Severity indices for contingency screening in dynamic securityassessment

At present, the computational requirement for dynamic security assessment (DSA) is a hurdle for a comprehensive on-line DSA to be implemented in energy management systems. In addition to faster time domain solutions, novel approaches and techniques are being developed for contingency screening and remedial actions. This paper describes one such development in the area of contingency screening which can be seen as an extension of techniques developed over the years for static security analysis. Some new concepts and methods are suggested for both contingency ranking and contingency classification (stable/unstable). Results from realistic test systems illustrate the capabilities and performance of the new approach     

An online power system static security assessment module using multi-layer perceptron and radial basis function network

Efficient contingency screening and ranking method has gained importance in modern power systems for its secure operation. This paper proposes two artificial neural networks namely multi-layer feed forward neural network (MFNN) and radial basis function network (RBFN) to realize the online power system static security assessment (PSSSA) module. To assess the severity of the system, two indices have been used, namely active power performance index and voltage performance index, which are computed using Newton–Raphson load flow (NRLF) analysis for variable loading conditions under N − 1 line outage contingencies. The proposed MFNN and RBFN models based PSSSA module, are fed with power system operating states, load conditions and N − 1 line outage contingencies as input features to train the neural network models, to predict the performance indices for unseen network conditions and rank them in descending order based on performance indices for security assessment. The proposed approaches are tested on standard IEEE 30-bus test system, where the simulation results prove its performance and robustness for power system static security assessment. The comparison of severity obtained by the neural network models and the NRLF analysis in terms of time and accuracy, signifies that the proposed model is quick, accurate and robust for power system static security evaluation for unseen network conditions. Thus, the proposed PSSSA module implemented using MFNN and RBFN models are found to be feasible for online implementation.     

模糊子集和Taylor级数相结合的快速事故筛选方法

为避免在暂态稳定分析中稳定与不稳定状态的漏报,文中结合模糊子集理论和高阶Taylor级数,提出了一种用于在线暂态安全分析的快速事故筛选方法。该方法首先定义了7种 反映事故严重程度的性能指标,并把它们作为模糊隶属函数的组合特征输入量,然后通过多 元 多变量的模糊隶属函数,产生一个能够指示相对稳定裕度的连续分布的暂态稳定指标。基于这个连续分布的稳定指标,可为运行人员提供3条带,即“绝对”稳定带（稳定指标大）、“绝 对 ”不稳定带（稳定指标小）、“模糊”带（稳定指标处于中间值,即稳定与不稳定边界地带 ）,有了这3条带,就可对预想事故进行快速的暂态稳定识别。计算仿真结果表明了该方法 的快速性、可靠性和有效性。     

基于概率不安全指标的实时故障筛选策略

为了解决电力系统面临的故障筛选问题,提出了一种改进的故障筛选策略。利用动态安全域的分析方法,结合实用概率不安全指标作为对故障筛选排序的依据,将致命性故障与非致命性故障分别建模,以故障可能造成的损失作为目标函数进行排序。分析多种故障分类下系统面临的不同情况,综合考虑全局概率分布,通过权值控制反映系统安全性指标,通过目标函数反映经济性指标,采用离线计算在线应用的方式得到故障综合筛选情况。采用IEEE10机39节点系统算例进行验证性排序,结果符合事实依据,该方法鲁棒性好,对实际故障隐患的处理指导性强。     

在线动态安全评估中事故扫描的综合性能指标法

事故扫描可以大大减少需分析的预想事故数目,是在线动态安全评估的重要组成功能.文章定义了反映事故严重程度的多个性能指标,并综合这些性能指标提出了以滤除电力系统的不严重事故为目标的事故扫描的综合性能指标法.该方法滤除系统不严重事故的准确性较高,计算速度快,可以满足在线动态安全评估快速性的要求.     

ANN及FFT技术用于电力系统预想事故分析

本文开发了一种基于人工神经元网络和快速付里叶变换技术进行预想事故快速选的方法。利用快速解耦潮流计算的迭代一次法分别构造了反映预想事故严重程度的有功性能指标ＰＩｐ和无功性能指标ＰＩｖ,同是还构造了一个多层感知型神经元网络并用ＢＰ算法加以训练。     

基于统计学习的模糊暂态稳定事故筛选与排序

暂态稳定事故筛选与排序的目的是针对一组预想事故集合挑选出严重事故或滤除掉无害事故,以减少待分析的预想事故数目,满足在线动态安全分析的需要.文中提出一种基于统计学习的模糊暂态稳定事故筛选与排序方法,该方法采用了反映事故严重程度的10个性能指标,并通过样本学习,在每个指标集合上具体定义了系统稳定性的模糊隶属度函数;然后综合运用这10个性能指标的稳定性模糊隶属度得到的平均稳定性模糊隶属度,对预想事故集合按严重性进行了排序;接着根据排序结果,结合所设定的稳定阈值,将无害事故过滤掉.最后,用新英格兰10机39节点网络验证了该方法的有效性.     

基于灰色关联分析法的电压稳定故障筛选与排序

故障筛选与排序是电力系统电压稳定评估的重要部分。针对以往基于潮流计算筛选方法的单一性,提出了一种新的故障筛选与排序方法。首先结合感应电动机特性、负荷大小、电源支撑及输电线路情况构建一套故障筛选指标体系;其次针对单一指标反映故障严重程度的局限性,采用灰色关联分析法计算综合指标,综合多方面因素评估故障严重程度。采用存在电压稳定问题的实际电网数据对所提方法进行验证,结果表明基于灰色关联分析法的电压稳定故障筛选与排序方法是合理和有效的。     

电网在线暂态电压安全分析的降维方法

近年来,随着中国可再生能源的发展以及交直流混联电网的形成,电力系统暂态电压安全问题越来越突出。对于大电网进行在线暂态电压安全分析十分必要,但因存在维数灾问题导致其在线应用困难。关键挑战在于需要处理高维电压时序轨迹(时间维)、大量预想故障(故障维),以及众多节点和无功设备(空间维)。传统的无功电压分区方法无法应对以上挑战。为此,提出了一种面向暂态电压安全分析的降维方法,包括基于高维电压时序轨迹的暂态电压安全性量化评估方法、面向大量预想故障的代表性严重故障筛选方法,以及故障相依的动态电压分区方法。这3种关键方法分别从时间、故障和空间维度对原问题进行降维。基于IEEE 39节点系统和实际电网模型的仿真验证了所提方法的可行性和有效性。     

基于风险的电力系统安全预警的预防性控制决策分析

针对事故发生的可能性和严重性进行电力系统安全分析的风险评估,将基于风险的安全性评估指标应用到电力系统安全预警中定量分析电力系统的运行状态转换风险,并进行电力系统预防性控制研究.根据系统低电压风险指标、系统过负荷风险指标和系统电压失稳风险指标3种风险指标综合表征的系统安全等级,在事故发生前进行预防性控制决策分析,以灵敏度确定参与决策的关键节点,用遗传算法确定参与决策的节点的最优有功和无功的注入量,从而有效地降低电网的运行风险,提高电网的安全预警等级.以上海电网84节点系统的仿真表明算法的可行性和有效性.     

Supervised learning approach to online contingency screening and ranking in power systems

This paper proposes a supervised learning approach to fast and accurate power system security assessment and contingency analysis. The severity of the contingency is measured by two scalar performance indices (PIs): Voltage-reactive power Performance Index, PI_VQ and line MVA Performance Index, PI_MVA. In this paper, Feed-Forward Artificial Neural Network (FFNN) is employed that uses pattern recognition methodology for security assessment and contingency analysis. A feature selection technique based on the correlation coefficient has been employed to identify the inputs for the FFNN. The effectiveness of the proposed methodology is demonstrated on IEEE 39-bus New England system at different loading conditions corresponding to single line outage. The overall accuracy of the test results for unknown patterns highlights the suitability of the approach for online applications at Energy Management Center.     

A METHODOLOGY OF SECURE AND OPTIMAL OPERATION OF A POWER SYSTEM FOR DYNAMIC CONTINGENCIES

ABSTRACT

Just as in static security constrained optimization of power systems, there is need to do preventive scheduling if the system state is found to be insecure through dynamic contingency analysis. Current work in this area based on energy functions and sensitivity considerations only computes another feasible and normal operating point either through the controlling u.e.p or the potential energy boundary surface method. In this paper we use the hybrid method which involves integration of the system equations only once till the controlling u.e.p is reached to compute the energy margin. Based on the sensitivity of the energy margin to generation powers, rescheduling is done through an OPF algorithm resulting in a secure but optimal solution. Results on a 3 machine, 9 bus system are very encouraging. This methodology could form a basis for integrating current OPF packages into the DSA package.     

A coherency based rescheduling method for dynamic security

For on-line dynamic security analysis, the preventive control or remedial action should be an integral part of the function if instability for a contingency is detected. Research done so far in on-line remedial action has been in rescheduling generation and most of the suggested methods for determining such preventive control use the sensitivities of the stability energy margin to the generator power injections. In this paper, a new coherency based sensitivity method is proposed for generation rescheduling. Different coherency indices have been defined and then compared by ranking the contingencies according to these indices as well as the energy margin index. Since the coherency indices are always functions of the rotor angles, the sensitivity trajectories of a coherency index, such as the most critical rotor angle, with respect to changes of generation can be calculated at every time step of the integration process. This paper suggests that these sensitivities calculated shortly after fault clearing be used for rescheduling the generation. The calculation of these sensitivities are obviously faster than the calculation of the energy margin sensitivities. This paper also shows, with test results using several different systems, that the rescheduling achieved by this method provides the necessary remedial action. It is also noted that this method is intuitively more direct as it uses the sensitivities of the worst affected generator angles for rescheduling     

配电网安全性指标的研究

该文从配电网供电安全性出发，在K（N-1 1）安全性准则的基础上，通过比较配电网和输电网的差异，指出配电网静态安全分析需要不同于输电网的安全性指标和分析方法。以此为前提提出了事故后果严重程度指标，并在此基础上进一步提出系统网架结构强弱指标和系统整体安全性指标，作为配电网静态安全分析的基础。文中还对指标的应用进行了探讨，并利用算例对安全性存在差异的系统的各项安全性指标进行了计算、分析和比较。算例表明文中提出的配电网安全性指标是可行的。它能够定量地刻画事故后果的严重程度，准确地反映系统安全性的高低，为配电网静态安全分析奠定了基础。     

Calculation of weighting factors of static security indices used in contingency ranking of power systems based on fuzzy logic and analytical hierarchy process

Contingency screening and ranking is one of the most important issues for security assessment in the field of power system operation. The objective of contingency ranking is to quickly and accurately select a short list of critical contingencies from a large list of potential contingencies and rank them according to their severity. Then suitable preventive actions can be implemented considering these contingencies that are likely to affect the power system performance. In this paper a novel approach is presented for contingency ranking based on static security assessment. This method employs weighted performance index with the application of fuzzy logic based analytical hierarchy process in order to select appropriate weighting factors to be imposed. The proposed method is applied to IEEE 30 bus system and the results are presented.     

Fast real power contingency ranking using counter propagation network: feature selection by neuro-fuzzy model

In deregulated operating regime power system security is an issue that needs due consideration from researchers in view of unbundling of generation and transmission. Real power contingency ranking is an integral part of security assessment. The objective of contingency screening and ranking is to quickly and accurately shortlist critical contingencies from a large list of credible contingencies and rank them according to their severity for further rigorous analysis. In the present work, modified counter propagation network (CPN) with neuro-fuzzy (NF) feature selector is used for real power contingency ranking of the transmission system. The CPN is trained to estimate the severity of a series of contingencies for given pre-contingencies line-flows. But for larger size system it becomes rather difficult to cope with the increased size of input pattern and network as well. And it adversely affected the performance of the network and computational overhead. The proposed NF feature selector prunes the size of input pattern by exploring the individual power of features to characterize/discriminate different clusters. The reduced set of discriminating inputs not only ensures saving in training time but also improves estimation accuracy and execution time and these are the deciding parameters in evaluating the performance of particular contingency ranking technique. The effectiveness of proposed approach is demonstrated on IEEE 30-bus test system and practical 75-bus Indian system.     

A corrective control for angle and voltage stability enhancement onthe transient time-scale

This paper deals with the development of a nonlinear programming methodology for evaluating load shedding (LS) as a corrective action to improve the dynamic security of power systems when angle or voltage instability is detected. A centralized corrective control is developed, on the basis of online DSA computations, in order to ensure corrective actions when a threatening contingency actually occurs. The algorithm is implemented and tested on the actual Italian grid managed by ENEL S.p.A     

基于时间裕度的全局电力系统暂态安全风险评估

利用预想事故的时间裕度和发生概率定义了预想事故的风险指标，并定义了度量系统在特定类型事故集合下的暂态安全风险指标，然后据此提出了一种对系统进行暂态安全评估的方法。该方法使得将某类型预想事故的评价结果联合起来评估全系统在该类型预想事故集合下的暂态安全性成为可能。计算实例验证了该方法的有效性。     

基于EMS的动态安全分析系统

描述了在线动态安全分析(DSA)系统设计中的几个重要方面,包括预想事故集的构造、电力系统实时状态的获取和抽象、动态安全分析算法的选取、动态安全分析开放式平台的研究。为快速分析系统运行模式,设计了可涵盖所有类型故障、可任意设置故障发生序列和故障切除规则的预想事故集。阐述了在线DSA系统的构造方案,并给出了基于该DSA平台的实际电网算例。     

On-line preventive control for power system transient stability based on the energy function method

For the purpose of maintaining the power system security, an integrated security monitoring and control (ISMAC) system, is being developed in which both preventive and emergency control have important roles. Static security control strategies which deal with the steady state after the contingency is cleared, have been studied by various researchers including the authors. However, the basic research on dynamic security control which deals with the transient state immediately after the contingency has occurred is seldom found. This paper presents a method of dynamic preventive control for the transient stability considering plural contingencies and coordinating in a flexible way the requirements of both security and economy. In the preventive control for transient stability, it is necessary to judge the transient behaviors properly and also to evaluate the security quantitatively for a postulated contingency. The authors define a security index which represents absorbing capacity of post-fault kinetic energy based on the energy function method. The index has these advantages: it is possible to calculate values rapidly; and physical meanings are easily understood. The effectiveness of the proposed method is ascertained through numerical examples for model power systems.