The ampacity of high-voltage power cables depends, among others, on their core cross-sectional area as well as thermal resistivity of the thermal backfill surrounding the cables. The cross-sectional area of the power cables’ core is selected according to the expected power to be transferred via the cable system. Usually, the higher the power transfer required, the higher the cross-sectional area of the core. However, the cost of high-voltage power cables is relatively high and strictly depends on the dimensions of the core. Therefore, from the economic point of view, it is interesting to focus on the improvement of the thermal condition around the cables, by changing the dimension of the thermal backfill, instead of increasing the power cables’ core cross-sectional area. In practice, it is important to find the optimal dimensions of both cable core and thermal backfill to achieve the economically attractive solution of the power cable transfer system. This paper presents a mathematical approach to the power-cable system design, which enables selecting the cost-optimal cross-section of a power cable core depending on the dimensions of the thermal backfill. The proposal herein allows us to indicate the condition in which it is advantageous to increase the core cross-sectional area or to expand the dimension of the backfill. In this approach, the optimal backfill geometry can also be evaluated. The investment costs of the 110 kV power cable system with the core cross-sectional areas consecutively equal to 630, 800 and 1000 mm2 have been compared.

Article citation info: IntroductionDistribution of power in power networks is performed with the use of overhead power lines as well as underground power cables. The investment cost of the underground power cable distribution systems is higher compared to the use of overhead lines but gives higher reliability of supply, especially reflected in improved SAIDI and SAIFI indicators [1,19,24].Power cables are usually buried in the ground, but in many cases, their ending sections are placed in air, to be connected with conductors of overhead lines, as it is presented in Fig. 1. Depending on the height of the pole, length of the power cables in air can be from a few to several meters. Given that the cable section in the air is connected in series with a section buried in the ground, the ampacity of the whole power cable line depends on the section for which thermal condition for heat transfer from the cables is the worst. The worst thermal condition is expected for the section in air, during sunny weather and without any wind.The problem of power cables heating and calculation of their ampacity are the subject of many papers and standards, especially [12-

Nonlinear effects of planar magnetosound perturbations in a plasma are discussed. Plasma is non-adiabatic due to optically thin radiation and external heating. For these reasons, thermal instability of a plasma may appear which makes it acoustically active. The plasma is assumed to be initially homogeneous ideal gas with infinite electrical conductivity permeated by a straight magnetic field which is orthogonal to the trajectories of gas particles. The instantaneous dynamic equations which describe nonlinear effects of intense sound in quasi-isentropic plasma, are derived. Nonlinear interaction of periodic and aperiodic magnetoacoustic perturbations with the non-wave modes, are discussed. The conclusions concern dissipative or active behavior of magnetoacoustic perturbations which is determined by the kind of the heating-cooling function.

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