SF6/N2混合气体是一种简便有效的SF6环保化措施,己逐步应用于GIS等气体绝缘电力设备中,全面研究雷电冲击下的放电特性及协同效应,可以为绝缘设计及气体参数选择提供依据,具有重要的学术研究与工程应用价值.为此开展了 SF6/N2在稍不均匀场和极不均匀场中正负极性雷电冲击放电特性与协同效应研究.发现在稍不均匀场中,正负极性雷电冲击均呈协同效应,负极性下更显著;随电场不均匀度增加,协同效应类型从协同效应向负协同效应转变.协同效应系数C法并不能完整描述SF6/N2的协同效应与负协同效应,提出了一种适用的归一化系数h方法,量化表征了电场不均匀度、电压极性、气压和SF6体积分数的影响,提出了 GIS绝缘设计时最优SF6体积分数为20％～25％等建议.

GIS母线使用SF6/N2混合气体主要考虑气体的绝缘性能,已有研究成果表明,使用SF6/N2混合气体替代纯SF6气体可显著降低SF6使用量,在不降低绝缘性能的前提下减少温室气体使用量,但国内尚未在GIS上进行工程应用.国家电网公司响应国家节能减排号召,组织开展了SF6/N2混合气体用于GIS母线的研究工作,包括混合比、在运GIS母线替换为SF6/N2混合气体的适应性研究等,确定了SF6/N2混合气体GIS母线可采用统一的30％混合比,多个产品已通过型式试验和新产品技术鉴定,并在8座变电站开展了工程试用,为实现混合气体在GIS母线的推广应用奠定基础.

In order to analyze and diagnose internal discharge failure of two ± 500kV SF6 gas-insulated valve side bushings in converter transformers, insulation characteristics before and after the discharge and internal characteristics after disassembly are tested and checked. Temperature distribution of current-carrying conductor and insulator are simulated with finite element method. DC resistance of conductor, content of SF6 decomposition products, temperature calculation results, overheating and discharge traces show thatbushing discharge failures in Yimin and Baoji convertor station are caused by contact resistance abnormal heating of transitional copper-aluminum contact in conductive tube and contamination of nylon guide cone decomposition along SF6/epoxy insulation interface. According to IEC hottest spot temperature standard and fault bushing temperature field calculation results, a new diagnostic criteria of internal heating defects with temperature difference of 25 ℃ between the hottest point and ambient temperature are put forward. And this method is verified by a bushing of the same type with abnormal thermal defect. 75 bushings of the sametype are repaired on-site without shifting converter transformers and removing the defective bushings. The results provide a method and basis for diagnosis and management of heating defects in SF6 gas-insulated high voltage bushings.

Along with large-scale construction of UHVDC power transmission projects in China, the secure and stable operation of DC porcelain cap and pin insulator becomes more and more important. Under the affect of DC current the electrolytic corrosion of insulator cap is inevitable, and it becomes the key factor impacting the mechanical characteristic of DC porcelain cap and pin insulator, thus it is necessary to make the anti-electrolytic corrosion of insulator cap explicit. The electrolytic corrosion mechanism of insulator cap is presented and the summary of basic situation of DC insulator cap corrosion occurred in two ±800kV DC transmission lines in China is given, and the design method of two kinds of zinc collar for anti-electrolytic corrosion is proposed and through testing it is validated that the two kinds of the designed anti-corrosion zinc collars possess good anti-corrosion performances. The research results are available for reference to the anti-corrosion design for insulator cap of DC porcelain cap and pin insulators.

The successful construction and reliable operation of Xiangjiaba-Shanghai project fully proved the performance of ±800kV UHVDC technology. Considering the huge power export of Sinkiang and Tibet area, SGCC (State Grid Corporation of China) started R&D of higher voltage level UHVDC technology on 2008. Considering the capacity and distance of power transmission, the economics of different voltage level development were evaluated as well as the feasibility of key equipments. On the end of 2010, several key parameters are decided. For the 10,000MW power transmission over 2350kM or longer, the selected rated voltage is ±1100kV, and rated current is 4750A with capacity 10,450MW. In addition, the R&D schedule is presented. In this paper, the current R&D progress and the scheduled study of ±1100kV UHVDC are presented. The content is organized into six parts. In part I, the basics and operation status of Xiangjiaba-Shanghai project is given. Then, the demand of ±1100kV project is introduced, as well as pilot project. In part II, the R&D progress of key technology is given. Main circuit scheme and the technical specification of equipments are introduced. The main circuit configuration is same with Xiangjiaba project. The two series converter scheme is connected with equivalent voltage distribution in one pole. By optimizing the configuration and parameters of surge arresters, the over-voltage level is suppressed deeply including AC side and valve side of transformer, critical points in DC circuit, etc. The insulation level is also proposed. The study of external insulation and electromagnetic environment, are presented, which have significant impact on the project construction cost. The length of insulators and air clearance are proposed., In third part, the R&D progress of key equipment is introduced. Firstly, the crucial points of all DC equipments are reviewed, and give possible solution. Secondly, the roadmap and technical solution of converter transformer and wall bushing is discussed, In part IV, the scheme of converter transformer on-site assembling is proposed. Due to the transportation limit, it is impossible to transport the whole transformer to Sinkiang area by railway or road. Then, the on-site assembling idea is proposed and studied. In the scheme, the high-end valve hall of pole II is used for transformer assembling. The current technical solutions are introduced including manufacture, fault treatment and test. In addition, the preliminary manufacture and test equipment layout in valve hall is also given. Then, this paper discusses the key points in the solution, and ideas. In part V, the R&D of next step is presented.

Ultra high voltage DC(UHVDC) converter station possesses following features: large-scale,huge quantity of equipments and large building area,so energy conservation design of UHVDC project has demonstrative effect.In this paper the design idea and scheme in adopting high-capacity and energy conservation equipments which take less construction site,optimizing station site and plan layout,adopting energy conservation schemes in the design of buildings and accessory system are presented.

The lightning protection in the DC yard is a key problem of the ±800 kV UHVDC power transmission systems.Since the lightning rods in the DC yard can not meet the demands of lightning protection,the densely packed shield wires are proposed,showing a better effect than the lightning rods.The numerical method is applied to analyze the parameters of the shied wires.The safety clearance between the shield wire and the bus or apparatus is considered for the parameter selection of the shield wire.In addition,the surface electric field of the shield wire should also be small enough to avoid the corona discharge.As a conclusion,the duplex shield wires surpass the single shield wire due to the relatively low surface electric field and the robustness against the wire breaking.Finally,the diameter and the height of the shield wire above the bus or apparatus are provided,which had been adopted in the shield wire designs of Xiangjiaba-Shanghai and Jinping-Sunan ±800 kV UHVDC yards.

The equipment in ultra-high voltage(UHV) DC yard have a low lightning withstand level to direct striking lightning,much stricter protection measures than those for AC substations should be adopted when designing the protection system of UHV DC yard against direct lightning strike.We analyzed the protection range of the lighting rod on the basis of the fractal model of the lightning channel.Due to the lower probability of lightnings with lightning current directly striking the DC yard,densely packed shielding wires were suggested to be used to protect electrical equipment in the UHV DC yard.According to the lightning withstand level of different devices in the DC yard,the polyline method,rolling-sphere method,leader progression model,and fractal model were applied to analyze the spacing distances in different regions of UHV DC yard.The results from different methods are compared,and the recommended values of shielding wire spacing distances in different regions of UHV DC yard are suggested,which have been applied in the shield wire designs of Xiangjiaba-Shanghai and Jinping-Sunan ±800 kV UHVDC yards.

±1 000 kV ultra high voltage direct current(UHVDC)transmission technology can realize the optimal allocation of energy resources over a large area,and is suitable for the extra long-distance and super-capacity electrical power transmission.In this paper,the research and development(R&D)thought and plan of ±1000kV UHVDC transmission technology are presented.They are organized into five parts.In the first part,the necessity to carry out ±1000kV UHVDC projects and the necessity to conduct the corresponding R&D are analyzed.In part two,the system adaptability of ±1000kV UHVDC transmission is discussed,and the key points of researches are presented.Part three analyzes the technical feasibility of the transmission line and apparatus in converter stations.The key technical difficulties and R&D roadmap are discussed.In part four,a new thought to analyze economic advantages of ±1000kV UHVDC transmission technology from the perspective of converter station cost,transmission line cost and energy price is put forward.Part five introduces the R&D plan of ±1000kV UHVDC transmission technology of the State Grid.

The ±800 kV UHVDC transmission system now is the main project for the state grid corporation of China (SGCC) to fulfill the mission of delivering the clean hydropower from Southwest China to East China (the load center), and it is an essential part of China's national energy strategy of "West-East Power Transmission". In the process of design and construction of the Xiangjiaba-Shanghai ±800 kV UHVDC project, new design philosophy and technologies are introduced, different from those used in the former HVDC projects by SGCC. All these new design features will be of good reference value for the future HVDC projects. In this paper these features are studied in detail, such as the main circuit design, insulation coordination and external insulation design, main DC equipment (including thyristor valve,converter transformer, smoothing reactor, etc.), control and protection, measures for the high reliability and availability,optimization design of the valve hall and converter transformer yard, features of the DC filter design and DC yard layout,audible noise control, innovative features of the ground electrode, design innovation of the de-icing.

If DC grounding electrode is near to the transmission corridor, DC current will flow through shielding wires and towers in different equipotentional surface, leading to erosion of the tower. Actual parameters of DC grounding electrode and its nearest AC transmission line of an ±800 kV ultra HVDC transmission project under construction is exmplified , The DC current flowing through each tower and its distribution character were studied . Results showed that the erossion quantity would be more with the increase of the resistivity of the middle earth layer and decrease of the grounding resistance of the tower, and the total erosion is not serious.In the end, some protective measurements are given.

±1000 ultra high voltage direct current (UHVDC) transmission technology can realize the optimal allocation of energy resources over a large area, and is suitable for the extra long-distance and super-capacity electrical power transmission. In this paper, the research and development (R and D) thought and plan of ±1000 kV UHVDC transmission technology are presented. They are organized into five parts. In the first part, the necessity to carry out ±1000 kV UHVDC projects and the necessity to conduct the corresponding R and D are analyzed. In part two, the system adaptability of ±1000 kV UHVDC transmission is discussed, and the key points of researches are presented. Part three analyzes the technical feasibility of the transmission line and apparatus in converter stations. The key technical difficulties and R and D roadmap are discussed. In part four, a new thought to analyze economic advantages of ±1000 kV UHVDC transmission technology from the perspective of converter station cost, transmission line cost and energy price is put forward. Part five introduces the R and D plan of ±1000 kV UHVDC transmission technology of the State Grid. © 2009 Chin. Soc. for Elec. Eng.

UHVDC system of Jinsha river first stage transmission project has capability of 6 400MW each, with complicated main circuit arrangement and long distance transmission line, thus higher reliability availability requirements. At the sending end, three converter stations, including Xiangjiaba, Xiluodu left bank and right bank converter station are very close to each other. Consequently, DC fault in any UHVDC system will have impact on the rest other 2 systems, even the whole sending end AC system. For the receiving end system, 6400MW is a bulk transmission capacity, i.e. generation power for receiving end system. It can be anticipated undoubtedly that there will be large impact even the lose of monopole of UHVDC system. Therefore, reliability is an important item for UHVDC system, which should be given enough emphasis. In this paper, analysis was carried out on operating HVDC systems, such as 3GC, 3GG, Tian-Guang, etc trying to indicate the fault apparatus as well as ratio of overall fault time based on operating experience, fault statistics, reliability result of present HVDC system in China. Thus, the reliability availability index for UHVDC system was analyzed and proposed in this paper considering main circuit arrangement as well as project characteristics of UHVDC system.

Some technical problems concerned in system design and engineering design of UHVDC transmission project are comprehensively researched.The feasibility of applying UHVDC to outward transmission project for electricity generated in Jinshajiang hydropower station is adequately expounded and proved.According to the experiences of conventional HVDC transmission projects and centering on the technical features of UHVDC transmission,several novel design approaches and viewpoints are proposed.

At the end of 2004, State Grid Corporation of China (SGCC) put forward the strategic objective of developing UHV power transmission. Here, the demonstration process of developing UHV power transmission in China by SGCC since 2005 and the significance and necessity of carrying out such demonstration, the selection of demonstration project for UHV AC power transmission and the demonstration process of UHV DC power transmission from Xiluodu and Xiangjiaba hydropower stations in Jinsha River valley, as well as the. research results on the key technologies of UHV power transmission, for instance the selection of voltage class for UHV power transmission, environment protection, AC over-voltage, etc., are presented. Above-mentioned substances show that the research and demonstration processes are scientific and democratic, the results of research and demonstration are reasonable and reliable, and these results can give strong and vigorous supports for the construction of domestic UHV power transmission.

The malfunction phenomenon of the low voltage capacitor component protection of the 3rd harmonic filter at the AC site of a HVDC station during the first energizing test is analyzed and the operating current is calculated according to the measured components parameters. It indicates that the initial operation settings does not consider the mistuning of the filter, and the capacitance variation due to temperature is not compensated inside the relay. the paper gives some proposals to improve the protection criterion.