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Partial discharge (PD) detection plays a vital role in on-line condition monitoring of electrical apparatus in the power systems. However, the noise of PD measurements significantly degrades the performance of detection algorithms. In this paper, we focus on developing an adaptive filtering technique for the PD denoising problem. Heretofore, there are just a few literature reviews addressing the PD denoising based on such a method. The proposed recursive continuous S-shaped (RCSS) algorithm integrates the advantages of recursive strategy and continuous S-shaped function into adaptive noise cancellation (ANC) system, yielding enhanced filtering performance. The proposed algorithm can tackle PD noises in both Gaussian and impulsive scenarios, which is easy to implement in practical applications. The convergence behavior is also analyzed. Extensive simulation and experimental results confirm that the proposed algorithm can address polluted PD pulses, even in excessively noisy conditions, resulting in smaller mean square error (MSE) as compared to other state-of-the-art algorithms. [ABSTRACT FROM AUTHOR]

This study investigates the microstructural changes of water trees in different stages of propagation. It is proposed that microstructural changes within a tree influence its macroscopic propagation. Five groups of XLPE cable samples with pinhole defects were subjected to an accelerated water tree aging experiment for different aging times. The morphologies and sizes of water trees in different aging periods were observed by optical and scanning electron microscopes. The microscopic observations show that the propagation rates of water trees can change during different aging stages. In the initial stage, the propagation rate of water trees can reach 0.46 μm/hour. However, in the stagnation stage, the propagation rate decreases considerably to as low as 0.01 μm/hour. In the late stage, water trees with irregular shapes can form, and the propagation rate of the longest water tree branches can rise to 0.33 μm/hour. In addition, the shape of the microvoids within the water trees can change. In the later period of the stagnation stage, microvoids with irregular shapes (not round shape) can form by the connection between microvoids with different sizes. The simulation results of the electric field indicate that the microstructural change within the water trees is the fundamental reason for the changes of the propagation rates. In different propagation stages, the changes in the density, the sizes, and the shape of the microvoids can lead to the changes of water distribution and electric field distribution in water tree regions, which further results in different propagation rates. [ABSTRACT FROM AUTHOR]

To understand abnormal water tree shapes under mechanical stresses, this paper reveals the mechanism of mechanical orientation for the effect of water tree propagation behaviors. A heated metal needle was used to produce pinhole defects in two groups of XLPE bar samples (group A and group B) to simulate the mechanical orientation of the XLPE material. The samples in group A were subjected to orientation analysis by an infrared spectrum (IR) method, and the samples in group B were subjected to an accelerated water tree aging experiment. According to the results of IR analysis, the XLPE material around the pinholes was oriented after the insertion of the heated metal needle. The microscopic observation results show that there are abnormal water tree shapes in the samples in group B. The abnormal water tree shapes are very similar to the morphology of the stress strips observed in the samples in group A. Based on the mechanical orientation theory, after the mechanical orientation, the XLPE material becomes anisotropic, and some performances of the material will change in the direction of orientation and in the transverse direction. As a result, in the direction of orientation, water tree propagation is promoted, whereas water tree propagation is inhibited in the direction perpendicular to orientation. Mechanical orientation is the main reason for the abnormal water tree shapes. A similar phenomenon is also verified in bent cable samples. The types, directions, and intensities of mechanical stresses determine the behaviors of mechanical orientation in cables, which can further influence the behaviors of water trees. [ABSTRACT FROM AUTHOR]

Polyimide nano-composite film (Kapton 100CR) is a special type of engineering plastic film, which is widely used in turn insulation of form-wound inverter-fed motor. Partial discharge (PD) caused by high-frequency surge impulse is one of the key factors leading to premature failure of turn insulation of inverter-fed motors. Aging experiments on turn insulation samples under repetitive bipolar square impulse voltage were carried out in this study. Experimental results show that, in the presence of PD, the damage to the structure of the polyimide nano-composite film under impulse voltage is concentrated on the surface layer of the sample. Moreover, the results indicate that with the increase of aging time, the discharge phase distribution becomes broader. Therefore, the appearance of the discharge at higher phase would be the reflection that the insulation of the sample reaches its terminal stage. Surface microscopic images taken by the scanning electron microscope (SEM) show that, because of PD erosion, the polymer matrix was carbonized and volatilized, the residual nano-fillers remained on the surface and formed a screen layer to resist further damages caused by PDs. It is a symbol that faults expand rapidly when the floccules and voids appear on the surface layer, which indicates the insulation could be breakdown soon. [ABSTRACT FROM AUTHOR]

In order to investigate the effects of inorganic nanofillers on the electrical properties of polyimide (PI), PI/Al2O3 nanocomposites films were prepared via the in-situ polymerization. The hybrids films were characterized by scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR). The dielectric behaviors of pure PI and PI/Al2O3 samples were studied as a function of the measured frequencies and temperatures. Meanwhile, the breakdown strength of pure PI and PI/Al2O3samples measured at 25 and 230 °C was analyzed. The corona-resistant lifetime of samples under bipolar continuous square impulse voltage (BCSIV) was performed. With the wt% content of Al2O3 nanoparticles increasing, the real (ε') and imaginary (ε") of relative permittivity present an increasing tendency, while electrical breakdown strength declines obviously. The Al2O3 nanofillers improved the corona-resistant property of PI and the corona-resistant lifetime of PI/Al2O3 sample with 25 wt% (weight percent) of nano-Al2O3 particles is over 23 times longer than that of the pure PI film. Besides, the temperature is an important factor which would significantly influence the electrical properties of pure PI and PI/Al2O3 samples. The elevated temperature would reduce the breakdown voltage and corona-resistant property [ABSTRACT FROM AUTHOR]

High-speed airflow, which is generated around trains running at a high speed, causes uneven pollutant distribution on insulator surfaces and changes their insulation properties. In this paper, a method has been proposed to calculate the residual pollutant resistance on polluted insulator. Based on the analysis of flashover model, the influence of pollution distribution along and around insulator was discussed. Analysis result showed that flashover voltage would increase when the pollutant distribution on insulator decreased compared to conditions with uniformly distributed pollutant, and vice versa. It implied that there should be a maximum pollutant accumulation value above and below the insulator shed. In this situation, the flashover voltage will be the lowest. Model analysis showed that the flashover voltage would increase with the length of the insulated plate and vice versa. The theoretical analysis was in good agreement with experimental result, which implied that this method might be able to provide reference for insulator shed design. [ABSTRACT FROM AUTHOR]