Calculation of the ampacity of high voltage cables by accounting for radiation and solar heating effects using FEM

Abstract

SUMMARY The paper presents a finite‐element model for the evaluation of the ampacity of an underground 110‐kV three‐phase system of cables in normal operation and in case of emergency. The proposed model takes the effects of convection, radiation, and solar heating at the trench surface into account, which enhances the previous approaches. The calculations performed have shown that these phenomena affect the heating of cables and that the IEC approach that treats the trench surface as an isothermal plane at ambient temperature, widely used in practice, might underestimate the ampacity of cables in certain cases. The model considers in detail the shape and construction of the cable trench, and the thermal properties of backfilling materials and concrete and asphalt covers including the effects of the drying out of soil. The effects of various approximations have been also investigated. The model has been applied to a real life example, and the calculation results have been compared to some experimental data. Copyright © 2011 John Wiley & Sons, Ltd.

Comparison of Conductor-Temperature Calculations Based on Different Radial-Position-Temperature Detections for High-Voltage Power Cable

“…In numerical methods, the finite element method (FEM) is the most used method that has been applied to various laying environments. For example, the rating of underground cables [7]; cables in a tray [8]; the effects of radiation, solar heating, duct structures, and back-filled materials [9]; and, the formation of the dry zone around underground cables [10] have been studied by FEM. Other numerical methods, including the finite difference method (FDM) [11] and the boundary element method (BEM) [12], have also been studied.…”

Calculation of the ampacity of high voltage cables laid in free air

“…which is an alternative, enhanced version of the approximation suggested in [11]. If the heat dissipated in the air from the surface of the cable should be determined, then for J 1 and J 2 the minimum and maximum temperatures for the outer sheathshould be inserted.…”

“…Indices c, h, r and s in (2) and (3) refer to conduction, convection, radiation and solar heating, respectively [11]. Index Q refers to the internal heat generation.…”

“…The matrices figuring in (1) -(3) have been obtained by transferring the corresponding relationships for elements written for their nodes in local coordinates [11] to entire network numbering scheme. Expressions (2) and (3) in their general form are relevant only for the boundary elements with edges on the outer surface of cables.…”

“…The finite element model for the evaluation of the ampacity of underground cables, elaborated in reference [10], has taken into account the drying out of soil and the heat transfer by convection from the soil surface. An enhanced version of this model, elaborated in reference [11], incorporating the radiation and solar heating effects. The latter model, for determining the current rating of the bunch of self-supporting insulated 10 kV cables, adequately adapted in reference [12], has been applied in this paper for comparison with analytical approaches.…”