After the wind power generators are connected to the distribution network, traditional reactive power optimization model no longer applies as a result of its intermittent and random output. Therefore, the scenario analysis method was adopted to deal with the output power of the doubly fed induction generator （DFIG）, and the scenario model was established for reactive power optimization of distribution network with DFIG. Considering the flexible reactive power regulation capability of DFIG, a model for fuzzy reactive power optimization was presented with a comprehensive objective function of reducing the network loss and restricting node voltage variations of distribution network. The location of reactive power compensation device for distribution network was determined by Monte Carlo simulation. Chaotic parallel differential evolution algorithm with feedback （CPDEF） was used to solve the reactive power optimization of distribution network with DFIG. Finally, the IEEE 33-bus system was used as a test case to simulate the proposed optimization model of reactive power. Simulation results show that the active power loss of distribution network is reduced significantly, and its voltage profile is improved. It also proves that the proposed method is feasible and effective.
An operable market operation mechanism considering the fundamental characteristics of microgrid was designed to realize the intelligent operation of microgrid under transmission and distribution separated electricity markets. "Load Driven by Generation" mode was proposed. On the premise of ensuring the compatibility with the main grid electricity market, based on the market operation control system of multi-agent systems, customers could submit the bidding information to microgrid power exchange controller （MPEC） in the multi-agent market operation control system according to their relative demands, with considering the flexible market behavior of interruptible load and energy storage devices, as well as the demand-side response mechanism. The contract market and the real-time balance market were constructed for grid-connected microgrid, together with the bidding rules and the mathematical models. Finally, several key questions were discussed.
With the increasing of the capacity of distributed energy resources, the problem of power quality and power loss caused by distributed energy resources paralleling in the grid has become a big challenge, which can be effectively alleviated by applying DC supply in distribution networks. In recent years, because of the rapid development of power electronic technology and the significant improvement of work efficiency and rated capacity of AC/DC converter and DC/DC converter, the network loss of DC power supply system has been reduced. Meanwhile, the compatibility of household appliances with DC power supply has been improved, so the residential DC power supply technology will inevitably become the trend of research and development in the future. The research status of residential DC power supply technologies around the world were systematically reviewed, and the advantages and feasibility of these technologies were analyzed. Finally, a typical residential DC micro-grid model was proposed. The involved technical problems, such as the determination of voltage level, the choice of networking mode and the system protection and control were discussed in detail. Some prospects on the development of DC power supply technologies were also presented.
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Taking 220 kV Chaoyangmen underground substation and its coupled architectures as the test object, the vibration and noise signals of testing points were acquired which were located on the concrete floor, wall, foundation and transformer tank in the transformer room and each stories of overground and underground. The time domain analysis and frequency spectrum analysis for the test data were carried out. The results show that: firstly, the vibration amplitude of transformer tank wall is large, the vibration spectra of transformer tank are mainly 100 Hz and resonant frequency, and the vibration spectra of the concrete foundation, floor and wall in the transformer room are very similar； secondly, during the design of the underground or indoor substation, structure vibration and noise must be considered which can spread to the whole underground substation and building structure； thirdly, the attenuation of vibration, noise and low spectrum characteristics are not obvious with the increase of distance or the rise of floors.
With the large-scale spread and application of intelligent substation, it has a higher demand on the dynamic performance testing of secondary system under various fault and abnormal situations. Based on real-time digital simulator （RTDS）, the dynamic test method for the secondary system of intelligent substation was studied, and the test mode was proposed. Then, the close-loop test scheme was designed for the secondary system of intelligent substation, which could be applied in protection performance test, secondary system special test and station overall test, etc. Finally, combined with the integration test of a 500 kV intelligent substation project, the digital dynamic test was conducted for the secondary system to assess its performance. The results show that the test scheme is scientific and effective.
For a long time, the research of power system has been focused on its security; with the development of power system, people realize that its economy and security are equally important. This paper studied the coordination calculation of the economy and security, analyzed the academic and engineering problems of modeling and simulation in security-economic coordination calculation, and put forward the overall framework and research method for the security-economic coordination calculation. The feasibility of the proposed research framework was preliminarily verified through actual power grid example. The results show that： compared with the traditional method only considering system’s security, this coordination calculation framework can comprehensively considered the system’s security and economy, which can be used to guide the power grid planning.
At present, high voltage （HV） reactors are mainly used to restrain the power frequency overvoltage and secondary arc current, not for the voltage control purpose. With the spreading and changing of power grid, part of HV reactors cannot be put into operation. In order to improve the use efficiency of assets, an optimization configuration method of HV reactor was proposed. Firstly, this method comprehensively considered the capacitance effect and power loss of transmission lines, as well as the existing inductive reactive power compensation degree of the two end stations of the lines； and set of alternative configuration schemes were designed for HV reactors. Then, a comprehensive evaluation system of reactive voltage was established for the configuration schemes of HV reactors with considering the maximum voltage fluctuation and deviation, average power loss, and switching action quantity of inactive power adjusting devices as evaluation indexes. A weighted method based on the variance of fuzzy memberships was introduced for a more scientific and objective optimal scheme decision strategy. Finally, combined with the configuration problem of HV reactors in Shaanxi power grid, the proposed method was proved to be effective and feasible.
Aiming at the few investigation of 220 kV icing composite insulator with four sheds at home and abroad, this paper analyzed the influence of icicle length and grading ring parameter, position on the electric field distribution of 220 kV icing composite insulator with four sheds with using the finite element analysis software Ansoftmaxwell. The results show that: （1） under the icing condition, when the gap between wet iced and large shed is 1 mm, the composite insulator bridged with icicle will not discharge when its large sheds, but it will have discharge risk under over voltage when the composite insulator is not bridged with icicle； （2） grading ring can significantly improve the electric field distribution between high voltage side and the first large shed； （3） the electric field distribution of the gap between high voltage terminal and nearby icicle can match best when grading ring’s vertical distant from fitting connection point is 0 mm, its outer diameter is 306 mm and pipe diameter is 36 mm.
Contrastive analysis on lightning protection characteristics of overhead transmission line can be the reference for the lightning protection strategy of transmission line. Taking 110 kV to 1 000 kV AC transmission lines and ±500 kV to ±800 kV DC transmission lines in China as analysis object, the characteristics of back striking and shielding failure were analyzed, and the lightning protection keys for overhead transmission lines with different voltage grades were proposed. For the 110 kV and 220 kV AC transmission lines, back striking should be focused on. For the 500 kV and 750 kV AC transmission lines, back striking should be focused on in the area with high grounding resistance and shielding failure should be noticed in mountain area. For the 1 000 kV AC transmission lines, due to the low flashover rate of back striking, the construction cost could be reduced by applying the natural grounding body of the tower, and it also should focus on the shielding failure of side conductors in mountain area. For ±500 kV, ±660 kV and ±800 kV DC transmission lines, the shielding failure flashover in mountain area should be focused on.
The current status of the development and application of flexible AC transmission system （FACTS） were introduced. According to the problems in the planning and development of Jiangsu power grid, taking middle across-Yangtze-river transmission channel, western-Nanjing inter-city circle grid and southern-Suzhou system as examples, the feasibility that the application of FACTS could improve the reliability and transfer capacity of Jiangsu power grid was studied and analyzed through system simulation. The results show that： with the application of FACTS, the power flows in the system can be effectively controlled, the transfer capacity can be obviously improved, so as to avoid the huge investment and difficult construction for the new across-river transmission channels and across-city cables, and solve the voltage unstable problem caused by severe faults such as bipolar latched in UHVDC system, etc. In summary, the application of FACTS can prominently improve the efficiency and reliability of Jiangsu power grid, which can achieve good economic and social benefits.
Modular multilevel converter （MMC） is a novel voltage sourced converter, which has been successfully applied in HVDC transmission and has broad development prospects. But the working performance and system losses of MMC are directly affected by the existing arm circulating current, so the circulating current suppressing is a problem needed to be resolved for the MMC engineering applications. The active disturbance rejection control （ADRC） technology was introduced in response to the requirements of system non-linearity, robustness and dynamic performance. A circulating current suppressing controller （CCSC） for MMC with good adaptation and robustness was designed based on ADRC technology, which did not depend on the detailed model of arm circulating current. Finally, the simulation results of the MMC system with using PSCAD/EMTDC verified the validity of the proposed CCSC.
Due to the complex topography of high altitude mountain areas, it is difficult to obtain enough observed wind data from local meteorological departments. To solve the lack of data for the macrositing of wind farms in high altitude mountain area, based on NCEP （National Centers for Environmental Prediction） meteorological data and SRTM （Shuttle Radar Topography Mission） terrain data, this paper used the Inverse Distance Weight （IDW） interpolation method and Topography Weight （TW） interpolation method to obtain two types of simulated wind speed data： with or without considering topographical factors. Then, the simulated wind speed data was compared with measured data, and the wind resource assessment method was discussed for high altitude mountain area. The results show that the simulated wind speed data by TW interpolation method is more consistent with the measured wind speed in Yunnan Province. Therefore, the wind resource assessment based on NCEP meteorological data combined SRTM terrain data can be regarded as an alternative to the macrositing of wind farms in high altitude mountain area.
The planned islanding has great significance to improve the reliability and security of the key load in active distribution network. In order to reduce the influence of the intermittent and uncertainty of wind power on the planned islanding, the equivalent output model of wind storage combined system under the planned islanding condition was analyzed based on the forecasting curve of wind power and the energy storage capacity. Then, the planned islanding model of the active distribution network with wind storage system was built by comprehensively considering the important level and operation characteristics of the load. Furthermore, a fast and flexible heuristic islanding algorithm was presented based on the depth-first searching method. Finally, the feasibility and validity of the proposed model and algorithm were validated by American PG&E69 node system. The simulation results show that the planned islanding model and solving algorithm can give consideration to the operation characteristics of wind storage system and the important level of load.
Packing is the most important part of the heat exchanger in natural draft wet cooling tower, which accounts for 60%-70% of the total heat transfer, so it has a great potential in energy saving. According to the arrangement of packing layer, this paper put forward the idea that used arc-shaped packing layer instead of traditional horizontal packing layer； established a heat and mass transfer model for the arc-shaped packing layer in wet cooling tower with using simulation software Fluent. Then, the impact of packing layer arrangement with different radians on the thermal performance of cooling tower was studied and compared； the relevant parameters’ changes of arc-shaped packing layer in wet cooling tower, such as air flow field and outlet water temperature, were calculated and analyzed under different natural crosswind conditions. The research results show that： the arc-shaped packing layer can increase the heat exchange area, improve the air flow field in rain zone, thus increase the heat exchange quantity and pumping power of cooling tower, and reduce the outlet water temperature； this improvement is more significant under natural crosswind conditions. In the case of 0.12 rad packing layer, when the natural wind speed is 6 m/s, the outlet water temperature can be reduced up to 0.36 ℃.
