Towards the prospection of an optimal thermal response of ZnO surge arrester in HV power system

In order to understand the thermal and electrical properties of surge arrester under standard climatic conditions, it would be useful to evaluate the heating progression in its different elements. These are constituted of heterogeneous materials, which have physical and electrical nonlinear properties along the surge arrester. Temperature predicting solutions for zinc oxide ceramic blocks provide fundamental elements of the electrothermal material characteristics in view of the lifetime estimation. Electrothermal phenomenon analysis of surge arresters is based on empirically-determined parameter models, using finite element method (FEM) simulated on COMSOL Multiphysics software which is a more precise approach compared to the existing models. In this paper, the behavioural model has been developed to study the surge arresters in both cases: the steady state and overvoltage state (lightning). Previous published works validate the first simulation results. This work is therefore extended to consider other operating states, which illustrate the dependence of the type of surge on the amplitudes and durations of electrothermal phenomena

Statistical approach for insulation coordination of high voltage substation exposed to lightning strikes

Introduction. Insulation coordination requires accurate prediction of overvoltages at various points within a substation. Computer simulations of electromagnetic transients in real structures of substations become more precise due to the improvements of used models. Goal. This paper discusses in a first step the use of the modified ZnO arrester dynamic model alongside other substation equipment models, considering electrical phenomena like the corona model for reproducing the stresses that lightning can cause in an air-insulated substation and (method) then conducting a statistical approach based on the Monte Carlo method. The implemented MATLAB/ATP procedure estimates not only the substation Mean Time between Failures (MTBF), but also is used to select surge arresters or substation basic insulation levels (BILs). In this procedure ATP transients program is used to calculate lightning overvoltages and multicore environment for the calculations. Results. The obtained MTBF curves offer guidance for selecting appropriate insulation levels based on specific system requirements and conditions. The obtained results comply well with existing international insulation standards. This valuable approach significantly contributes to the field of lightning protection. References 31, tables 3, figures 10

Almost global attitude stabilization of a rigid body for both internal and external actuation schemes

One of the recent developments in attitude control is the notion of almost-global asymptotic stabilization (AGAS) using coordinate-free control laws. In this paper, we examine two aspects related to this line of research. The first is the problem of AGAS with internal actuation. Since all of the results concerning AGAS so far focus on external actuation, we address the internal actuation case and show that there exists a class of control laws that can almost globally stabilize the desired equilibria either by external or internal actuation. The second aspect we analyze is the construction of potential functions leading to AGAS. We show that it is possible to construct such potential functions in such a way that the resulting control torque depends only on two vector observations, thus avoiding the need for explicitly computing the attitude matrix for the purpose of feedback. We also show that these potentials are nothing but the commonly used error functions, namely the modified trace functions. (C) 2013 European Control Association. Published by Elsevier Ltd. All rights reserved

Stress and strain-driven algorithmic formulations for finite strain viscoplasticity for hybrid and standard finite elements

This work deals with the formulation and implementation of finite deformation viscoplasticity within the framework of stress-based hybrid finite element methods. Hybrid elements, which are based on a two-field variational formulation, are much less susceptible to locking than conventional displacement-based elements. The conventional return-mapping scheme cannot be used in the context of hybrid stress methods since the stress is known, and the strain and the internal plastic variables have to be recovered using this known stress field.We discuss the formulation and implementation of the consistent tangent tensor, and the return-mapping algorithm within the context of the hybrid method. We demonstrate the efficacy of the algorithm on a wide range of problems

Voltage distribution on ZnO polymeric arrester under pollution conditions

At working voltage levels and under the knee of breakdown, the voltage distribution along ZnO arresters is affected by stray capacitances. The existence of any stray capacitance will cause a non-uniform voltage distribution. When ZnO arrester operates under polluted conditions, it can be stressed with severe non uniform field distribution which could cause external breakdown, internal partial discharges and a rise in the temperature of the varistors. In order to obtain the voltage distribution in the ZnO arrester, a full equivalent circuit, which takes into account the ZnO material properties and the stray capacitances, is derived and implemented in the EMTP-ATP package in order to simulate the internal and external leakage currents flowing through the surge arrester with and without pollution under power frequency voltage. When subjected to fog conditions, pollution layers on the arrester housing will become conducting and could result in a significant redistribution of the voltage. This paper presents an equivalent circuit for a ZnO surge arresters under polluted conditions. The voltage distributions under various scenarios of pollution and applied voltage are computed. Areas of highly stressed regions were determined which could be used to predict design weaknesse

Analysis of textured silicone rubber performance under contaminated conditions

Electric field analysis around high-voltage insulators is with an extreme importance during the development of new polymeric insulators design. In this study, the authors combine the finite-element method (FEM) with the design of experiment method to investigate and describe the behaviour of textured silicone rubber insulators. First, a 3D FEM model of different silicone textured surfaces is developed. The maximum electric field is calculated taking into account various available patterns of hemispherical protuberance having different diameters. Then the design of experiment methodology is adopted to reduce the number of simulations and to give more significance to the results. Various influencing factors were considered in this stage. Finally, the analysis of variance is used to evaluate the contribution of the studied factors and their interaction on the total variation of the studied responses