This paper studied the influence of AC system on the operating range of MMC-HVDC （modular multilevel converter-high voltage direct current） under steady-state condition, and analyzed the key factors to limit the DC power transmission capacity. Firstly, the equivalent mathematical model of a one-terminal MMC-HVDC was derived. Secondly, the impacts of the short circuit ratio （SCR） of AC system, the capacities of converter transformer and converter station on the steady-state operating range of converter station were studied. Lastly, this paper analyzed the influence of the parallel reactive power compensator on the operating range of MMC-HVDC. The calculation results show that: the operating range of MMC-HVDC is mostly limited by the converter transformer capacity under large SCR of AC system; while the operating range is largely depended on the value of SCR under small SCR. Additionally, the use of reactive power compensator can improve the operating range of MMC-HVDC.
Its necessary to study corresponding voltage control strategies for different wind conditions because the active power fluctuation caused by wind speed fluctuation is the fundamental reason of voltage problem. Considering tremendous changes of wind farm clusters running status under extreme wind conditions and limited closed-loop control capability of local reactive power continuously adjustable equipment, a corresponding voltage control strategy was proposed, which could provide preventive voltage control and corrective voltage control for conditions before/after extreme wind speed based on ultra-short-term wind power prediction. Its optimization algorithm could decouple the MINLP （mixed-integer nonlinear programming） problem through reactive power-voltage sensitivity method with considering active power change and turned it into an iteration containing a MILP （mixed-integer linear programming） problem and some nonlinear algebraic equations. By comparing the examples, the limitation of the traditional closed-loop control method and the superiority in voltage control and wind farms internal feeder voltage balance through the proposed control strategy can be verified, which can provide an effective method for solving the high voltage off-grid accident under extreme wind conditions.
To study the impacts of penetration rate and integration methods of DFIG-based （doubly fed induction generator） wind farm on system stability, firstly, the dynamic model of doubly-fed induction generator was described by the differential algebraic equations, and the coefficient matrix of total system was derived. Then, the eigenvalue and participation factors of wind farm system were calculated according to the small signal analysis theory, and the dominant oscillation modes of system were determined. Finally, taking augmented IEEE 3-generator and 9-bus test system as example, the damping changes of electromechanical oscillation modes were analyzed under different penetration rates and various integration methods. The research results show that, the increasing of penetration rate of wind generation has a detrimental impact on the power angle stabilities of the adjacent synchronous machines when their capacities are reduced at the meantime and the system is without compensation. The stabilities of systems voltage and power angle are improved greatly with the increasing of SVC （static var compensator） compensation capacity, under same penetration rate. The improving effect of the SVC compensation on the system stability will decrease with the increase of penetration rate. It follows that the penetration rate and integration methods of DFIG-based wind farm have great influences on the system stability.
Flat finned tube bundle is the basic radiating element of direct air-cooling system in thermal plant, so the study on its structure feature, flow and heat transfer property has important significance to the optimization design and efficient operation of air-cooling system in power plant. Taking the typical continuous serpentine fin flat tubes of direct air-cooling system as examples, this paper studied the impact of different fin spacings on the flow and heat transfer property of the cooling air and the changes of fins heat transfer performance under vertical and tilt flow conditions. The result shows that the heat transfer coefficient of fin grows up with the decrease of its spacing at the constant wind speed, while its resistance coefficient varies complexly. Under the experimental conditions, the flat tube with fin spacing of 56.8 mm has the best property. When the fin spacing is constant, with the growth of wind speed, the heat transfer coefficient increases and the resistance coefficient decreases gradually. However, the trends become gentle at high wind speed. The research results can provide basic datas for the further optimization of the structure of continuous flat tube fin.
According to the impact of mountain fire of transmission line in complex environment, the mountain fire prediction model was proposed based on the methods of empirical mode decomposition （EMD） and extreme learning machine （ELM）. Firstly, the noise of collected wind speed time series was analyzed by using wavelet transform, and the classification and reconstruction were carried out according to the different sequences, in order to reconstruct new wind speed time series. Secondly, the factors of the mountain fire were decomposed into a series of sub-sequences with different characteristics scales by using EMD. Thirdly, cross-validation method and phase space reconstruction method were used to determine various parameters and input dimensions of machine learning, and then the modeling and forecasting analysis was carried out for the mountain fire of transmission line by using ELM. The simulation results show that the combined forecasting model for the mountain fire of transmission lines based on EMD and ELM can effectively predict fire spread speed within 24 h, which can provide the possibility to realize the online prediction of the mountain fire in transmission line with high precision.
Accreted ice on conductors in transmission lines may cause mechanical and electrical faults to power grid system, leading to the fact that the determination of designed ice thickness on conductors plays an important role for the safe operation of power grid. When determining the designed ice thickness of conductors in transmission lines, the standard ice thickness on different diameters should be computed to the specific diameter with using diameter correction formula. Related ice data was acquired through experiments in artificial climate chamber, and the diameter correction coefficients of conductors were fitted respectively according to different types of accreted ice. The results show that the conductor diameter correction coefficients of rime and mixed-phase icing decrease with the increase of conductor diameter, and the decreasing trend of the correction coefficient of rime is larger than that of mixed-phase icing; the conductor diameter correction coefficients of glaze icing increases with the increase of conductor diameter.
To alleviate the environment and energy crisis, and promote energy conservation and emission reduction, three charging facilities for electric vehicles were analyzed and compared, whose result showed that charging piles would be the main infrastructure of public charging facilities. Two power supply schemes （AC and DC） were proposed, which combined the constructions of LED street lamp and charging piles. Taking the transformation of high pressure sodium lamp of six urban areas in Beijing as example, this paper compared these two schemes from aspects of environment demand, function structure and energy-saving benefit. The results show that: the construction of AC supply scheme is simple and quick; but the DC supply scheme reduces the number of AC-DC conversion, improve the AC/DC conversion efficiency, and has better energy-saving benefit, which can be beneficial to the combination with distributed power in the future, promote the new energy consumption and the construction of the charging network of new electric vehicle.
To solve the flexibility problem of communication network for electric power big data platform, its implementation method in data integration platform was presented according to the research on the technique architecture of OpenFlow. The standardization status and architecture of OpenFlow were analyzed from aspects of data processing and service configuration. The advantage of OpenFlow in future electric power big data platform was analyzed, and the perspectives of SDN functional unit and technology extensibility were also studied. OpenFlow has been included in the key technology of electric power big data platform in State Grid Corporation. OpenFlow Supporting technology and popular SDN controlling protocols can significantly improve the flexibility of electric power service. By decoupling the control plane and data plane, the controlling function can be separated so that the high efficiency requirement of data network efficiency can be satisfied for State Grid Corporation.
Electrical equipment of composite material has been applied in some substations, due to its characteristics of lighter quality and higher breaking strength. However, little research has been done in the seismic behavior of electrical equipment of composite material, especially for the experimental study of earthquake simulation shaking table. Based on the Sichuan-Tibet interconnection project, this paper summarized the researches on the seismic behavior of electrical equipment of composite material at home and abroad, and then studied its assessment method combined with the existing research on the seismic behavior of electrical equipment in China. Then, the input waveform, the peak acceleration and the judging principle of seismic ability also had been confirmed for the shaking table test of composite materials electric equipment. With using this method, 800 kV HV reactor bushing, 220 kV GIS external insulation bushing, 110 kV and 220 kV lightning arresters were tested respectively on earthquake simulation shaking table, and the dynamic characteristics and seismic response of the equipment were obtained. The test results show that the stresses on the tested electrical equipments of composite material all meet the seismic requirements of 0.4 g designed basic acceleration.
±800 kV Mengxi-Hubei UHVDC transmission lines will be built in 2017, which will have formed a UHADC parallel power system with the existing UHVAC transmission lines in Hubei province. It will have a great influence on the structure and operation characteristics of Hubei power grid. Based on the operation during high flow periods and planning capacity of power delivering of Hubei power grid in 2017, the network structure model was set up with using PSASP software. The continuation power flow （CPF） algorithm was used to calculate the power transfer limit of Mengxi-Hubei UHVDC transmission lines. The stability of Hubei power grid was verified with the Mengxi-Hubei UHVDC transmitting limit power, which included static security analysis, transient stability check of single and serious fault.
Conventional undervoltage load shedding（UVLS） scheme only focuses on local voltages without considering the response characteristics of transient voltage in whole gird. This paper analyzed the relationship between transient voltage drops and disturbance scale, proposed discriminant index for the disturbance scale of transient voltages based on the offset of voltage drops, and divided the transient voltage disturbance into two categories: the whole-grid transient voltage disturbance and the partial-region transient voltage disturbance. On the basis of the discriminant index results, an adaptive UVLS strategy based on the disturbance scale discrimination of transient voltages was constructed, with consideration on the dynamic process of voltage and frequency after the disturbance, which could solve the whole-grid transient voltage disturbance and the partial-grid transient voltage disturbance respectively with two adaptive load shedding schemes. Finally, the effectiveness and superiority of this strategy in different instability scenarios were verified by the simulation on the IEEE 39-bus system.
As the nonlinear load increases, a large number of harmonic will back to fill the grid which may result in the power pollution and measuring inequality. However, the traditional fast Fourier transform （FFT） detection methods are difficult to meet the harmonic detection requirements for accuracy due to the limitation of their own technology. Combined with the characteristics of power harmonic form, this paper analyzed the principle of wavelet transform and Fourier transform, and put forward a kind method with double-spectrum-line and window function based on the wavelet packet combined with FFT. This paper mainly studied the characteristics of different window functions, and added them to get the optimal window function for power harmonic detection by comparison. The simulation results verify that the harmonic measurement method has a good measurement effect in time domain and frequency domain, and the simulation experiment provides a good reference for the detection method of power harmonic of harmonic watt-hour meter and the selection of window function of signal interception.
This paper proposed a new location method for the single-phase grounding fault of power cable based on time-reversal technology. When the single-phase grounding fault of power cable occurred, this method used the time-reversal symmetry of voltage wave equation, inverted the time-domain voltage wave collected at the line terminals into an equivalent current wave and returned it to the transmission line; then calculated the energy value of the current through the assumed fault point, determined the distance of fault point to the line terminal based on the time-space synchronization focusing properties. Matlab simulation results show that the method can accurately and effectively achieve the single-phase grounding fault location of power cable, and not only be applicable to the ground faults with different fault resistances, also have the characteristics of fast convergence speed and high fault location precision.
Scholars have demonstrated the necessity of installing generator circuit breaker （GCB） in large capacity generator terminal, but they did not make in depth study on whether GCB should be installed in small capacity generator （≤30 MW） terminal or feeder line. So in this paper, transient recovery voltage （TRV） of circuit breaker in small capacity generator（12-30 MW）terminal and feeder line was researched with using electromagnetic transient program PSCAD/EMTDC, under three-phase short circuit fault in the worst breaking condition. Then, this paper determined whether distribution circuit breaker could replace GCB to be installed at generator terminal or feeder line. The calculation results show that when three-phase short circuit fault occurs in generator terminal or feeder line, respectively, the TRV rising rate of circuit breaker is no more than 0.34 kV / μs, thus distribution circuit breaker can replace GCB to be installed at generator terminal and feeder line.
As the large-scale usage of auxiliary system inverter in power plants, large tripping problems of thermal power units caused by voltage sag are more and more obvious. Combining with the field test data of low voltage ride through（LVRT） for coal feeder inverter in thermal power units in Shaanxi Grid, this paper analyzed the effect of main factors of voltage sag on the output characteristics of inverters, and used dynamic voltage restorers （DVR） as a rapid compesation method to solve voltage sag. The sag dephth, duration time, load, sag types and other factors had great influence on the operating featuer of coal feeder inverters in thermal power units, which might lead to the DC working voltage of inverter reducing, even triggering inverter circuit tripping out of service. The voltage sag experiments and compensation stimulation model were established with using PSCAD/EMTDC. The results show that DVR have good ability to steady the DC working voltage and can promote inverter through the serious voltage sag.
To study the effect of the relative humidity of air on heat transfer performance, a heat transfer performance test of water film based on evaporative condenser was carried out. The cooling water temperature, the water film temperature of plates and the temperature above and below the surface of filler were investigated by test equipments under the condition that the relative humidity of air was adjusted, and other parameters remained the same. The results show that the temperature of water film increases when the relative humidity of the air between plates increases from 85% to 90%. The temperature of water film at different position is obviously different. With the increase of humidity, the heat transfer mass of spray water increases, while the heat transfer mass of wet air, the average heat flux and surface heat transfer coefficient of plate decreases.
With the standards of wind power in China are published, all the doubly-fed induction generator （DFIG） wind turbines manufacturers in China are equipped with low voltage ride through（LVRT） ability. But some of the wind turbines are born with LVRT ability, the others are reformed by the manufacturers. So that the LVRT strategies of different wind turbines are all unlike, which make some of control strategies of wind turbines are not perfect, so that these turbines cannot meet the requires of recover power rate after the low voltage fault. In the same time, some control strategies of wind turbines may cause power saltation condition. If lots of wind turbines in a wind farm all use this strategy to proceed the LVRT, the voltage of this area will increase suddenly because of the power saltation, which will bring a secondary impact to the grid, and cause the wind turbines of this area into voltage-overtop status. But the wind turbines in China are not equipped with high voltage ride through（HVRT） ability, so that it will result in more wind turbines out of work. This paper proposed an elaborate control strategy for DFIG, which could both protect the crowbar system and get LVRT application.
Only by using the annual average wind speed and wind power density to determine the quality of wind energy resources is not comprehensive enough in wind resource analysis, which can not reflect the output capability of the wind resource. Investigating the k value，which is the shape parameter of two-parameter Weibull distribution wind conditions,is to find out its inherent relationship with the wind energy, wind speed distribution and wind energy distribution. And further research is put forward to find out the relationship between the k value and the effective wind energy utilization for different Cp curves of wind turbine generators.The above research will supply a scientific guidance for wind resource assessment and wind turbine generator pre-selection during the consultation, decision-making, design and other stages of wind farm construction.
In the off-grid power distribution system which is powered by wind power generator and uses energy storage device as power source of seawater desalination device, in order to maximize the use of wind energy and reduce the dependence of distribution system on the capacity of energy storage device, the seawater desalination device adopts the power regulation mode combined with stair-like and smooth tactics, and the energy storage device adopts V/f control. Further, the stair-like power regulation mode is implemented by dividing the load operation into conditions. The smooth power regulation mode adopts frequency converter to change the speed of motor, and uses its characteristics of soft start and reactive power output to effectively maintain the voltage stability of distribution system. Based on the control strategy above, the calculation was processed through a dynamic load model which was established in PSCAD simulation software, and analyzed combined with the load test data. The results of both simulation and experiment show that, the control strategy can achieve effective tracking of wind energy output power for seawater desalination system; finely adapt to the dynamic of wind waves; make full use of the wind generator output power; reduce the dependence on the capacity of energy storage device; and improve the stability and economy of the operation of whole system.
Combined with specific project examples, the safety reliability and space adaptability of the public urea hydrolysis technology for flue gas denitrification were compared with that of the unit system urea hydrolysis technology, as well as their arrangements, through the research methods of surveys, case studies and lessons. And compared with the unit system configuration, the main advantages of the public system are embodied in the following aspects: the public system is safer and more reliable because of the mutual standby for the hydrolysis reactor; the main pipeline based on transporting ammonia, reduces the possibility of the blockage of the pipeline; which can adapt to the concentration fluctuation of inlet NOx; the space layout is more flexible and compact; more boilers, more advantages can be taken by the public system. The public layout of urea hydrolysis system is recommended priority for the condition that the loading rate is not high, the concentration of nitrogen oxides fluctuations high and the power plant locates in cold regions.
With the establishment of each business system platform of power grid planning and the rapid increase of heterogeneous business data, the barriers are badly needed to be broken between business system platforms to establish a perfect business information sharing and interaction system. Based on the analysis of the existing business system data format and the status quo of storage situation, this paper researches the key technology of heterogeneous data integration and storage, and proposes a cross-platform power grid planning data fusion and storage pattern. Heterogeneous data have been fused by establishing a unified business data information model. The distributed file storage system has been established based on Hadoop to implement fast and efficient storage and index of massive heterogeneous data. Thus, the research results can provide theoretical guidance and architecture support for massive heterogeneous data and information sharing in power grid planning system and electric power industry.
Rational planning of distributed generation in power grid can improve the energy efficiency and the economy, reliability and flexibility operation of power system. This paper constructed the multi-objective planning model with minimizing total investment cost in the construction and operation of the distributed power system and the power loss of system, as well as maximizing the investment the static voltage stability index as optimization subgoals. This paper used and improved a new bionic algorithm-bat algorithm, which could effectively solve the problems of easily trapping into local optimal solution and slow convergence speed in the later stage. Then, 14-node distribution network test systems were used to simulate and analyze the location and capacity of distributed generation. The simulation results show that, compared with the traditional bat algorithm and particle swarm optimization, the improved bat algorithm can better and faster get the optimal planning scheme of distributed generation connected to distribution network, which can validate the correctness and feasibility of the algorithm.
