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The examination of the specific thermal resistivity and moisture of cable bed in laboratory conditions
University of Belgrade, Electrical Engineering Institute 'Nikola Tesla'

emailninoslav.simic@ieent.org
Keywords: power cable; specific thermal resistivity of the soil; soil drying; temperature; cable bed
Abstract
This paper at first hand briefly presents examples of the maximum permitted current changes for one cable depending on the specific thermal resistance soil value rz. It is emphasized that the permanently permissible current load of the cable should be calculated using a constant value rz in design - Then, for two cases from field, two samples were examined. The first sample is undisturbed soil from the cable route and the second sample is specially prepared cable bed. The corresponding rz values were obtained using the needle probe method in the laboratory. The difference is pointed out between the measured values of specific thermal resistivity and moisture of the samples. Some samples were being dried in thermal chambers and the others were being dried on ambient temperature. For drying in thermal chambers, based on experience for cross-linked polyethylene cables, the temperatures of 60°C to 90°C were selected for the first case while in the second case the temperature of 20°C over a long period of time was applied. The results obtained were analyzed and shown in appropriate tables and graphs. At the end of this paper the moisture of the soil was calculated for sampled cable bed that corresponds to the value of rz of 1(Km/W). The composition of the cable bed that allows the designed value of the rated power of the cable to be achieved is proposed.
References
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*** (1994) Standard power cable ampacity tables. New York: IEEE, IEEE standard 835-1994
*** (2015) Electric cables: Calculation of the current rating: Part 2-1: Thermal resistance: Calculation of thermal resistance. IEC 60287-2-1
*** (2015) Sistem za merenje i monitoring temperature plašta 110kV kablova. Elektrotehniĉki institut Nikola Tesla, Studija 351109
*** (2017) IEEE guide for thermal resistivity measurements of soils and backfill materials. IEEE Std 442™ (Revision of IEEE Std 442-1981)
Neher, J.H., McGrath, M.H. (1957) The calculation of the temperature rise and load capability of cable systems. AIEE Transactions, (3)752-772
Oh, H. (2014) Thermal resistivity dry-out curves for thirteen sandy soils. Madison: University of Wisconsin
 

About

article language: Serbian
document type: Professional Paper
DOI: 10.5937/zeint32-41463
received: 29/11/2022
accepted: 05/12/2022
published in SCIndeks: 13/01/2023
peer review method: single-blind
Creative Commons License 4.0

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