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

On the effects of lamination artificial faults in A 15 kVA three-phase transformer core

Cutting and punching of the steel used in power transformer core may cause edge burrs. This, along with the degradation of the lamination insulation, can lead to interlaminar short circuits. Analysing these faults helps understanding their effect on the transformer reliability and performance. In this light, the actual paper aims to experimentally simulate and analyse both faults using a 15 kVA three phase power transformer. Effects produced from both selected faults are experimentally investigated in this paper where different scenarios are considered such as the area of the affected regions and the number of short-circuited laminations. Various flux densities are considered ranging from 0.5 to 1.8 T. Of interest, the current at no load is recorded and the test is repeated for any given scenario. The obtained results are presented and discussed to study the effect of each fault on the transformer performance. Overall, the transformer current increases with the number of short-circuits between laminations for both faults. This increase is related to the flux density, which is dependent and sensitive to the short circuit location. Such findings represent a good indication of the severity of short circuits relative to their position in the transformer core, and can be exploited to discuss the power losses in the transformer core

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

Impact of DC filters energies on the commutation failure in HVDC CIGRE benchmark

The present work is devoted to study and simulate of the functioning of monopolar HVDC LCC system of 500 kV in the presence of an AC power grids voltage disturbance. The CIGRE HVDC LCC Benchmark was simulated using MATLAB/Simulink in presence of AC grids voltage variations: first an overvoltage in AC grid 1 and second voltage drop in AC grid 2 have been simulated. All of these simulations are done to evaluate the robustness of the CIGRE HVDC LCC benchmark against AC grids voltage variation, and to investigate the ability of HVDC link function after disappearing of the simulated variation. The results showed that the HVDC LCC system is sensitive to overvoltage higher than 15 % appearing at the rectifier level, and is sensible too to voltage drops with more than 10 % at the invert level. In these conditions, a commutation failure leading to short-circuit was observed, which interrupt the HVDC link operation, and doesn’t permit re-establishment of link function after fault disappearing. To find the reason of the commutation failure appearing, the magnetic and electrostatic energies stored in DC filter elements have been measured and analyzed. The analysis show that when the magnetic energy is greater than the electrostatic one, the commutation failure appears

On the optimization of grounding design of rods covered by low resistivity materials

Reducing the grounding resistance using low resistivity materials (LRM) is a widely used technique to improve the grounding system performance, especially under high resistivity conditions. In this light, the present paper deals with cost-effective design of a typical configuration of grounding systems with LRM coverings. Indeed, optimization problems are proposed and resolved using particle swarm optimisation. Considering vertical ground electrodes partially and fully covered by LRM, the objective is devoted to obtain the geometrical configuration that gives simultaneously an economical and safe grounding design. Each step in the optimization is discussed to help generalise the technique for more complex grounding designs. The results show that soil treatment can significantly reduce the grounding resistance by more than 50% compared to identical systems without LRM coverings. Moreover, the optimal geometrical parameters are senssitive to the variation of the soil resistivity as well as the maximum tolerable limits

On the performance of a 21-level asymmetrical multilevel voltage inverter

This paper deals with a 21-level asymmetrical voltage inverter with a reduced number of switching components and isolated DC sources. A brief description of the used multilevel inverter is provided, including the circuit configuration and control signals. A pre-calculated switching technique is implemented where the inverter performance is achieved throughout a parametric analysis (THD and fundamental component amplitude). Therewith, selected simulation results are shown to discuss the output voltage and current for different RL-loads and modulation index. The computed current and load voltage signals show a reduced THD that is varying in the permissible limits

Cap-pin glass insulator simulation and leakage current waveform extraction

This paper presents a simulation of a HV glass insulator and a methodology to extract leakage current signal. Using 3D profiles, COMSOL-based simulations are conducted at a 50 Hz voltage waveform of different magnitudes. The 1512L cap and pin glass insulator is employed since it is widely used in Algerian desert regions. Potential and electric field distributions, along with the temperature rising, are presented and discussed. The current density is extracted and used to compute the leakage current signal. The obtained results are presented and discussed

On the contribution of A PV generation in Adrar's isolated power system

This paper aims to study and analyse a 220 kV isolated power plant of Adrar, Algeria. This power system is mainly composed of nine buses and seven PV power plants. Simulations are conducted using this power system where the irradiance, power demand and temperature variations are considered. Firstly, the effect of PV module temperature on the generated power is presented and discussed. Secondly, the load flow is analysed during 24 hours in order to evaluate the overall contribution of the PV generation, especially during rush hours. Finally, the transmitted power is also studied, showing the purpose of the related high voltage lines

On the impact of soil resistivity measurement and modelling on grounding performance

This study highlights the heterogeneity impact of fields on the grounding system modelling and the uncertainty of soil resistivity measurements/models caused by this reason. Using Wenner method, six sounding profiles are considered over a square shape area within the same site. Test arrangements and associated results, including soil equivalent models, are presented in order to discuss the soil heterogeneity aspect. The impact of this latter on grounding modelling is determined by simulations over a wide range of frequencies using HIFREQ module of CDEGS software. The results show that soil resistivity measured results can be different with respect to the selected profile, providing different equivalent models of the same soil. Grounding modelling process is affected by this variety of models in a dependent manner with the frequency range of the injected current. Additional analyses are also considered for a second site in a different location. The same conclusions are obtained - arbitrary selection of survey profile and/or soil equivalent model may significantly influence the grounding design, affecting the associated protective systems. Such findings lead to extending relevant standards to cover this aspect, especially for large-scale ground networks or grounding systems for surge arresters