Showing papers by "Madjid Teguar published in 2016"

Optimal design of corona ring on HV composite insulator using PSO approach with dynamic population size

Abstract: This paper deals with the use of corona ring at the HV end fitting for improving the electric field and potential distributions and then for minimizing the corona discharges on 230 kV AC transmission line composite insulator. A single corona ring is installed at the energized end side. Three-dimensional finite element method (FEM) software is employed to compute the electric field. As the performance of high voltage insulator strings closely depends on designs and locations of corona ring, the effects of the corona ring radius, the ring tube radius and the ring vertical position are examined. The minimization of the electric field necessitates the optimization of corona ring. For this purpose, new nonlinear mathematical objective function linking the electric field strength to the corona ring structure parameters is established. The optimization problem is achieved by minimizing the objective function using a modified particles swarm optimization (PSO) algorithm with a dynamic population size. The algorithm adjusts the size of population for each iteration. Based on the average value and the best solution of the objective function, we propose a new mathematical model to update the population size. This algorithm enables the population size reduction leading to computing time decrease. According to the results, FEM-PSO hybridization technique could be very helpful in optimization of corona ring design.

Effect of space charge layers on the electric field enhancement at the physical interfaces in power cable insulation

Abstract: This paper intends to investigate the effect of two vented water trees w 1 and w 2 growing simultaneously from both conductor and insulation screens of medium voltage cable in the presence or not of space charge, on the electric field distribution. +12 kV DC voltage has been applied. Such simulation has been implemented under Comsol Multiphysics® environment using the finite element method. Particular interest is assigned to the effect of the polarity, density and layers thickness of the space charge as well as to the behavior of this charge initially accumulated at water trees tips. Note that for the polarity influence, the four polarities configurations related to the space charge accumulated at w 1 and w 2 have been considered. As results, the electric field enhancement at the semiconductor layers especially close to the water tree defect is strongly dependent not only upon the relative permittivity distribution inside water trees, but also on the amount, density and layers thickness of the space charge. In the absence of space charge, we show that, with regard to the inhomogeneous (linear and parabolic) distribution of the permittivity, the homogeneous one causes much more local enhancement of electric field at the trees tips. Moreover, the electric field distribution depends on the geometrical parameters (length and width) and shape of trees; the spherical form engenders a higher electric field than elliptical one. In addition, the association of the space charge could lead to the initiation of the electric trees even at lower voltages. Furthermore, the initiation of electrical trees from the physical interfaces is more probable in the case of opposite polarities especially for negative-positive configuration. Such electrical trees start not only from the tip but also from the water tree root (interface of treed region, un-treed one and semiconductor) which is particularly more vulnerable than inside.

Investigation into the dissipated energy under accelerated thermal aging in PVC/B used in low-voltage cables insulation

Abstract: Due to their excellent insulating characteristics, polymer materials are widely used in electric power transmission and power cables. However, the thermal stress is one of the most severe service constraints that can lead to the reduction of insulating polymers lifetime. In light of this, an experimental study on polymer samples was carried out to investigate the impact of the accelerated thermal aging on the dissipated energy through the insulating material. In this study, polyvinyl chloride (PVC, class B or PVC/B), used as electrical insulation in low-voltage cables, was chosen as the studied material. Accelerated thermal aging on circular shaped samples of PVC/B was performed at two temperatures, 80°C and 120°C, during 3024 hours (126 days). The measurements of the cumulative charge were carried out in order to follow the evaluation of energy at different aging stages and for five AC applied voltage levels ranging from 3 kV to 12 kV. The variation of mechanical characteristics as well as the evolution of dissipated energy were examined and analyzed. The investigation results show a significant increase of the dissipated energy with thermal aging due to material degradation. This increase was clearly observed at 120°C. Furthermore, a good correlation between the mechanical properties and the dissipated energy of the material has been found. Through this paper, the dissipated energy and mechanical properties have commonly proved to be effective to evaluate the aging level of insulating materials, which can be used to assess the conditions of low-voltage cables operating.

Evaluation of electric field distribution on a 400 kV composite insulator under various service conditions

Abstract: In this paper, we evaluated electric field distribution along core, weather sheds surface and corona ring of a 400 kV composite insulator under different surface conditions (dry and clean, polluted, in presence of water droplets). Electric field was found higher nearer triple junction point (air-end fittings-housing material). We noticed that the presence of water droplets and pollution layer distributed on weather sheds enhance the local electric field but it doesn't really affect the electric field distribution inside the FRP core. Moreover, for the polluted case, the effect of pollution layer conductivity is insignificant contrary to its thickness. For thicker pollution layer, the maximum electric field point moves from the triple junction point. Finally, corona ring is necessary for a 400 kV insulator for both ends (HV and ground) and its behavior is affected under polluted and wetted conditions. Corona ring parameters (corona ring diameter, corona ring tube diameter and corona ring height) were kept constant through the whole study.