2021(6):3-10. DOI: 10.19781/j.issn.1673-9140.2021.06.001
Abstract:The delay of analoginput DC merging unit is widely used in HVDC system, and it has an important influence on the DC metering accuracy, control stability and protection rapidity. In order to ensure that the overall delay of analoginput DC merging unit meets the delay requirements, the hardware delay and software delay should be configured reasonably, and the overall delay of the system should be tested. This paper analyzes the delay characteristics of a typical analog input DC combining unit, and analyzes the delay of each link respectively. It is found that the delay of signal conditioning and filtering, A/D conversion and other hardware links are relatively stable, and plays a large proportion of total delay. The specific delay of CPU software link is related to the algorithm actually used and the software execution path caused by the measured parameter state Certain randomness. The experimental results are in good agreement with the theoretical analysis. This paper provides the reference and guidance for the design, manufacture and delay correction of analoginput DC merging unit.
2021(6):11-19. DOI: 10.19781/j.issn.1673-9140.2021.06.002
Abstract:The huge investment is required in the construction of the distribution automation system and the grid capacity expansion, however, it is often impossible to complete it in a short time. Hence the grid company should make longterm plans for the development of distribution system. As there is a coupling relationship between distribution automation system planning and grid capacity expansion planning, this paper proposes a new comprehensive planning method to deal with this complex planning problem. Firstly, a mixed integer nonlinear programming (MINLP) model is established with the consideration of the dominant software and hardware infrastructure of distribution system. The objective function of the planning model is to maximize the profits of power grid companies within the planning time range. Then the genetic algorithm is utilized to solve the planning problem of distribution automation system considering grid capacity expansion, which can obtain the best scheme and schedule capacity expansion and construction. The proposed method is tested according to a 24bus system.The performance of the proposed method is compared with another method, which carries out the capacity expansion planning first and then carries out the distribution automation system planning. The results show that the proposed method can greatly improve the profits of power grid companies with a small amount of revenue reduction.
2021(6):20-27. DOI: 10.19781/j.issn.1673-9140.2021.06.003
Abstract:Accurate diagnosis of power transformer faults is essential to the reliable operation of the power grid. To achieve this goal, this paper proposes a new multiclass probabilistic diagnostic model based on bayesian network and hypothesis testing of dissolved gas analysis. The bayesian network model can embed expert knowledge, learn data patterns from data and infer uncertainties related to diagnosis results, and improve the data selection process through hypothesis testing. Based on the IEC TC10 data set, this paper compares three traditional diagnostic methods to perform diagnostic experiments to verify the effectiveness of the proposed model. The results show that the maximum diagnostic accuracy of the proposed diagnostic model is 88.9%, which is greatly improved compared to traditional diagnostic methods.
2021(6):28-39. DOI: 10.19781/j.issn.1673-9140.2021.06.004
Abstract:As an important realization form of the energy Internet, the integrated energy system enhances energy utilization efficiency through multienergy complementation and market mechanisms. However, it introduces more risk at the same time. To ensure the safety of the integrated energy system, the importance of establishing a risk assessment system for the integrated energy system has become increasingly important. This paper identifies and explores the risk factors in the integrated energy system, divides the risks into three categories: risks in planning, dispatch and operation. A comprehensive risk evaluation index system is established. Furthermore, the corresponding preventive measures or countermeasures are proposed for each type of risk to improve the resistance of the integrated energy system to various risks. Finally, in the case studies, the harm grade caused by different type of risk to further control the risk based on the risk assessment is evaluated and the effectiveness of the results are verified. It is found that the proposed method improves the risk management level.
2021(6):40-46. DOI: 10.19781/j.issn.1673-9140.2021.06.005
Abstract:The problem of oilpaper insulation partial discharge has attracted widespread attention in the industry. In order to explore the characteristics of partial discharge under ACDC composite voltage, this paper builds a measurement platform and designs four typical types of discharge model for oilpaper insulation defects: air gap discharge, suspension discharge, and cylindrical surface discharge models. The experimental results of these four kinds of partial discharges indicate that, the partial discharges of the four typical defects will change differently under different composite voltage ratios. The variation characteristic of average discharge for the first three defect types are opposite to which of DC component and positive to which of initial voltage at the initial period. Compared with the other three typical defects, the initial voltage of partial discharge in the suspended insulation discharge model under AC and DC mixed voltage is obviously increased, and the average discharge under AC voltage is reduced. The results obtained provide basic data for the application of partial discharge tests to determine the effect of the type of commutation transformer defect and the voltage form on the partial discharge.
2021(6):47-55. DOI: 10.19781/j.issn.1673-9140.2021.06.006
Abstract:Synchronous condenser (SC) has a fast reactive power response and extensive reactive power adjustment range, which is suitable for China HVDC transmission system that has a great demand for dynamic power support. However, when the steadystate reactive power output of the SC is large, its transient reactive power output will be limited. In order to make full use of the SC′s transient reactive power output capability and increase its transient reactive power margin, the SC is configured with static reactive power compensation devicescapacitors and reactors, which are different from filter banks in the HVDC converter station. In addition, the SC′s capacity configuration and coordinated control strategy with capacitors and reactors are proposed.Coordinated control makes the response frequency bands of two types of reactive power compensation devices different to make full use of the steadystate reactive power output capacity of capacitors and reactors and the SC′s transient reactive power supporting capability. Finally, the model of an HVDC transmission system with SCs is constructed on the PSCAD platform, and the effectiveness of the capacity configuration and coordinated control strategy is verified.
2021(6):56-66. DOI: 10.19781/j.issn.1673-9140.2021.06.007
Abstract:There are many types of energy storage devices including cooling storage, heating storage and power storage in the CCHP campus microgrid with photovoltaics. Its reasonable and coordinated configuration can cut peaks, fill valleys on the daily load curve and suppress uncertain fluctuations in photovoltaic output, then improving the safety and economy of microgrid operation.This paper uses a boxtype uncertainty set to describe the uncertain fluctuation characteristics of photovoltaic output and cooling, heating, and electrical load to establish a coordinated and robust optimization configuration model for multiple types of energy storage in CCHP park microgrid with photovoltaics.This twolayer optimization model takes the minimum sum of the annual equivalent investment and operating cost of the microgrid as the objective function. By adopting the Benders decomposition method, the twolayer optimization problem is decomposed into the main problem of finding the configuration scheme in a certain scenario and the typical problem of finding the microgrid. The extreme scenario subproblem with the largest daily operating cost is solved alternately and iteratively to obtain a coordinated and optimized configuration scheme of cold storage, heat storage and power storage devices that is robust to uncertain fluctuations in photovoltaic output and cooling, heating, and electrical loads.Finally, taking a CCHP park microgrid as an example, the comparison with the deterministic optimal configuration scheme and the optimal configuration of batteryenergy storage only schemeshows that the robust configuration scheme is more conducive to smoothing the uncertain fluctuations in photovoltaic output and load, and effectively improving the safety of microgrid operation.Meanwhile, the coordinated configuration of multiple types of energy storage has better economic benefits than the battery energy storage only solution.
2021(6):67-76. DOI: 10.19781/j.issn.1673-9140.2021.06.008
Abstract:The modular multilevel converter (MMC) modification combined with the characteristics of DC circuit breakers is one of the economical and feasible solutions to realize the DC fault clearing. Under the background, this paper proposes a MMC modification program based on resistance energyconsuming branches. The scheme realizes the rapid transfer and attenuation of the fault current through the mutual cooperation between the MMC and the additional ports and the resistance energy consumption branch of the line and the shutoff isolation branch. In addition, this solution utilizes the current flowing through the switch module of line resistance energyconsuming branch to accurately determine the fault type, and proposes a restart recovery strategy for the faulty line. Finally, a bipolar direct current transmission (MMCHVDC) system is established in PSCAD to verify the effectiveness of the proposed scheme and the restart recovery strategy of faulty lines. The simulation results show that the proposed scheme has a short fault clearing time and a small fault peak value, and the fault line restart process is stable and reliable.
2021(6):77-84. DOI: 10.19781/j.issn.1673-9140.2021.06.009
Abstract:When a highvoltage fault occurs near the voltage zerocrossing point or with a large transition resistance, the attenuation of generated weak fault transient signal is obvious. Thus, the traditional fault ranging method might fail due to the difficulties to detect the wave head. Under the background, a distributed traveling wavebased fault location method which considers the fault transient signal attenuation is proposed in this paper. Firstly, according to the exponential decay law of the current traveling wave transmission distance, the maximum arrangement distance of the current traveling wave measurement unit is determined under the weak fault signals. Secondly, based on the attenuation characteristics of the frequency components in the first wave head of the current traveling wave, the fault interval identification is realized by recognizing the difference of amplitude ratio of frequency components between fault intervals and healthy intervals. Finally, the faults are accurately located by utilizing the arrival time of the current traveling waves through the three measuring points on both sides of the fault interval. The simulation model of IEEE 30bus system is set up in PSCAD/EMTDC,and the simulative results show that the proposed method can cover the different fault types, fault resistances, and fault initial phase angles. The high positioning accuracy and ideal reliability are verified.
2021(6):85-93. DOI: 10.19781/j.issn.1673-9140.2021.06.010
Abstract:The multiobjective optimal dispatching of electric vehicles charging and discharging need take into account the benefits of both grid and users. Under the background, based on the improved membership function in vehicletogrid (V2G) mode, a multiobjective optimal scheduling model for electric vehicles charging and discharging is proposed, which aims to minimize the total load variance and the cost of the vehicle users. At the same time, the introduction of timeofuse price guides vehicle owners to orderly charge and discharge electric vehicles to reduce system load peaktovalley difference and promote the absorption of wind power. An improved membership function is proposed by using a reverse Sigmoid function to replace the traditional decreasing linear function, and the maximum fuzzy satisfaction method is utilized to convert the multiobjective optimization problem into a singleobjective problem. Then, the problem is solved by the Cuckoo Search algorithm. Finally, the impact of different timeofuse price, the number and average initial charge of participating vehicles on the optimization result is analyzed.
2021(6):94-103. DOI: 10.19781/j.issn.1673-9140.2021.06.011
Abstract:Aiming at the stress concentration problem existing in the front part of the highvoltage cable joint protective device, this paper presents a method to balance the stress distribution by optimizing the deflection angle of the folding line and the flange size. Finite element method of temperature field, flow field and displacement field coupling is adopted to calculate the stress value of the front part of joint protective device inner cavity on the 220 kV metal cable under different structure. Thus, the stress distribution of protective inner cavity is obtained. Through simulation analysis, combined with the practicability and economy of the protective device, the final chosen deflection angle α of the 220 kV metal cable joint explosion proof device folding line on the front part is 60°. The optimal structure of the flanges added at the fronttoshell connections is determined as 50 mm in height and 20 mm in width, which can reduce the stress distortion coefficient of the inner wall of the protective device to 1.48. The reliability of the design method is verified by the explosion stress test of the protective device of 220 kV highvoltage cable joint with broken line terminal. By comparing the polygonal structure to the curved structure, it is considered that under the same technical conditions, the polygonal structure has better economic benefits. The paper provides a reliable theoretical calculation method for the design of the protective device.
2021(6):104-112. DOI: 10.19781/j.issn.1673-9140.2021.06.012
Abstract:To improve the status evaluation accuracy of protection systems, a smart status evaluation method based on GAN model and random forest algorithm is proposed. Firstly, a system state indicator set is established in combination of the field conditions and expert opinions. To address the problem of the imbalance of relay protection equipment state data, a state data generation method is proposed based on the generation countermeasure network. Then, a comprehensive evaluation model of protection systems based on random forest is established. Finally, combining with the preceding state evaluation results, the health index curve of the equipment and its deterioration trend are given to provide corresponding state earlywarning. The realdata experimental results show that this method can more accurately evaluate the system status, and has reference value for rationally arranging the maintenance cycle and formulating the maintenance plan.
2021(6):113-119. DOI: 10.19781/j.issn.1673-9140.2021.06.013
Abstract:Aiming at the ambiguity of the evaluation results in the evaluation of the investment benefits of transmission projects and the subjective errors in the weighting of evaluation indicators, this paper proposes a method for evaluating the investment benefits of transmission grid projects based on the improved matterelement extension model. Firstly, a grid project investment benefit evaluation index system is constructed under consideration of the improvement of the power grid by the project being put into operation. A graph model index weighting method based on the principle of graph theory is also proposed to reduce the subjective error of the traditional subjective weighting method. Secondly, the matter element extension model for investment evaluation of transmission projects is established. Finally, 220 kV transmission projects put into operation in a certain area is taken as example for empirical analysis. The investment benefit rating and influencing factors of the projects put into production are studied to verify the scientific practicability of the model.
2021(6):120-127. DOI: 10.19781/j.issn.1673-9140.2021.06.014
Abstract:The load frequency control plays an important role in ensuring the security and reliable operation of the power grid. The appropriate controller parameter setting ensures frequency stability and longterm security of power systems under various random disturbances. To achieve the optimal setting of load frequency controller of a singlearea twogenerator power grid, this paper proposes a controller parameter tuning method based on particle swarm optimization adaptive bacterial foraging optimization (PSOABFO), which is based on the standard BFO and combines the idea of PSO to introduce global optimization, individual optimization and adaptive step size, etc. The speed and accuracy of the proposed algorithm is significantly improved. A load frequency control system (LFC) model is established to test the performance of the proposed algorithm. The results verifies that the improvement of the dynamic performance of the system.
2021(6):136-143. DOI: 10.19781/j.issn.1673-9140.2021.06.016
Abstract:The leaked stray current during the metro operation causes a change of the nearby surface potential, which results in a variation of the ground potential of grounding transformers, then the transformer DC bias. By studying the stray current leakage mode in the traction power supply system for rail transit and the flow path which causes the transformer DC bias, the mechanism of transformer DC bias generated by the metro stray current is revealed. With the consideration of the action mechanism of stray current on transformer DC bias, the equivalent resistance model of the transformer DC bias caused by the stray current is built with doubleend power supply which is based on the discrete model of the stray current distribution. The mathematical equation of the transformer neutral point current with the changing operating conditions of the rail transit is established, and the numerical calculation of the transformer neutral point is realized. The validity of the model is verified by the CDEGS simulation, which has certain guiding significance for the planning and construction of subway stations and substations.
2021(6):144-150. DOI: 10.19781/j.issn.1673-9140.2021.06.017
Abstract:Aiming at the problems of low efficiency and low accuracy of fault diagnosis of electromagnetic current transformers, a fault diagnosis method based on variational mode decomposition (VMD) and sample entropy is proposed. The original fault signal is decomposed into an Intrinsic Mode Function (IMF) series through VMD and optimized. The sample entropy is calculated as the feature value of the new transformer feature extraction object, which is combined with the common timefrequency domain feature index to input the Knearest neighbor classifier for training. Matlab simulation experiments show that the new characteristic index of this method is effective and feasible for fault diagnosis of lowvoltage current transformers, which can provide a reference for fault diagnosis of the electromagnetic current transformer.
2021(6):151-156. DOI: 10.19781/j.issn.1673-9140.2021.06.018
Abstract:PI control can rapidly track the gridconnected current, however, the harmonic components of current are high due to the power electronic device of the inverter. In addition, PI parameters are difficult to adjust in practical application, and it is difficult to achieve optimization in the regulation process, which exacerbates the distortion of grid connected current. To achieve the best possible performance, an improved genetic algorithm is considered to optimize parameters of PI control. By calculating the error of practical current with setting current, this algorithm builds the current fitness function. The optimal PI parameters are obtained by iterating remarkably and the distortion rate is reduced. The combination of repetitive control technique significantly improves the steady performance by building the specific frequency notch filter and second order low pass filter. Through Matlab/Simulink, a model of gridconnected inverter with LC filter is built and the performances of the three control strategies of PI control, PI repetitive control and improved genetic PI repetitive control are compared to verify the effectiveness of proposed control strategy.
2021(6):157-163. DOI: 10.19781/j.issn.1673-9140.2021.06.019
Abstract:The widespread application of airconditioning equipment has brought a large amount of airconditioning load to the power grid, which has an increasing impact on the safe and economic operation of the power system. In order to correctly estimate the airconditioning load scale, this paper proposes a winter airconditioning load calculation method that considers the correlation between temperature and load.Firstly, by calculating the correlation coefficient between temperature and load in the screening process, the abnormal temperature day is excluded from the reference day. Secondly, considering the daily growth of basic load, regression analysis method is used to fit the basic load curve of each day in winter. In view of the characteristics of the rapid decline of the power system load during the Spring Festival, the Spring Festival coefficient is proposed to modify the basic load of the winter base load. The winter airconditioning load is the difference between the winter power system load and the winter base load. This method is used to calculate the airconditioning load in Chongqing in 2018.The results show the effectiveness of the method.
2021(6):164-170. DOI: 10.19781/j.issn.1673-9140.2021.06.020
Abstract:Power stealing detection can find power stealing users efficiently and then reduce the operation cost of the power system. In this paper, a detection model of power stealing behavior based on improved fuzzy cmeans clustering is proposed, which is suitable for the situation without many known power stealing user samples. The model includes factor analysis, local outlier calculation based on improved fuzzy cmeans clustering, model evaluation and parameter adjustment with ROC curve, and the selection of the best detection threshold. Firstly, through factor analysis, the dimension specification of the user's power consumption characteristics (including power load data and abnormal events of electric energy meter) is carried out to improve the efficiency of model detection. Then, the FCM clustering algorithm integrated with a genetic simulated annealing algorithm is applied to detect the user's power consumption characteristics. Finally, compared with the existing mature algorithm, the result indicates that the model has a high detection accuracy for electricity theft. The detection model can output the power consumption behavior outlier and all the tested users' power stealing probability order. The output of the detection model can detect the power stealing users with high precision. The results can be employed into the field inspection, and the efficiency of antistealing work will be improved.
2021(6):171-181. DOI: 10.19781/j.issn.1673-9140.2021.06.021
Abstract:Due to the opening of the electricity retailing market, the competitive electricity retailing market allows users choose any electricity company to provide electricity and corresponding services, which will cause the loss of customers and reduce market share of power utilities. At the same time, with the sustainable development of the modern hightechnology industries, the loss and impact of the power quality disturbance of users are continuous increasing. Therefore, power companies have necessary to provide highquality service that meets customer's requirements to effectively attract customers and improve market competitiveness. However, there is a lack of customer classification method considering the demand of both power company and electricity user, which hinders the development of highquality power service. In this paper, a new classification index system of premium users is proposed by considering the lifetime value and power quality demand of users, which combining the comprehensive demand of power grid companies and users. Then, the fuzzy theory is adopted to achieve data standardization, an improved kmeans clustering algorithm is proposed to classify the massive user index data, and the fuzzy AHP based on entropy weight is used to calculate the index weight. Finally, the numerical results show that the evaluation information contained in this method is more comprehensive, which weakens the subjectivity of the general method, and make the result classification results of highquality user more objective and reasonable.
2021(6):182-188. DOI: 10.19781/j.issn.1673-9140.2021.06.022
Abstract:Rotorcraft unmanned aerial vehicle (UAV) has been applied rapidly in the domestic electric power system. However, when loaded with patrol equipment, the drone's endurance time becomes only 20 minutes, which is limited. Therefore, based on machine vision, this paper proposes a key technology of automatic charging control to build the leapfrog automatic charging system. The system comprises of leapfrog type UAV charging platform, UAV automatic charging platform and ground control system. According to the flight control and intelligent control, with the aid of machine vision and image recognition technology to realize high precision positioning and automatic charging platform of intelligent precision landing, considering the connection of the clamping position and charging interface of UAV charging platform, the UAV battery automatic charging and the automatic takeoff and landing recharge are realized. The experimental results show that the problem of high precision positioning during UAV charging is effectively solved by using the leapfrog charging platform and machine vision image recognition and shutdown technology.
2021(6):189-195. DOI: 10.19781/j.issn.1673-9140.2021.06.023
Abstract:In order to effectively locate shortcircuit faults in the highvoltage singlecore cable, this paper presents a new method based on the electromagnetic timereversal (EMTR) theory. As the fault location is the maximum energy point, this method monitors the sheath current at the grounding position of the highvoltage terminal and calculates the energy of each guessing fault location by the transfer function of the fault signal. A typical highvoltage cable structure is simulated and analyzed. The results show that the method can effectively locate the fault point, and the accuracy can be improved with the increase of the sampling rate. It is recommended of the above 10 MHz sampling rate in practical applications.
2021(6):196-203. DOI: 10.19781/j.issn.1673-9140.2021.06.024
Abstract:The intelligent control system of substations faces several challenges, such as the long information collection time and low control efficiency. In order to solve these problems, this paper designs an intelligent management and control system of substation based on threedimensional (3D) model. Users can flexibly access the relevant information of substations by using 3D model built in 3D Max. On the basis of the 3D model, multiple tasks, including semantic Schema information design, implicit geometric design, and so on, can be achieved to accomplish the intelligent management and control system of substations according to CityGML standard. The experimental results show that the information acquisition time of the proposed system is significantly reduced, and management and control efficiency and quality are improved. Hence the proposed system can be further applied in practice.
2021(6):204-210. DOI: 10.19781/j.issn.1673-9140.2021.06.025
Abstract:The relay protection equipment has many kinds and huge number of quantities. The traditional operation and maintenance mode of relay protection equipment that combines paper records and manual management has problems such as the heavy workload and errorproneness. Based on the application value of twodimensional code technology in the management of relay protection equipment, this paper uses twodimensional code with the characteristics of large capacity, small size, and high recognition rate, and applies it to the operation and maintenance of secondary equipment and the storage of asset information.By recording the information of each relay protection equipment in different stages of installation, operation, defect and return, the life cycle management of relay protection equipment is realized.Taking a specific secondary equipment as an example, the storage of equipment defects and asset information is realized through twodimensional code technology.The results show the twodimensional code technology can solve the problems of inconsistent accounts and low efficiency in manual management and is of great significance to improve the efficiency of onsite operation and maintenance of relay protection.