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The improvements in signal-to-noise ratio (SNR) are indispensable to obtain the desired output signal of partial discharge (PD) under square wave pulsewidth modulation (PWM) voltage. In this article, the effect of complex PWM voltage parameters (rise time, fall time, frequency, duty cycle) on the SNR of PD tests is investigated. The results revealed that the sensor's high-frequency gain should be increased to improve the SNR under faster switching. PD impulses are more likely to be submerged in the residual interference under high-frequency voltage. The SNR can be improved by only detecting the PD at the rising front because the PD signal overlaps with commutation noise at the falling front of short duty cycle voltage, such as 0.03% duty cycle. The above results can reference the PWM parameters and improve the SNR in PD tests for rotating machines controlled by power electronics. [ABSTRACT FROM AUTHOR]

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]

To improve the reliability of power systems, online cable condition monitoring must be implemented to replace traditional regular power outage maintenance. Existing online monitoring methods have certain limitations. In this article, a novel method based on low-frequency signal injection is proposed to monitor power cable insulation conditions online. For this method, a low-frequency signal is injected into the power system via the potential transformer (PT) open delta configuration. The cable conductor voltage and leakage current are detected. The interpolating windowed fast Fourier transform (FFT) algorithm is applied to calculate the dielectric loss angle. Then, the cable tangent delta ($\tan \delta $) can be deduced, and the cable condition can be assessed. A distribution network system is built based on the power system computer-aided design (PSCAD) software. The frequency and amplitude of the injected signal are simulated and discussed. An online monitoring platform is established in the laboratory. Thermal-aged cable samples and water tree-aged cable samples are prepared and measured. The experimental results confirm that the proposed method can effectively assess power cable insulation. [ABSTRACT FROM AUTHOR]

This paper presents a novel oscillation wave test system (OWTS) to detect the partial discharge (PD) of mounting defects in power cable insulation. In the proposed system, a charging capacitor is added to the circuit topology based on the traditional OWTS. The charging capacitor is charged to the desired voltage by a high-voltage DC power source. After the charging process, the test cable sample is charged by the capacitor. The resonant circuit is formed by the charging capacitor, the test cable, and the resonant reactor to create an oscillating decay voltage. With this novel method, no space charge is injected into the cable insulation. The effect of the charging capacitance on the charging efficiency is calculated with the Multisim software. This paper describes the working principle and the assembly of a laboratory prototype for the PD detection of a 500 m cable circuit. The test results show the feasibility of the novel OWTS method. [ABSTRACT FROM AUTHOR]

The onsite partial discharge (PD) detection of cable insulation is of great importance for power system maintenance. To preserve more basic features of denoised PD signal, in this paper, a PD denoising by a new class of affine projection algorithm (APA) is proposed based on the high-order error power (HOEP) criterion. We propose a new affine projection least mean absolute third algorithm (APLMATA), which exploits the HOEP criterion ($p=3$) and can achieve reliable performance under Gaussian interference. We further develop a modified APLMATA (MAPLMATA) to reduce the misadjustment with moderate computational burden. Analytical models are derived for MAPLMATA for Gaussian signals. To enhance the stability of the algorithm in generalized Gaussian noise scenarios, an affine project least mean $p$ th power algorithm (APLMPA) that includes the $p$ th power dependence on the error is presented. In particular, we apply the proposed APA-based algorithms to suppress the noise from PD signal in power cables. Simulation and experimental results demonstrate the effectiveness of the proposed algorithms for system identification and PD denoising. [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]

The second-order Volterra (SOV) filter is a powerful tool for modeling the nonlinear system. The Geman–McClure estimator, whose loss function is non-convex and has been proven to be a robust and efficient optimization criterion for learning system. In this brief, we present a SOV filter, named SOV recursive Geman–McClure, which is an adaptive recursive Volterra algorithm based on the Geman–McClure estimator. The mean stability and mean-square stability (steady-state excess mean square error) of the proposed algorithm is analyzed in detail. Simulation results support the analytical findings and show the improved performance of the proposed new SOV filter as compared with existing algorithms in both Gaussian and impulsive noise environments. [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]

Pantograph–catenary (PC) arc has become an obstacle for the further development of high-speed railway. Understanding on the underlying physical mechanisms of PC arc dynamics is still far away from satisfactory; therefore, researches from both experimental and numerical aspects are urgently required. This paper focused on the dynamic characteristics of PC arc during the pantograph lowering process by numerical simulation method. A PC arc model was established based on the classical magnetohydrodynamics theory, with the temporal evolution of PC arc dynamics considered. The dynamic mesh technique was utilized to take care of the departure process between the pantograph and the catenary. Detailed behaviors of arc plasmas during the pantograph lowering process were presented by the temperature distribution and flow filed. Two interesting vortexes located below the catenary were found. The vortexes rotated in the opposite direction, resulting from the special gas flow motion during the pantograph movement. Furthermore, the gas flow brought about a thermal pinch effect on arc column, which had a significant influence on the next behaviors of arc plasmas. Besides, the effects of input current on the arc characteristics were studied. [ABSTRACT FROM AUTHOR]

Phenomena of the pantograph arcing have become a challenge for the further development of high-speed electrified railway system. Despite of the large attention that has been paid to the radiated electromagnetic interference, materials ablation as well as the power-quality decline resulted from pantograph arcing, the specific dynamics of pantograph arcing with a high time resolution are still in absence. In this paper, the pantograph arcing phenomena in a laboratory simulation system were experimentally studied by high-speed photography. Synchronized electrical voltage and current waveforms were obtained to acquire a more comprehensive understanding on the underlying physics. The overall dynamics of the pantograph arcing from ignition to extinguishment were recorded. Three stages of the electric-contact process, from approaching arc, mechanical contact to the drawn arc, were well distinguished. A much intensified drawn arc was observed than the approaching arc. Typical lasting time of the drawn arcing is found $\sim 4$ times larger than the approaching arcing for our test setup. Maximum diameter of 3.3 mm was reached at around the current-peak moment. An interesting stable arc voltage of \sim 23$ V was found during the drawn arcing. Intense material splash above the carbon strip was observed during the arcing process. The transient resistance during a typical arcing period was also analyzed, and a minimum value of \sim 100~\text{m}\Omega was determined. [ABSTRACT FROM PUBLISHER]

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]