Voltage source converter based high voltage direct current (VSC-HVDC) technology has unique advantages in island power transmission, offshore wind power DC transmission, etc. It is the development direction of DC transmission in the future. This paper summarizes the development status and application prospect of VSC-HVDC, including the research progress of key equipment such as power electronic devices, flexible DC converter valve, HVDC circuit breaker, flexible DC transformer and DC cable, and the landmark VSC-HVDC projects in China. The application prospects of VSC-HVDC in large-scale new energy consumption, offshore wind power DC transmission, multi terminal DC and DC power grid, long-distance high-capacity overhead line DC transmission, DC distribution network and island power transmission are pointed out.

In the method of fault location using empirical wave velocity, because of the dispersion characteristics of travelling wave, the wave velocity changes with the change of frequency, and the fault distance is obtained by calculation has a large error. To solve this problem, it is necessary to accurately extract the time-frequency characteristics of travelling wave. This paper proposes a fault location method of DC line based on multisynchrosqueezing transform (MSST). Due to the multiple extrusion characteristics of MSST, the fault location method can effectively improve the time-frequency aggregation of signals, and identify the time-frequency characteristics and wave heads of traveling waves more accurately. By using this method, the time and frequency information of the traveling wave arriving at the measuring point are obtained, and the corresponding wave velocity is further obtained, and the fault distance is calculated based on the wave velocity, which reduces the error caused by the inaccurate identification of the wave velocity and the arrival time of the wave head. Finally, the effectiveness of the proposed method is verified by simulation and actual engineering data.

The platinum pin-type grading electrodes are widely installed in the practical high voltage converter valve cooling system to limit the leakage current between the cooling water pipe and metallic heat sink. Then the deposited products on the grading electrodes fall off easily and probably result in water pipe blockage. Therefore a new design of ring-type grading electrode is proposed to replace the traditional pin-type grading electrode in this paper. The simulation deposition tests are carried out in the laboratery between the ring-type grading electrode and pin-type grading electrode. The distribution characteristics of deposited products on the two types of grading electrodes are analyzed contrastively. The test results show that the ring-type grading electrodes will effectively reduce the deposition rate to one tenth of the pin-type electrodes, and then lower the probability of falling off of deposition produt. Besides, the ring-type grading electrodes can eliminate the electric potential difference between the two ends of the tributary cooling water pipe, thus further inhibit the corrosion of metallic heat sinks led by the leakage current.

Large-scaled wind-farm connected to VSC-HVDC transmission system (WF-VSC system) may induce a new type of sub-synchronous oscillation which threatens the stability of the AC grid, this type of oscillation is the results of the interactive behaviours among the power electronic controllers through the AC grid, the interactive behaviours cause the impedance coupling characteristics of the WF-VSC system from sub-synchronous frequency range to twice fundamental frequency range, leading to significant inaccuracy when analyzing the impedance coupling characteristic using one-dimension impedance model. In this paper, the coupling characteristic is taken into account, and the sub-synchronous oscillation conditions of the WF-VSC are elaborated based on the coupled impedance model and the freuqency response characteristics of the integrated impedance, and the impacts of the oscillation conditions, such as the number of the wind turbines, the length of the AC transmission line, the output power ratio of the wind turbines, and the parameters of the VSC controllers, on the sub-synchronous oscillations stability are also analyzed. The simulation results verity the the effectiveness of the coupled impedance model and the analysing results.

The backbone grid with anti-disaster performance can reduce the damage and loss of power systems caused by extreme natural disasters such as typhoons. In this paper, a multi-objective planning method for backbone grid considering economy and multi-stage anti-disaster performance is proposed. First, the economy, survivability, invulnerability and recoverability of backbone grid are taken as multi-objective functions; the constraints, such as network connectivity, important nodes and lines reservation and safe operation are considered to construct the multi-objective planning mode for backbone grid. Next, the improved non-dominated sorting genetic algorithm (NSGA-Ⅱ) embedded in graph theory restoration strategy is utilized to solve the proposed model, and the Pareto optimal solution set of backbone grid planning strategies is obtained. Then, the entropy weight method is utilized to select the Pareto optimal compromise solution from the Pareto optimal solution set. Finally, the effectiveness of the proposed model is verified by the case study based on an actual regional transmission network.

To improve the automation level of large power grid analysis and construct more accurate power system calculating topology, a multi-granularity power flow calculation data construction method based on common information model (CIM) is proposed. Firstly, the connection relationship of CIM topology is analyzed and reformed. Then, subject to different abstraction depth and power system operation state, the power flow calculation topology is constructed based on graph theory. Finally, the method is tested with actual grid CIM data and DSP power flow calculation software. Results show that the proposed method can provide different granularity power flow calculation topologies through online system CIM data.

To solve the problems of noise interference in low-frequency oscillation pattern recognition and parameter extraction of power system, a low-frequency oscillation modal identification method based on the combination of Hilbert Transformation (HT) and energy function of empirical mode decomposition (EFEMD) is proposed. Firstly, EMD is used to decompose the low-frequency oscillation -area measurement signal in power system with noise to obtain each intrinsic mode function (IMF). Then EFEMD-HT energy method is used to calculate the energy of each intrinsic mode function and weight it, and the dominant oscillation mode of the system is screened out. Finally, Hilbert transform is used to extract the parameters of the dominant oscillation mode. The feasibility and effectiveness of the proposed EFEMD-HT energy method are verified by the simulation of ideal signal, EPRI-36 system simulation signal and the measured PMU signal of the power grid, and the dominant oscillation mode of the system can be accurately identified.

To reasonably sectionalize the large system into multiple sub-regions and restore them in parallel is an effective strategy to rapidly recover the system. In this paper, a new system optimal partition model and its solving algorithm are proposed, considering the influence of the parallel recovery process of the subsystems. The modal takes into account the influence of recovery time approximately, the objective function of the model is to minimize the sum of the loss of power outage and the number of tie lines between subsystems, and the constraints are the uniqueness of unit attribution, the power balance of subsystems and the connectivity of subsystems, which makes the partition scheme gained by the model more reasonable and scientific. Since the model is a complex mixed integer nonlinear programming issue, which is difficult to be solved directly, the paper further proposes a decomposition solution strategy, that is, the model is decomposed into a simple partition sub-problem with known recovery time of each load node and a set of subsystems recovery sub-problem with given partition schemes. The two sub-problems are mixed integer linear programming problems and can be easily solved by CPLEX solver. The approximate solution of the original model can be obtained by iteratively solving the two sub-problems. The effectiveness of the model and its solving algorithm is verified by several examples.

Under the background of electric energy substitution, to improve the economy in on-grid operation and improve the energy reliability in off-grid of heat pump heating industrial and commercial park, an optimal operation model of industrial and commercial park considering important loads demand during un-planned off-grid is established. On the load side, considering the demand response characteristic of flexible load, the price response characteristic of flexible electric load and the elastic regulation characteristic of flexible thermal load are utilized to regulate the load demand. On the energy storage side, the state of energy level is divided, according to the important electric and thermal loads demand, the reserve capacities during unplanned off-grid at each moment is proposed and calculated, then it is taken as the constraint of energy storage device. The model takes the minimum operation cost as the objective function, the simulation shows that considering the demand of important loads during unplanned off-grid will increase the operation cost slightly, different energy storage capacities and state of energy levels have different operation economics and reliabilities. The model can improve the economy in on-grid operation and ensure the short-term demand of important electric and thermal loads during off-grid can be met, improve the reliability of energy use.

Due to the reliability evaluation result based on a single data source is not accurate enough caused by the field data of the smart meters not covering its entire life cycle and the difference between the stress of accelerated life test and the actual operating environment, a reliability assessment method of smart meters combining Bayes and Bootstrap methods is proposed. The proposed method uses Bootstrap method to process the field data to obtain the discrete distribution of the reliability model parameters of the smart meters, then adopts the Bayes method to fuse the discrete distribution, as prior information, and the accelerated life test data to obtain the parameter estimates, and realizes the reliability assessment of smart meters. The result of the example shows that the reliability model of the smart meters obtained by the proposed method approximates the actual field situation in the first half and is supported by test data in the second half, which can be used for the reliability assessment of the entire life cycle of the smart meters.

The operating mechanism and its electronic control circuit are the main components that affect the reliability of high-voltage breaker. The development of intelligent and digital switches demands higher requirements for the reliability of the switch mechanism. It is of great application value to research on modular circuit breaker mechanism for improving the reliability of switch operation. This paper studies the modularization transformation method of the circuit breaker mechanism, and proposes a modular design scheme of the secondary system of the circuit breaker mechanism, including the primary part of the mechanism and the modularization of the secondary circuit. The modularization of the primary part of the mechanism realizes the overall modular improvement of the mechanism box and the modular design of the components, and the modularization of the secondary circuit integrates the discrete secondary components into five functional modules. A quick replacement method of circuit breaker mechanism is also studied, the consistency of mechanism output is kept by technical means to realize the on-line replacement of different mechanisms. The accelerated aging test method is designed and the modified circuit breaker mechanism is tested with the method. The results show that the reliability of the modified mechanism meets the requirements.

Since the main material of the plug-in foundation transmission tower legs is directly connected to the foundation, this unique structure causes the traditional transmission tower reliability calculation method to be no longer accurate. For this reason, this paper considers the soil-structure dynamic interaction (SSI) between the foundation soil and the tower legs, replaces the upper limit of the natural circular frequency and frequency ratio of the original iron tower with the corresponding value after considering the SSI, and proposes an SSI-based insertion analysis method of vibration reliability of type foundation iron tower. First, the modal analysis of the tower is performed to obtain the natural circular frequency of the tower considering SSI; then according to the external load of the tower under the icing of the wire and the tower vibration displacement equation considering the SSI, the comprehensive amplitude amplification factor expression of the tower is derived, and then the expression is obtained. The upper limit value of the frequency ratio and the function function considering SSI are considered; finally, the normal distribution is combined to solve the problem, and the vibration reliability of the plug-in foundation tower considering SSI is obtained. The proposed method has been applied to the galloping accident analysis of the 500 kV Yidu-Xinglong Ⅰ circuit line. The maximum reliability of the damaged 6-base plug-in foundation tower obtained by this method is 0.971 3, which is less than the target reliability of 0.999 3.

Under the background of power Internet of Things, massive heterogeneous data are in urgent need of processing and the demand for computing and communication resources is increasing dramatically. It’s an important application scenario for multi-edge computing terminals to cooperate with each other to improve the capacity of regional autonomy. For improving the information flow distribution and resource utilization of the system, this paper proposes a method of edge computing terminal deployment and service allocation. Firstly, the services processing architecture and the method of dividing data source node cluster are proposed. Secondly, a bi-layer model considering terminal deployment and service allocation is established. The outer model solves the problem of service allocation in edge computing terminal, and the inner model solves the problem of edge computing terminal deployment. Thirdly, the coupling relationship between the two-level optimization models is analyzed, and a bi-level optimization algorithm based on CPLEX is proposed to solve mentioned model. Finally, a numerical example is given to verify the effectiveness of the proposed method.

Characterized by low cost, low-power consumption and flexible deployment, long range radio (LoRa) is able to effectively meet the communication requirements of many scenarios in power Internet of Things. At current stage, the lack of analysis tools and research methods to evaluate the performance of LoRa in power Internet of Things makes it difficult to carry out related researches and large-scale applications. Therefore, by comprehensively analyzing the LoRa communication network protocol, this article establishes LoRa communication message information and critical equipment models based on OPNET simulation software, so as to provide an effective analysis tool for quantitative analysis of the application performance of LoRa. Furthermore, considering the business scenarios of low-voltage centralized automatic meter reading and environmental monitoring in power Internet of Things, this article also completes quantitative analysis on real-time performance, reliability and business support capability of LoRa communication network through multi-scenario LoRa communication performance simulation, including business parameters configuration, quantity of devices and access distance, etc. The simulation results verify the effectiveness of the modeling method. Meanwhile, the corresponding evaluation conclusions can also provide us scientific and reasonable guidance for the engineering application of LoRa in power Internet of Things and other fields.

Due to the influence of different climate conditions, topography and other factors, the distribution of thunder varies greatly in different regions. It is of significant practical value to study the law of thunder distribution in complex terrain. In this paper, the local terrain division of transmission line area is carried out, and the improved cluster analysis method based on DBSCAN algorithm and OPTICS algorithm are used to obtain the temporal and spatial distribution of single lightning activity in different terrain. According to the results, it is found that the temporal and spatial distribution of lightning activity is slightly different in different terrain. Among them, the lightning activity tracks along the canyon wind channel and ridge terrain are more than the lightning activity tracks along the valley and river terrain. At the same time, the lightning frequency and lightning current amplitude before and after a single lightning activity passing through different terrain are analyzed to further analyze the influence of terrain on lightning activity. The research on the distribution law of lightning on the macro terrain and local terrain near the transmission line can provide engineering reference and theoretical reference for the future differentiated lightning protection work.

The crimping quality of the strain clamp in the transmission line affects the safety of the power grid. At present, the quality inspection method of the strain clamp crimping is mainly to take X-ray images and perform manual identification. However, due to the small size and tightly packed of the defect parts in the X-ray image of the strain clamp, the manual method appears to be time-consuming and labor-intensive and the accuracy rate is not high. Aiming at the above problems, an X-ray image detection system for crimping defects of strain clamps based on deep learning is proposed. The principle of hierarchical detection is adopted, Firstly, the CenterNet algorithm is used to locate the defective crimping part and cut out the crimping part to increase the proportion of crimping defects in the image. Secondly, the data are used to enhance the data set, and finally the RetinaNet algorithm is used to detect the crimp defect. By verification that the hierarchical detection strategy in this paper improves to a certain extent in accuracy and detection speed compared with the traditional detection algorithm, which meets the application requirements in actual engineering.