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dc.contributor.authorAbid, Fahim
dc.date.accessioned2020-04-29T14:23:26Z
dc.date.available2020-04-29T14:23:26Z
dc.date.issued2020
dc.identifier.isbn978-82-326-4659-3
dc.identifier.issn1503-8181
dc.identifier.urihttps://hdl.handle.net/11250/2652971
dc.description.abstractAn increasing number of wind farms and mining operations located far off the coast will lead to the development of offshore substations. To avoid the large costs associated with platforms and floaters, such a substation can be placed on the seabed and controlled remotely. The conventional solution is to place the power components, e.g. switchgear placed inside thick-walled pressure-proof vessels to protect them from water and high pressure on the seabed. For current switching in medium voltage applications, there are mainly two options: vacuum circuit breakers or gas circuit breakers (filled at atmospheric or slightly elevated pressure). Whichever option is chosen, power cable feed-throughs or penetrators from the high-pressure water environment into the low pressure inside the vessel are required. These features add substantial technical complexity and costs, in particular at large sea depths. A novel concept is used in this thesis, where the interruption chamber of the circuit breaker can be gradually filled as the switchgear is lowered until finally reaching the same pressure as on the seabed. Reducing the differential pressure on the encapsulation will reduce the overall cost and complexity of such subsea substations. The gas pressures in this case may be in the range of up to tens of bars. If the temperature and pressure of a gas exceed its critical point, it enters a supercritical state. In this state, the physical properties are between that of a gas and a liquid. The properties include high diffusivity, high heat conductivity, high heat capacity, high dielectric strength and an absence of vapour bubbles. These properties of the supercritical fluid are believed to be in favour of a successful current interruption medium. However, there is a distinct lack of knowledge on arc properties and the current interruption capability of extremely high-pressure gasses as well as on the supercritical region. In this thesis, nitrogen (N2) is chosen for its low critical point (33.5 bar, 126 K), good insulation strength and environment-friendly nature. As the critical temperature of N2 is lower than room temperature, the transition to supercritical state can be achieved by pressurizing N2 above 33.5 bar. This thesis reports on the experimental investigation of the characteristics of N2 arc as a function of filling pressure as well as in the supercritical state. For the bulk of the study, filling pressures of 1, 20, 40 and 80 bar are investigated, the latter two being in the supercritical state. A fixed electrode arrangement is used where the arc is initiated by the melting of a copper ignition wire. The investigated arc current amplitude is in the range of 85 A to 450 A at a frequency of 190 Hz to 950 Hz. Based on the focus area of different phases of the arc, this thesis can primarily be divided into three major parts. First, the arc properties during the high-current phase, i.e. during current peak time, are investigated for free-burning and tube-constricted arcs. In the second phase, the investigation is focused near the current zero (CZ) where the thermal phase of the arc is studied. In the final phase, the post-arc dielectric recovery characteristics are studied. The effect of the forced gas flow is investigated in both the thermal and dielectric phase of the arc. Based on the experimental results, the arc voltage is found to increase with the filling pressure without any abrupt change during the transition from gas to the supercritical state. Increased current density due to the constriction of the arc at high filling pressure turned out to be the dominant factor for the high arc voltage. When the free-burning arc is physically constricted by means of burning inside a tube, an inverse relation between the arc voltage and the inner tube diameter is observed at 1 bar, as expected. At higher filling pressures, however, such a simple relationship does not exist. The reduced arc radius and the increased absorption of radiation at high filling pressures may limit the interaction between the arc and the tube. The energy deposition in the arc increases while the arc radius decreases with increasing filling pressure. The arc gets constricted and as a result the temperature of the arc core increases. In the free-burning arc, in the absence of forced cooling, the arc core fails to dissipate the stored thermal energy quickly. As a result, without efficient cooling a high post-arc current is often observed at a high filling pressure compared to at 1 bar. The high energy deposition in the post-arc channel due to increased post-arc current causes an early re-ignition at high N2 pressure compared to at 1 bar. A forced gas flow, however, significantly enhances cooling at high filling pressures and improves the interruption performance. In the free-burning arc arrangement, the post-arc dielectric strength of the gap increases rapidly with increasing filling pressure, only after a critical time delay following CZ. This critical time delay is probably linked to the temperature decay of the gap. Below the critical time delay, however, the dielectric strength of the gap is lower at a higher filling pressure in contrast to at 1 bar, similar to what is observed in the thermal re-ignitions of the freeburning arc. Forced gas flow significantly enhances the dielectric recovery of the arc channel at a high filling pressure, also in the thermal phase. The experiments indicate that although the thermal phase is the critical phase of the ultrahigh-pressure N2 arc interruption, the dielectric phase is inherently superior at a high filling pressure compared to atmospheric pressure. With the help of efficient cooling, the thermal phase can be improved, and hence the ultrahigh-pressure N2 reveals its potential to be used as a current interruption medium.en_US
dc.language.isoengen_US
dc.publisherNTNUen_US
dc.relation.haspartPaper 1: Abid, Fahim; Niayesh, Kaveh; Jonsson, Erik; Støa-Aanensen, Nina Sasaki; Runde, Magne. Arc voltage characteristics in ultrahigh-pressure nitrogen including supercritical region. IEEE Transactions on Plasma Science 2017 ;Volum 46.(1) s. 187-193 http://doi.org/10.1109/TPS.2017.2778800en_US
dc.relation.haspartPaper 2: Abid, Fahim; Niayesh, Kaveh; Støa-Aanensen, Nina Sasaki. Ultrahigh-pressure nitrogen arcs burning inside cylindrical tubes. IEEE Transactions on Plasma Science 2018 ;Volum 47.(1) s. 754-761 http://doi.org/10.1109/TPS.2018.2880841en_US
dc.relation.haspartPaper 3: Abid, Fahim; Niayesh, Kaveh; Støa-Aanensen, Nina Sasaki. Nozzle Wear and Pressure Rise in Heating Volume of Self-blast Type Ultra-high Pressure Nitrogen Arc. Plasma Physics and Technology 2019 ;Volum 6.(1) s. 23-26 https://doi.org/10.14311/ppt.2019.1.23 (CC BY 3.0)en_US
dc.relation.haspartPaper 4: Abid, Fahim; Niayesh, Kaveh; Espedal, Camilla; Støa-Aanensen, Nina Sasaki. Current interruption performance of ultrahigh-pressure nitrogen arc. Journal of Physics D: Applied Physics 2020 ;Volum 53.(18) https://doi.org/10.1088/1361-6463/ab7352 Original content from this work may be used under the terms of (CC BY 4.0)en_US
dc.relation.haspartPaper 5: Effect of Filling Pressure on Post-Arc Gap Recovery of N2 Fahim Abid, Kaveh Niayesh, Egil Viken, Nina Støa-Aanensen, Erik Jonsson, and Hans Kristian Meyeren_US
dc.relation.haspartPaper 6: Abid, Fahim; Niayesh, Kaveh; Thimmappa, Shashidhara Basavapura; Espedal, Camilla; Støa-Aanensen, Nina Sasaki. Thermal interruption performance of ultrahigh-pressure free-burning nitrogen arc. I: Proceedings of the 21st International Symposium on High Voltage Engineering. Springer 2020 ISBN 978-3-030-31676-1 The final authenticated version is available online at: https://doi.org/10.1007/978-3-030-31680-8_65en_US
dc.relation.haspartPaper 7: Abid, Fahim; Niayesh, Kaveh; Støa-Aanensen, Nina Sasaki. Arc Voltage Distribution Measurement in Tube Constricted Ultrahigh-Pressure Nitrogen Arc. I: Proceedings of the 21st International Symposium on High Voltage Engineering. Springer 2020 ISBN 978-3-030-31676-1 The final authenticated version is available online at: https://doi.org/10.1007/978-3-030-31680-8_66en_US
dc.relation.haspartPaper 8: Abid, Fahim; Niayesh, Kaveh; Støa-Aanensen, Nina Sasaki; Jonsson, Erik; Runde, Magne. Arc voltage measurements of ultrahigh pressure nitrogen Arcs in cylindrical tubes. I: Proceedings of the 22nd International Conference on Gas Discharges and their Applicationsen_US
dc.relation.haspartPaper 9: Abid, Fahim; Niayesh, Kaveh; Støa-Aanensen, Nina Sasaki. Post-arc Dielectric Recovery Characteristics of Free-burning Ultrahigh-Pressure Nitrogen Arc. I: 2019 5th International Conference on Electric Power Equipment - Switching Technology - ICEPE-ST 2019. IEEE 2019 ISBN 978-1-7281-5218-9. s. 105-108 https://doi.org/10.1109/ICEPE-ST.2019.8928793en_US
dc.titleCharacteristics of Switching Arc in Ultrahigh-pressure Nitrogenen_US
dc.typeDoctoral thesisen_US
dc.subject.nsiVDP::Technology: 500::Electrotechnical disciplines: 540::Electrical power engineering: 542en_US


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