Ivan Sarajčev

Mathematical model of lightning stroke development

This paper presents a mathematical model of the lightning stroke path development. Any lightning model is a mathematical construct design to reproduce certain aspects of the physical process involved in the lightning discharge. This mathematical model resides on the underlying observed physical properties of the lightning stroke development. It uses Monte Carlo based algorithm in order to simulate stochastic and dynamic movement of the lightning stroke stepped leader descent. Influence of the lightning stroke current amplitude on the path development is also taken into account. Two examples of the lightning stroke stepped leader propagation paths are presented.

Current reduction factor of compensation conductors laid alongside three single-core cables in flat formation

The three-phase cable line consists of three single-core cables, which can have conductive sheaths, grounded at either one end only, or at both ends. If they are grounded at both ends, currents flow through sheaths of single-core cables during both balanced and unbalanced loads and the line-to-ground short circuit in a grounded network. During the line-to-ground short circuit, currents flow through cable sheaths and through the ground. When cable sheaths are grounded at one end only, currents do not flow through the sheaths and the influence of the short circuit current on neighboring electrical circuits is greatest. Compensation conductors are used to reduce this effect. Reduction effect of compensation conductors laid alongside three power single-core cables in flat formation is analyzed in this paper. Calculation methods of current reduction factor are also described.

Determining currents of cable sheaths by means of current load factor and current reduction factor

A new method for determining sheath currents as the consequence of electromagnetic coupling during line-to-ground short circuit is described in this article. This method is based on using both the current load factor and the current reduction factor. The model cables are selected to represent major constructions encountered in practice. The cable line consists of three single-core cables laid in trefoil formation and touching each other. Cable sheaths are grounded at both ends. Current load factor and current reduction factor are characteristic data of the analyzed cable line. The method presented in this paper is easy to use.

Influence of earthing conductors on current reduction factor of a distribution cable laid in high resistivity soil

Various types of system circuit faults are possible. The most common is the phase-earth fault. During this fault, currents flow through earthing grids as well as through the earth. These currents are the consequence of electromagnetic coupling of conductors and earthing grid potentials and can be presented by current reduction factor. When earthing conductors are laid together with cables, the current reduction factor is very difficult to define. In this paper a mathematical determination model of current reduction factor is presented for the cable and earthing conductors laid in the same trench. Influence of both electromagnetic characteristics and earthing conductor geometrical characteristics as well as influence of geophysical features on the current reduction factor is analyzed in this paper.