Operational concepts of HVDC in the context of security assessment in the German transmission grid

Because of the realization of HVDC connections parallel to the synchronous grid in Germany, operational concepts become more important in the context of system security aspects. In this article commonly known concepts are analyzed regarding their suitability for the German transmission system. Therefore, an approach for the analysis was developed and exemplary results are given using this approach. Under consideration of the overall system, the concepts of reducing losses in combination with minimizing(n-1)-warnings or-indications^1 as well as the sole minimization of(n-1)-warnings and-indications are the most reasonable approaches. However, under grid security aspects best results can be achieved by reducing operational limits and therefore, by the minimization of(n-1)-warnings.

Combined hybrid energy storage system and transmission grid model for peak shaving based on time series operation simulation

This study proposes a combined hybrid energy storage system(HESS) and transmission grid(TG) model, and a corresponding time series operation simulation(TSOS) model is established to relieve the peak-shaving pressure of power systems under the integration of renewable energy. First, a linear model for the optimal operation of the HESS is established, which considers the different power-efficiency characteristics of the pumped storage system, electrochemical storage system, and a new type of liquid compressed air energy storage. Second, a TSOS simulation model for peak shaving is built to maximize the power entering the grid from the wind farms and HESS. Based on the proposed model, this study considers the transmission capacity of a TG. By adding the power-flow constraints of the TG, a TSOS-based HESS and TG combination model for peak shaving is established. Finally, the improved IEEE-39 and IEEE-118 bus systems were considered as examples to verify the effectiveness and feasibility of the proposed model.

A Brief Introduction to Features of Equipment and operating Condition of 500 kV Transmission Lines and Substations in Northeast China Electric Power Network

This article introduces the features ofequipment and operating condition of 500kV transmission lines and substations inNortheast China Electric Power Networkfrom the operation Point of view. The operatingand technical levels of domestic equipment arethe focus of discussion in the article.

EIGENFUNCTION EXPANSION FOR STURM-LIOUVILLE PROBLEMS WITH TRANSMISSION CONDITIONS AT ONE INTERIOR POINT

The purpose of this article is to extend some spectral properties of regular Sturm- Liouville problems to the special type discontinuous boundary-value problem, which consists of a Sturm-Liouville equation together with eigenparameter-dependent boundary conditions and two supplementary transmission conditions. We construct the resolvent operator and Green＇s function and prove theorems about expansions in terms of eigenfunctions in modified Hilbert space L2[a, b].

Research on Evaluating Index of Lightning Protection Safety Performance of High Voltage Overhead Transmission Line

In order to improve the lightning protection performance of transmission lines, lightning protection management has been divided into every tower that lightning protection performance has been evaluated respectively. According to factors such as landform, span, tower type, grounding resistance, isolator type, and so on, relative ratio of tripping operation of every tower in the line has been calculated to evaluate its lightning protection safety performance, it is beneficial to operation maintenance and lightning reconstruction of transmission lines.

Crack Localization Using Transmissibility of Operational Deflection Shape and Its Application in Cantilever Beam

Due to the nonlinearity of breathing crack, cracked structure under excitation of a single frequency always generates higher harmonic components. In this paper, operational deflection shape (ODS) at excitation frequency and its higher harmonic components are used to map the deflection pattern of cracked structure. While ODS is sensitive to local variation of structure in nature, a new concept named transmissibility of operational deflection shape (TODS) has been defined for crack localization using beam-like structure. The transmissibility indicates the energy transfer from basic frequency to higher frequency. Then, Teager energy operator (TEO) is employed as a singularity detector to reveal and characterize the features of TODS. Numerical and experimental analysis in cantilever beam show that TODS has strong sensitivity to crack and can locate the crack correctly.

Reliability Improvement Strategies for HVDC Transmission System

This paper analyses reliability data of HVDC systems of Southern China Power Grid. The weak links of HVDC systems’ operational reliability are DC control and protection, valve hall and valve cooling system and transmission lines. Some improvement measures and HVDC system reliability technology are proposed in this paper.

Towards Optimal Transmission Switching in Day-Ahead Unit Commitment

Co-optimizing transmission topology with generation dispatch, and leveraging grid controllability could be a viable way to improve economic efficiency of system operations in control centers. In particular, day-ahead unit commitment is a typical business process that electric utilities deploy to ensure enough generation capacity is committed day-ahead to meet the load for the next day. In a market environment, day-ahead reliability unit commitment (DA-RUC) performs a simultaneous solution of minimizing the cost of commitment for resources to meet forecasted load, net scheduled interchange and operating reserve requirements using security constrained unit commitment (SCUC). The commitment may then be further checked by running security constrained economic dispatch (SCED) to verify that the commitment solution can be feasibly dispatched subject to system constraints and activated transmission constraints for each hour identified in the study period. This paper applies Optimal Transmission Switching (OTS) in DA-RUC using some heuristic pre-screening techniques to reduce the dimension of the OTS problem. Various pre-screening methods of candidate transmission lines for switching are proposed and compared. Simulation results will be presented to demonstrate generation dispatch combined with OTS in each hour could reduce congestion cost and significantly lower generation cost.

A Stream Control Transmission Protocol Based OAM System of 3G Cellular Network

OAM (Operations, Administration and Maintenance) system is a very impo rtant component of 3G cellular network. In order to acquire overall managemen t, fast response and steady operation, an SCTP (Stream Control Transmission Prot ocol) based OAM, i.e., SOAM system was proposed. SOAM implements new characters of SCTP such as multi-stream, enforced SACK and heartbeat mechanism on its tran sport layer. These characters help SOAM decrease the message transmission delay and accelerate the link failure detection. Besides, a new component named SOAM agent was introduced to improve the operation efficiency of SOAM. The experim ental results prove the proposed SOAM system achieves better performance on sign aling transmission compared with conventional TCP based OAM system.

Counterformal contacts of full toroidal continuously variable transmission

The point and the line contacts of a toroidal continuously variable transmission (CVT) are studied. The contact shapes between the roller and input and output disks are formulated by using the classical Hertz contact theory. Based on the formulated equations, different system factors affecting the maximum Hertz stress in the elliptical and strip contacts of the full toroidal CVT are explored, which include the properties of the contacting material (Young’s modulus), operating condition (pushing load) and geometrical parameters (aspect cavity ratio, aspect roller ratio). The comparative results reveal the relations between the maximum Hertz stress and the speed ratio in the form of graphs. These graphs give useful information for designer to know the maximum Hertz stress during operation in such systems.

Design of 1000-kV AC Single-Circuit Overhead Transmission Line

The UHVAC 1 000-kV transmission system is so far the one with the most advanced transmission technique applied and highest operation voltage.There are no guidelines or standards available for the design of 1 000-kV overhead transmission line in China.Study on key technologies and design schemes shall be carried out to ascertain the technical principles and construction standards for project construction,which are presented in this paper based on the Southeast Shanxi-Nanyang-Jingmen test and demonstration transmission line.A comparison and analysis of technical data and economic indices between UHV line and other lines are also described.

高质量发展阶段中国货币政策调控方式的转型——研究述评与展望

当前中国正积极探索构建符合中国式现代化的中央银行制度,完善符合国情的宏观调控体系。推动货币政策调控方式适时转变,是促进宏观金融调控同经济高质量发展需要相适应的重要一环。文章从基础货币投放机制、价格型货币政策操作目标、利率调控模式、市场化利率形成机制及传导机制等角度,对中国货币政策调控方式转型的代表性研究进行了系统归纳和总结。与此同时,文章从基础货币注入主渠道的优化方向、操作目标的选择与培育、中国式利率走廊机制的完善、中国式利率市场化的难点及配套改革等方面,对未来可继续深入研究或拓展的方向进行了分析。研究表明,如何推动国债成为未来中国人民银行向市场投放基础货币的主渠道,如何进一步提升DR的市场基准性和流动性、优化DR的统计、发布、监测和评估机制,如何促进中国式利率走廊与公开市场操作实现有机结合,以及如何在恰当的时机取消存款基准利率、系统推进利率市场化进程、建立更加市场化的存贷款FTP机制等问题将是未来研究的重点和难点。

Modal macro-strain identification from operational macro-strain shape under changing loading conditions

To develop modal macro-strain （ MMS ） identification techniques and improve their applicability in a continuous health monitoring system for civil infrastructures, the concept of operational macro-strain shape （OMSS） and the corresponding identification method are proposed under unknown ever-changing loading conditions, and the MMS is then obtained. The core of the proposed technique is mainly based on the specific property that the macro-strain transmissibility tends to be independent of external excitations at the poles of the system and converges to a unique value. The proposed method is verified using the experimental data from a three-span continuous beam excited by an impact hammer at different locations. The identified results are also compared with the commonly used methods, such as the peak- picking （PP） method, the stochastic subspace identification （SSI） method, and numerical results, in the case of unknown input forces. Results show that the proposed technique has unique merits in accuracy and robustness due to its combining multiple tests under changing loading conditions, which also reveal the promising application of the distributed strain sensing system in identifying MMS of operational structures, as well as in the structural health monitoring （SHM） field.

车用高速机电复合传动系统固有振动特性及共振转速研究

车用高速机电复合传动系统(Electro-Mechanical Transmission,EMT)结构高紧凑、零部件高转速,导致系统机电耦合效应显著,易产生共振。针对串联式EMT系统进行机电耦合固有振动特性分析,推导系统的机电耦合固有振动模型,研究其固有频率及模态振型,基于各阶模态的振型特点,总结系统的6种典型振动模式。研究高速运行工况和机电磁耦合效应对系统固有频率和模态振型的影响,并基于坎贝尔图和模态能量法研究宽速域运行范围内系统的共振转速。研究结果表明,机电磁耦合效应改变了系统的低频振动特性,高速运行工况可显著改变系统的某些固有频率,在动力学建模中应对二者进行充分考虑,共振转速研究为系统动力学调控和优化提供了参考。

J-selfadjointness of a class of high-order differential operators with transmission conditions

This paper is to investigate the J-selfadjointness of a class of high-order complex coefficients differential operators with transmission conditions.Using the Lagrange bilinear form of J-symmetric differential equations,the definition of J-selfadjoint differential operators and the method of matrix representation,we prove that the operator is J-selfadjoint operator,and the eigenvectors and eigen-subspaces corresponding to different eigenvalues are C-orthogonal.

Operation Analysis on T&D Equipment in Three Gorges LeftBank Hydropower Station

The paper outlines the Yangtze Three Gorges water conservancy complex. It describes the power transmission and distribution equipment in the Three Gorges LeftBank Hydropower Station, especially large high-voltage distribution devices. It elaborates the measures for suppressing GIS over-voltage and the tests on VFTO, besides technical measures to ensure safety and stability of power system in the station. It also makes some analyses and summaries about the problems encountered in operation of the equipment.

基于多电平变流器模块的直流输电系统控制

为了保证直流输电系统在发生三相短路故障时输电电压的稳定性,有效控制输电系统的运行,该文提出了基于多电平变流器模块(modular multilevel converter,MMC)的直流输电系统运行控制方法。利用反并联二极管与并联电容来设计多电平变流器模块,获得交流等效电感,保证换流站交直流量与有功功率相同,明确换流站内功率情况;将该模块与前馈解耦补偿项相结合,运用PI获得电流内环运行控制器的输入值,实现电流解耦,增强直流电压的稳定控制,提高输电系统抗扰动性能;通过修正与控制环节获得对应参考值,以及最佳运行控制结果。通过实验表明:设计的模块既能保证输电系统在正常工作状态下平稳运行,也能在发生故障时将影响控制在安全范围内,保证电力系统输电稳定。

红外系统对战机的探测性能仿真分析

通过新建战机尾焰的红外辐射椭圆体模型,改进了战机红外辐射的计算方法,并得到了战机在3~5μm波段红外辐射的空间分布曲线。通过对该曲线的分析,发现该战机的红外辐射在机尾和机头各有4个辐射强度相同的极值方向。考虑到臭氧在3~5μm波段内的吸收、地面遮挡红外辐射传输和探测大气层外目标等因素,引入红外辐射大气传输距离概念进一步完善3~5μm波段红外辐射大气传输模型。以归一化探测度不同的2种红外探测器构建的红外系统为例,仿真得到战机的作用距离随探测方向变化的曲线。计算结果表明,红外系统对战机的作用距离极值并不在战机红外辐射极值方向上,且当系统作用距离较远时,大气衰减对作用距离的影响将超过战机红外辐射的影响。

基于凸包算法的极端运行方式提取方法

在电力系统规划与运行的安全稳定计算中,一般选择对安全稳定最不利的运行方式进行校验,但随着新能源渗透率的增加,电网越发复杂多变,人工选择场景主观性较强,针对此问题,提出了一种基于快速凸包算法的极端运行方式提取,从而满足场景选取进行安全校核需求。从电源规划、发输电协调规划两个角度,考虑发电充裕性、火电爬坡需求、网络传输安全3个方面,分析影响规划的极端运行方式;基于凸包算法分别从上述3个方面构建坐标系进行极端运行方式提取;采用中国西北地区电网为算例进行极端运行方式提取,并与基于K-means算法的极端场景提取做对比,结果表明:所提方法能为场景选取提供有效数据支撑,满足电网规划要求。