Selection of the conductor is important in the design of power transmission lines.This paper demonstrates possibilities of using quadri-split conductors in 750 kV transmission lines,including comprehensive analysis and comparison of its electrical properties,mechanical performance and economic performance.The study results show that in the areas of lower altitude and smaller corona loss,the quadri-split conductors with the adequate aluminum cross-section meet the electromagnetic environment limits,reduce the preliminary investment,and their long-term operation economy are equivalent to those of the six-split conductors,therefore help substantially to reduce the project cost.

It is the first time in China to apply composite cross-arms in 750kV AC transmission system, and in view of its high voltage grade and complex structure the uneven distribution of potential and electric field in 750 kV AC transmission system have to be researched in depth. Utilizing three-dimensional finite element analysis software ANSYS and considering influences of such factors as tower, earth, wires and inter-phase interaction, the distributions of potential and electric field under different design schemes are researched, and the influences of spacer flange and grading ring and sharing ring, which are configured at the terminals of the cross-arm, on potential distribution on composite cross-arm, meanwhile the potential distribution on insulator string for 750kV suspension tower and the potential distribution on composite cross-arm are contrasted. Based on the first design scheme of the cross-arm, a final scheme for the composite cross-arm is chosen, in which the suspension insulator string is canceled, the length of composite cross-arm is prolonged and the grading and shielding devices are configured reasonably, thus the potential distribution of the composite cross-arm is better than that of suspension tower. Verification results of electrical tests performed by China EPRI show that the composite cross-arm adopting the finally chosen scheme possesses good electrical performances that can meet operational requirements.

As the most widely used device in the var compensation field,static var compensator(SVC) plays an important role in enhancing the grid reliability,improving the transmission limit and damping power oscillation,etc.The capacity of SVC installed in the key substations grows with the expansion of the power grid.This has put forward the heat increase of the valve.Based on the design of valve cooling-system of high-voltage large capacity,this paper briefly summoned the basic demands and constitution of cooling-system,analyzed the heat-dissipation in detail,and proposed a new design scheme to adopt dual parallel branch waterway for each level cooling-circuit of valve.

A digital simulation laboratory of sending-end power grid with multi-type power sources was constructed by Northwest China Grid Company in 2009 to enhance its capability of power grid simulation and to deal with the grave technical issues including large-scale wind power integration,high-capacity DC multiple-point sending,FACTS technology application and very large-scale synchronous power gird stability.This paper introduces the configurations,functions,and main performance index of the laboratory as well as some of the major simulation works based on the laboratory.Finally,the development prospect of laboratory is discussed.

In IEC 60071-1 and 62271-102, there is neither standard voltage shape nor standard peak value for very fast transient overvoltages (VFTO). Previous work by other researchers had classified VFTO into two types. A new type was identified in this paper based on an onsite test on a commercially-operated 800 kV GIS. Disconnectors were opened/closed under real operation conditions. Characteristics of the new VFTO type were analyzed, including times of the arc restrikes between the contacts of the disconnectors, trapped charge, damping time constant, magnitude, rise rate, and oscillating frequency. The results of this paper are expected to be of help for the completion of standards on VFTO.

对750 kV新疆—西北联网第二通道应用串补可能带来的次同步谐振问题进行了研究.采用系统频率扫描及时域仿真方法,分析了750 kV新疆—西北联网第二通道应用串补后周边火电厂发生次同步谐振的风险.研究结果表明,西北750 kV电网应用串补后,在个别极端情况下存在发生次同步谐振的风险,而采用750 kV可控串补可对次同步谐振起到抑制作用.由于西北电网现阶段发生次同步谐振的可能性较低,建议在实际运行中避开危险工况并加装扭应力继电器等保护措施；而是否采用750 kV可控串补宜结合经济性方面的因素综合考虑.

This paper presents the results of VFTO measure-ment at Guanting substation.By analyzing the oscillograms,characteristics of VFTO are achieved,including times of the arc restrike between the contacts of disconnectors,remnant voltage caused by trapped charge,VFTO′s duration,magnitude,rise rate,and frequency.The possible maximum of the magnitude and rise rate,estimated through an extrapolation method,are 2.46 pu and 12.64 pu/μs respectively.The research indicates that equipping closing/opening resistors in disconnectors is an effective way to suppress VFTO.

为掌握西北主网与新疆电网联网后可能存在的运行风险,通过小干扰分析方法对联网后系统的稳定特性进行了研究,结果表明全网动态稳定问题较为突出.在对新疆的强相关机组优化配置PSS后,应能明显加强系统阻尼,消除低频振荡风险.新疆向主网的送电通道还需接纳酒泉地区的大规模风电上网,而电网较为薄弱,动态稳定、频率稳定、电压控制等多种问题同时出现,需加快研究落实相关安全稳定控制措施,并做好多种控制措施之间的协调.

In this paper,the author,firstly,summarizes the important functions of the on-line monitoring system in the smart substation,and classifies the substation on-line monitoring systems according to the category of the high voltage equipment and then analyzes the basic working principle and the application method of each of the systems and presents the current application conditions of the on-line monitoring system.Based on the analysis,the paper puts forward the deployment proposal and the system structure of the on-line monitoring systems in the 750kV smart substations of Northwest Power Grid.

On the basis of theoretical calculations,measurements of on-site parameters,as well as a large number of measured data and waveforms in the process of system debugging,corrections are made on the power frequency parameters of the 750 kV double-circuit transmission line to generate the actual power frequency parameters more in conformity with to the actual situation,so that reliable power frequency parameters for the power grid control and follow-up studies are thus provided.

Since the 750 kV pilot project in China startedoperating,VFTO on the GIS has been one of the focuses of concern.Afield test was carried out at the 750 kV Guanting Substation in 2009.In this paper the on-site recorded VFTO wave forms are analyzed,and the VFTO magnitude at different operation modes is achieved.The possible maximum of the magnitude and rise rate are extrapolated,which are 2.46 pu and 12.64 pu/s,respectively.Basedon the comparisons,the current research suggested that the closing/opening resistors should be equipped in disconnectors to effectively suppress VFTO.

The feasibility of DC modulation technology application in the Northwest China grid was studied in this paper.The simulation results indicated that the frequency stability and transient stability of the power systemafter severe failure can be improved,and the overload of AC power system can be eliminated,so the power transmitting capacity of AC power systemcan be increased.

It is the first time since Sept.2005 when the 750 kV transmission pilot project in Northwest China for GuantingSubstation was put into commercial operation,that the Very Fast Transient Overvoltage(VFTO)in the 750 kV GIS was tested in field.In the test, the disconnecting switchgears(DS)in the 750 kV GIS were switched normally,with one side or both sides charged by the system voltage. Quite a number ofdata and oscillographs are acquired,valuable for analyzingand understandingthe characteristics ofVFTO.The field testing of VFTO and the main results is overviewed.Furthermore, sugg-ests are put forward for improving the switching of DS in 750 kV GIS.

During the test process of 750 kV transmission and transformation project from Easten Lanzhou to EastenYinchuan Substation, the cause of the inner short circuit to ground fault of 750 kV circuit breaker in the Easten Yin Chuan Substation is analyze, and suggestions are put forward to make 750 kV commissioning test better and improve the reliability of the 800 kV circuit breaker.

This paper introduced two typical accidents about insulation pull arms in the first batch 750 kV circuit breaks made in China,and analyzed the cause of faults.This paper confirms that the caster mater between different types of insulate materials is the main reason for internal arc discharge breakdown,which leads to insulation malfunction for pull arms.Based on the above situation,this paper proposes some suggestions,including improving process,adding the tests of partial discharge and mechanical performance for insulation pull arm.,etc.

Aiming at accurate assessment of wind resource in large area and high precision prediction of wind power, the necessity of synthetical regional wind power measurement system is analyzed, and the main capability of the wind power measurement and power forecast control system is presented. With the help of this system, technical guide and support can be provided for planning of regional wind power, construction of large wind power farm and reliable operation of power grid.

The main development aims of the Northwest China 750 kV power grid in the eleventh 5-year planning are put forward in this paper.Firstly,the framework of 750 kV network covering most of the five northwest provinces should be constructed.Secondly,a large volume of electrical power should be delivered from the northwest to the central and eastern areas of China.Thirdly,interconnections with the Sinkiang and Tibet power network should be accomplished,synchronously or asynchronously.Also,the key of the 750 kV grid planning is presented,for example,to guarantee reliable power delivery between bulk power generation and loads,to enhance the capability of Northwest grid for power exporting,etc.Moreover,issues are discussed which will emerge with the fast growing of the Northwest 750 kV grid,such as the safety and stability of a large power system,the risks of electromagnetic loop circuit,the coordination of networks in different voltage levels,and so on.