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| Compact Design of 550 kV Basin-Type Spacer in Gas Insulated Switchgear (Part Ⅲ) —— Downsized Structure Verification |
| Wang Chao1, Li Wendong1, Chen Junhong1, Li Jinshu1, Gong Ruilei2, Zhang Guanjun1 |
1. State Key Laboratory of Electrical Insulation and Power Equipment Xi’an Jiaotong University Xi’an 710049 China;
2. Shandong Taikai High Voltage Switchgear Co. Ltd Tai’an 271000 China |
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Abstract Solid insulators are key components in gas insulated equipment including gas insulated switchgear (GIS) and gas insulated transmission line (GIL). Surface flashover across the spacer/gas interface threats the running of GIS/GIL. Hence, it is urgent to enhance the surface insulation strength of spacer especially in the situations where compact design and/or the usage of eco-friendly gases are required. Numerous studies revealed that locally intensified electric (E) field caused by dielectric mismatch or metal particles mainly accounts for the insulation failure of spacer. To design and fabricate a downsized 550 kV spacer in GIS that takes both the structure optimization and dielectric distribution optimization into account, a fabrication method that considering E field mitigation effectiveness and the fabrication efficiency was proposed.
Firstly, 1:10 downsized dielectrically graded 550 kV spacers were fabricated by combining stereolithography 3D printing technology with epoxy resin casting technique. Specifically, alumina/UV-cured resin composite was prepared as a low relative permittivity (3.98<εr<4.20) 3D printed slurry to fabricate the main parts of insulators. The characterizations of composites’ photocuring and rheological behaviors indicated that the doping of alumina fillers decreases the photo-curing depth and increase the viscosity particularly in high fillers’ loading content. The processing performance of composite deteriorated when loading content exceeds 30%, since the viscosity pronouncedly increases. After determining fillers’ loading content and printing parameters, the main part of spacers with low permittivity was fabricated by stereolithography 3D printing. Characterization of its dielectric properties confirmed the correctness of permittivity range. Subsequently, titania/epoxy resin composite was prepared as high relative permittivity (11.32<εr<14.58) vacuum casted slurry. To guarantee good match at interface, composite with 30% titania loading content was selected. The characterizations of composites’ rheological behaviors indicated that the viscosity of composite dramatically decreases with the increase of temperature, benefiting the flowing of slurry in the reserved high permittivity region in the 3D printed spacer. After determining the curing conditions, the slurry was heated and then cured to finish the downsized spacer manufacturing.
Secondly, flashover tests of spacers before and after optimization ware carried out in compressed SF6 gas. Characterizations of power frequency withstand voltage indicated that insulation structures after optimization exhibit improved electrical performance. Comparing with an original insulation structure, geometrically optimized spacer shows a 13.6% flashover voltage improvement, and this improvement increase to 13.8% for geometrically/dielectrically optimized spacer. After reducing a 15% of insulation distance, geometrically/ dielectrically optimized spacer shares the same insulation level with the original structure. When a metal wire existing in the wedgy airgap at the flange side, improved electrical strength of the geometrically optimized spacer at the same insulation distance reduces to 6.7%. In contrast, owing to the low electric field area forming by the spacer with further optimized dielectric distribution, a 13.1% flashover voltage improvement still could be maintained, indicating the insulation excellence of the geometrically/dielectrically optimized spacer.
The proposed spacer construction strategy takes both optimization effectiveness and fabrication efficiency into account, and the fabricated dielectrically graded 550 kV spacers exhibit excellent surface electrical insulation properties, offering the possibility of reducing size of GIS tank, and is considered as an essential step towards the industrial application of 3D printed spacer in GIS/GIL.
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Received: 25 November 2021
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2023, Vol. 38 
