An improved model for protective-system reliability

A Markov model extends and improves previous models for determining the unreadiness probability and unavailability of a protective system, such as those found on electric-power transmission and distribution systems. Improved definitions of unreadiness probability and other relevant measures are proposed, based on a new Markov model of the system. This new model provides a more direct and physically important definition of unreadiness, and can be computed based on typical system-transition rates. Using this model, it is possible to estimate the optimal value of the protection inspection interval, viz, the time between inspections of the protective system. The model accounts for the operation of backup protection, the removal of protection for inspection, the occurrence of common-cause failures, and the usual clearing of faults     

浅谈电力变压器的保护设计

电能作为当今社会的一种重要能源,它影响着国民经济的发展。如今的电力系统更是由电能的产生、输送、分配包括用电等环节组成的一个复杂系统。而电力系统的发展对继电保护也提出了更高层次的要求。变压器是电力系统中必不可少的设备,它的可靠性直接影响着系统的安全运行。由于变压器的重要性及其自身的昂贵价值,一旦它发生故障或遭到了破坏,其影响范围大,将造成严重的后果,所以应该根据变压器在实际运行中可能发生的各种故障及不正常工作状态装设必备和可靠地保护,以提高电力系统安全经济的运行水平。因此,文章研究了变压器的故障类型,并针对10 000 kVA(35 kV/10 kV)油式变压器设计了其应有的保护类型。     

Reliability Calculations for Electrical Transmission Systems on the Basis of Mean Failure Indices

In an electric power transmission network, a fault occurring on any one of its components sometimes causes an' active event' as a result of interaction between the power system and its protection system. An outage of sections adjacent to the faulted one for a small duration is characteristic of these events. In this paper, the mean failure indices (mean probability-of-failure and mean frequency-of-failure) of a network are defined as functions of the failure indices at various load points. Several types of active events including those caused by failure of protection system are considered and their contribution to the mean failure indices of the network evaluated. The effectiveness of providing normally open paths in reducing the mean failure indices of the network is explained. The points are illustrated by examples.     

CAWS600B气象站电源控制系统应用解析

随着大气监测自动化系统建设全面建设完成,越来越多的自动气象站投入了业务运行,占据了国内近8成CAWS600B型自动气象站维护保障工作成为气象技术装备工作的新问题。此类型自动气象站的故障很大一部分是由于电源控制系统造成的,为方便同行更好的做好气象技术装备保障工作,对CAWS600B型自动气象站的电源控制系统原理进行了详细的应用解析,并重点分析了几种常见典型故障及处理方法,可为气象装备技术保障人员提供参考依据。     

An Architecture for Differentiated Protection Against Single and Double Faults in GMPLS

In the context of an optical network GMPLS can be used to provide network robustness to faults through end-to-end path protection techniques. In this paper, we present a dynamic distributed model supporting five different classes of protection, including protection against single and double fault, with and without sharing of backup bandwidth. Beyond link and node failures we also consider protection against shared risk link group (SLRG) failure. In this paper, we briefly describe the protection model and the underlying algorithms for route selection and backup bandwidth sharing. After that we face the following issue: Which subset out of the five possible protection classes is convenient for an operator to support on the same network infrastructure? To answer this question it is fundamental to have a clear view of the trade-offs between the costs and the performances associated to each class. To achieve that we carried out an extensive performance analysis by means of simulations. For each protection class, we evaluated two fundamental performance metrics: the recovery probability under multiple faults, and the average per-demand resource usage. On the basis of such results, we are able to identify some basic guidelines driving the choice of the more convenient subset of protection classes to be implemented within a single network.     

基于数字信号处理的远方保护设备

远方保护设备是用于电力系统的传输保护命令信号装置。当电力系统发生故障时,线路两端的继电保护装置所产生的命令信号借助远方保护设备并经PLC(电力线载波)、光纤等通信通道,把跳闸命令信号传送到远端保护屏用以跳闸、切机或切除负荷,起到故障保护作用。采用DSP(数字信号处理)函数查表法产生对应保护命令的各种单频信号发送到远端远方保护设备,并对由通道传输来的含有噪声的模拟单频信号,首先通过远方保护设备中的一组带通滤波器,再用功率谱估计法计算,选择出相应可靠的保护命令信号,满足电力系统保护命令传输的基本要求——及时性、安全性和可信赖性。     

Thermal reliability prediction and analysis for high-density electronic systems based on the Markov process

Thermal-mechanical fatigue is one of the main failure modes for electronic systems, particularly for high-density electronic systems with high-power components. Thermal reliability estimation and prediction have been an increasing concern for improving the safety and reliability of electronic systems. In this paper, we propose a stochastic process prediction model to estimate the thermal reliability of an electronic system based on Markov theory. We first divided the high-density electronic systems into four modules: the energy transformation and protection module, the electronic control module, the connection module, and the signal transmission and transformation module. By integrating failure and repair characteristics of the four modules, a stochastic model of thermal reliability analysis and prediction for a whole electronic system was built based on the Markov process. The feature parameters of thermal reliability evaluation, including thermal reliability, thermal failure probability, mean time between thermal faults, and thermal stable availability, were derived based on our comprehensive model. Finally, we applied the model to an indoor electronic system of DC frequency conversion conditioning. The thermal reliability was estimated and predicted using tested failure and debugging repair data. Effective methods for improving thermal reliability are presented and analyzed based on the comprehensive Markov model.     

Shared partial path protection in WDM networks with shared risk link groups

For 100% shared risk link group (SRLG) failure protection, conventional full path protection has to satisfy SRLG-disjoint constraints, i.e., its working path and backup path cannot go though the same SRLG. With the increase of size and number of SRLGs, capacity efficiency of conventional shared full path protection becomes poorer due to SRLG-disjoint constraints and the blocking probability becomes much higher due to severe traps. To solve these problems, we present a partial path protection scheme where SRLG-disjoint backup paths may only cover part of the working path. Full path protection becomes a special case of partial path protection, in which the backup path covers the full working path. By choosing the most survivable partial backup path as backup path, we can make the impact of SRLG failures as low as possible and accept as many as possible connection requests. Assuming every SRLG has the same probability to fail, we present a heuristic algorithm to find the most survivable partial backup path by choosing full path protection first, iteratively computing partial backup paths and choosing the most survivable one. The benefit of this heuristic algorithm is that it can find the optimal results within less iteration. Analytical and simulation results show that, compared to conventional full path protection, our proposed scheme can significantly reduce blocking probability with little sacrifice on survivability. The proposed scheme is very useful particularly when the network contains a lot of SRLGs and the blocking probability of conventional full path protection becomes too high.

BP-2B微机型母线差动保护校验

母线是电能集中和供应的枢纽,母线故障的处理不当将破坏电力系统的安全稳定运行。母线保护装置能及时检测到母线故障,并快速有选择性地切除故障母线,将故障点从系统隔离。母线保护装置运行的可靠性对电力系统的稳定运行有着重要意义。文章从普通比率制动特性的母线差动保护出发,对南瑞BP-2B型微机母线差动保护的原理和特性进行分析,提出了一种适用于保护定检及装置单独调试的具有普遍适用性的复式比率差动校验方法,对电网微机型母差保护装置的安全稳定运行具有一定意义。     

Performance enhancement for impairment-aware SRLG failure protection in wavelength-routed optical networks

With the increase of size and number of shared risk link groups (SRLGs) in WDM networks, path protection tends to have longer working paths and backup paths due to SRLG-disjoint constraints, which makes physical impairment a major concern in working path and backup path provisioning, particularly in large-sized all optical networks. As a simple and efficient algorithm, the working path first algorithm is often used for path protection against SRLG failures, where the working path is calculated first by using the shortest-path algorithm on the graph, followed by using the SRLG-disjoint shortest path as backup path. Compared with the working path, the backup path calculated after the working path in the working path first algorithm is more vulnerable to physical impairment, since it may be much longer than the working path. As a result, if we reject those connections that cannot meet the physical impairment requirement, with SRLGs the blocking probability of path protection will be much higher. We argue that impairment must be taken into account together with capacity efficiency in a comprehensive way during SRLG-disjoint working path and backup path selection. To solve this problem, we motivate the needs to study physical impairment-aware shared-path protection by considering two policies. Policy I uses two SRLG-disjoint least impairment paths as working path and backup path, respectively, and Policy II tries to benefit from both the shortest path and the least impairment path by choosing them intelligently. Analytical and simulation results show: (1) compared with impairment-unawareness, impairment-aware SRLG failure protection performs much better in terms of blocking probability especially with strong physical impairment constraints; (2) impairment-aware SRLG failure protection can significantly reduce physical-layer blocking probability; and (3) the algorithm based on Policy II achieves a good balance between capacity efficiency and physical impairment requirement.     

Capacity Optimization for Surviving Double-Link Failures in Mesh-Restorable Optical Networks

Most research to date in survivable optical network design and operation, focused on the failure of a single component such as a link or a node. A double-link failure model in which any two links in the network may fail in an arbitrary order was proposed recently in literature [1]. Three loop-back methods of recovering from double-link failures were also presented. The basic idea behind these methods is to pre-compute two backup paths for each link on the primary paths and reserve resources on these paths. Compared to protection methods for single-link failure model, the protection methods for double-link failure model require much more spare capacity. Reserving dedicated resources on every backup path at the time of establishing primary path itself would consume excessive resources. Moreover, it may not be possible to allocate dedicated resources on each of two backup paths around each link, due to the wavelength continuous constraint. In M. Sridharan et al., [2,3] we captured the various operational phases in survivable WDM networks as a single integer programming based (ILP) optimization problem. In this work, we extend our optimization framework to include double-link failures. We use the double-link failure recovery methods available in literature, employ backup multiplexing schemes to optimize capacity utilization, and provide 100% protection guarantee for double-link failure recovery. We develop rules to identify scenarios when capacity sharing among interacting demand sets is possible. Our results indicate that for the double-link failure recovery methods, the shared-link protection scheme provides 10–15% savings in capacity utilization over the dedicated link protection scheme which reserves dedicated capacity on two backup paths for each link. We provide a way of adapting the heuristic based double-link failure recovery methods into a mathematical framework, and use techniques to improve wavelength utilization for optimal capacity usage.     

变压器相间后备保护现存问题及改善措施

在导致变压器损坏或者故障的外部因素中,变压器相间后备保护方面的问题是最主要的因素之一,其对低压侧相间故障的灵敏程度不够,而且动作的时间限制较长是故障的主要原因。文中介绍了变压器的后备保护,分析了变压器相间后备保护中存在的问题,并且提出了针对性的改善措施。     

Design of Adaptive Procedures for Fault Detection and Isolation

An algorithm is presented for designing minimum-expected-cost test trees for detecting and isolating single faults in a system. A test is specified by the subset of components that must be good for the test to pass, and with each test is associated a fixed cost. Each component is assumed to have an a priori probability of failure. The test tree specifies an adaptive testing procedure that detects a failure and isolates the faulty component while minimizing the expected cost of testing.     

多相补偿距离继电器的保护范围浅析

多相补偿距离保护在电力系统中有着比较广泛的应用。该继电器保护范围与传统距离保护相同,不需要选相,具有较强的抗过渡电阻能力,还具有明确的方向性。该保护在输电线路发生接地故障时,也可以动作,保护范围会有所变化。本文详细分析了保护的动作原理,给出了保护范围计算的依据。该分析方法可以帮助学生深刻掌握电力系统各种故障发生时的序分...     

Hybrid survivability approaches for optical WDM mesh networks

This paper studies the problem of providing recovery from link failures in optical wavelength division multiplexing (WDM) networks. One of the widely studied mechanisms is dynamic link restoration, which provides recovery by determining restoration paths around a link after a failure occurs. This mechanism leads to a lower backup resource utilization, fast failure signaling rate, and a scalable operation. However, one of the main drawbacks of uncoordinated dynamic restoration is the inability to provide a 100% recovery for all connections, especially at high network loads. An alternate solution is proactive protection, where backup capacity is reserved during connection setup that can guarantee recovery under certain conditions (e.g., single link failures) but requires higher backup capacity and has low spare capacity utilization when failures do not occur. This paper presents two hybrid survivability approaches that combine the positive effects of restoration and protection. The proposed algorithms make use of available or collected network state information, such as link load, to identify critical links or segments in the network that are then proactively protected. The overall goal of the proposed approaches is to improve the restoration efficiency by providing a tradeoff between proactive protection and dynamic restoration. This paper presents a detailed performance analysis of the proposed algorithms. Experimental results show that under high loads, both the proposed approaches maintain a consistent restoration efficiency of at least 10%, or higher, when compared to the basic restoration scheme.     

Effect of System Processes on Error Repetition: A Probabilistic and Measurement Approach

This paper presents an approach to system reliability modeling where failures and errors are not statistically independent. The repetition of failures and errors until their causes are removed is affected by the system processes and degrades system reliability. Four types of failures are introduced: hardware transients, software and hardware design errors, and program faults. Probability of failure, mean time to failure, and system reliability depend on the type of failure. Actual measurements show that the most critical factor for system reliability is the time after occurrence of a failure when this failure can be repeated in every process that accesses a failed component. An example involving measurements collected in an IBM 4331 installation validates the model and shows its applications. The degradation of system reliability can be appreciable even for very short periods of time. This is why the conditional probability of repetition of failures is introduced. The reliability model allows prediction of system reliability based on the calculation of the mean time to failure. The comparison with the measurement results shows that the model with process dependent repetition of failures approximates system reliability with better accuracy than the model with the assumption of independent failures.     

QoS约束的链路故障多备份路径恢复算法

链路故障的恢复,不仅仅是选择一条连通的备份路径问题,还应考虑网络业务故障恢复过程中的QoS需求。针对此问题,该文基于多备份路径策略,构建概率关联故障模型和重路由流量丢弃量优化目标。并基于该优化目标,以业务的QoS需求为约束,建立故障恢复问题的数学模型,提出一种QoS约束的链路故障多备份路径恢复算法。该算法构建单条备份路径时,以最大程度地减少重路由流量丢弃为目标,并采用改进的QoS约束的k最短路径法进行拼接,且给与高优先级链路更多的保护资源。此外还证明了算法的正确性并分析了时间空间复杂度。在NS2环境下的仿真结果表明,该算法显著提升了链路故障恢复率和重路由流量QoS满足率,且QoS约束条件越强,相较于其它算法优势越明显。     

基于专家系统的广域后备保护

对电力系统中的多点信息进行采集,通过计算动作系数确定故障影响范围,如专家系统不能做出决策再通过二级策略确定,逐步缩小故障范围以及最终得出故障隔离方案,使故障对系统的影响降低.通过算例对比分析,验证了基于专家系统的广域后备保护优于传统后备保护,提高了传统后备保护的选择性.     

硬盘播出系统备份实现方式与完善措施

分析了十堰市电视台硬盘播出系统重点设备的备份原理,并根据自身特点和系统运行中出现的问题,完善了周边设备的备份措施.从而使得播出系统内硬件安全得到了更高的技术保障,也进一步确保了播出素材的安全,对电视台播控机房长期稳定运行具有积极的借鉴意义.     

The “Bayesian Anomaly” and Its Practical Mitigation

A fundamental logical problem in the Bayesian inference of a series system's failure probability is described, a practical means for its mitigation is discussed, and its application to space launch vehicles is illustrated. The problem is the ldquoBayesian Anomaly,rdquo the difference in the system's failure probability per operation inferred from prior estimates, and test or operational experience applied at a lower-level of the system; and from the convolution of the same priors, and of the same experience applied at the system level (or any level above the first). In particular, unlike in a classical inference, the mean estimates differ critically. Although it is not possible to entirely resolve the problem, a practical procedure for mitigating it, establishing consistency among the mean and variance estimates at the two levels, is delineated.