TU Darmstadt / ULB / TUbiblio

Long-Term Tests of a DC Gas Insulated Transmission Line (DC GIL) embedded in Temporally Flowable Backfill: Soil-Mechanical and Thermic Interaction

Neidhart, Thomas ; Lerch, Maximilian ; Wiesinger, Doris ; Hallas, Martin ; Hinrichsen, Volker ; Tenzer, Michael (2021)
Long-Term Tests of a DC Gas Insulated Transmission Line (DC GIL) embedded in Temporally Flowable Backfill: Soil-Mechanical and Thermic Interaction.
VDE Hochspannungstechnik 2020. Online-Veranstaltung (09.-11.11.2020)
doi: 10.26083/tuprints-00014129
Konferenzveröffentlichung, Zweitveröffentlichung, Verlagsversion

Kurzbeschreibung (Abstract)

At present DC transmission systems for long distance transmission are of special interest, particularly with regard to transmission systems that proved ability for directly buried installation. Some service experience has been collected with directly buried AC GIL technology, but none with directly buried DC GIL. First pilot projects with directly buried AC GIL were designed conservative regarding the mechanical GIL support and the maximum allowable current. The aim is to optimize the mechanical and thermal design of directly buried DC GIL to offer cost efficient transmission line solutions. Therefore, a ±550 kV DC GIL prototype with a current carrying capacity of 5000 A is currently investigated in a HVDC test facility, both in above-ground installation and a buried installation. This report presents results gained on the embedded installation for studying the soil mechanics and long-term thermic interaction with the backfill material and the adjacent soil. A DC GIL with a total length of 130 m is embedded in a temporarily flowable backfill (“TFB”) as re-use of the excavated soil on site, which minimizes transportation costs and energy use. TFB is characterized by high contact forces that restrain the DC GIL displacements and by stable thermal conductivity, which optimizes the heat transfer. In order to monitor the mechanical soil-structure-interaction (“SSI”), various temperatures and moisture content sensors were installed inside and around the DC GIL, in the TFB and the adjacent soil as well down to 4 m below the ground surface. Displacement and strain sensors measured the elongations and dilatations of the embedded enclosure tube. Compressive stresses caused by restrained displacements are monitored with load cells. A fiber optical cable is used to monitor the temperatures in the aluminum conductor, on top and at the base of the enclosure tube, as well as in the TFB and the sand cover layer and the adjacent soil. The measurements were completed with some single sensors for temperature, moisture content and porewater-tensions which were mainly concentrated nearby the DC GIL in the TFB and the cover layer. During 15 months, several load cycles impact on the embedded DC GIL. Each load cycle consists of a DC current feed of 5000 A for 4 weeks followed by another 4 weeks without current. Since the SSI is independent of voltage stress, this test is carried out with current only. After 4 load cycles only moderate temperatures are monitored at the enclosure tube and in the TFB, much lower as expected. Seasonal effects predominate the temperatures of the TFB, the cover layer and the adjacent soil, while the DC GIL generates only marginal increases. Moisture contents and porewater-tensions remain constant apart from some variations caused by rainfalls and vegetation cover. The elongation of the enclosure tube is shorter than 5 mm and the forces are lower than 500 kN. It can be concluded that the DC GIL with a current carrying capacity of 5000 A DC embedded in TFB shows temperature-rises far below the technical GIL limits after 4 load cycles. The TFB ensures high and stable heat conductivity and contact forces, thus restraining the GIL movement. The temperature-rises of the natural soil due to GIL heating are comparatively low in comparison to other effects like sun radiation. The TFB shows a good thermal and mechanical performance.

Typ des Eintrags: Konferenzveröffentlichung
Erschienen: 2021
Autor(en): Neidhart, Thomas ; Lerch, Maximilian ; Wiesinger, Doris ; Hallas, Martin ; Hinrichsen, Volker ; Tenzer, Michael
Art des Eintrags: Zweitveröffentlichung
Titel: Long-Term Tests of a DC Gas Insulated Transmission Line (DC GIL) embedded in Temporally Flowable Backfill: Soil-Mechanical and Thermic Interaction
Sprache: Englisch
Publikationsjahr: 2021
Ort: Darmstadt
Verlag: VDE Verlag
Buchtitel: VDE Hochspannungstechnik : 9. - 11. November 2020, Online-Veranstaltung
Reihe: ETG-Fachberichte
Band einer Reihe: 162
Kollation: 7 ungezählte Seiten
Veranstaltungstitel: VDE Hochspannungstechnik 2020
Veranstaltungsort: Online-Veranstaltung
Veranstaltungsdatum: 09.-11.11.2020
DOI: 10.26083/tuprints-00014129
URL / URN: https://tuprints.ulb.tu-darmstadt.de/14129
Zugehörige Links:
Herkunft: Zweitveröffentlichungsservice
Kurzbeschreibung (Abstract):

At present DC transmission systems for long distance transmission are of special interest, particularly with regard to transmission systems that proved ability for directly buried installation. Some service experience has been collected with directly buried AC GIL technology, but none with directly buried DC GIL. First pilot projects with directly buried AC GIL were designed conservative regarding the mechanical GIL support and the maximum allowable current. The aim is to optimize the mechanical and thermal design of directly buried DC GIL to offer cost efficient transmission line solutions. Therefore, a ±550 kV DC GIL prototype with a current carrying capacity of 5000 A is currently investigated in a HVDC test facility, both in above-ground installation and a buried installation. This report presents results gained on the embedded installation for studying the soil mechanics and long-term thermic interaction with the backfill material and the adjacent soil. A DC GIL with a total length of 130 m is embedded in a temporarily flowable backfill (“TFB”) as re-use of the excavated soil on site, which minimizes transportation costs and energy use. TFB is characterized by high contact forces that restrain the DC GIL displacements and by stable thermal conductivity, which optimizes the heat transfer. In order to monitor the mechanical soil-structure-interaction (“SSI”), various temperatures and moisture content sensors were installed inside and around the DC GIL, in the TFB and the adjacent soil as well down to 4 m below the ground surface. Displacement and strain sensors measured the elongations and dilatations of the embedded enclosure tube. Compressive stresses caused by restrained displacements are monitored with load cells. A fiber optical cable is used to monitor the temperatures in the aluminum conductor, on top and at the base of the enclosure tube, as well as in the TFB and the sand cover layer and the adjacent soil. The measurements were completed with some single sensors for temperature, moisture content and porewater-tensions which were mainly concentrated nearby the DC GIL in the TFB and the cover layer. During 15 months, several load cycles impact on the embedded DC GIL. Each load cycle consists of a DC current feed of 5000 A for 4 weeks followed by another 4 weeks without current. Since the SSI is independent of voltage stress, this test is carried out with current only. After 4 load cycles only moderate temperatures are monitored at the enclosure tube and in the TFB, much lower as expected. Seasonal effects predominate the temperatures of the TFB, the cover layer and the adjacent soil, while the DC GIL generates only marginal increases. Moisture contents and porewater-tensions remain constant apart from some variations caused by rainfalls and vegetation cover. The elongation of the enclosure tube is shorter than 5 mm and the forces are lower than 500 kN. It can be concluded that the DC GIL with a current carrying capacity of 5000 A DC embedded in TFB shows temperature-rises far below the technical GIL limits after 4 load cycles. The TFB ensures high and stable heat conductivity and contact forces, thus restraining the GIL movement. The temperature-rises of the natural soil due to GIL heating are comparatively low in comparison to other effects like sun radiation. The TFB shows a good thermal and mechanical performance.

Status: Verlagsversion
URN: urn:nbn:de:tuda-tuprints-141295
Sachgruppe der Dewey Dezimalklassifikatin (DDC): 600 Technik, Medizin, angewandte Wissenschaften > 620 Ingenieurwissenschaften und Maschinenbau
Fachbereich(e)/-gebiet(e): 18 Fachbereich Elektrotechnik und Informationstechnik
18 Fachbereich Elektrotechnik und Informationstechnik > Institut für Elektrische Energiesysteme > Hochspannungstechnik
18 Fachbereich Elektrotechnik und Informationstechnik > Institut für Elektrische Energiesysteme
Hinterlegungsdatum: 17 Dez 2021 13:50
Letzte Änderung: 21 Dez 2021 12:13
PPN:
Zugehörige Links:
Export:
Suche nach Titel in: TUfind oder in Google
Frage zum Eintrag Frage zum Eintrag

Optionen (nur für Redakteure)
Redaktionelle Details anzeigen Redaktionelle Details anzeigen