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101.
A stochastic study of hidden failures in power system protection 总被引:3,自引:0,他引:3
Recent studies have shown that power systems protection mechanisms have played a major role in propagating disturbances. All of the last five major Western Systems Coordinating Council (WSCC) events (the North Ridge earthquake, December 14, 1994, July 2 and 3, 1996, and August 10, 1996), involved either false trips of line protection relays or generator protection equipment. Using an importance sampling based algorithm on the 179-bus WSCC equivalent system, we modeled the sequence of rare events involving generator trips and incorrect zone 3 relay operations. Due to possible loss of generation and load, frequencies were monitored for the necessary of load shedding. The algorithm uses the Newton–Raphson method for accuracy but reverts to DC load flow when the Newton–Raphson algorithm fails to converge within three iterations. The resulting sequence of rare events and its corresponding probability are used to detect weak links in the power system. This information can be beneficial not only in areas such as service and maintenance scheduling and in planning, but also in determining locations where an investment in improving the protection system is warranted. 相似文献
102.
基于累积量的递归最小二乘算法研究 总被引:2,自引:0,他引:2
从基于累积量的均方误差(CMSE)准则,本文推导了一种基于累积量的递归最小二乘(CRLS)算法.并从信号检验和估计的角度对三阶CRIS算法中出现的加权求和系数给出的一种物理解释,以说明其抗高斯噪声的机理.本文提出应根据三种不同条件下信号的最优估计来确定最佳窗口函数的原则,并进一步证明了在极大似(ML)和线性均方(LMS)估计意义下的最佳窗口都是矩形窗而非Delopoulos和Giannakis建议的Hamming窗~[3]。仿真实验证实:CRLS算法采用矩形窗确定比采用Hamming窗具有更上的结果偏差。 相似文献
103.
Lori R. Johnson-Payton Yacov Y. Haimes James H. Lambert 《Reliability Engineering & System Safety》1999,65(1):77
This paper studies the approximation of the partitioned multiobjective risk method's (PMRM) extreme event risk function for time-to-failure models. The analytic expression of the approximation for the extreme event risk function is derived through the use of the statistics of extremes for the case where the underlying distribution is of an extreme-value type III for minima. This analytic expression provides an effective theoretical tool for understanding the behavior of conditional expected values for time-to-failure models for a large class of distribution functions used in reliability. The results are confirmed for example problems of exponential and uniform distributions. 相似文献
104.
从SPC的发展历史及运用系统的观点,阐述了SPC在现代制造业中推行的基本要求,并提出了SPC系统控制图。 相似文献
105.
本文以两晋至明清时期的湖北寺院为研究对象,通过湖北地方志等资料的爬梳整理,在数据统计的基础上,对该时期湖北寺院的时间分布进行分析,并探讨形成这些特征的原因。结果表明:(1)从两晋至明清四个时间段来看,湖北寺庙修建数量从两晋至明清呈现稳步上升的趋势;(2)早期湖北寺庙大多以新建为主,随时间后移,重修寺庙比重增加;(3)佛寺分布的时间特征受政治、经济和文化三个方面的影响,呈现正相关关系。 相似文献
106.
107.
为了有效地度量不同失真类型的图像质量,提出一种基于自然场景统计(NSS)模型的空域无参考图像质量评价算法。该算法利用自然图像归一化亮度系数的统计特征趋向于服从广义高斯概率分布的特性,首先在空域计算自然图像的梯度,通过梯度密度选取自然图像的兴趣区域,提取兴趣区域图像统计特征,建立多元高斯分布(MVG)模型;然后对测试图像建立同样的MVG模型;最终通过计算测试图像和自然图像在统计规律上的偏差来对测试图像的质量做出评价。实验证明该算法与主观评价具有较好的一致性。 相似文献
108.
109.
Arttu Miettinen Cris L. Luengo Hendriks Gary Chinga-Carrasco E. Kristofer Gamstedt Markku Kataja 《Composites Science and Technology》2012
An improved method based on X-ray microtomography is developed for estimating fibre length distribution of short-fibre composite materials. In particular, a new method is proposed for correcting the biasing effects caused by the finite sample size as defined by the limited field of view of the tomographic devices. The method is first tested for computer generated fibre data and then applied in analyzing the fibre length distribution in three different types of wood fibre reinforced composite materials. The results were compared with those obtained by an independent method based on manual registration of fibres in images from a light microscope. The method can be applied in quality control and in verifying the effects of processing parameters on the fibre length and on the relevant mechanical properties of short fibre composite materials, e.g. stiffness, strength and fracture toughness. 相似文献
110.
Sara Casciati 《Canadian Metallurgical Quarterly》2010,136(9):1131-1142
Linear response surface (RS) models are used to represent the relationship between samples of response time histories measured by sensors placed across a structure. Different structural states of a general time-variant system are considered for short intervals capturing a linearized model of each state. Within this framework, the error associated with each RS model is sensitive to a modification of the structural state. A method that relates the changes of the statistical characterization of the error to the occurrence of a structural modification is developed for damage detection. The localization of damage is then pursued by identifying the largest discrepancies resulting from the comparison between the statistics of the sum of the squares of the error obtained at each sensor location. The generality of the method is shown by applying it to the experimental data of a realistic structure, which is representative of a continuous body affected by distributed cracking. 相似文献