A. S. Brookes

Bio: A. S. Brookes is an academic researcher. The author has contributed to research in topics: Thermal resistance & Nobelium. The author has an hindex of 1, co-authored 1 publications receiving 12 citations.

The Thermal Behavior of Cable Backfill Materials

Abstract: The thermal behavior of a number of soils including those frequently used for high-voltage cable backfill has been studied in the laboratory and in the field. Initially, thermal resistivity tests using a probe and thermal moisture migration tests were carried out in the laboratory. From these tests it was found that well-graded granular materials behaved the best. In particular "limestone screenings," a by-product from rock quarries, was found to have highly desirable thermal properties. A full-scale field test was made by means of a simulated cable installation. The materials tested included a uniform sand, a manufactured sand and "limestone screenings." The placement moisture and density of the materials was varied as well as the heat input. Observations of moisture and temperature gradient were made over a two and one- half year period. The results of this study confirmed the results of the earlier laboratory tests. The screenings and the manufactured sand, both of which were well graded, exhibited a low resistivity which remained stable during both dry and wet periods. The uniform sand had a higher initial thermal resistivity and became unstable due to moisture migration during dry periods of the year. Subsequently, a few simple tests have been made to investigate the flow of vapor and liquid in soil under a thermal gradient. A tentative explanation of the varying behavior of the materials, based on their respective porosity characteristics, is given.

Thermal Stability and its Prediction in Cable Backfill Soils

Abstract: Thermal instability, in the context of heat dissipation from buried cables, refers to the condition tion in which the thermal resistivity of the soil continuously increases with time to a value close to that of its dry state. This "thermal runaway" condition leads to a large increase in cable temperature. The thermal instability in cable backfills is a direct result of net moisture migration away from the heat source below a critical moisture level. Moisture migration in cable backfills can be caused by either a natural drying process resulting from evapotranspiration or by the thermal gradient from the heat source. This paper deals with the latter case, for which a theoretical prediction and experimental verification are provided. A transient heat probe method of predicting thermal instability in cable backfills is discussed.

Effective Thermal Resistivity for Power Cables Buried in Thermal Backfill

Abstract: Existing methods for calculating cable ampacities assume that buried cables are surrounded by a single, homogeneous material. These ampacity programs have limited application when a thermal backfill material is used to increase the current carrying capability of underground cables. This paper presents a method of calculating an effective thermal resistivity for any combination of backfill materials that are placed adjacent to the cable. Results are presented for a rectangular region of backfill covered by a protection layer. The concept of an effective thermal resistivity can extend the use of existing ampacity programs to cases involving non-homogeneous soil layers.

Application of Oil-Cooling in High-Pressure Oil-Filled Pipe-Cable Circuits

Abstract: Circulation of oil in pipe-type feeders has been employed, to a limited extent, to accomplish either of the following two objectives: 1) temperature-averaging to minimize the effect of unknown hot-spot zones, or 2) an increase in circuit capacity above the self-cooled level. This paper reports, in two sections, on both types of application, which were initiated in 1952 and carried out subsequently on an increasing scale. Particular attention is givein to a large program of 138-and 345-kV pipe-type feeder installations.