Analytical methods for probabilistic short-circuit studies

Probabilistic short-circuit design of substation equipment requires the probability density distribution of short-circuit current magnitudes. This distribution can be calculated for specific systems using Monte Carlo simulation or the analytical methods described in this article. The analytical methods are easily formulated and require much reduced computational effort, although in certain cases these advantages may be offset by a somewhat reduced accuracy of results.     

中性点不接地系统非对称短路故障分析

为提高分布式电源接入配电网的可靠性,以对称分量法为基础,重点分析了中性点不接地系统各种短路故障特性。给出了单相接地短路、两相相间短路、两相接地短路以及各种经过渡阻抗短路时故障点系统电压、电流的变化特性。得出中性点不接地系统两相相间短路与中性点接地系统一致,且不发生中性点漂移。而中性点不接地系统两相接地短路与中性点接地系统两相相间短路一致,但发生中性点漂移。所得结论能够为分布式电源接入配电网后的短路故障分析以及继电保护整定提供理论参考。     

Parallel implementation of probabilistic short-circuit analysis bythe Monte Carlo approach

This paper describes the implementation of a Monte Carlo based short-circuit analysis package in a hypercube parallel computer. The program generates accurate estimates of short-circuit current probability distribution curves which can be used in a variety of planning and design studies. Both network modeling aspects, such as network reduced equivalencing and mutual coupling representation, as well as the impact of the sample sizes used in Monte Carlo simulations are fully analyzed and illustrated by numerical results obtained testing on real-world systems, These examples clearly illustrate how computational efficiency in parallel machines varies with the ratio of communication to computation (communication overhead) and of the load balancing among the parallel computer processors     

一种电网等值分解及短路计算新方法

近年来我国电网规模及复杂性不断增加,现有继电保护离线整定方法已越来越难满足保护性能的要求。随着广域信息测量及电网通信技术的快速发展,继电保护在线整定无疑是解决上述问题的有效措施,而对大型电力系统网络结构及运行方式进行快速短路计算是在线整定技术发展的一项重要前提。首先提出了一种电力系统扰动域划分方法,在此基础上将复杂大电网等值分解为若干小型子网以简化短路及整定计算求解过程,并进一步基于LDU分解法设计了一种采取并行运算的快速短路计算新方法。基于OPENMP并行计算平台的程序计算结果证明了新方法与传统单核串行计算相比运算速度显著提升,为在线整定技术的发展提供了新的思路及解决方案。     

A methodology for probabilistic simultaneous transfer capabilityanalysis

This paper presents a methodology for simultaneous transfer capability analysis based on a probabilistic approach. All areas in a large scale power system are divided into three groups: (a) study area, (b) transfer participating areas, and (c) external areas which have no direct transactions or they have fixed transactions with the study area. A performance index based contingency selection procedure is applied within the study and transfer participating areas to rank those contingencies which will affect simultaneous transfer capability. The contingency ranking order is utilized by a variation of the Wind Chime diagram to selected contingencies which are then evaluated by an optimal power flow algorithm. Subsequently, the probability distribution of simultaneous transfer capability is computed based on the electric load, circuit and unit outage Markov models. The 24×3 bus IEEE RTS is utilized to evaluate the proposed method. The performance of the proposed method is also demonstrated on an actual large scale system (2182 bus, 8 area system)     

Compliance verification and probabilistic analysis of state-wide power quality monitoring data

This paper introduces the implementation and data analysis associated with a state-wide power quality monitoring and analysis system in China. Corporation specifications on power quality monitors as well as on communication protocols are formulated for data transmission. Big data platform and related technologies are utilized for data storage and computation. Compliance verification analysis and a power quality performance assessment are conducted, and a visualization tool for result presentation is finally presented.     

Experimental performance evaluation of a wavelet-based on-linevoltage detection method for power quality applications

This paper evaluates the performance of a wavelet-based, online (real-time) voltage detection scheme for power quality applications. The objectives are: (1) to demonstrate suitability of the proposed method in detecting faults/disturbances in a power system; and (2) to compare its performance with that of a conventional scheme. Two (STS) systems are chosen as frameworks for comparison; a low-voltage laboratory STS setup for which measured results are provided, and a medium-voltage STS system for which detection times are derived based on simulation, using the EMTDC/PSCAD     

A new methodology for determining transmission capacity margin inelectric power systems

The authors define transmission capacity margin, illustrate how the built-in margin method can cause simulation inaccuracy and how this inaccuracy can lead to erroneous analysis, and describe a new approach to implementing margin, referred to as the interpreted margin method, whereby simulation results are interpreted according to a margin criterion. This method requires accurate simulation models, intelligent quantification of margin, and a methodology for determining sufficiency of margin. In addition, terminology is developed that can be used to pursue further discussion of this topic. Although the focus is on margin as it is affected by operating studies, the ideas could also be applied to margin as it is affected by planning studies, recognizing that more uncertainty is associated with planning studies due to the longer time interval between study completion and implementation of recommendations     

A comparative evaluation of new silicon carbide diodes and state-of-the-art silicon diodes for power electronic applications

Recent progress in silicon carbide (SiC) material has made it feasible to build power devices of reasonable current density. This paper presents results including a comparison with state-of-the-art silicon diodes. Switching losses for two silicon diodes (a fast diode, 600 V, 50 A, 60 ns Trr), an ultrafast silicon diode (600 V, 50 A, 23 ns Trr), and a 4H-SiC diode (600 V, 50 A) are compared. The effect of diode reverse recovery on the turn-on losses of a fast insulated gate bipolar transistor (IGBT) are studied both at room temperature and at 150 /spl deg/C. At room temperature, SiC diodes allow a reduction of IGBT turn-on losses by 25% compared to ultrafast silicon diodes and by 70% compared to fast silicon diodes. At 150 /spl deg/C junction temperature, SiC diodes allow turn-on loss reductions of 35% and 85% compared to ultrafast and fast silicon diodes, respectively. The silicon and SiC diodes are used in a boost converter with the IGBT to assess the overall effect of SiC diodes on the converter characteristics. Efficiency measurements at light load (100 W) and full load (500 W) are reported. Although SiC diodes exhibit very low switching losses, their high conduction losses due to the high forward drop dominate the overall losses, hence reducing the overall efficiency. Since this is an ongoing development, it is expected that future prototypes will have improved forward characteristics.     

新能源发电项目多维度后评价方法体系研究

为了客观科学地评价新能源发电项目的性能和效益,建立了将"宏观层面"的综合评价方法与"微观层面"的基本评价方法相结合的"多维度评价方法体系"。在宏观层面上,确立技术性能、经济效益、社会影响三个评价维度,分别采用灰色关联度分析法、数据包络/保证域法、成功度模糊综合评判法进行综合评价。在三个维度评价结果的基础上,采用雷达图法评价项目的总体效果。在微观层面上,针对重要指标评价维度选择对比分析法、比率分析法、因素替换法、曲线拟合法等基本评价方法进行深入分析评价。通过算例验证了所提评价方法体系的实用性和有效性。     

适用于新能源并网变压器匝间故障识别的新判据

为增加功率输送能力,新能源并网变压器采用两电压等级三绕组、接线形式为星角角的变压器。变压器在低压侧发生匝间故障时,差动保护灵敏度不足,同时变压器空载合闸于匝间故障时,涌流闭锁判据会闭锁差动保护,延长故障切除时间。基于星角角接线型式的新能源并网变压器零序等值回路,文中通过建立零序节点电压方程,利用区外故障及匝间故障节点电压方程特征构建匝间故障识别判据,该判据与差动保护原理相比,不受励磁涌流的影响,具有较高的可靠性及速动性。文中利用实时数字仿真系统(RTDS)进行故障仿真,验证新判据的有效性及可靠性,发现采用新判据能够可靠灵敏地识别变压器匝间故障,弥补差动保护的不足。     

基于多重故障和混合仿真算法的风电系统概率短路分析

多重故障、风电并网增加了概率短路计算难度。引入双馈风电机组潮流算法,计及风速不确定性,得到概率短路前初始运行方式。引入多重短路算法,计算节点电压和支路电流的期望、方差以及概率分布。对枚举故障线路进行概率加权,抽样确定其他故障参数,建立混合仿真算法。综合考虑解析枚举和概率抽样特点,提出混合概率仿真方差计算公式。算例分析对比了风电出力波动、双重短路对概率短路计算结果的影响,比较了三序电压和电流的收敛性。研究结果为电气设备选择和电网安全分析提供了参考数据。     

A probabilistic methodology for distributed generation location in isolated electrical service area

Distributed generation unlike centralized electrical generation aims to generate electrical energy on small scale as near as possible to load centers, interchanging electric power with the network. This work presents a probabilistic methodology conceived to assist the electric system planning engineers in the selection of the distributed generation location, taking into account the hourly load changes or the daily load cycle. The hourly load centers, for each of the different hourly load scenarios, are calculated deterministically. These location points, properly weighted according to their load magnitude, are used to calculate the best fit probability distribution. This distribution is used to determine the maximum likelihood perimeter of the area where each source distributed generation point should preferably be located by the planning engineers. This takes into account, for example, the availability and the cost of the land lots, which are factors of special relevance in urban areas, as well as several obstacles important for the final selection of the candidates of the distributed generation points. The proposed methodology has been applied to a real case, assuming three different bivariate probability distributions: the Gaussian distribution, a bivariate version of Freund's exponential distribution and the Weibull probability distribution. The methodology algorithm has been programmed in MATLAB. Results are presented and discussed for the application of the methodology to a realistic case and demonstrate the ability of the proposed methodology for efficiently handling the determination of the best location of the distributed generation and their corresponding distribution networks.     

DC short-circuit analysis for systems with static sources

When calculating available sustained fault currents for DC systems with static converters as sources, the internal resistance of the source must be adjusted based upon the terminal voltage of the source. If the system has a single source, an iterative technique is normally used. However, this becomes cumbersome when solving systems with multiple sources and multiple fault locations. Previous methods have adjusted the resistance of all static sources by a fixed percentage. Methods for providing multiplying factors to adjust the fault contributions of static sources which differentiate between local and remote sources are discussed. Individual multiplying factors for each source may be calculated by means of a formula, or an approximate multiplying factor for all sources may be found by iteration. The multiplying factors are then applied to the results of a single-step matrix solution for the short-circuit currents. This facilitates the use of computer spreadsheet programs for the solution of the problem. It is concluded that the use of a fixed multiplying factor may offer the most conservative solution method     

A new control algorithm of active power line conditioner for improving power quality

In this paper, a new control algorithm for active power line conditioner (APLC) is proposed. The proposed APLC contains two power converters, a series power converter and a shunt power converter. The series power converter is operated as a current source, and it has the function of a harmonic isolation to block the harmonic current from the nonlinear load to mains and the harmonic voltage from the mains to load. The shunt power converter is operated as a voltage source to supply a clean and regulated output voltage to the load. Both power converters use the same dc bus. To demonstrate its performance, a prototype is developed and tested. The tested results show that the proposed APLC has the expected performance.     

一种新的UPFC潮流计算模型

以往的统一潮流控制器UPFC(Unified Powernow Controller)的潮流计算模型要用到牛顿一拉夫逊法进行迭代求解，需要重新编制与之相应的潮流计算程序，因此费时费力。现提出一种新的UPFC等值模型，该模型适合利用已有的商业软件计算潮流，无需因为UPFC加入系统而重新编制潮流程序，因而可以大大减少工作量。该模型的主要设计思想是将系统中的UPFC用注入功率和恒定电压等值表示，从而将UPFC从等值网络中移去。该模型分为两部分，第一部分适用于UPFC的控制方式1和方式2，第二部分适用于控制方式3和方式4。一个IEEE—9节点的算例验证了该模型的有效性。     

A new methodology for the identification of PD in electrical apparatus: properties and applications

Applications of a new methodology, aimed at the identification of defects occurring in insulation systems of HV apparatus and based on partial discharge (PD) measurements, are presented in this paper. This methodology relies upon the digital acquisition of a large amount of PD pulses and separates the acquired pulses into homogeneous subclasses. Signal processing tools recognize the presence of noise among the different classes. Identification of basic PD source typologies (i.e., internal, corona and surface discharges) is then achieved, resorting to fuzzy algorithms. The proposed procedure is applied to measurements performed on different HV apparatus, such as cables, transformers and rotating machines. The purpose of this paper is to show that the identification process is robust, regarding the measuring circuit, and flexible, so that it can constitute an advanced tool for condition based maintenance, guiding maintenance experts in making decisions on the condition of the insulation system under test.     

一种用于含风电场电力系统电压稳定概率分析的混合方法

为了进行风电并网后电力系统电压稳定性的评估,利用具有概率特征的负荷裕度指标,提出了一种含风电场电力系统电压稳定概率分析的混合方法。当系统随机参数扰动量很小时将系统简化为线性化模型,根据线性方程的叠加性原理,在计算负荷裕度关于随机参数的灵敏度矩阵的基础上运用叠加性原理并结合正态分布的特性,将系统负荷裕度在期望值附近的随机扰动分解为单独考虑负荷随机变化和风速随机变化两种情况下求得的负荷裕度扰动量之和。该方法与Monte Carlo法和半不变量法同时在IEEE-30节点系统上进行仿真计算,通过对比分析表明了本文方法在保证准确性的基础上节省了计算时间。     

电能质量评估灵敏度分析及在改进密切值法中的应用

为了了解电能质量评估结果的稳定性,即评估结果对指标参数变化的敏感性,引入了电能质量评估灵敏度分析的概念和方法。通过定义绝对最优和最劣方案,利用汉明距离计算式代替欧氏距离计算式,对传统密切值法进行了改进。基于改进密切值法,推导了灵敏度分析中两个方案优先序的充要条件,在此基础上推导了电能质量指标属性值和权重值的灵敏度区间充要条件。经算例分析表明,该方法能有效计算指标参数和评估样本的灵敏度,为决策者控制灵敏度高的指标参数及方案决策提供了参考依据。     

一种用于含风电场电力系统电压稳定概率分析的混合方法

为了进行风电并网后电力系统电压稳定性的评估,利用具有概率特征的负荷裕度指标,提出了一种含风电场电力系统电压稳定概率分析的混合方法.当系统随机参数扰动量很小时将系统简化为线性化模型,根据线性方程的叠加性原理,在计算负荷裕度关于随机参数的灵敏度矩阵的基础上运用叠加性原理并结合正态分布的特性,将系统负荷裕度在期望值附近的随机扰动分解为单独考虑负荷随机变化和风速随机变化两种情况下求得的负荷裕度扰动量之和.该方法与Monte Carlo法和半不变量法同时在IEEE-30节点系统上进行仿真计算,通过对比分析表明了本文方法在保证准确性的基础上节省了计算时间.