In actual engineering and simulation research, it is found that the DC commutation failures may occur when the AC fault is removed, which worsens the recovery performance of the system, and even leads to DC blocking in serious cases. Firstly, the mechanism of commutation failure during AC fault removal is analyzed, and it is concluded that the forward shift of commutation voltage and high DC current are the main factors causing the commutation failure. Then, on this basis, the influence law of AC fault and fault duration on this commutation failure is studied; Finally, according to the evaluation of commutation voltage area, an improved strategy to suppress commutation failure at fault removal moment is proposed, and the simulation is carried out based on CIGRE HVDC standard model. The simulation results show that the proposed strategy can effectively suppress the occurrence of commutation failure during fault removal. The research conclusion can provide ideas for the suppression strategy of commutation failure at fault removal moment.

The flexible DC transmission system based on modular multi-level converter is a low-inertia and weak-damping system. Once DC short-circuit fault occurs, the rapidly rising fault current will damage power electronic equipment and destroy the safe operation of power grid. In order to study the fault current limiting method, the modular multi-level converter (MMC) is equivalent to a controlled current source according to the power balance principle firstly, and the DC impedance models in frequency domain under different control modes are established considering the ratio of inserted submodules. Then the influence law of converter circuit parameters and control parameters on fault current is analyzed. It is concluded that the key influencing factors are arm inductance and the ratio of inserted submodules. A fault current limiting control strategy based on DC impedance remodeling is proposed to suppress the rise of fault current by adaptively reducing the ratio of inserted submodules. Finally, the accuracy of the DC impedance and the effectiveness of fault current limiting control are verified by simulation.

To study the overheat mechanism and risk of valve saturated reactor, the technical characteristics and working principles of valve reactors are analyzed, and an approximate calculation method for core temperature rise is proposed, and by fitting with temperature rise test data under actual operating conditions, a mathematical model of saturated reactor core temperature rise is developed. Based on the results of faulty saturated reactor test and disassembly inspection, it is concluded that the manufacturing process defects will cause the heat concentration in the core during operation, which accelerates the aging of insulating materials. The simulation analysis of the saturable reactor combustion shows that the flame, smoke and temperature of the valve reactor gradually enter the steady-state within 100 s after the reactor being on fire. The results show that the valve reactor is not easy to catch fire. Even if it catches fire under extreme conditions, the combustion diffusion rate is low after tripping.

The grounding electrode shall be under safe and stable operation as it is one of the most essential infrastructures in HVDC power transmission system. The selection of grounding electrode design standard determines the key technical parameters of a design scheme. The DL/T 5224—2014, DL/T 437—2012 and IEC 62344—2013 are the technical base for the electrode design in China. However, the design of other international projects mainly follows the technical requirement of EL 2020, CIGRE 14.21-TF2—1998, CIGRE 675—2017, etc. This paper compares Chinese, IEC and CIGRE design standards/guidelines on maximum allowable step voltage and thermal stability. The main reasons for the difference of maximum allowable step voltage are introduced, at the same time, the relevant requirements of the Chinese and foreign codes for step voltage under transient fault conditions such as partial pole ring exiting running are discussed. Three methods for the calculating of the temperature rise are compared and their design margin is evaluated respectively. In addition, aiming at the limiting value of the grounding resistance which is proposed in the example in CIGRE 675 and also required by some projects, this paper analyzes the relationship between the resistance and other technical parameters. Furthermore, the design scheme and parameters of ±660 kV HVDC Project from Matiari to Lahore, Brazil Belo Monte II UHVDC transmission project, and Lingshao HVDC project in China are presented to give a further explanation about the comparison in this paper, aiming to provide reference for selection of the design standards and technical evaluation principles of grounding electrode engineering in the future.

The DC circuit breaker is the core equipment for the safe operation of the DC transmission system. In this paper, a capacitor-commutated HVDC circuit breaker topology with reclosing function is proposed. This topology utilizes the symmetry of the current-limiting branch, which not only realizes the bidirectional fault current breaking function, but also realizes the reclosing function in both transient and permanent faults. In this paper, the working principle of the extracted topology is studied and analyzed in stages, and then the parameter design is carried out. Finally, the PSCAD software is used to build a system simulation model to verify the simulation model. The verification results show that, compared with the traditional circuit breaker, the proposed DC circuit breaker can not only effectively reduce the rise rate of the fault current and reduce the energy consumption requirements of the arrester, but also greatly reduce the number of IGBT used and the cost.

The multi-chamber structure formed by connecting a plurality of semi-closed arc-extinguishing chambers in series divides the long arc flashed by lightning into several short arcs, and the high-speed airflow generated by the arc-extinguishing chambers has a strong arc blowing effect, which can effectively inhibit the burning of lightning flashover arc. In this paper, in order to improve insufficent performance of single arc-extinguishing chamber, the impact arc model in the arc-extinguishing chamber considering the external magnetic field is established, the movement characteristics of the impact arc in the chamber are studied and the effectiveness of the simulation modal is proved by quenching arc experiment. Based on the existing chamber structure, the movement characteristics of impact arc in semi-closed arc-extinguishing chamber and the influencing factors of external magnetic field acceleration effect are studied. The results indicate that the external magnetic field can accelerate the movement of impact arc in the chamber, and the stronger the magnetic field is, the more obvious the effect is. At the same time, optimizing the structural parameters of the chamber under the action of external magnetic field plays a positive role in improving the arc speed.

A full understanding of lightning activitiy characteristics in different regions is a premise of effective transmission line construction and differentiated lightning protection transformation. Based on the land cover type and lightning data of Yunnan Province in the past 10 years, both statistical method and Apriori algorithm are used to analyze the relationship between the land cover types and the positive flash ratio, ground flash density, ground flash intensity, and the cumulative probability distribution of lightning current amplitude. The results show that the type of land cover is closely related to lightning activity. For the bare rock area and grassland with medium coverage, the ground flash intensity is large. Due to the urban heat island effect, the density of positive and negative ground flash in urban areas is higher than that in other areas. The proportion of positive lightning flashes in woodland is relatively high, so it is necessary to pay attention to the protection of the transmission lines in forest areas against positive lightning.

A three-dimensional fluid-temperature field simulation model is established in this paper based on the design parameters of the air core reactor. The detailed temperature field of the reactor with and without the rain cover and sound arrester are obtained, and the heat dissipation characteristics of reactor are achieved by analyzing the temperature of coils and flow velocity of fluid. According to the change of fluid velocity, the reason for the significant increase in the temperature rise of the reactor under the rain cover and sound arrester can be obtained. In order to reduce the temperature rise of the reactor, the structural parameters of the rain cover and sound arrester, which affect the temperature rise of the reactor, is selected. Combined with the Latin square experimental design and finite element simulation method, the temperature field simulation results with different structural parameters are given. On this basis, the Kriging approximate model is constructed, which build the correlation between the maximum temperature of the reactor and the structural parameters of the rain cover and sound arrester. Meanwhile, the influence degree of the structural parameters on the highest temperature of the reactor is achieved by sensitivity analysis technology. The best structural parameters of the rain cover and sound arrester are obtained based on the particle swarm optimization algorithm. The optimization results show that the maximum temperature rise of the reactor drops dramatically from 73.6 ℃ to 61.2 ℃ under the best structural parameters. Thus, the optimization method has an important guiding significance in improving the heat dissipation capacity of the reactor.

With the continuous optimization and development of intelligent substation, the path planning of substation inspection robot based on traditional ant colony algorithm has many problems, such as weak optimization ability, slow convergence speed and easy to fall into local optimum under complex working environment. In order to improve the work efficiency of substation inspection robot, an improved ACO-SA algorithm is proposed. This algorithm defines a new heuristic function to improve the global search ability. The uneven distribution mechanism of initial pheromone and the introduction of dynamic volatile factor of pheromone can avoid the blindness of the initial search and improve the search efficiency of the algorithm. The tempering mechanism of simulated annealing algorithm is introduced to eliminate local optimization. According to the working environment of the substation inspection robot, the environment model is established by grid method, and the simulation results prove the feasibility of the improved algorithm.

With the massive integration of renewable energy during the 14th Five-Year Plan, Yunnan Power System changes from the traditional power system based on hydro-power to the new power system based on wind and solar seasonally, which leads to the challenges of operation scenarios with system non-synchronous penetration (SNSP) larger than 60% in dry season and intermittent shortage of flexible reserves. In this paper, operation scenarios of high SNSP in some typical independent synchronous power systems in the world are analyzed, the main operation problems and corresponding measures are summarized. Based on the simulation and analysis of Yunan Power System high SNSP scenario in 2025, several suggestions on constructing an operation and control system for Yunnan new power system are proposed.

On March 3, 2022, a large blackout occurred in Chinese Taiwan Power Grid. Almost all cities of Taiwan province, including Kaohsiung and Taipei, suffered power outages, with the loss of 8.46 GW loads and 5.49 million households approximately. The blackout is the worst power outage of Chinese Taiwan Power Grid since the violent earthquake in 1999. This paper firstly introduces the general situation of Chinese Taiwan Power Grid. Then, the blackout situation is described, including pre-accident operation condition, the accident process and the recovery process. The causes of the accident are analyzed from many aspects. Next, this paper compares and analyzes the major blackouts of Chinese Taiwan Power Grid in recent years. Finally, combined with the reality of China Southern Power Grid, the lessons and enlightenment from this blackout are summarized.

In order to solve the problem of cross-subsidy transfer arising in the process of slow opening of the electricity market in market-based trading, firstly, a theoretical transmission and distribution tariff measurement model for different user types at different voltage levels is constructed, secondly, the scale of transfer cross-subsidy after each type of user participates in market-based trading is measured using the price difference method, and a transfer cross-subsidy balance model for the semi-open electricity market environment is constructed, and finally, the 2019 electricity data of China’s province S is used as an example to verify the feasibility and superiority of the model. The results show that the proposed equilibrium model can effectively mitigate the transfer cross-subsidy problem within the electricity market when the increase of the market-based trading degree in province S does not exceed 21%, and it can also provide ideas to mitigate the regional transfer cross-subsidy problem in China.

Facing the gradually open power market, the incorporation of microgrid into distribution network as a new interest subject will have an impact on the economy and security of distribution network.Therefore, a bi-level dispatching model considering demand response and power interaction between microgrids is proposed. Firstly, the mathematical models of the interruptible load and the direct control load are established, and the compensation price of demand response load is determined. Secondly, considering the distribution network and microgrid belong to different stakeholders, a bi-level optimal dispatch model is established. The lower layer takes into account the power interaction among multiple microgrids and minimizes the operation cost of multiple microgrids by coordinating the output of dispatching resources of each microgrid. According to the dispatching results of the microgrid layer, the upper layer determines the power interaction between the distribution network and each microgrid, and optimizes the active and reactive power resources of the distribution network layer, so as to achieve the optimal economy of the distribution network layer while meeting the voltage security of the distribution network. Finally, an example of IEEE 33 node is used for simulation analysis. It is verified the proposed dispatching model can not only improve the coordination ability between distribution and microgrid, but also improve the economy and security of the system.

To improve the power quality of the bus voltage, the bus harmonic voltage feed-forward is often added to the original control of the inverter. However, in the traditional design process of the bus harmonic voltage feed-forward control, the coupling effect of the phase-locked loop (PLL) and the bus harmonic voltage extraction is ignored, which causes design error of system parameters and weakens the power quality. To deal with this problem, this paper explores the coupling relationship between PLL and bus harmonic voltage feed-forward process in detail and proposes an approach of bus harmonic voltage extraction that can eliminate the mentioned coupling. The small signal model of PLL and bus harmonic voltage coupling is established, effectively revealing the coupling mechanism of PLL and the extraction process of the bus harmonic voltage. It is found that when the bandwidth of PLL is increased, the accuracy of bus harmonic voltage is seriously reduced, which further worsens the control accuracy and performance of the inverter. To solve the above harmonic coupling problem, a bus harmonic voltage and frequency extraction method based on αβ axis is proposed. Finally, the simulation model is built in MATLAB /Simulink to prove the correctness of the theoretical analysis.

Based on a small number of low-resolution transmission line samples from the Huma Mountain experimental laboratory of Yunnan Power Grid and predecessors, using the super-resolution algorithm, a data augmentation algorithm based on dynamic background and random transformation is proposed, which generates 7 000 clear transmission line images, and solves the data diversity problem of random target positions, random angles and random sizes. Meanwhile, YOLOv5 target detection algorithm is developed to achieve real-time and robust detection of transmission lines, loose strands and broken strands, and reach an average F1 score of 94.7%. The proposed super-resolution and data augmentation method can be widely used in low-resolution images and small sample datasets in various fields. The proposed transmission line and its defect detection algorithm can be applied to the field of transmission line inspection, which make inspection more efficient and intelligent.

The particle swarm optimization (PSO) of mitigation measures to AC interference of buried-pipelines in common corridor is reseached. A pipeline distribution parameter circuit including a solid-state decoupler drainage device and an equivalent model of an insulating flange is established. The influences of soil resistivity uniformity, shielding effect of earthing electrodes, grounding resistance and other geographical constraints on the optimization of pipeline protection measures are analyzed, and the combination optimization of various protection measures is studied considering various factors. And the effects of PSO and trial-and-error method in pipeline protection are compared. Finally, taking the Wulan common corridor as an example, particle swarms are used to optimize the AC interference mitigation measures during normal operation. The research can provide technical support for engineering practice.