model for a load flow analysis of the electric power system. The proposed model is derived based on the power formulations of the WPP—namely, DFIG power, DFIG power loss, and WPP power output formulas. The model can be applied to various DFIG power factor operating modes. In the present paper, applications of the proposed methods in two representative electric power systems (i.e., IEEE 14-bus and 30-bus systems) have been investigated. The investigation results verify the proposed method's capability to solve the load flow problem of the system embedded with DFIG-based variable-speed WPPs. [ABSTRACT FROM AUTHOR]

Epoxy resin is widely used as an insulation material in many electrical apparatuses because of its excellent electrical and manufacture characteristics. It is usually mixed with filler to improve mechanical and thermal characteristics. In order to qualitatively clarify the effect of fillers on treeing phenomena, treeing tests were performed with epoxy specimens mixed with different kinds of fillers. The property of the interface is also clarified by the treatment of silica filler using silane coupling. Although tree initiation voltage decreased with introducing silica fillers, the fillers prevented the growth of the tree. The effect of filler shape was more significant on round-shape filler than on square-shape filler. Silane coupling treatment to the fillers did not bring a significant change in tree initiation voltage, however, brought a reduction in tree propagation. The change in tree propagation rate was explained by considering the field relaxation and energy dispersion due to branching at the filler-resin interface. Tree propagation along the interface between resin and a quartz plate was observed and analyzed in order to ensure the above explanation. Index Terms--Epoxy resin, filler, treeing, silane coupling treatment, release agent, adhesion property, moisture.

The effect of silica filler and moisture absorption on the structural characteristics of tree growth in epoxy resin has been investigated. The physical properties of the resin were varied by changing its filler concentration and immersed in distilled water at 50 [degrees]C. The fractal dimension of the electrical tree and its relationship with filler and moisture contents were determined. The damaged area of tree in various concentrations of filler was also estimated. Furthermore, the lacunarity of tree with identical fractal dimension was calculated as a complement of fractal dimension characterization. In addition, moisture absorption and diffusion properties of the specimens used were also examined. It is considered that the filler would create such an obstruction to the tree growth both in moisture and non-moisture conditions. Under non-moisturized condition, the more filler concentration, the more obstruction would be generated, leading to the significant suppression of tree growth. Likewise, the introduction of filler brought a rise in fractal dimension due to the increase of branches. It is concluded that the existence of filler makes the tree structure more complicated by introducing obstacles to tree propagation, leading to the high fractal dimension of the tree. In addition, it was found that the fractal dimension of the tree was related to the fractal dimension of the composite material including filler particles. On the other hand, the lacunarity of 'without-filler' specimen would be lower than that of in filled specimens. It is considered that the tree growth in filled specimen would have 'localized-branching' at the interface between filler and resin leading to the heterogeneous inherent structures of the trees. As a complement of the complexity characterization by fractal dimension, the lacunarity can be a useful tool to quantify the heterogeneous structures of trees growth in composite materials. The moisture could hardly be absorbed into the filler compared to the resin. It is shown by the higher value of diffusion coefficient of without-filler specimens than with-filler. 20 h of immersing is appropriate to achieve 40% in moisture content at the needle tip. Index Terms--Epoxy resin, filler, moisture, diffusion coefficient, electrical tree, fractal dimension, damaged area, lacunarity.

Weibull distribution has been used widely by many researches around the world especially in the analysis of high voltage experimental data. Unfortunately, the statistical techniques used to analyse the high voltage experimental data are not highly accurate. In view of the foregoing, this paper presents a new statistical approach to analyze the tree inception voltage of silicone rubber and epoxy resin. The tree inception voltage of silicone rubber and epoxy resin was measured via camera-equipped online monitoring system. The leaf-like specimen was used as test sample. AC ramp voltage was applied to obtain the tree inception voltage of silicone rubber and epoxy resin. It was observed that, the electroluminescence emission and ultraviolet (UV) radiation occurred indicating the early stage of tree occurrence. The obtained results were analysed statistically by using fitting method. Anderson-Darling goodness-of-fit test was performed in order to obtain the best fitting distribution. Comparison was made between the best-fitted distribution and Weibull distribution. Based on Anderson-Darling tests, the tree inception voltage of silicone rubber and epoxy resin was best fitted with Johnson SB distribution. Based on this fitted distribution, the value of tree inception voltage for silicone rubber and epoxy resin was calculated and equalled to 11.80 kV and 20.11 kV respectively. From this study, it was found out that the best-fitted distribution for the value of tree inception voltage for silicone rubber and epoxy resin is the Johnson SB distribution by means of Anderson-Darling goodness-of-fit test. [ABSTRACT FROM AUTHOR]

The issue of high voltage equipment tropicalization is critical particularly when high voltage equipment designed for temperate application are imported to areas in the tropics. It raises the question whether the insulation used in these equipments can performance under the impact of high relative humidity level and the intense midst noon sun rays. This paper presents the study of dielectric material performance under the impact of relative humidity and plasma exposures to simulate the material aging in service by studying the discharge characteristics of PMMA which was used as the basis of study. The discharge characteristics in cylindrical void bounded by dielectric of polymethylmethacrylate (PMMA) which were exposed to different levels of relative humidity (RH) and plasmas intensity were investigated. The insulation material under test was subjected to AC excitation. The partial discharge (PD) signatures produced were measured with the aid of a CIGRE Method II (CM II) electrode system. It was found that when the void cavity was humidified from 33 % up to 98 %(extreme level), the PD inception voltage decreased about 15 %. For negative AC cycles, the following discharges occur with larger number of pulses, however, with small number of magnitudes. PD seems easily to occur with larger number of pulses as the surface of specimen was degraded by plasma (especially under humid environment).So it is recommended that high voltage equipments imported from temperate countries must performance in the tropics adverse environmental conditions. [ABSTRACT FROM AUTHOR]