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The thermal regime around buried submarine high voltage cables

The thermal regime around buried submarine high voltage cables
The thermal regime around buried submarine high voltage cables
The expansion of offshore renewable energy infrastructure and the need for trans-continental shelf power transmission require the use of submarine High Voltage (HV) cables. These cables have maximum operating surface temperatures of up to 70°C and are typically buried 1–2 m beneath the seabed, within the wide range of substrates found on the continental shelf. However, the heat flow pattern and potential effects on the sedimentary environments around such anomalously high heat sources in the near surface sediments are poorly understood. We present temperature measurements from a 2D laboratory experiment representing a buried submarine HV cable, and identify the thermal regimes generated within typical unconsolidated shelf sediments—coarse silt, fine sand and very coarse sand. We used a large (2 × 2.5 m) tank filled with water-saturated spherical glass beads (ballotini) and instrumented with a buried heat source and 120 thermocouples, to measure the time-dependent 2D temperature distributions. The observed and corresponding Finite Element Method (FEM) simulations of the steady state heat flow regimes, and normalised radial temperature distributions were assessed. Our results show that the heat transfer and thus temperature fields generated from submarine HV cables buried within a range of sediments are highly variable. Coarse silts are shown to be purely conductive, producing temperature increases of >10°C up to 40 cm from the source of 60°C above ambient; fine sands demonstrate a transition from conductive to convective heat transfer between c. 20°C and 36°C above ambient, with >10°C heat increases occurring over a metre from the source of 55°C above ambient; and very coarse sands exhibit dominantly convective heat transfer even at very low (c. 7°C) operating temperatures and reaching temperatures of up to 18°C above ambient at a metre from the source at surface temperatures of only 18°C. These findings are important for the surrounding near surface environments experiencing such high temperatures and may have significant implications for chemical and physical processes operating at the grain and sub-grain scale; biological activity at both micro-faunal and macro-faunal levels; and indeed the operational performance of the cables themselves, as convective heat transport would increase cable current ratings, something neglected in existing standards.
heat flow, permeability and porosity, heat generation and transport
0956-540X
1051-1064
Emeana, C.J.
3161b965-d8b0-405c-9786-7bea64b7e476
Hughes, T.J.
ac4f634b-d741-49b9-b0ac-cdc2eef32606
Dix, J.K.
efbb0b6e-7dfd-47e1-ae96-92412bd45628
Gernon, T.M.
658041a0-fdd1-4516-85f4-98895a39235e
Henstock, T.J.
27c450a4-3e6b-41f8-97f9-4e0e181400bb
Thompson, C.E.L.
2a304aa6-761e-4d99-b227-cedb67129bfb
Pilgrim, J.A.
4b4f7933-1cd8-474f-bf69-39cefc376ab7
Emeana, C.J.
3161b965-d8b0-405c-9786-7bea64b7e476
Hughes, T.J.
ac4f634b-d741-49b9-b0ac-cdc2eef32606
Dix, J.K.
efbb0b6e-7dfd-47e1-ae96-92412bd45628
Gernon, T.M.
658041a0-fdd1-4516-85f4-98895a39235e
Henstock, T.J.
27c450a4-3e6b-41f8-97f9-4e0e181400bb
Thompson, C.E.L.
2a304aa6-761e-4d99-b227-cedb67129bfb
Pilgrim, J.A.
4b4f7933-1cd8-474f-bf69-39cefc376ab7

Emeana, C.J., Hughes, T.J., Dix, J.K., Gernon, T.M., Henstock, T.J., Thompson, C.E.L. and Pilgrim, J.A. (2016) The thermal regime around buried submarine high voltage cables. Geophysical Journal International, 206 (2), 1051-1064. (doi:10.1093/gji/ggw195).

Record type: Article

Abstract

The expansion of offshore renewable energy infrastructure and the need for trans-continental shelf power transmission require the use of submarine High Voltage (HV) cables. These cables have maximum operating surface temperatures of up to 70°C and are typically buried 1–2 m beneath the seabed, within the wide range of substrates found on the continental shelf. However, the heat flow pattern and potential effects on the sedimentary environments around such anomalously high heat sources in the near surface sediments are poorly understood. We present temperature measurements from a 2D laboratory experiment representing a buried submarine HV cable, and identify the thermal regimes generated within typical unconsolidated shelf sediments—coarse silt, fine sand and very coarse sand. We used a large (2 × 2.5 m) tank filled with water-saturated spherical glass beads (ballotini) and instrumented with a buried heat source and 120 thermocouples, to measure the time-dependent 2D temperature distributions. The observed and corresponding Finite Element Method (FEM) simulations of the steady state heat flow regimes, and normalised radial temperature distributions were assessed. Our results show that the heat transfer and thus temperature fields generated from submarine HV cables buried within a range of sediments are highly variable. Coarse silts are shown to be purely conductive, producing temperature increases of >10°C up to 40 cm from the source of 60°C above ambient; fine sands demonstrate a transition from conductive to convective heat transfer between c. 20°C and 36°C above ambient, with >10°C heat increases occurring over a metre from the source of 55°C above ambient; and very coarse sands exhibit dominantly convective heat transfer even at very low (c. 7°C) operating temperatures and reaching temperatures of up to 18°C above ambient at a metre from the source at surface temperatures of only 18°C. These findings are important for the surrounding near surface environments experiencing such high temperatures and may have significant implications for chemical and physical processes operating at the grain and sub-grain scale; biological activity at both micro-faunal and macro-faunal levels; and indeed the operational performance of the cables themselves, as convective heat transport would increase cable current ratings, something neglected in existing standards.

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Emeana - Complete Manuscript - GJI-S-15-0933-R2 - Clean File.pdf - Accepted Manuscript
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Emeana - Supplementary Information - GJI-S-15-0933-R2.pdf - Accepted Manuscript
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More information

Accepted/In Press date: 19 May 2016
e-pub ahead of print date: 23 May 2016
Published date: August 2016
Keywords: heat flow, permeability and porosity, heat generation and transport
Organisations: Geology & Geophysics, Electronics & Computer Science

Identifiers

Local EPrints ID: 394828
URI: http://eprints.soton.ac.uk/id/eprint/394828
ISSN: 0956-540X
PURE UUID: 361e2951-800e-407e-a1e4-014eb79df65f
ORCID for T.J. Henstock: ORCID iD orcid.org/0000-0002-2132-2514
ORCID for J.A. Pilgrim: ORCID iD orcid.org/0000-0002-2444-2116

Catalogue record

Date deposited: 19 May 2016 15:53
Last modified: 18 Feb 2021 16:54

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