SUMMARYAn engineering approach to numerical modelling of power cable heating due to a line-to-earth short-circuit caused by previous mechanical damages of a cable sheath and insulation is proposed in this paper. Nonlinearity of the finite element model is based on the soil thermal conductivity and heat sources as functions of temperature and time. The nonlinear transient analysis is applied to an authentic example of line-to-earth shortcircuit caused by a mechanical damage of the cable sheath and insulation that has arisen during the previous removal of tree roots. The represented fault occurred on 14 November 2007 in a buried 0.4 kV cable line installed in the city of Bijelo Polje, Republic of Montenegro. Also, this paper outlines a proposition of a technical report prescribing procedures for the removal of tree roots from the soil surrounding cables and for laying power cables nearby high vegetation. The proposed engineering approach is applicable to power cables of all voltage levels laid in soils with changeable moisture content.

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The first part of the article presents a motion analysis of a vibro-impact system based on an oscillator moving along a rough circle line in a vertical plane, under the action of an external single-frequency force. Non-ideality of the bond originates of sliding Coulomb's type friction force with coefficient μ = tgα 0 . The oscillator consists of one heavy mass particle whose forced motion is limited by one stabile angular elongation limiter. The differential equation of motion of the analyzed vibro-impact system cannot be solved explicitly (in closed form). For its approximately solving, the software package WOLFRAM Mathematica 7 is used. The results are checked by using the software package MATLAB R2008a. The combination of the analytical-numerical results for the defined parameters of the analyzed vibro-impact system, is base for the motion analysis visualization, as a first part of this analytic research. In the second part, the influence of parameters (amplitude and circle frequency) of the external single-frequency force to the system motion, based on real geometry and kinetic parameters of the analyzed vibro-impact system, is investigated. As a result of this study in the second part of this article, there is a conclusion that the motion of the analyzed vibro-impact system in or out of the resonant area can be influenced, and this is significant for engineering practice.

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