A wind farm mode was established aiming at resolving the problem of the reactive voltage. And reactive voltage coordinated control strategy was proposed with comprehensively considering both doubly-fed induction generator （DFIG） and static var compensator （SVC）. With considering the voltage deviation of the point of common coupling （PCC） and the reactive power margin of the reactive power source for wind farm, an objective function was established. Chaotic quantum-behaved particle swarm optimization （CQPSO） was used for the reactive voltage control of wind farm； by coordinating the reactive power output of DFIG and SVC, the voltage of PCC connected with power system was enabled to meet the requirement, and the reactive power margin of reactive power source was improved at the same time. Finally, a wind farm in North China was taken as an example for analysis, and the simulation results verified the feasibility and effectiveness of the proposed reactive voltage coordinated control strategy.
Traditional unified power flow controller （UPFC） based on voltage source controller （VSC） has high switch frequency, obvious voltage harmonic and lower voltage level. Meanwhile, UPFC has big risk and possibility to suffer the short circuit fault, which can cause the damage to device, especially in the situation of large capacity and high voltage. Thus, this paper applied modular multilevel converter （MMC） in the UPFC, and improved the control strategy of MMC to meet the requirements of the proposed topology, but the system might suffer larger risk of short circuit fault. So this paper also designed the current limiting module based on MMC-UPFC, which could effectively restrain the short-circuit current in the short circuit fault, without increasing any burden to the system in the normal condition. In all, the topology of entire UPFC system has advantages of higher modularity level, smaller harmonic wave, capacity extension, rapid current-limiting in short circuit fault and so on, which can increase systems reliability, safety and economy for the designed topology.
Along with the increasing scale of wind power, the electric grid stability and safety problems in wind farms have become increasingly prominent due to the DFIG （doubly-fed induction generator） fleet off-grid under grid failure conditions. In order to inhibit DFIG fleet off-grid, this paper presented a wind farm reactive power compensation configuration method with considering the inhibition of DFIG. Firstly, the wind farms were taken as the center to analyze the reactive power balance. Using the quantitative relationship between reactive power demand and active transport, this paper calculated the needed capacity of low-voltage reactor bank and low-voltage capacitor bank in wind farm. Secondly, through the reactive analysis on the fluctuation of wind power output under different load modes and the bus voltage of wind farm during N-1 line running, this paper checked the adaptability of initial configuration scheme to the systems static security. Finally, based on the analysis on the reactive power demand characteristics of DFIG fleet under grid failure condition, this paper added a STATCOM （static synchronous compensator） with certain capacity to inhibit the fleet off-grid, which could make the reactive power compensation scheme meet the safe operation requirements of the system. The proposed method has been used to configure the reactive power compensation in 220 kV wind farm with large capacity in a province, which can prove its feasibility and effectiveness in economy and technology.
To solve the multi-objective optimal power flow （OPF） problem, genetic algorithm （GA） was used to find the Pareto front, and fully reflect the interaction and deviation internal relation of different optimal objective functions. On this basis, Nash Bargaining Game was used to get the global optimal solution. This paper discussed the multi-objective OPF problem with considering the minimum generation cost （or coal consumption） and the minimum system loss simultaneously. This paper firstly verified that the problem could satisfy the Nash Bargaining axiom, secondly obtained the Pareto front by strong Pareto evolution algorithm 2 （SPEA2）, which could ensure faster convergence rate and more uniform Pareto front, and then used Nash Bargaining to find the optimal solution and solve the possible contradiction between the different objective function. Case study on IEEE 14-bus system verified the effectiveness of the proposed algorithm.
People pay more and more attention on the sustainable development of generation expansion planning. Based on the comprehensive consideration on the economy, technology, environment of generation expansion planning, some evaluation indexes for generation expansion planning with sustainable development were proposed, and a multi-objective decision making model for generation expansion planning with sustainable development was constructed. Different subsets were divided according to the factor variable characteristics in model such as target variables, attribute variables, etc. And based on the theory of Bayesian network, a logical relationships analysis method for different subsets was obtained, which could reduce the complexity of the planning model. Application examples show that the proposed model and its solution method are feasible and effective.
Applying the topology structure of modular multilevel converter （MMC） in unified power quality controller （UPQC） can improve the applicative capacity and voltage level of UPQC, which can expand the application of UPQC in medium voltage field, and make UPQC has wider application prospects. However, when the short-circuit fault occurs on the load side, how to logically operate to ensure the safe and reliable operation of UPQC, is not only the system requirement for the device, but also its own requirement for the device to protect itself. On this basis, this paper presented the principle of fault protection strategy for MMC-UPQC, which adopts the interaction between the branch of anti-parallel thyristor and circuit breaker to isolate the MMC in series from the fault line, and ensure the effective protection for the device. The simulation results in PSCAD/EMTDC environment have demonstrated the effectiveness and feasibility of the proposed method.
The problems such as induced voltage and so on in 1 000 kV double-circuit transmission lines on the same tower were calculated and analyzed under different transposing forms. From the viewpoint of restricting induced voltage, secondary arc current and unbalanced degree of line parameters, 4 segment transposition is better than 3 segment transposition, but 1 more transposition tower is needed； while 5 segment type B transposition is better than 6 segment type A transposition and 1 transposition tower is saved. The effects of 4 segment transposition and 6 segment type A transposition are similar. Therefore, three kinds of transposing forms should be emphatically considered for double-circuit transmission lines on the same tower: 3 segment transposition （l/3, l/3, l/3））, 4 segment transposition (l/6, l/3, l/3, l/6） and 5 segment type B transposition （l/6, l/6, l/3, l/6, l/6）. It is not recommended to use more than 2 complete cycle transpositions in general.
Room temperature vulcanized silicone rubber （RTV） has good antifouling properties, which has been widely used in the power system, but different types of RTV coatings antifouling performances are unlike. Static contact angle of different RTV coatings were determined and the hydrophobicity recovery properties after pollution flashover and AC/DC flashover characteristics were tested and analyzed. The test results show that the hydrophobicity of long-acting RTV coating （P-RTV） is stronger than that of high self-cleaning RTV coating （S-RTV）； and under the same pollution degree, the pollution flashover voltage of P-RTV is higher than that of S-RTV, which shows stronger hydrophobicity means higher antifouling performance. In addition, surface flashover can cause the temporary loss of P-RTV hydrophobicity, which will lead flashover voltage amplitude decreasing 11.1 %-21.1%, while the loss of S-RTV coatings hydrophobicity is unrecoverable. The surfaces of RTV coatings all have burning marks in varying degrees distributed on the lower surface of the insulator connected with the high voltage, which is one of the factors causing anti-pollution performance decreasing. And the signs of burning on RTV surface are more obvious under DC voltage； its dielectric tracking performance is poor. Moreover, the comprehensive performance of P-RTV is better than that of S-RTV, so the priority of actual application should be given to P-RTV. The result has a certain guiding significance to the development and use of RTV coatings.
The transmission line joints play the role of mechanical and electrical connection in power grid. In the actual operation, joint faults such as joint loose or joint shedding will cause the loss of power energy or even cause other faults that greatly threaten the safe and steady operation of the power system. So, the operation department of power system focuses on finding a practical method to detect the running state of transmission line joints. In this paper, the typical faults of transmission line joint were simulated, including joints nut loosing/shedding, screw loosing, bolt dislocation, bending and broken strands. The UV imager was applied to detect the corona discharge photon number of the fault joints. The results show that the photon numbers of joints under different faults increase with the rising of the applied voltages. Under the operation voltage, the photon numbers vary among the different type of joint faults, and the UV imager can be effectively identify the faulty of transmission line joints. The research results can provide references for the running state detection of transmission lines.
A design method was proposed for multi-loop DC coordination damping controller, which used subspace identification to reduced order modeling for system, used genetic algorithm for parameter optimization, and estimated the stability of time-delayed system. Firstly, the wide-area input signal of DC controller was selected by using dominate mode ratio index calculation method based on Prony analysis； the input and output data of the system under disturbance were obtained according to the simulation； and the open-loop state space equation was obtained by system subspace identification based on the data. Secondly, adding the controller in the open-loop system to get closed-loop system state space equation. Moreover, with maximizing the minimum damping ratio of the system under various operation modes as the optimization goal, genetic algorithm was used to coordinately optimize the controller parameter in closed-loop system state space equation. The stability criterion of system with time-delay based on free-weighting matrices was used to analyze the stability of system with time-delay for wide-area power system with multi-loop DC coordination controller. Finally, taking China Southern Power Grid as an example, the multi-loop DC coordination damping controller was simulated. The simulation results show that the multi-loop DC coordination damping controller obtained by this method can better improve the damping level of power gird, and meet the requirements of the stability of time-delayed system.
As for new bottleneck to limit the transmission capacity of power grid caused by equipments capacity in substation, the dynamic capacity-increase technology of substation equipments were studied, and the dynamic capacity-increase system was designed for substation equipments. Through collecting condition monitoring parameters such as the temperature and current of transformer, this paper calculated the load capacity of transformer according to the ‘Guide for Oil Immersed Power Transformer Load’ （GB/T 1094.7） and the thermal equivalent circuit model of transformer. Then, the load capacities of circuit breaker, transformer and isolating switch in substation circuit after overload were checked by using current shunt algorithm. Combined with the operation mode of power grid and the risk assessment value, the running state and capacity-increase ability of substation equipment were analyzed and estimated. The pilot application shows that the calculation results of the system can provide a scientific basis for the operation of scheduling personnel.
For the coordinate control of interconnecting transformer and reactive power compensation device in active distributed network, this paper proposed a global coordinated control model based on multi-agent technology. Multi-agent technology with its flexible structure and agent autonomy could combine the centralized control with the distributed control better； and realize the dynamic tracking of weak-voltage node in voltage over-limit area through building the regional leading agent decision model. By combining CNP （contract net protocol） and voltage regulation priority principle, it could achieve the timing optimization for the compensation amount calculation of interconnecting transformer and regional reactive power compensation elements, through the competition of reactive power-voltage sensitivity index. Finally, this paper carried on the simulation in IEEE33 distribution system, whose results showed that the multi-agent technology could realize the voltage regulation by combine interconnecting transformer with reactive power compensation device.
Tianzhong UHVDC project is the first UHVDC transmission system with using domestic DC control and protection technology. The operation reliability of DC control and protection system is very important to the safe and stable operation of the UHVDC project. Analog is the source of DC control and protection system, its correctness determines the correctness of control and protection logic implementation and affects the operation reliability of DC transmission system. Taking Zhongzhou converter station in Tianzhong UHVDC project as an example, the self-checking logic of DC control and protection system was analyzed in detail in order to provide references for the design, construction and maintenance of the UHVDC transmission project. Firstly, the analog configuration of DC control and protection system in Zhongzhou converter station was introduced. Secondly, the self-checking logic of analog using in DC control or DC protection was respectively analyzed in detail. Then, according to the engineering debugging problems, this paper pointed the shortcomings of the self-checking logic for existing analog. Finally the suggestions and comments were proposed to improve the self-checking logic of analog.
A tuned mass damper （TMD） is often used to reduce the seismic response of transmission tower, which is designed based on the previously designed tower, so the influence of TMD on the structural dynamic characteristics is often neglected. This paper proposed an integrated design method for the transmission tower-TMD system, which selected the H∞ norm of system transfer function as the optimization objective, and used Genetic algorithm （GA） to optimize the section of angle steel. The multi-degree-freedom model was adapted to simulate tower structure to simplify the calculation of its H∞ norm. In order that the optimized structure satisfied the static loads and the total mass was not increased, the penalty function was also introduced to adjust the GA fitness. Taking the structure of a practical tower as example, the optimization calculation result shows that the proposed integrated design can further reduce the seismic response of transmission tower, with the static load case satisfied and the same total mass. This method avoids calculating the time domain response, and thus has high computation efficiency.
The reasonability of conductor selection is the key link in large-crossing transmission line design. Depending on the large-crossing section of a 1 000 kV UHVAC transmission line, this paper technically, economically compares and demonstrates the selected conductors from aspects of the material, current-carrying capacity, electrical performance, mechanical characteristics and economy. The 6×JLHA1/EST-640/170 extra-high strength aluminum alloy conductor steel reinforced was recommended, which was first applied in UHV large-crossing project at home and abroad. Domestic manufacturers have been fully equipped with they production capacity of this type conductor.
To develop the strong and smart grid, promote the construction of 1 000 kV smart substation, this paper studied the intelligent modes of 1 000 kV substation and the key design technology of the digital process layer. Firstly, the paper analyzed the intelligent situation of 1 000 kV substation, put forward five intelligent modes of 1 000 kV substation, and recommended no-digital mode for the process layer. Then, this paper studied the key design technology of the digital process layer for 1 000 kV substation, and suggested that it should adopt conventional transformer + merging unit to realize digital sampling, and ‘conventional primary equipment + intelligent terminal’ to realize networked control. Meanwhile, this paper proposed the configuration optimization scheme of the protective winding for 1 000 kV and 500 kV current transformer. Finally, based on the network reliability principle in switch N-1 and N-2 fault mode, this paper proposed a new design scheme for 1 000 kV process level network, and recommended that SV and GOOSE should set up the network together, each one of double protections should set up independent dual network.
Due to the characteristics of new energy power generation: intermittent and variable, the reserve capacity deficiency issue of frequency modulation （FM） for power grid has become increasingly prominent, along with the gradual increase of the installed capacity. Traditional FM units rarely achieve real-time equivalency of actual output with the theoretical values because of their inherent characteristics, and are difficult to deal with the problem of frequency stability caused by the rapid development of power system and the generation and paralleling in gird of new energy. Energy storage technology, as a new technology, has advantages of fast response speed, strong short-term power capacity, easy-changing adjust direction and so on, which can be combined with conventional FM technology and used as an effective assistant mean of power grid FM. This paper studied the capacity allocation of energy storage based on the actual situations of different grids； discussed the control strategy of traditional units FM assisted by energy storage system, which could provide references for the engineering application of energy storage system in grid FM in future.
According to the demand of the development of wind power and the development and construction of islands in South China Sea, the meteorological observation data of 6 islands were investigated for the wind resource assessment and wind turbine selection, including Dongsha Islands, Xisha Islands, Nansha Islands, etc. The two-parameter Weibull distribution was utilized to assess wind power resource for each station. The capacity factors of wind turbines were estimated according to the wind power output characteristics curves of several small wind turbines. Combined with the Peak over threshold approach based on generalized Pareto extreme value distribution model, this paper estimated the extreme wind speed of 50-year recurrence interval, with using maximum likelihood estimation method. The analysis results show that: both the wind resource and extreme wind speed have obvious regional features in South China Sea. The wind resource of Dongsha Islands and Renjuntang are the highest while the wind resources in Yongxing, Shanhu, Taiping, and Nanzi Islands are much poorer. In addition, since tropical cyclones tend to occur in the higher latitude, the extreme wind speed of 50-year recurrence interval in Renjuntang Island in the southern of South China Sea is 35 m/s and much lower than that of other Islands.
A system process of Cyclic Calcinations/Carbonation based on the method of calcium-based sorbents was proposed for the CO2 capture in a 1 000 MW supercritical power unit. The impact of purge rate, the gas-solid separation efficiency and the molar ratio of Ca and C on the energy consumption of calcination, the power generation thermal efficiency and the flow rate of circulating solids was studied. The results show that: after the introduction of carbon capture systems, the thermal efficiency of electricity generation for the unit is 34.6%, which is 9.6 % lower than the designed value； while after using heat recovery of carbon capture system to generate electricity, the net increase in the output power of the power plant reaches 113.4MW. With the increase of purge rate, the thermal power generation efficiency and the mass flow of solid circulating material decrease, and the energy consumption of calcination decreases first and then increases. With the increase of the efficiency of gas-solid separation, the thermal power generation efficiency and the mass flow of solid circulating material increase, and the energy consumption of calcination decreases first and then increases. With the increase of the mole ratio of Ca and C, the energy consumption of calcination, the thermal power generation efficiency and the mass flow of solid circulating material all increase.
According to the requirement on the ultra-low emission of fly ash, SO2 and NOx from coal-fired plants, the mechanism, characteristics, and industry applications of various air pollution control technologies, including low-low temperature electrostatic precipitation, wet electrostatic precipitator, dual-loop desulfurization, two-dimension low NOx combustior, and selective catalytic reduction （SCR） were introduced. An ultra-low air pollutant reduction protocol was proposed, including two dimension low NOx combustion, SCR denitration, low-low temperature electrostatic precipitation, dual-loop desulfurization in single tower and wet electrostatic precipitator. The economy of the ultra-low air pollutant control technologies for coal-fired power plants was analyzed.
Technical and economic analysis on aqueous sodium-ion battery （ASIB） in the energy system containing thermal power and wind power was studied by EnergyPLAN software. The research results show that the reduced quantity of critical excesses electricity production （CEEP） in the energy system gradually increases in the wake of the decrease of capacity ratios of wind power to battery energy storage. Moreover, the higher the penetration ratio of wind power, the larger the reduced quantity of CEEP. Annual CO2 emission and coal costs both gradually reduce along with the decrease of capacity ratios of wind power to battery energy storage. Approximate ratio of 2.5：1—2：1 is the optimalizing capacity ratio of wind power to battery energy storage with provision for technical and economic weighing between annual total costs and CEEP.
Since to the situation that the technical and economic evaluation system in the power terminal access network construction for smart grid was imperfect, this paper proposes the index set of technical and economic evaluation for power terminal access network from three aspects: cost of construction, benefit and cost-benefit ratio. By means of analytic hierarchy process （AHP） and entropy analysis in object assessment, each index weight in evaluation index set was determined. Then, the complete technical and economic evaluation system was constructed for power terminal access networks.
