The ampacity of underground power cable lines is limited by the maximal allowable temperature of the conductor. Normally the IEC 60287 standard is used for steady state ampacity calculation. The standard employs the concept of thermal equivalent circuit. An alternative to the standard is the finite element (FEA) simulation of electromagnetic and thermal field around cables. This paper presents a systematic comparison of IEC calculation vs. FEA simulation for various cable line layout. The simulation includes coupled AC magnetic formulation with attached circuit and heat transfer formulation. The comparison shows that IEC and FEA gives almost same results with single-core cables laid in trefoil or flat formations. In case of cable duct bank with a number of lines, FEA shows a stronger electromagnetic and thermal interference than predicted by the IEC 60287 standard.

The new topology of three-winding welding transformer is proposed. Each secondary winding is connected in parallel through the separate bridge rectifier to the welding arc. The main feature of the proposed device is parallel working of two secondary windings with different rated voltage. The advantage is nonlinear transformation ratio of current that provides unprecedented power efficiency. The self- and mutual leakage inductances, which are important in power conversion, are calculated by 2D FEA model. The operational current of the device is modelled numerically via P-Spice simulator. The proposed topology is up to 30% more power effective than conventional welding transformer provided that the leakage inductances of primary and secondary windings are correctly fitted. This transformer is used for manual arc welding

Many electrical problems involve the simultaneous solution of equations from different physical domains, i.e. require multiphysics solution. Multiphysics problems are typical for many electrical applications. Most of difficulties arising here are subject of study and classification. For example, for multi-physics analysis is typical to combine several physical models with different level of details. Another complicating factor is multiscaling, i.e. significant difference in space or time scale between different physical domains. The numerical strategy for multiphysics problem depends heavily on the assumptions made and level of physical details taken into account. In the paper some features of multidisciplinary problems are considered, typical problems are classified, and an approach to the solution is outlined. As a typical multiphysics problem we consider the modelling of current carrying capacity of underground three-phase power cable line. Such analysis demands the solution of the electromagnetic field equations, Kirchhoff's equations for grounding circuitry, and the heat transfer equations coupled together. Each physical domain can be modeled with appropriate level of details. Several variants of geometric location of single-phase cables of three-phase are considered: in line, in triangle, and with separation of one phase from two others. One-sided and two-sided grounding of cable shield and armor is taken into account. The conducted study validates a number of the engineering simplifications, which are typical for multiphysics problems in the electrical engineering.

Numerical simulation of polypropylene laminated paper insulation is a serious challenge, as it must take into account the layered structure and presence of longitudinal and radial gaps in the coils of the winded tape for cables with sector-shape conductive cores. Thus far, it has been performed only with serious simplifications. We propose a technique for numerical modeling of electric parameters in this type of insulation by reducing a complex 3D problem to a simplified 2D model that takes into account the main influencing factors. The results of modeling the distribution of electric field strength and current density in insulation are presented, and the influence of the location of gaps between the edges of winded tape on the conductivity of cable insulation is estimated. Analytical expressions are obtained for estimating the electrical resistance of insulation while taking into account the parameters of the butt gap between the insulating tapes. The results of calculations, numerical modeling, and experimentally measured values of electrical resistance are compared, showing that there is a good match. The main effects affecting the properties of polypropylene laminated paper insulation are described.