Feasibility tests of a 320 kV gas-insulated DC switchgear with Clean Air
Publikation: Beitrag zu Konferenzen › Paper › Beigetragen › Begutachtung
Beitragende
Abstract
High-voltage direct current (HVDC) transmission technology enables the interconnection of wind energy, generated at large distances from the shore, with the power grid onshore. Moreover, it supports the efficient exchange of large amounts of energy over long distances. HVDC transmission requires converter and transition stations, which can be of considerable dimensions. In several cases there is a need for a compact design to minimize the footprint, particular in the case of offshore converter platforms as well as in the case of transition stations in the context of long DC cable lines.
To meet these demands, compact gas-insulated DC systems (DC GIS) offer significant advantages in terms of space requirements. Based on the mature SF6 technology, a gas-insulated system for a rated DC voltage of ±550 kV has been developed, type-tested and introduced to the market in recent years. Within the next years, this technology will be applied within several ±320 kV DC switchyards on offshore converter platforms to reduce their size and weight.
On the one hand, SF6 gas enables extremely compact dimensions of the system, but on the other hand it requires very careful handling throughout the whole life cycle, as it is a gas with a high global warming potential (GWP). In recent years, the demand for SF6-free solutions is increasing to contribute to an enhanced sustainability of the energy supply. A consistent solution is the application of the fluorine-free and climate-neutral insulating gas Clean Air (synthetic air with 80% nitrogen and 20% oxygen). The insulation properties of Clean Air are not on the same level as of SF6 at the same pressure, but it provides many advantages concerning ecological aspects (GWP = 0), easy and riskless gas handling, chemical stability and low chemical interaction with other materials.
Within the frame of a feasibility study, the applicability of Clean Air technology for use in DC GIS of the ±320 kV voltage level has been investigated. ±320 kV is a typical nominal DC voltage used for grid access in the North Sea. In the first step, the requirements in terms of voltage and current were compiled, to meet the demands for typical applications. In accordance with these requirements, the suitability concerning the dielectric strength was investigated, based on electric field calculations and high-voltage tests on DC GIS components of the ±550 kV SF6 solution. To enhance the dielectric performance, an increase of the minimum functional pressure was assumed. In the next step, the applicability in terms of mechanical performance, especially concerning the increased gas pressure, was proven. Continuous current test data were evaluated, and temperature-rise calculations were conducted. Further, the temperature gradient between inner conductor and enclosure was determined, which is an important factor for interfaces of insulating gas and solid insulator in DC GIS. Moreover, the feasibility in terms of insulation basics has been investigated. Differences between SF6 and Clean Air concerning insulator surface charging were considered. Specific tests were performed on the criticality and the detectability of typical imperfections as free-moving conductive particles or protruding tips at the high-voltage conductor. Partial discharge measurements at DC voltage of both polarities and varied gas pressure were performed with the conventional method and with ultra-high frequency (UHF) method. Pulse sequence analysis (PSA) was applied as an appropriate solution to identify defects in gas-insulated systems at DC voltage.
This contribution provides an insight into the different investigations on the dielectric, mechanic and thermal performance as well as the basic research on typical imperfections and charge accumulation. Furthermore, it summarizes the results of the study. Based on the given requirements, the feasibility of Clean Air application in DC GIS was confirmed.
To meet these demands, compact gas-insulated DC systems (DC GIS) offer significant advantages in terms of space requirements. Based on the mature SF6 technology, a gas-insulated system for a rated DC voltage of ±550 kV has been developed, type-tested and introduced to the market in recent years. Within the next years, this technology will be applied within several ±320 kV DC switchyards on offshore converter platforms to reduce their size and weight.
On the one hand, SF6 gas enables extremely compact dimensions of the system, but on the other hand it requires very careful handling throughout the whole life cycle, as it is a gas with a high global warming potential (GWP). In recent years, the demand for SF6-free solutions is increasing to contribute to an enhanced sustainability of the energy supply. A consistent solution is the application of the fluorine-free and climate-neutral insulating gas Clean Air (synthetic air with 80% nitrogen and 20% oxygen). The insulation properties of Clean Air are not on the same level as of SF6 at the same pressure, but it provides many advantages concerning ecological aspects (GWP = 0), easy and riskless gas handling, chemical stability and low chemical interaction with other materials.
Within the frame of a feasibility study, the applicability of Clean Air technology for use in DC GIS of the ±320 kV voltage level has been investigated. ±320 kV is a typical nominal DC voltage used for grid access in the North Sea. In the first step, the requirements in terms of voltage and current were compiled, to meet the demands for typical applications. In accordance with these requirements, the suitability concerning the dielectric strength was investigated, based on electric field calculations and high-voltage tests on DC GIS components of the ±550 kV SF6 solution. To enhance the dielectric performance, an increase of the minimum functional pressure was assumed. In the next step, the applicability in terms of mechanical performance, especially concerning the increased gas pressure, was proven. Continuous current test data were evaluated, and temperature-rise calculations were conducted. Further, the temperature gradient between inner conductor and enclosure was determined, which is an important factor for interfaces of insulating gas and solid insulator in DC GIS. Moreover, the feasibility in terms of insulation basics has been investigated. Differences between SF6 and Clean Air concerning insulator surface charging were considered. Specific tests were performed on the criticality and the detectability of typical imperfections as free-moving conductive particles or protruding tips at the high-voltage conductor. Partial discharge measurements at DC voltage of both polarities and varied gas pressure were performed with the conventional method and with ultra-high frequency (UHF) method. Pulse sequence analysis (PSA) was applied as an appropriate solution to identify defects in gas-insulated systems at DC voltage.
This contribution provides an insight into the different investigations on the dielectric, mechanic and thermal performance as well as the basic research on typical imperfections and charge accumulation. Furthermore, it summarizes the results of the study. Based on the given requirements, the feasibility of Clean Air application in DC GIS was confirmed.
Details
Originalsprache | Englisch |
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Seitenumfang | 13 |
Publikationsstatus | Veröffentlicht - Aug. 2022 |
Peer-Review-Status | Ja |
Extern publiziert | Ja |
Konferenz
Titel | CIGRE Paris Session 2022 |
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Veranstaltungsnummer | |
Dauer | 28 August - 2 September 2022 |
Bekanntheitsgrad | Internationale Veranstaltung |
Ort | Palais de congrès de Paris |
Stadt | Paris |
Land | Frankreich |
Schlagworte
Ziele für nachhaltige Entwicklung
Schlagwörter
- DC GIS, HVDC, Gas-insulated system, Clean air, Dry air, SF6 alternatives, Offshore