An evaluation method for power transfer capability enhanced by lightning countermeasures

Various countermeasures are taken against lightning faults in power transmission lines to decrease their occurrence and improve transmission reliability. However, how much they enhance the power transfer capability has not yet been quantitatively evaluated. The conventional deterministic approach, which is widely used in power system planning methodology, is inadequate to deal with this issue. This paper proposes a new method for numerically defining the power transfer capability enhanced by countermeasures against lightning. The proposed method is based on a probabilistic approach in which several fault patterns are taken into consideration with their occurrence frequency and maximum transferable power. This paper also gives an example application of the proposed method to a model trunk transmission system. The effect of a third overhead ground wire on the increase of transfer capability of a 500 kV transmission line has been quantitatively evaluated.     

Economic evaluation of independent power producers viewed from total generating costs of electric power systems

In Japan, electric power utilities purchase electricity from independent power producers (IPPs) through competitive bidding; the IPP evaluation is based on the avoided costs of corresponding generators of utilities. In this evaluation, however, nonpricing factors such as power flow constraints in the electric power system cannot be considered. In this paper, we propose a new approach to evaluate economic impacts of IPPs, the IPP electricity being priced on the basis of total generating costs of the electric power utilities. Such a price to purchase the electricity of IPPs is referred to as the “break‐even cost.” The main results are summarized as follows: 1) Break‐even cost depends on not only the power flow constraints in the system, but also various IPP factors such as generating pattern, location, and capacity, 2) Break‐even cost for the base‐type IPP is higher than the avoided cost of corresponding utility generators, because IPPs located on demand sides can reduce the transmission power loss in the electric power system, 3) Break‐even cost is affected by available capacity of utility generators, especially for the peak‐type IPP generating only during peak demand periods. © 2000 Scripta Technica, Electr Eng Jpn, 133(2): 20–30, 2000     

Development of power system reliability analysis program with consideration of system operation

This paper describes a new program which analyzes the reliability of composite power systems with consideration of power system operational aspects. It uses the sequential Monte Carlo method and calculates annual risk indices for each load point. The program deals with the system problems involved in load flow, voltage, frequency, and small‐signal stability if necessary. The distinctive feature of the program is consideration of power system operation in a sequential manner, such as generation dispatch and system restoration after equipment failure. This makes possible the evaluation of both power system planning and operation from the reliability point of view. Several new methods of reducing calculation time are developed and implemented, including the concurrent LP/load flow method, which improves solvability. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(4): 20–31, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20138     

Decomposition-coordination strategy to improve power transfer capability of interconnected systems

The maximum power transfer across critical corridors or interfaces is limited by various system constraints such as thermal, voltage, and stability limits. In an open transmission access environment, these constraints would be deeply influenced by the interactions among the path flows in different control areas. In particular, small signal stability, commonly in the form of low frequency oscillations, is considered a crucial factor since it limits the power transfer capability of transmission paths in interconnected multi-area systems. Based on such considerations, the focal point of this paper will be a new approach to coordinating the path transfers across multiple control areas, giving exclusive attention to the small signal stability. The differential eigenvalue method is used to derive the damping ratio constraints for satisfying the small signal stability criteria which are linear inequality constraints expressed in terms of the control parameter. Using Bender’s decomposition, the proposed methodology is formulated as a master problem and a set of sub-problems, each associated with one area motivated by the improvement of the overall computational efficiency via parallel processing. The performance of the decomposition-coordination method is illustrated with a 68-bus system from which it might be deduced that inter-area transfer margin could be improved by reasonable rescheduling of the neighboring tie-line flows.     

Study on the principle of contactless electric power transfer via electromagnetic coupling

In recent years, contactless transfer of electric power has received worldwide attention. Among many contactless electric power transmission systems, an electromagnetic resonant system showed a remarkable ability to turn on a 60‐watt light bulb located at a distance of 2 meters from a power source. Several papers that explain principles of the system have been published, but no analytical explanation of these principles has been provided. In this paper, the author provides an analytical explanation of the principle underlying the power transfer system. The analysis can facilitate the evaluation of the system characteristics, such as resonant frequencies, transferable power, efficiency, coil voltages, etc., and may be useful in the synthesis of contactless power transfer systems. Electr Eng Jpn, 182(2): 53–60, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21285 2     

A study of thyristor controlled series capacitor models for power system stability analysis

The thyristor‐controlled series capacitor (TCSC) is promising as a powerful device to increase power transfer capability and transient stability. The basic configuration of the TCSC consists of a series of capacitors connected antiparallel with thyristor‐controlled reactors, so that firing angle control of the thyristors makes the TCSC capable of achieving impedance control in a wide range with quick response. It is important to clarify the relationship between the fundamental reactance of the TCSC and the firing angle of the thyristors, thus leading to practical applications of the TCSC for enhancement of power transfer capability and transient stability in transmission lines. Two relationship equations for the TCSC's fundamental reactance have already been proposed. One is the relationship equation derived from a TCSC circuit whose source is a voltage. The other is the relationship equation derived from a TCSC circuit whose source is a current. For TCSC installed in a transmission line, it is clear which equation is more adequate for analyzing power system stability. In this paper, the authors determine whether either of the equations is valid for analyzing a power system stability.

• 1. In the steady state, the TCSC fundamental reactance is analyzed and compared with the two equations and EMTP. It is clear that the TCSC reactance based on current source is adequate.
• 2. The swing angle of a generator when the firing angle is stepped up is analyzed with EMTP and an analytical model using the TCSC model based on current source. It is shown that the proposed model is effective for power system stability analysis. © 1999 Scripta Technica, Electr Eng Jpn, 129(1): 20–28, 1999

     

混合双馈入高压直流系统最大传输功率控制方法

常规高压直流(LCC-HVDC)与柔性高压直流(VSC-HVDC)落点之间存在电气通路时就构成了混合双馈入高压直流系统。VSC-HVDC系统具有有功、无功功率独立可调的特点,通过调节VSC-HVDC系统输出的有功、无功功率,可以提高在同等受端电网强度下LCC-HVDC系统的功率输送能力。在建立混合双馈入高压直流系统的数学模型和仿真模型的基础上,通过给出求解混合双馈入高压直流系统临界稳定状态的数值解法,分析了混合双馈入高压直流系统在不同受端电网强度下的功率输送能力,总结出调节VSC-HVDC系统输出的有功、无功功率对LCC-HVDC系统功率输送能力的作用规律,并在此基础上根据系统状态参数随受端电网强度的变化规律提出了混合双馈入高压直流系统基于定虚拟点电压控制的最大传输功率控制方法,该控制模式能针对受端电网强度的变化自动调节系统的功率参考值,使得混合双馈入高压直流系统能始终运行在输送最大有功功率的工作状态。     

配电项目最大供电能力及增供电量效益的评估

提出一种配电网供电能力评估方法及配电网项目增供电量效益的预评估方法。基于主变负载率均衡的原则,以变电站负载率为自变量,以系统最大供电能力为目标函数,以主变N-1故障情况下负荷转移不超过变电站之间联络线传输容量以及变压器自身容量裕度为约束条件,构建配电系统最大供电能力评估模型,并提出基于线性规划的求解方法以简化运算。以项目投运前后系统最大供电能力与负荷预测值确定增供电量效益评估模型。既考虑了联络线及变压器容量的充分利用,同时兼顾了变电站负载均衡,保证了系统的安全供电和供电质量;既评估了配电系统最大供电能力,也实现了对配电系统项目增供电量效益的评估。通过实例分析,验证了该模型的有效性。     

提高南方电网交流通道2010年西电东送能力研究

南方电网规划的2010年输电网络虽然可满足送电广东的要求,但仅有7.5%～13%的送电裕度,且"强直弱交"送电形式明显,一旦发生直流故障,大规模功率转移到交流系统,可能使电压崩溃和功角失稳相互耦合,进而破坏整个系统的稳定.研究显示,交流输电通道广西-广东断面的电压支持能力不足对送电能力的限制是决定性的,在交流输电通道的广西-广东断面安装串联补偿、静止无功补偿和新建输电系统等措施都可以改善这种情形,但加装串联电容补偿装置是最好的办法.若在广西-广东断面的4个交流通道均装设串联电容补偿装置,可使西电东送输电通道各断面的送电极限裕度提高到18%～23%.     

含高渗透率间歇性电源的电力网络规划评价体系初探

首先概述了在风电和光电方面发展比较领先的国家在电力系统规划评价方面已取得的成果和经验。然后, 分析了高渗透率间歇性电源并网与电力网络规划之间的相互影响, 并在此基础上对含高渗透率间歇性电源的电力网络规划综合评价指标体系做了初步探索。以传统指标体系为基础,引入了风险评估、接纳间歇性电源最大能力、输电能力、间歇性电源可置信容量及污染物减排量等指标, 来评估间歇性可再生能源规模化并网后的网络规划方案的经济性、供电质量、灵活性、环保性等。最后, 针对巴西南部46节点系统的2个备选网络规划方案对所提评价指标体系做了说明。分析结果表明,间歇性电源接入电力系统的适应程度对电力系统接纳间歇性电源的能力和运行风险具有重要影响, 因此在确定电力网络规划方案时需要在经济性与对间歇性电源并网的适应性方面适当折衷。     

电力系统区域间功率交换能力的研究(一):连续型方法的基本理论及应用

作为电力系统区域间功率交换能力研究的基础,重点介绍了连续型潮流计算方法的数学理论,即非线性系统分析中的参数化连续型数值方法.总结了该方法的原理、算法及其在电力系统中的应用.连续型潮流计算方法与常规潮流计算方法相比,其最大的优点就是可以克服在潮流解曲线鞍型分叉点处由于常规雅可比矩阵奇异而导致的计算困难,这一方法特别适用于最大功率交换能力的求解.     

基于主从递阶决策模型的TRM评估

市场化环境下的电能交易可能引起系统潮流的频繁变化,系统运行不确定性增大,支路过负荷、节点电压越限等故障发生的可能性更大,因此对评估电网功率传输能力提出了更高要求,特别是如何有效评估输电可靠性裕度(TRM),对于电力市场的安全、可靠、经济运行具有重要意义.文中引入至少输电容量的概念,综合考虑了系统中的不确定因素,构建了基于主从递阶决策的TRM双层优化模型,并给出了求解该模型的一种简便、实用的方法.最后通过对IEEE118节点系统进行数据仿真,说明了该模型的合理性和有效性.     

电网规划风险评估工程综合应用研究

阐述了风险评估技术在输电网规划实际工程中的应用,基于输电通道建设时序、网架加强、单一工程对电网风险影响等工程实例进行静态风险分析。通过建立的静态安全最优控制模型和方法,评估“晋、陕、蒙”能源基地不同外送通道建设时序方案的风险水平,以及通道中关键线路可靠性参数变化、通道送电规模变化对系统风险水平的影响;以华中电网某局部500 kV电网为例,量化规划方案风险水平,找出电网的薄弱环节,从降低风险角度判断加强网架的必要性,明确电网建设投资方向;以华东电网1 000 kV环网工程为例,从风险分析的角度,量化分析单一输变电工程投产前后对电网静态风险水平的影响。     

基于系统熵变特征分析的电网关键线路辨识方法

针对电力系统线路故障对系统的冲击与系统对故障消纳的耦合动态行为，提出了基于电力系统熵变特征分析的关键线路辩识模型。定义了考虑系统结构与状态变化特征的电力系统熵变及其数学表达，包括基于线路热稳容量裕度变化情况的线路功率裕度熵变（正熵流）和基于系统对故障冲击能量消纳能力的线路潮流冲击熵（负熵流）；建立了基于系统熵变模型的关键线路辨识思路及流程，并给出了基于后评估检验的线路关键性校验指标。最后，通过IEEE-39节点系统和IEEE-118节点系统仿真计算分析，验证了所提思路和模型的合理性和有效性。     

Formulation, computation and improvement of steady state security margins in power systems. Part II: Results

A steady state security margin for a particular operating point can be defined as the distance from this initial point to the secure operating limits of the system. Four of the most used steady state security margins are the power flow feasibility margin, the contingency feasibility margin, the load margin to voltage collapse, and the total transfer capability between system areas. This is the second part of a two part paper. Part I has proposed a novel framework of a general model able to formulate, compute and improve any steady state security margin. In Part II the performance of the general model is validated by solving a variety of practical situations in modern real power systems. Actual examples of the Spanish power system will be used for this purpose. The same computation and improvement algorithms outlined in Part I have been applied for the four security margins considered in the study, outlining the convenience of defining a general framework valid for the four of them. The general model is used here in Part II to compute and improve: (a) the power flow feasibility margin (assessing the influence of the reactive power generation limits in the Spanish power system), (b) the contingency feasibility margin (assessing the influence of transmission and generation capacity in maintaining a correct voltage profile), (c) the load margin to voltage collapse (assessing the location and quantity of loads that must be shed in order to be far away from voltage collapse) and (d) the total transfer capability (assessing the export import pattern of electric power between different areas of the Spanish system).     

电力改制后的电力工业协调扩容规划

电力市场化改革使得原本垂直一体化的电力工业需要进行统一的协调规划。研究给出了市场条件下考虑用户需求的发、输协调规划投资的数学模型,并对如何求解该数学问题进行了分析说明。在现阶段厂网分开、竞价上网以及建设区域电力市场的环境下,给出了实施电力工业协调扩容规划的若干建议,研究了实施协调规划时需要考虑的机构设置、实施步骤、效益评估以及一些特殊情形的扩容规划。对发展中国家实施电力工业协调扩容有一定参考作用。     

计及FACTS装置的可用输电能力计算

利用功率注入法,建立广义统一潮流控制器(generalized unified power flow controller,GUPFC)和线间潮流控制器(interline power flow controller,IPFC)的数学模型。将GUPFC和IPFC的目标控制约束及运行约束即内部功率平衡约束和考虑等效功率注入模型的潮流约束嵌入到最优潮流计算模型中,得到计及GUPFC和IPFC的可用输电能力(available transfer capability,ATC)计算模型,并利用跟踪中心轨迹内点法对模型进行求解。IEEE-30节点系统的仿真计算显示GUPFC对节点电压和多条线路甚至某一子网络潮流的灵活控制能力及IPFC对线间潮流的合理分配能力;同时验证模型和算法的有效性和可行性。     

Optimal CBM of tie lines between control areas in a deregulated environment

In order to keep power supply reliability at a certain level, electric power utilities have a certain amount of reserve capacity. When no generator outage or no unexpected large power demand occurs, however, the reserve capacity is regarded as surplus facility. To reduce the reserve capacity, some margin is reserved in tie lines between utilities. This margin is called the capacity benefit margin (CBM). In this study, a method of calculating optimal CBM in tie line under deregulated environment is described and two kinds of optimal CBM are proposed. As a result, it is shown how the deregulation affects the optimal CBM by using numerical simulation for the IEE Japan West 30 test system. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(1): 35– 48, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20654     

南方电网西电东送暂态功率传输极限研究

对2005年南方电网的暂态功率传输能力进行了仿真分析以研究各种大扰动条件对西电东送传输功率极限的影响.仿真结果表明,直流线路的单/双极闭锁故障对南方电网暂态功率传输能力的影响相对较小,贵广直流闭锁故障对功率传输的影响最大;交流系统发生单一故障时,合理分配云南和贵州的机组发电功率、适当减少临界机组的发电功率及在某些关键节点加装静止无功补偿装置(SVC)等措施,可以明显提高暂态条件下西电东送的功率传输极限.     

配电系统供电能力的修正计算方法

在评估配电系统供电能力时,基于主变互联关系的供电能力计算方法的结果在一些情况下会产生过量裕度,为此,针对裕度产生的原因,以联络单元负载率矩阵为突破口,在保留原计算方法优势的基础上形成新的配电系统供电能力修正算法。首先搜索联络单元负载率矩阵的全局最小项,并以此为基准来调整同列元素;然后在满足"N 1"校验的前提下将调整过程产生的裕度差额分配到同行各元素,依次遍历矩阵各行之后即完成修正过程;最终,通过某地区实际电网的算例分析,验证了该文中方法能够得到更加准确的计算结果。