The temperature distribution and ampacity in a multilayered soil surrounding a system of three cables are calculated in the steady state and in emergency situations. In this paper, we present the mathematical model, which solves the heat diffusion equation in cylindrical coordinates inside the cables and in Cartesian coordinates in the surrounding soil. The finite difference method is used to solve the equations. In order to reduce the number of points studied that are of no interest to the results, a variable step discretization is used. Here, we present the development of the model and the effect of some of the parameters which influence the convergence and accuracy of the method. The application of the model in different configurations and situations is given in the second part of this work, sent for publication at the same time. The model is applicable to the study of buried cables in both the steady state and transient states for short-circuit and overload situations.

Theoretical model to calculate steady-state and transient ampacity and temperature in buried cables

The boundary-element method (BEM) is used to solve the underground cable thermal field problem. Because attention is focused on the region boundaries rather than on its interior, the computational effort is reduced very significantly. Examples of application of the BEM include homogeneous soil and multimedia systems. Single and multicable geometries are investigated. The results exhibit accuracy better than can be expected for commonly used domain-type methods, since region truncation with an artificial boundary is not needed. >

Calculation of thermal fields of underground cables using the boundary element method

Methods for analysis of temperature distributions around buried power cables are reviewed None accurately models the true geometric conditions or properties or enables prediction of the time- dependence of temperature change

Temperature Distributions Around Buried Cables

A 3-D nonlinear thermal circuit model of underground MV power cables and their joints

The study presents an algorithm to compute the heat transfer coefficient for thermal cable rating when modelling the non-isothermal earth surface with the additional wall method. The position of the fictitious images is computed analytically by recognising that the complex geometrical arrangement can be converted into a much simpler one using the Fourier transform. This allows for the estimation of the heat transfer coefficient with simple formulas. The resulting equations are very easy to implement and are entirely compatible with the standardised methods (IEC and IEEE) for rating power cables. Hundreds of finite elements simulations have been performed to validate the proposed method which yielded results with typical differences of <5% for standard installations.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-gtd.2013.0721

Conrad A. Bauer

Papers

A study of the superposition of heat fields and the Kennelly formula as applied to underground cable systems

Soil Factors Affecting Buried-Pipe-Cable Temperatures