Search results

The purpose of this paper is to present a new calculation method for increasing the shielded volume in which the external electromagnetic field is maximally reduced. In a space shielded in the way mentioned in this paper, it is possible to introduce measurement instruments and increase the accuracy of results obtained with them, as well as reduce the risk of unwanted electrostatic field influence on living organisms.

A new numerical procedure for the optimization of the coaxial ring conductor system for electrostatic shielding is developed in the paper. The optimization of the functional that consists of electrostatic energy density and a system of equations derived from the equipotential character of the conductor system is used. The system of nonlinear equations is obtained and then numerically solved by minimizing this functional. The first presented optimization procedure is based on the analytical optimization method using the Lagrange coefficients and gradient of the objective function.

It is possible to design a large number of protective ring formations. Applying the differential evolution optimization method, an optimal arrangement can be obtained for any specific number of rings. The differential evolution optimization method, which belongs to the class of evolutionary algorithms, is used for solving this very complex optimization problem. In combination with the above-mentioned method, excellent results in the elimination of the external electric field have been obtained. Although a larger number of rings provides more efficient protection, this number is limited from the economic point of view. Therefore, it is necessary to achieve a compromise between the number of rings, the size of volume shielded and the quality of protection.

There are few papers that address this problem, although the elimination of the influence of the external electromagnetic field has gained more importance lately. The presented method can be applied to increase the reliability of measured data, protection of the environment, in space research, etc. The main limiting factor for using a larger number of rings that provide better protection is the economical one.

The proposed method is suitable for the generalization of procedures, for the protection of the space where the external electric field needs to be reduced or eliminated.

This paper aims to present a new approach to the numerical solution of skin effect integral equations in cylindrical conductors. An approximate, but very simple and accurate method for calculating the current density distribution, skin-effect resistance and inductance, in pulse regime of cylindrical conductor, having a circular or rectangular cross-section, is considered. The differential evolution method is applied for minimization of error functional. Because of its application in the practice, the lightning impulse is observed. Direct and inverse fast Fourier transform is applied.

This method contributes to increasing of correctness and much faster convergence. As the electromagnetic field components depend on the current density derivation, the proposed method gives a very accurate solution not only for current density distribution and resistance but also for field components and for internal inductance coefficients. Distribution of current and electromagnetic field in bus-bars can be successfully determined if the proximity effect is included together with the skin effect in calculations.

The study shows the strong influence of direct lightning strikes on the distribution of electrical current in cables used in lightning protection systems. The current impulse causes an increase in the current density at all points of the cross-section of the conductor, and in particular the skin effect on the external periphery. Based on the data calculated by using the proposed method, it is possible to calculate the minimum dimensions of the conductors to prevent system failures.

There are a number of approximations of lightning strike impulse in the literature. This is a limiting factor that affects the reliability and agreement between measured data with calculated values.

In contrast with other methods, the current density function is approximated by finite functional series, which automatically satisfy wave equation and existing boundary conditions. It is necessary to minimize the functional. This approach leads to a very accurate solution, even in the case when only two terms in current approximation are adopted.