Search

In practical power systems, it is still very challenging to figure out a cost-effective undervoltage load shedding (UVLS) scheme that can reliably and adaptively react to the short-term voltage stability (SVS) problem. Faced with this challenge, this paper develops an intelligent data-driven predictive UVLS scheme for online SVS enhancement. Inspired by valuable ideas in model predictive control and supplementary excitation control in power systems, a novel deep feedback learning machine (DFLM) is designed to precisely predict future voltage violations after UVLS execution. With the help of the DFLM, the UVLS scheme is aware of potential effects of various candidate UVLS actions. Owing to this desirable nature, it can adaptively respond to diverse SVS conditions and optimize UVLS decisions in a non-iterative way. Further, two well-designed strategies, i.e., stepwise constraint relaxation and incremental DFLM adaptation, are introduced to enhance the scheme's reliability and adaptability during online application. Numerical test results on the Nordic test system and the realistic North GZ Power Grid in China showcase the excellent performances of the proposed scheme. [ABSTRACT FROM AUTHOR]

In this paper, a special control solution called virtual voltage source (VVS) is developed for no-load tests of induction machines. This concept is applied to a 2 × 27 MVA high-power machine test bench where the test bench is requested to precisely characterize, e.g., 3 MW machines at no-load currents. The developed VVS thoroughly solves the stability issue of induction machines at low-speed ranges. A set of optimizations is presented here that systematically improves the voltage precision of the test bench. Experimental results prove that the proposed concept achieves 0.08–0.12% voltage unbalance, less than 3% current unbalance, with less than 0.3% harmonic-voltage-factor, and verified by more than 100 induction machines. [ABSTRACT FROM AUTHOR]

With the increasing demand of electricity, the development of the urban power grid has drawn a lot of attention in China. In order to focus on the analysis of an urban power grid, the remaining part of the large-scale power grid used is to be reduced. The accuracy of the equivalence is key to urban power grid research. In this paper, a multistep dynamic equivalent method based on district dividing is proposed. Based on the electrical distance, voltage level, and geographic location, the external system is divided into outer layer, inner layer, and buffer subsystem. Each district is separately reduced by different methods. The proposed technique is illustrated by a real large-scale power grid in the south of China. [ABSTRACT FROM PUBLISHER]

A multi-purpose balanced (MPB) transformer is proposed in this paper for electric railway applications. The MPB transformer is developed from impedance-matching (IM) transformers widely used in China's railway systems. The proposed MPB transformer has three main functions: 1) it provides a symmetrical two-phase voltage of 27.5 kV for railway overhead lines to power electric trains; 2) it supplies a three-phase balanced voltage of 10.5 kV for railway substations; and 3) it can accommodate a three-phase harmonic filter with improved power factor and reduced manufacturing cost. In this paper, the operating principles of the MPB transformer are elaborated, the design of the harmonic filters is discussed, and the results of computer simulations are provided. A 16-MVA MPB transformer was designed and commissioned, and real-time field measurements are provided. [ABSTRACT FROM AUTHOR]

China’s transport sector is facing enormous challenges from soaring energy consumption and greenhouse gas (GHG) emissions. Transport electrification has been viewed as a major solution to transportation decarbonization, and electric vehicles (EVs) have attracted considerable attention from policymakers. This paper analyzes the effects of the introduction of EVs in China. A system dynamics model is developed and applied to assess the energy-saving and emission-reducing impacts of the projected penetration of EVs until the year 2030. Five types of scenarios of various EV penetration rates, electricity generation mixes, and the speed of technological improvement are discussed. Results confirm that reductions in transport GHG emissions and gasoline and diesel consumption by 3.0%–16.2%, 4.4%–16.1%, and 15.8%–34.3%, respectively, will be achieved by 2030 under China’s projected EV penetration scenarios. Results also confirm that if EV penetration is accompanied by decarbonized electricity generation, that is, the use of 55% coal by 2030, then total transport GHG emissions will be further reduced by 0.8%–4.4%. Moreover, further reductions of GHG emissions of up to 5.6% could be achieved through technological improvement. The promotion of EVs could substantially affect the reduction of transport GHG emissions in China, despite the uncertainty of the influence intensity, which is dependent on the penetration rate of EVs, the decarbonization of the power sector, and the technological improvement efficiency of EVs and internal combustion engine vehicles. [ABSTRACT FROM AUTHOR]

Abstract: This paper makes an analysis of the essential reasons for a continuously high percentage of electrical fire occurrences in China. The analysis of the genesis of electric fires in the electric circuit is also described in the article. Based on the different genesis of electric fire in the electric circuit, different features, including short circuit, circuit overload, bad contact of the terminals, increasing of the contact resistance in the circuit, ageing and charging in the circuit and leakage current fault, are described in this paper. Corresponding methods of fire preventions & control to the different electric circuit faults are put out. With respect to different electrical fire genesis and features, an overall plan for electrical fire prevention & control in a low voltage distribution system is put forward here. [Copyright &y& Elsevier]

This paper attempts to address the influence of sugar as a contaminant on outdoor insulation characteristics of insulators in a substation. Strong discharge activity was occurred under relative humidity less than 80% on insulators in a 500 kV substation at south China. A preliminary viewpoint that sugar as a contaminant leads to this strong discharge was drawn by investigating pollution sources around the substation and analyzing pollution layer conditions of discharged insulators. In order to further confirming this viewpoint and proposing the appropriate solutions for avoiding this discharge activity, the outward appearance, the surface conductivity, the discharge inception voltage and the flashover voltage of glass insulator and room temperature vulcanized (RTV) coated insulator under sugary and non-sugary contamination were investigated in detail in the lab. Furthermore, the hydrophobicity and hydrophobicity transference of RTV coated insulator were also investigated. The research results show that sugary contamination is very absorbent and viscous, outdoor insulation characteristics of insulators covered with sugary contamination are worse than that covered with non-sugary contamination, but outdoor insulation characteristics of RTV coated insulator covered with sugary contamination is still better than that of non-RTV coating insulator with non-sugary contamination. So it is still a specific solution to inhibit the discharge activity of insulators in the substation by spraying RTV coating. Of course, removing the sugar canes themselves from this area is the best solution. [ABSTRACT FROM PUBLISHER]

In order to predict the potential of electric energy substitution in the next decade in China, this paper proposes a prediction method based on Logistic curve fitting and improved BP neural network algorithm. The amount of electric energy substitution is defined to quantify the potential of electric energy substitution. Then the important influencing factors of electric energy substitution based on the Impact by Population, Affluence and Technology (IPAT) model are established and quantified. For different influencing factors, logistic curve fitting and polynomial function fitting method were used to estimate the data fitting. A two-node output layer model of BP neural network is established and improved with additional momentum factors and adaptive learning rate to learn and train the data related to electric energy substitution from 2003 to 2017, and calculate the amount of electric energy substitution which are substitution potential from 2018 to 2020, 2025 and 2030. The calculation results show that the method has higher computational accuracy and fewer iterations. The prediction results are reasonable and effective, which can be the reference of the research of energy substitution. [ABSTRACT FROM AUTHOR]

Jinsha River has very abundant hydro power reservation, ranking first in all the hydro power bases of China. To deliver the 38-GW hydro power from Jinsha power stations by HVDC transmission lines to load centers 1000-2000 km away, it is necessary to determine the right voltage level and the capacity of each bipole. This paper proposes three preliminary power delivery scheme and presents an optimization method for transmission capacity, dc voltage and conductor size. Based on a comprehensive comparison of cost-effectiveness, technical feasibility and network security and stability, it was recommended that the 3 bipolar ±800-kV ultra HVDC (UHVDC) links with rated capacity of 6.4 GW for each link be adopted as transmission scheme of Phase I Hydro Power station on Jinsha River. [ABSTRACT FROM AUTHOR]

Abstract: A smart power system demands a strong and self-healing communication system with greater capacity. In China, as the ultra high voltage transmission lines and large scale interconnected grids are expanding throughout the nation, disaster-tolerant communication network is essential for reliable system operation and control. In this paper, we propose a hybrid communication network utilizing both terrestrial and satellite links to improve the system reliability. The adaptive link selection protocol at network layer is developed to facilitate the network integrity. A modification of transport protocol over satellite communication is also proposed to better exploit the limited bandwidth resources. The performance analysis and field trial of the proposed scheme based on the practical network configuration in Sichuan power grid is thoroughly studied. The results showed a great bandwidth saving of satellite resources without loss of network integrity. [Copyright &y& Elsevier]

In China, a special anode design with a button in each stub hole is adopted by many smelters. To investigate the effects of the stub hole button on the anode, numerical simulations of the anode rodding process and the running process of the conventional anode without a stub hole button (design A) and the special design (design B) were conducted. In anode rodding, design B shows worse cooling capacity than design A, while the air gap of design B (0.39 mm to 0.94 mm) is larger than that of design A (0.3 mm to 0.45 mm). During the anode running process, the stub hole button could contact neither the cast iron nor the stub, and the anode voltage drop of design B is 26 mV larger than that of design A because the larger air gap deteriorates the cast iron–carbon contact. In conclusion, the stub hole button should be removed. [ABSTRACT FROM AUTHOR]

Operational data from Chinese railways indicate a number of challenges for traction four-quadrant converter (4QC) control including low-order voltage and current harmonics and reference tracking. A control strategy for a single-phase threelevel neutral-point-clamped 4QC employed in the electric multiple unit traction system is proposed in this study. The strategy is based on a multiple frequency tuned quasi-proportional resonant controller in the ac-side current loop and a multiple frequency tuned notch filter in the dc-link voltage loop. Under the typical supply voltage distortion present in the network, the proposed control strategy improves the current tracking performance and reduces the line current harmonics, when compared with conventional control strategies. Experimental results, both under purely sinusoidal and distorted supply voltages, validate the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

The dc arcing performance of composite insulators with contaminated surfaces has been investigated at high altitudes because of the program of building ±800 kV dc transmission lines in China, because much of their intended routes will be at relatively high altitudes. As the length of the arcs on the composite insulator depends on the repeat distance and the arcs are initiated on the core rod between the sheds, the effect of the repeat distance and the shed dimensions on the dc flashover voltages was studied for composite insulators under contaminated conditions. The experimental results confirmed that the shed design parameters do have a great influence on the flashover voltages. It was found that, with the same insulation distance, the flashover voltage had a maximum at a particular value of the radial extent of the shed and of the betweenrepeat distance, and that the influence of these two factors on the flashover voltage was independent of each other. It was also found that, for the alternate large and small shed design, the ratio of the radial extent of the major shed to the minor shed should not be too great. [ABSTRACT FROM AUTHOR]

Low-voltage compact gyrotron is under development at the University of Electronic Science and Technology of China (UESTC) for industrial applications. Due to the low operating voltage, the relativistic factor is weak, and interaction efficiency could not be high. Therefore, a magnetron-injection gun (MIG) with an extremely high-velocity ratio α (around 2.5) is selected to improve the interaction efficiency. As beam voltage drops, space charge effects become more and more obvious, thus a more detailed analysis of velocity-ratio α is significant to perform low-voltage gyrotrons, including beam voltage, beam current, modulating voltage, depression voltage, cathode magnetic field, and magnetic depression ratio. Theoretical analysis and simulation optimization are adopted to demonstrate the feasibility of an ultra-high velocity ratio, which considers the space charge effects. Based on theoretical analysis, an electron gun with a transverse to longitudinal velocity ratio 2.55 and velocity spread 9.3% is designed through simulation optimization. The working voltage and current are 10 kV and 0.46 A with cathode emission density 1 A/cm2 for a 75 GHz hundreds of watts' output power gyrotron. [ABSTRACT FROM AUTHOR]

To achieve sustainable social development, the Chinese government conducts electric power substitution strategy as a green move. Traditional fuels such as coal and oil could be replaced by electric power to achieve fundamental transformation of energy consumption structure. In order to forecast and analyze the developing potential of electric power substitution, a forecasting model based on a correlation test, the cuckoo search optimization (CSO) algorithm and extreme learning machine (ELM) method is constructed. Besides, China's present situation of electric power substitution is analyzed as well and important influencing factors are selected and transmitted to the CSO-ELM model to carry out the fitting analysis. The results showed that the CSO-ELM model has great forecasting accuracy. Finally, combining with the cost, policy supports, subsidy mechanism and China's power consumption data in the past 21 years, four forecasting scenarios are designed and the forecasting results of 2019–2030 are calculated, respectively. Results under multiple scenarios may give suggestions for future sustainable development. [ABSTRACT FROM AUTHOR]

A novel high-voltage powerline inspection system was investigated, which consists of the cooperated ground vehicle and drone. The ground vehicle acts as a mobile platform that can launch and recycle the drone, while the drone can fly over the powerline for inspection within limited endurance. This inspection system enables the drone to inspect powerline networks in a very large area. Both vehicle' route in the road network and drone's routes along the powerline network have to be optimized for improving the inspection efficiency, which generates a new Two-Layer Point-Arc Routing Problem (2L-PA-RP). Two constructive heuristics were designed based on "Cluster First, Route Second" and "Route First, Split Second". Then, local search strategies were developed to further improve the quality of the solution. To test the performance of the proposed algorithms, different-scale practical cases were designed based on the road network and powerline network of Ji'an, China. Sensitivity analysis on the parameters related to the drone's inspection speed and battery capacity was conducted. Computational results indicate that technical improvement on the inspection sensor is more important for the cooperated ground vehicle and drone system. [ABSTRACT FROM AUTHOR]