Abstract:In view of the difficulty in calculating the life cycle cost, a hierarchical calculation method is proposed based on the characteristics analysis of various costs for the main transformer. The proposed method obtains the basic data by the data fusion of PMS and ERP systems. Then, the regression analysis and blind number theory are introduced to calculate the mathematical model of life cycle cost for the main transformer. Considering the time value of funds, the net present value method in economics is utilized to classify the cost of each stage into the cost of the base year for analysis, which makes the model closer to the reality. Finally, 220 kV, 180 MV·A power transformer of two domestic and foreign manufacturers are taken as an example to analyze the specific calculation method of life cycle cost. The results show that the datadriven hierarchical calculation method is effective.

Abstract:As a typical air gap, the sphere gap is a kind of important electrode structure for studying air gap breakdown characteristics. Firstly, an electric field feature set is defined on the basis of electric field distribution on the shortest path. 271 power frequency breakdown voltages collected from IEC 60052: 2002 are considered as samples set. Then, four feature selection methods including the Pearson correlation coefficient, sensitivity coefficient, genetic algorithm and random forest are adopted to select features. In the end, the support vector regression (SVR) is trained by small sample data to predict power frequency breakdown voltages of other samples. The prediction results show that without the feature selection, the mean absolute percentage error is 4.21% for breakdown voltages of all samples with test results as the reference. Thus, the effectiveness of the feature set is verified. The mean absolute percentage errors of the results by adopting four feature selection methods are 1.92%, 2.00%, 3.86% and 2.04% respectively. Pearson correlation coefficient corresponds to the highest prediction accuracy. By comparing the results, it is concluded that the features of Emin and Lw90 play crucial roles in the model. The proposed method has a guiding significance to the study on discharge characteristics of complex gaps and engineering gaps in the future.

Abstract:With the development of photovoltaic power generation, largescale photovoltaic plants gridconnection has a significant impact on power system stability. A damping control introduced in photovoltaic gridconnected inverters helps to increase the damping of the power system. However, too large a damping control parameter causes a new oscillation mode. Under this background, a smallsignal model is established for photovoltaic plants connected to a singlemachine infinite bus system to analyze the influence of photovoltaic plants gridconnection on system damping and design active power additional damping controller for the photovoltaic gridconnection. Furthermore, the contribution of the additional damping controller is theoretically analyzed to the system damping, and the system root locus is utilized to clarify the mechanism of oversize additional damping control coefficient affecting the system stability. And then, the computation method of the control parameters is proposed when the system is at the maximum damping. Finally, the correctness of the theoretical analysis is verified by the simulation on PSCAD software.

Abstract:In order to evaluate the insulation status of transmission line and ensure power system stability, a method is proposed to identify several flashover factors for the transmission line insulation in this paper. Firstly, the impact test platform superimposed by the power frequency is utilized to simulate three types of transmission line faults to obtain flashover current data. Secondly, the flashover current signals are transformed into reconstructed signals in different frequency band using the wavelet transformer. Finally, the wavelet energy spectrum is used to construct the highfrequency energy center of gravity as the identification feather, combined with the low frequency energy value to propose a comprehensive identification criterion. Furthermore, three types of inducement data are analyzed and distinguished. The results show that these three flashover under power frequency superimposed shockspollution, icing and vegetation flashover, can be accurately identified by the proposed method, and the correct identification rate can reach 91.1%.

Abstract:In order to solve the problem of uncertainty caused by the inherent prediction error in the unit commitment decisionmaking involving the wind generation, this paper establishes a twostage symmetric fuzzy optimization model with both fuzzy constraints and fuzzy targets. The first stage of the model determines the fuzzy parameters of the system. While, in the second stage, the actual fuzzy solution and the corresponding fuzzy level are calculated, and the uncertainty of the unit commitment is quantified.Due to the introduction of unsolved fuzzy variables, a simplified operation based on the outerpoint iteration method is proposed. In case of the dayahead prediction, the 4 h rolling prediction in the day, the 1 h ultrashort rolling prediction, the adaptability to the forecasting error of this method is analyzed though comparing with the actual situation.The results show that the fuzzy optimization can reduce the scheduling error caused by the prediction error to a certain extent, so it is suitable for the usage of system scheduling with a high uncertainty.

Abstract:In order to solve the problems of poor safety performance, nonuniversality and low power of inductive power on transmission line, this paper designs and studies the optimal design of induction power supply device on transmission line. A double protection circuit of relays and TVS diodes is proposed to protect the power grid and its equipment.Then, the parameters of induction coil are analyzed to ensure that the output power can reach 33 W at a low current, and the output voltages of 12 V and 5 V can be output stably.The optimized device can be applied in transmission line monitoring, thunderstroke orientation,fault locating and conductor temperature monitoring devices.The wide applicability of the induction power supply device is guaranteed. Meanwhile, a status display function of lithium battery is integrated in the device to avoid overcharge or over discharge.Finally, the feasibility of the optimized design is verified by the Saber software simulation and experiments.It is indicated that the improved induction device is a secure, stable, reliable, universal and highefficiency power supply device.

Abstract:The largescale new energy accessed into a substation would bring in problems of the overload, harmonic and short circuit and then affects the life of power appliances. Therefore, it is of great significance to study the thermal life loss of transformer for the grid economic operation. Firstly, the power loss of the transformer in harmonic current is analyzed quantitatively and the load factor is derived simultaneously. On this basis, the calculation method of hot spot temperature considering the load factor and harmonic distortion rate is given. Then, considering the special case of sudden shortcircuit of transformer, the calculation method for the winding hot spot temperature is improved. Thirdly, the thermal life loss model based on the hot spot temperature of the transformer is established. Finally, the simulation analysis of a 35 kV transformer in included for verification. It is shown that after new energy resources access, the overload operation causes the great increase of the thermal life loss while the harmonic and shortcircuit have little effect on the thermal life.

Abstract:By modeling the threephase inverter circuit and reducing the model order, a secondorder power supply model with power electronic interfaces is proposed for the lowfrequency oscillation analysis. Firstly, the eigenvalue analysis is performed in a fourmachine tworegion system including power electronic interface power supply. Then, the results of the analysis are compared with those of higherorder models to verify the validity of the proposed model. In addition, based on this model, this paper also analyzes the influence of power electronic interface power supply capacity on the oscillation frequency and damping ratio of interval and local oscillation. The analysis results show that as the capacity of power electronic interface power supply increases, the oscillation frequency of interval oscillation and local oscillation would increase. The damping ratio also increases. Finally, based on the reducedorder model, the droop controller gain for the power supply of power electronic interface is adjusted, and the higherorder model of the power electronic interface power supply is used to simulate the setting parameters. The simulation results further verify the validity of the reduction order model proposed in this paper.

Abstract:In order to solve the instability problem caused by the changing output of distributed generation and load switching in the island microgrid, this paper puts forward a hierarchical control strategy based on the voltage and frequency power quality level. The voltage and frequency power quality are divided into three grades: superior, medium and poor. For the case that the power quality of the microgrid is excellent, the hybrid energy storage system is used to maintain the voltage and frequency stability of the microgrid. When the power quality of the microgrid is medium, the hybrid energy storage system and the drooping control are employed to maintain the voltage and frequency stability of the microgrid. If the power quality of the microgrid is poor, the droop characteristic of distributed generation curve is adjusted by the secondary frequency modulation theory similar with it in the power system, so that the voltage and frequency are keeping around the rated values. The simulation results verify the feasibility of the proposed hierarchical control strategy. Compared with the traditional control method, the hierarchical control strategy can improve the operating stability of the island microgrid when the distributed generation output is changing and load switching.

Abstract:With the consideration of the effect of harmonic and threephase unbalance on ripple and the superposition of ripple in AC side grid, the ripple problem in AC/DC hybrid micro grid is studied in this paper. Firstly, It is proposed that if the phase angle of the korder harmonic source changes in its three phases, the amplitude of the k+1 and k1 ripple generated by the kth harmonic source is the reciprocal relationship,which has an impact on the superposition of ripple.Then, it is found that the effect of the initial phase difference of harmonics on the amplitude of the superimposed ripple has a certain regularity by superimposing the positive order harmonics of the same number, the negative order harmonics of the same number and the positive order and negative order harmonics of adjacent times.Finally, the above studies are confirmed by Matlab/Simulink modeling. It is shown that the amplitude of ripple superposition in ACDC hybrid micro grid is related to the harmonic frequency and initial phase difference of harmonic source. The research of this paper is of great significance to the analysis and management of power quality in hybrid micro grid.

Abstract:In order to comprehensively, accurately and reasonably allocate the investment amount of the countylevel distribution network (110 kV and below), this paper builds a countylevel distribution network investment benefit indicator system by considering the county investment benefits of a new round investment firstly. Then, the indicator system is evaluated by using the fivelevel set pair analysis model. Furthermore, Based on the singleindex evaluation result and the comprehensive evaluation result of the indicator system, the investment allocation adjustment factor model is constructed. In the end, the countylevel grid investment allocation amount is analyzed and calculated combining with the future electricity demand. The example shows that the proposed method can be used to formulate the investment strategy precisely for the countylevel distribution network to realize the refined planning of the countylevel distribution network and the scientific, reasonable and effective use of limited funds.

Abstract:The medium and low voltage distribution network has a large number of faults with complex types.The low level of fault monitoring makes it impossible to discover and clear the faults in time after a fault occurs. In response to his problem, this paper analyzes the operating conditions of 10 kV distribution transformers at different load rates, winding connection groups,threephase unbalance rates,and system voltages.The changing law of electrical signal on the lowvoltage side is obtained for typical faults such as the disconnection of medium and low voltage lines, singlephase loss of distribution transformers, and singlephase grounding of low voltage line.Then relevant fault diagnosis rules are summarized and formulated to provide a basis for the judgment of medium and low voltage faults.On this basis, a comprehensive fault judgment platform including the data integration, fault warning, fault research and other functions is built and successfully applied in the actual operation and maintenance, repair and decisionmaking in Jiangxi power grid. The results show that the platform can detect faults in low and medium voltage distribution network timely, reduce user power outage time and improve power supply reliability.

Abstract:The reasonable selection of blackstart scheme is significant to the fast restoration of power systems however most previous studies are based on complete evaluation information without consideration for cases with incomplete evaluation information. Under this background, the Affinity Propagation (AP) algorithm and Slope One method are adopted to assess blackstart schemes with incomplete evaluation information in this paper. Firstly, the Affinity Propagation algorithm is utilized to cluster the blackstart schemes to generate similar sets of schemes. Then, the Slope One algorithm is employed to predict the absent values according to the evaluation value of the blackstart schemes in the same cluster. Finally, the standard deviation and the TOPSIS methods are applied to rank the schemes. The relative data of Guangdong power system are selected to evaluate the performance of the proposed method. Four existing blackstart decision making methods with complete information are compared with the proposed method. The result shows that the proposed method solves the problem of incomplete evaluation information well.

Abstract:The black start scheme for VSCHVDC can maintain the voltage stability of the converter bus and effectively suppress the possible overvoltage problems. Under this background, an evaluation method is proposed for the black start scheme of VSCHVDC considering aftereffects. Firstly, the operation characteristics of VSCHVDC are introduced; Secondly, the initial recovery evaluation index and aftereffects evaluation index are comprehensively combined to characterize the pros and cons of the scheme. A comprehensive evaluation system is then established to fully reflect the pros and cons of the scheme. Thirdly, the order relation analysis method and the improved CRITIC method are utilized to determine the subjective and objective weight respectively. The combination weighting method based on game theory is then employed to obtain the combination weight of each index to be evaluated. Furthermore, a comprehensive evaluation of the black start scheme of HVDC satisfying all kinds of constraints is analyzed to determine the advantages and disadvantages. Finally, the feasibility of proposed method is verified by the restoration of the power supply with Luxi backtoback VSCHVDC system after a blackout in Yunnan power grid.

Abstract:The characteristics of DC power transmission have reciprocal effects on wind farms and it would possibly give rise to the transient overvoltage. The influence of collector parameters on overvoltage level in wind farms cannot be ignored. Under this background, for the modeling problem of wind farm near the DC region, this paper firstly proposes an equivalent modeling method considering power loss of collector networks by combining the power characteristics of transient overvoltage. And then, the effect of collector parameters on the generator terminal overvoltage can be quantified. Finally, the actual grid is included as an example. The characteristics of transient overvoltage and output characteristic of equivalent model are analyzed by simulating the case of two continuous commutation failures of HVDC system. It is shown that the variation of generator terminal voltage in the farend wind turbines is lower than that of the nearend, and the difference is about 2.5% compared to the rated voltage. Therefore, it is necessary to consider the collector parameter equivalence of wind farms. Meanwhile, the power loss and average voltage of this equivalent wind farm model in this paper are fairly remain consistent with that of actual model, so that it has a certain practical application value.

Abstract:Aiming at the complex and timeconsuming problem of the existing threephase power flow calculation method for distribution network, a hybrid power flow model based on πtype interfaces is proposed in this paper. In the hybrid model, a threephase model for threephase asymmetrical network, and a singlephase model for threephase symmetrical network are considered separately. Then, the hybrid power flow model is established by connecting the two parts of network through a πtype equivalent interface. In addition, the node admittance matrix, the node power injection equation of the interface and its influence on Jacobian matrix are obtained.The correctness and superiority of the proposed model is verified by comparing the calculation accuracy and speed of the proposed model and the full threephase power flow model under different threephase unbalance conditions based on IEEE standard example.

Abstract:According to the fact that the existing icing prediction methods has a slow convergence speed and poor prediction accuracy, a method based on particle swarm optimization with extended memory (PSOEM) is proposed under the consideration of the icing thickness influence to optimize parameters. It is applied to the least squares support vector machine (LSSVM) to predict icing thickness. The proposed method introduces an extended memory factor into the traditional particle swarm algorithm to make the particles have stronger search capabilities, thereby speeding up convergence and improving prediction accuracy. Finally, the actual line icing data is utilized to test the accuracy of the prediction model. It is shown that the average relative error of the prediction model based on PSOEMLSSVM is less than 3%. Compared with other models, the prediction effect is the best.

Abstract:Energy storage is an effective way to smooth out fluctuations in the photovoltaic power generation. Aiming at the typical application scenarios of the optical storage type AC/DC hybrid system, a power adjustment topology based on the isolated dual active bridge (DAB) is proposed in order to solve the problem of the access and power adjustment of the photovoltaic unit and the energy storage unit. Based on the theory of direct power feedback, a coordinated control strategy for optical energy storage is then designed. A simulation model is built in MATLAB/Simulink and further analyzed. The results indicate the correctness and effectiveness of the proposed method.

Abstract:As the deepen development of smart grids construction, more and more monitoring data are collected in power distribution network, and gradually forming big data on the user side of smart grids. The traditional data analysis model does no longer meet performance requirements of huge data processing. Thereby new storage and data analysis models are urgently needed to be established. Under this background, this paper proposes a cluster analysis method for massive electricity consumption data based on the Alibaba Cloud big data analysis platform MaxCompute. The characteristics of power consumption data are fully considered, and a multilevel partition tablebased power consumption data storage mode are designed by adopting the threephase voltage, threephase current, threephase power factor, etc. to establish multidimensional data characteristics. Furthermore, the MaxCompute Graph framework design is employed to achieve an efficient clustering and partitioning algorithm for massive electricity consumption data. Experimental results show that the designed storage mode can effectively improve the retrieval efficiency of electricity consumption data. The clustering accuracy rate reaches 88% for clustering of users with different electricity consumption types. The effectiveness and high efficiency of clustering is verified.

Abstract:In order to solve the problem of low accuracy in wind energy resource assessment, this paper uses NCEP data to extract meteorological data of wind farms, and uses STRM data to obtain macroscopic topography of wind farms. With the support of WAsP software, the key indicators of wind energy resources such as wind speed and wind power density are then calculated. After knowing these indicators of the distribution of wind energy resources, the Weibull distribution of the two parameters are obtained. Then the frequency distribution of wind speed are simulated and the power generation are estimated. The proposed method provides a theoretical basis for the construction of wind farms and guidance for the precise positioning of the wind farms in the later period. Finally, an example is included to verify that the proposed method is feasible, effective and has high prediction accuracy.

Abstract:The parameters of Siemens PSS3B power system stabilizer are difficult to tune, therefore, a parameter tuning method is proposed in this paper. Firstly, the PSS3B feedback transfer function structure is equivalently converted into a series transfer function structure by analyzing the transfer function structure of the power system stabilizer. Then the phase compensation parameters of transfer function is adjusted based on the phase compensation principle. Finally, the gain coefficient of the power system stabilizer is adjusted by checking the damping ratio corresponding to the dominant characteristic root of the closedloop transfer function and the oscillation frequency. After the adjustment, the PSS3B power system stabilizer has a good suppression effect on the lowfrequency oscillation of active power, which verifies the effectiveness of the method.

Abstract:The voltage stability problem of load center threatens the safe operation of Hunan power grid due to the unbalanced distribution of loads and sources, especially after integrating with ±800 kV QiShao UHVDC transmission line in 2007. In this paper, the relationship between the transient voltage and angle stability is analyzed. In addition, the voltage stability is also analyzed for power grid integrated with UHVDC in the aspects of the effective short circuit ratio (ESCR), static voltage stability and load characteristics. It is shown that the sensitive spot, weak spot of voltage stability and the UHVDC links location are all located in Xiangdong power grid. The ESCR can be increased by shortening the electrical distance of the internal structure in Hunan power grid. However, the voltage sag would be more serious when suffering a large disturbance. The voltage stability level of Hunan grid can be improved effectively by reinforcing the connection between Hunan and Central China power grid. Since the grid structure cannot be strengthened within a short period, the transient voltage stability level of Hunan power grid can by improved by decreasing the short circuit capacity of Heling substation or optimizing the parameters of UHVDC inverter station.

Abstract:Due to the influence of the acid rain, salt spray and ice hazard, the hydrophobicity of composite insulators would be reduced gradually. It is necessary to detect the hydrophobicity of insulators regularly. The periodic detections of insulators are difficult due to the problems as the long operation time, high labor intensity and high risk coefficients. Therefore, a hydrophobicity detection method of composite insulators based on the multirotor UAV (unmanned aerial vehicle) is proposed and the corresponding device is also developed in this paper. The device is composed by a sixrotor UAV, an automatic water spray system, a wireless remote control system, a video capture transmission system and a hydrophobicity detection system. The live working is carried out by controlling the DC microelectronic diaphragm pump to generate adjustable diffused water to spray on the target composite insulator evenly. During this process, the visual mode function of camera can be employed to assist the spraying operation. Then, photos of the target composite insulator are taken by the camera and then transmitted for hydrophobicity analysis. Finally, a test is included for verification. It is shown that the method and device have the advantages of automation, unmanned and remoteness in the whole detection process. The safety of operators can be guaranteed, and the hydrophobicity of composite insulators can be detected accurately.

Abstract:In order to quickly check the leakage point, the leakage detection system is widely used in the low voltage radio station area ("station area"). Due to the zeroorder harmonic caused by the nonlinear load in the station area, the accuracy of leakage current detection in the leakage detection system is seriously reduced, and the existing frequency domain filtering method is difficult to measure the transient leakage current accurately. Therefore, a separation method of leakage current base wave and harmonic component is proposed, that is, a singlephase dq transformation filtering method. Comparing with the frequency domain filtering method, It can suppress the zeroorder harmonics in the station line well without causing the attenuation of the temporary leakage current base wave value. The leakage current is detected by the leakage system and the problem of zeroorder harmonic interference is then solved. The feasibility of the method is verified by MATLAB software simulation finally.

Abstract:The new MCPPID control technology is often used to improve the calibrated furnace temperature control. In order to improve the control effect, this paper firstly adopts the PSObased step response test modeling method to model the calibrated furnace temperatureand then uses MCPPID technology to control the model. The realtime control test carried out on the automatic temperature control test device of the tube calibrated furnace shows that the PSObased step response test modeling method is effective.Compared with the traditional ZNPID, the MCPPID control has the advantage of small overshoot. Results show that the PID realtime control program developed on deploytool software is successful.