@misc{NeidhartHallasHinrichsenetal., author = {Neidhart, Thomas and Hallas, Martin and Hinrichsen, Volker and Tenzer, Michael and Neumann, Claus}, title = {Langzeitversuche an einer direkt erdverlegten DC GIL: Bodenmechanische und thermische Wechselwirkungen bei Bettung in zeitweise fließf{\"a}higem Verf{\"u}llbaustoff}, series = {22. Fachtagung Hochspannungsschaltanlagen: Anwendungen, Betrieb und Erfahrungen am 6. Okt. 2020, TU Darmstadt}, journal = {22. Fachtagung Hochspannungsschaltanlagen: Anwendungen, Betrieb und Erfahrungen am 6. Okt. 2020, TU Darmstadt}, language = {de} } @inproceedings{HallasHinrichsenNeumannetal., author = {Hallas, Martin and Hinrichsen, Volker and Neumann, Claus and Tenzer, Michael and Hausmann, Bruno and Gross, Detlev and Neidhart, Thomas and Lerch, Maximilian and Wiesinger, Doris}, title = {Cigr{\´e} Prototype Installation Test for Gas-Insulated DC Systems - Testing a Gas-Insulated DC Transmission Line (DC-GIL) for ±550 kV and 5000 A under Real Service Conditions}, series = {2020 CIGRE Session, CIGRE e-Session 48: Paris, France (virtual), 24.08.-03.09.2020}, booktitle = {2020 CIGRE Session, CIGRE e-Session 48: Paris, France (virtual), 24.08.-03.09.2020}, publisher = {CIGRE}, address = {Darmstadt}, doi = {10.26083/tuprints-00014132}, pages = {13}, abstract = {More and more generation facilities are installed far away from the load centers. Thus, long distance transmission is demanded, and with this regard DC transmission systems are of special interest. Transmission by overhead lines is a well-proven technology, but due to environmental concern and political decisions underground transmission systems are often requested. Besides DC cables, DC GIL are an interesting option. They enable transmitting high power by only one system in a small corridor only a few meters wide. GIL can be laid in a tunnel or directly buried in the soil. Meanwhile a lot of service experience has been collected with AC GIL technology, but no service experience is yet available with DC GIL. To close this knowledge gap and to investigate the long-term performance, a ±550 kV DC GIL prototype with a current carrying capacity of 5000 A is currently investigated in a HVDC test facility, both in directly buried and in above-ground installation. The test procedure follows the recommendations for long-term testing of gas-insulated systems, currently under preparation by Cigr{\´e} JWG D1/B3.57. This report describes the test sample arrangements, the high-voltage and high current test equipment and the commissioning procedure for the DC GIL. It illustrates the UHF PD monitoring system installed and the method to identify possible PD defects. The investigated DC GIL is subdivided into two parts: While an above-ground installation is simultaneously stressed by voltage and DC current, a directly buried part of the DC GIL is stressed with DC current only in order to investigate soil mechanics, the temperature distribution in the GIL and in the soil as well as the performance of the backfill material. The report also presents first results gained on the directly buried arrangement for studying the soil mechanics.}, language = {en} } @inproceedings{NeidhartLerchWiesingeretal., author = {Neidhart, Thomas and Lerch, Maximilian and Wiesinger, Doris and Hallas, Martin and Hinrichsen, Volker and Tenzer, Michael}, title = {Long-Term Tests of a DC Gas Insulated Transmission Line (DC GIL) embedded in Temporally Flowable Backfill: Soil-Mechanical and Thermic Interaction}, series = {VDE Hochspannungstechnik: ETG-Fachtagung, 9. - 11. November 2020, Online-Veranstaltung}, booktitle = {VDE Hochspannungstechnik: ETG-Fachtagung, 9. - 11. November 2020, Online-Veranstaltung}, edition = {CD-ROM}, publisher = {VDE-Verlag}, address = {Berlin}, isbn = {978-3-8007-5353-6}, pages = {518 -- 524}, 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.}, language = {en} }