Corona ring improvement to surface electric field stress mitigation of 400 kV composite insulator

This paper aims to enhance the performance of a 400 kV composite insulator by minimizing electric field stress along its surface using COMSOL Multiphysics. The study employs optimization techniques for the corona ring, initially targeting key parameters such as the ring tube radius, corona ring radius, and corona ring height. Recently used optimization algorithms for engineering applications, namely Constrained Optimization by Linear Approximation (COBYLA), Coordinate Search (CS), and Nelder-Mead (NM), are utilized to determine the most effective one for the optimization purpose. The results indicate that the three algorithms converge around similar values, with COBYLA exhibiting a lower iteration number. Furthermore, our research confirms that increasing the corona tube radius results in a reduction of electric field when considering the other optimized parameters; however, this leads to an increase in the corona ring weight. To resolve this concern, we conduct a re-optimization of the ring shape by targeting eight specific points that form a polynomial interface replacing the original ring. The obtained results demonstrate that the re-optimized shape effectively reduces surface electric field, although it leads to an increase in the ring weight. Nonetheless, this approach aids in identifying critical regions of surface deformation that interact with the electric field. In light of this, we explore an alternative approach that involves replacing the new shape with multiple corona rings positioned in the most deformed regions and then optimizing their positions. This approach helps to achieve better results of surface electric field and overall weight, under clean and polluted surfaces

Accuracy improvement of power transformer faults diagnostic using KNN classifier with decision tree principle

Dissolved gas analysis (DGA) is the standard technique to diagnose the fault types of oil-immersed power transformers. Various traditional DGA methods have been employed to detect the transformer faults, but their accuracies were mostly poor. In this light, the current work aims to improve the diagnostic accuracy of power transformer faults using artificial intelligence. A KNN algorithm is combined with the decision tree principle as an improved DGA diagnostic tool. A total of 501 dataset samples are used to train and test the proposed model. Based on the number of correct detections, the neighbor’s number and distance type of the KNN algorithm are optimized in order to improve the classifier’s accuracy rate. For each fault, indeed, several input vectors are assessed to select the most appropriate one for the classifier’s corresponding layer, increasing the overall diagnostic accuracy. On the basis of the accuracy rate obtained by knots and type of defect, two models are proposed where their results are compared and discussed. It is found that the global accuracy rate exceeds 93% for the power transformer diagnosis, demonstrating the effectiveness of the proposed technique. An independent database is employed as a complimentary validation phase of the proposed research

Quantifying time-dependent structural and mechanical properties of UV-aged LDPE power cables insulations

This paper reports effects of ultraviolet (UV) light radiation on the physicochemical, electrical and mechanical properties of low-density polyethylene (LDPE) cable insulating materials. Changes in structural and morphological properties of UV-aged samples were characterized by various analytical methods such as attenuated total reflection Fourier transform infrared spectroscopy (ATRFTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Additionally, elongation at break, tensile strength, dielectric strength, and optical properties were also evaluated. Changes in some physical properties of LDPE after exposing to UV irradiation clearly highlighted that the polymer underwent the structural degradation. In addition, it was also found that such degradation yielded both crosslinking and chain scission as two competing processes during UV aging

AC Conductivity Analysis and Chemical Changes of Thermally Aged PVC/B Insulation for Medium Voltage Cables

National audienc

A New Analytical Equation for the Linear Resistance of Discharge During Flashover of Polluted Insulators Under AC or DC Voltages

International audienceThis paper presents a new equation for the linear resistance of discharge channel during the flashover of polluted insulators basing on an electro-energetic balance and by using some mathematical formulations. This equation shows the dependency on the applied voltage, the temperature, thermal conductivity and length of the discharge channel, the resistance and capacitance of pollution layer; the radius of discharge channel is assumed to be variable. It is valid during the whole discharge process (i.e.; during the different steps of the discharge development) in AC and DC voltages and in both static and dynamic regimes. The proposed equation has the particularity to be an analytical equation, in opposition with the main equations used till today to determine the linear resistance of discharge propagating over polluted insulators up to flashover and which are empirical equations

A New Analytical Equation for the Linear Resistance of Discharge During Flashover of Polluted Insulators Under AC or DC Voltages

International audienceThis paper presents a new equation for the linear resistance of discharge channel during the flashover of polluted insulators basing on an electro-energetic balance and by using some mathematical formulations. This equation shows the dependency on the applied voltage, the temperature, thermal conductivity and length of the discharge channel, the resistance and capacitance of pollution layer; the radius of discharge channel is assumed to be variable. It is valid during the whole discharge process (i.e.; during the different steps of the discharge development) in AC and DC voltages and in both static and dynamic regimes. The proposed equation has the particularity to be an analytical equation, in opposition with the main equations used till today to determine the linear resistance of discharge propagating over polluted insulators up to flashover and which are empirical equations

Optimizing corona ring design for 400 kV cap-pin string insulator to minimize surface electric field under various surface conditions

The objective of this paper is to reduce the electric field stress along the surface of the 400 kV cap-pin string insulator by optimizing its corona ring design. The cap-pin string insulator, composed of glass material and consisting of 1512 L units, is designed and investigated within a 2D-axisymmetric environment using COMSOL software. Firstly, we optimize the corona ring’s radius, tube radius, and height. Secondly, the corona ring shape is optimized to more effectively decrease the surface electric field, despite the resulting increase in its weight. Finally, the optimized shape is replaced by multiple corona rings, each with a small radius, positioned in the most deformed area, to enhance the insulator’s performance in terms of both surface electric field and corona ring weight. The COBYLA algorithm is utilized as the optimization method throughout the study. This research examines clean, uniformly polluted, and Room Temperature Vulcanizing (RTV) silicon rubber-coated surface conditions. The obtained results are presented and discussed

Correlations between structural changes and dielectric behavior of thermally aged XLPE

International audienceThis study aims at elucidating the correlations between structural changes and the variation of dielectric properties of cross-linked polyethylene (XLPE) during thermal aging. For this purpose, thermal aging experiments were carried out on XLPE samples at 80, 100, 120 and 140 °C for different aging times for a maximum total duration of 5040 hours. Chemical changes were assessed by Fourier Transform Infrared Spectrum (FTIR). Besides, the crystallinity ratio and the melting temperature were evaluated using Differential Scanning Calorimetry (DSC). Frequency domain dielectric spectroscopy was used to investigate the evolution of the dielectric constant and losses of XLPE during aging. The results show that aging at 80 and 100 °C could help to improve the crystalline state of XLPE which leads to the decrease of the dielectric constant. However, for higher thermal stress, the main aging mechanism of XLPE is thermal oxidation which leads to deteriorate the morphology and increase both the polarization and losses, mainly at low frequencies. It has been found also that in some cases, the non-homogeneity of the color of XLPE seems to indicate the increase of interfaces in the material which could lead to increase the dielectric losses due to the interfacial polarization

AC Conductivity Analysis and Chemical Changes of Thermally Aged PVC/B Insulation for Medium Voltage Cables

National audienc