Investigation on the Dielectric Properties of CO2 and CO2-Based Gases Based on the Boltzmann Equation Analysis

In this paper, the dielectric properties of CO2, CO2/air, CO2/O2, CO2/N2, CO2/CF4, CO2/CH4, CO2/He, C02/H2, CO2/NH3 and CO2/CO were investigated based on the Boltzmann equation analysis, in which the reduced critical electric field strength （E/N）cr of the gases was derived from the calculated electron energy distribution function （EEDF） by solv- ing the Boltzmann transport equation. In this work, it should be noted that the fundamental data were carefully selected by the published experimental results and calculations to ensure the validity of the calculation. The results indicate that if He, H2, N2 and CH4, in which there axe high ionization coefficients or a lack of attachment reactions, are added into CO2, the dielectric properties will decrease. On the other hand, air, O2, NH3 and CFa （ranked in terms of （E/N）cr value in increasing order） have the potential to improve the dielectric property of CO2 at room temperature.

Development of Transient Electric Field Radiation Simulation Device during Gas Insulation Switch Operation

In gas insulation switch(GIS)substation,secondary devices such as linemonitoring devices are placed in the switching field,and these electronic devices are vulnerable to transient electromagnetic interference caused by switching operation.In order to facilitate the measurement and research of electromagnetic disturbance data under different working conditions,a simulation test device is developed in this paper,which can be used to simulate electromagnetic disturbance of GIS substation sensor and secondary device port under switch operation.A four-channel parallel gas switch was designed,and the main characteristic parameters of electromagnetic disturbance generated by the simulation device were measured by using high-frequency pulse power supply as the excitation source.The comparison between the measured waveform and the measured disturbance characteristic parameters of GIS substation shows that it is in good agreement with the measured waveform characteristics,conforms to the basic characteristics of damped oscillation wave,and can be used in the secondary equipment port disturbance voltage coupling characteristics,protection measures evaluation and assessment method research.

Current Situation of Power Development in the World and Its Enlightenment to China's Power Industry

Based on a detailed analysis of China's current power installed capacity,power generation,power structure,as well as the world's power installed capacity,power generation,power structure,and power regional distribution,some policy suggestions have been put forward through objective analysis and comparison.Firstly,power sectors in China should develop from high-speed growth to high-quality development,digest power excessive production capacity,control newly-added production capacity absolutely,and control the construction of power points orderly according to power planning.Secondly,non-fossil energy power generation needs to develop energetically,and should attach great importance to biomass power generation,in addition to gas power generation,wind power,and solar power.Lastly,on the basis of building a moderately prosperous society in all respects,electricity consumption per capita should be improved in the high-quality development stage in China,and the development of energy conservation and emission reduction,renewable energy,and distributed energy and so on should be considered collaboratively.

Re-understanding and Thinking about Environmental Impact of Coal-fired Power Plants under Ultra-low Emission

From the perspective of development background,concepts and related policies of ultra-low emission,according to work practice,some issues and difficulties that need to be paid attention to in the environmental impact assessment of ultra-low-emission thermal power projects were discussed from the aspects of evaluation criteria,evaluation grade and scope,pollution control technical lines,environmental benefit accounting,and total emission control,and corresponding recommendations were put forward.

Study on Flow Field Simulation at Transmission Towers in Loess Hilly Regions Based on Circular Boundary Constraints

When using high-voltage transmission lines for energy transmission in loess hilly regions,local extreme wind fields such as turbulence and high-speed cyclones occur from time to time,which can cause many kinds of mechanical and electrical failures,seriously affecting the reliable and stable energy transmission of the power grid.The existing research focuses on the wind field simulation of ideal micro-terrain and actual terrain with mostly single microterrain characteristics.Model boundary constraints and the influence of constrained boundaries are the main problems that need to be solved to accurately model and simulate complex flow fields.In this paper,a flow field simulation method based on circular boundary constraints is carried out.During the study,the influence of the model boundary and the selection conditions of themodeling range are systematically analyzed.It is more suitable to make sure that the air domain is 4 times higher than the height of the hill undulations,in addition to ensuring that there should be a minimum of 400 m between the study region and the boundary.Then,an actual terrain model of a power grid line in Shanxi is established,through the method proposed in this paper,the wind speed at the location of the transmission tower line under different wind directions is analyzed,and it is found that when the incidence direction is 45 degrees north by east the wind speed is the highest.The findings demonstrate that the circular boundary model has the advantage of more easily adjusting the wind incidence direction,in addition to theoretically reducing the errors caused by traditional models in boundary processing.It can accurately obtain the distribution characteristics of the flow field affected by the terrain,and quickly screen out the extreme working conditions that are most harmful to the transmission lines in the actual transmission line for energy transmission in complex loess hilly regions.

Stress Concentration Effect in Interface Between Conductor and Epoxy Resin in Coaxial Components of Power Equipment

The spacer used in gas insulated switchgear(GIS)plays a vital role in its safe operation.The mismatch of mechanical properties between conductor and insulating material in spacers results in stress concentration at the interface between them.During a hydrostatic test,mechanical damages are often initiated from the interface.In this paper,the stress between aluminum conductors and epoxy resin is studied by using a simplified coaxial structure specimen.The measurement system and finite element simulation are used to explore the generation of stress and strain during curing and shrinkage.The real-time measurement of strain at the interface shows that the residual strain in the entire process is primarily generated during the cooling stage.Consequently,the temperature and stress/strain distribution at the interface during the cooling stage are further studied,and combined with experiments and simulations.The consistency between the finite element simulation and the experimental measurement results verifies the validity of the simulation method used.The results show that the maximum of the first principal stress generated during the cooling stage of the production process is concentrated on the upper and lower edges of the interface which is critical to the impact of the production quality of the spacer.

Thermodynamic and Transport Properties of Real Air Plasma in Wide Range of Temperature and Pressure

Air plasma has been widely applied in industrial manufacture. In this paper, both dry and humid air plasmas＇ thermodynamic and transport properties are calculated in temperature 300 100000 K and pressure 0.1-100 atm. To build a more precise model of real air plasma, over 70 species are considered for composition. Two different methods, the Gibbs free energy minimization method and the mass action law method, are used to deternfinate the composition of the air plasma in a different temperature range. For the transport coefficients, the simplified Chapman-Enskog method developed by Devoto has been applied using the most recent collision integrals. It is found that the presence of CO2 has almost no effect on the properties of air plasma. The influence of H2O can be ignored except in low pressure air plasma, in which the saturated vapor pressure is relatively high. The results will serve as credible inputs for computational simulation of air plasma.

Properties of vacuum cast CuCr25 and CuCr25Te contact material

The CuCr25 and CuCr25Te contact materials were manufactured by vacuum casting process.The microstructures of two alloys were observed by metallographic microscope,the electrical conductivity,density and hardness were measured.The tensile test was done by universal testing machine while the fractography was observed by SEM,the breaking current tests were carried out in Weil Synthetic Circuit with arc-igniting branch in Xi’an Jiaotong University.The results show that the microstructures and physical parameters change after adding Te element.The tensile strength decreases and the toughness turns bad,which is propitious to improve the anti-welding property.But the breaking current capacity of CuCr25Te alloy is inferior to CuCr25 alloy.Thus,adding Te element has both advantages and disadvantages on main properties of CuCr contact material.

Energetics characteristics accounting for the low-level wind’s rapid enhancement associated with an extreme explosive extratropical cyclone over the western North Pacific Ocean

During mid-January 2011,a rarely seen twin-extratropical-cyclone event appeared over the western North Pacific Ocean.One of the twin cyclones developed into an extreme explosive extratropical cyclone(EEC),which was comparable to the intensity of a typhoon.Rotational and divergent wind kinetic energy(KE)analyses were applied to understand the low-level wind’s rapid enhancement associated with the cyclone.It was found that:(i)the total wind KE associated with the EEC showed a remarkable enhancement in the lower troposphere during the cyclone’s maximum development stage,with the maximum/minimum wind acceleration appearing in the southeastern/northwestern quadrant of the EEC;(ii)the rotational wind KE experienced an obvious increase,which corresponded to the total wind KE enhancement,whereas the divergent wind KE,which was much smaller than the rotational wind,mainly featured a decreasing trend;(iii)the rotational wind KE enhancement showed variational features consistent with the horizontal enlargement and upward stretching of the EEC;(iv)the nonorthogonal wind KE enhanced the total wind KE in regions with strong rotational wind,which resulted in the maximum lower-tropospheric maximum wind,whereas in regions with strong divergent wind it mainly reduced the total wind KE;(v)the northward transport of total wind KE and the rotational wind KE production due to the work done by pressure gradient force were dominant factors for the enhancement of winds associated with the EEC,particularly in its southeastern section.In contrast,an overall conversion from rotational wind KE to divergent wind KE decelerated the rotational wind enhancement.

Research on Operation of Electrothermal Integrated Energy System Including Heat Pump and Thermal Storage Units Based on Capacity Planning

In view of the Three North areas existing wind power absorption and environment pollution problems,the previous scholars have improved the wind abandon problem by adding electrothermal coupling equipment or optimizing power grid operation.In this paper,an electrothermal integrated energy system including heat pump and thermal storage units was proposed.The scheduling model was based on the load data and the output characteristics of power units,each power unit capacity was programmed without constraints,and the proposed scheduling model was compared with the traditional combined heat and power scheduling model.Results showed that the investment and pollutant discharge of the system was reduced respectively.Wind power was fully absorbed.Compared with the traditional thermal power unit,the proportion of the output was significantly decreased by the proposed model.The proposed system could provide a new prospect for wind power absorption and environment protection.

电池衰减诊断及状态评估研究进展

锂离子电池(LIB)广泛应用于储能及动力输出等领域.准确预测电池的健康状态对于优化性能、降低运营费用和防止电池故障等方面具有重要的意义.本文对预测LIB的荷电状态(SOC)、健康状态(SOH)和剩余使用寿命(RUL)方面的最新发展进行了全面回顾,重点关注机器学习技术方面的研究进展,深入分析了LIB的退化机制及其基本理论,评估了各种传统方法及机器学习技术在预测SOC,SOH和RUL方面的优势和限制.此外,还探讨了电动汽车动力电池在实际应用中面临的挑战,特别是性能退化问题.最后提出了对LIB未来研究方向有价值的见解.尽管机器学习方法在提高预测SOC,SOH和RUL准确性方面具有巨大潜力,但在实际应用中仍然有许多技术和实际障碍需要克服.

A fuse-based DC circuit breaker with vacuum interrupter enhanced by an external transverse magnetic field

Due to the increasing power system capacity,the interruption of large fault currents has gradually become a major challenge in power systems.At the moment,such currents are interrupted mainly via circuit breakers based on the method of active current commu-tation.However,these types of circuit breakers tend to be costly and oversized.One possible alternative—a fuse-based circuit breaker with current commutation process enhanced by an external transverse magnetic field(ETMF)—is proposed by the authors.Its main advantage lies in the fast current commutation achieved by an ETMF-enhanced three-stage increase of the vacuum arc voltage.The study of the current commutation process is mainly represented by the authors,and the influencing factors of the current commutation—contact opening speed and ETMF current—are discussed.At last,the proposed circuit breaker is verified by an experiment,whose results show that a short-circuit current of 42 kA can be interrupted within just 2 ms.

Wind power prediction based on variational mode decomposition multi-frequency combinations

Because of the uncertainty and randomness of wind speed, wind power has characteristics such as nonlinearity and multiple frequencies. Accurate prediction of wind power is one effective means of improving wind power integration. Because the traditional single model cannot fully characterize the fluctuating characteristics of wind power, scholars have attempted to build other prediction models based on empirical mode decomposition(EMD) or ensemble empirical mode decomposition(EEMD) to tackle this problem. However, the prediction accuracy of these models is affected by modal aliasing and illusive components. Aimed at these defects, this paper proposes a multi-frequency combination prediction model based on variational mode decomposition(VMD). We use a back propagation neural network(BPNN),autoregressive moving average(ARMA)model, and least square support vector machine(LS-SVM) to predict high, intermediate,and low frequency components,respectively. Based on the predicted values of each component, the BPNN is applied to combine them into a final wind power prediction value.Finally,the prediction performance of the single prediction models(ARMA,BPNN and LS-SVM)and the decomposition prediction models(EMD and EEMD) are used to compare with the proposed VMD model according to the evaluation indices such as average absolute error, mean square error,and root mean square error to validate its feasibility and accuracy. The results show that the prediction accuracy of the proposed VMD model is higher.

Multi-objective interval prediction of wind power based on conditional copula function

Interval prediction of wind power,which features the upper and lower limits of wind power at a given confidence level,plays a significant role in accurate prediction and stability of the power grid integrated with wind power.However,the conventional methods of interval prediction are commonly based on a hypothetic probability distribution function,which neglects the correlations among various variables,leading to the decrease of prediction accuracy.Therefore,we improve the multi-objective interval prediction based on the conditional copula function,through which we can fully utilize the correlations among variables to improve prediction accuracy without an assumed probability distribution function.We use the multi-objective optimization method of nondominated sorting genetic algorithm-II(NSGA-II)to obtain the optimal solution set.The particular best solution is weighted by the prediction interval average width(PIAW)and prediction interval coverage probability(PICP)to pick the optimized solution in practical examples.Finally,we apply the proposed method to three wind power plants in different cities in China as examples forvalidation and obtain higher prediction accuracy compared with other methods,i.e.,relevance vector machine(RVM),artificial neural network(ANN),and particle swarm optimization kernel extreme learning machine(PSO-KELM).These results demonstrate the superiority and practicability of this method in interval prediction of wind power.

Faulty Feeder Identification and Fault Area Localization in Resonant Grounding System Based on Wavelet Packet and Bayesian Classifier

Accurate fault area localization is a challenging problem in resonant grounding systems(RGSs).Accordingly,this paper proposes a novel two-stage localization method for single-phase earth faults in RGSs.Firstly,a faulty feeder identification algorithm based on a Bayesian classifier is proposed.Three characteristic parameters of the RGS(the energy ratio,impedance factor,and energy spectrum entropy)are calculated based on the zero-sequence current(ZSC)of each feeder using wavelet packet transformations.Then,the values of three parameters are sent to a pre-trained Bayesian classifier to recognize the exact fault mode.With this result,the faulty feeder can be finally identified.To find the exact fault area on the faulty feeder,a localization method based on the similarity comparison of dominant frequency-band waveforms is proposed in an RGS equipped with feeder terminal units(FTUs).The FTUs can provide the information on the ZSC at their locations.Through wavelet-packet transformation,ZSC dominant frequency-band waveforms can be obtained at all FTU points.Similarities of the waveforms of characteristics at all FTU points are calculated and compared.The neighboring FTU points with the maximum diversity are the faulty sections finally determined.The proposed method exhibits higher accuracy in both faulty feeder identification and fault area localization compared to the previous methods.Finally,the effectiveness of the proposed method is validated by comparing simulation and experimental results.

Heuristic Benders Decomposition Efficiency Improvement for SCUC

The Benders Decomposition method is widely used to manage large-scale problems in power system optimization.In this paper,a simple but effective method is proposed to improve the Benders Decomposition efficiency using the security constrained unit commitment(SCUC)problem as an example.The heuristic weights are introduced for constraint violations to accelerate their elimination,and thereby improving the Benders Decomposition efficiency.The validity of the proposed method is verified through case studies on multiple IEEE test systems.