Reliability indices for electric-power wheeling

Transmission networks are being used more extensively to accommodate energy transactions that use the economic benefits of pooling. This paper evaluates the probabilistic wheeling capability of an interconnected power transmission system. Large electric power wheeling can degrade the reliability of the electric power network. This problem is also important for power system control and planning purposes. This paper discusses, from the viewpoint of power network reliability, the problem of power wheeling from Western Europe to Greece through the Yugoslav electric power system. The relative cost of the wheeling due to reliability indices is 2% of the production cost for the power wheeled. The calculation of reliability indices of wheeling enable more adequate estimation of the wheeling rate for power transactions between utilities. This paper describes an approach to calculate cost of the average energy not supplied and load curtailed due to wheeling. This cost can even be negative, which depends mostly on the amount of wheeling power and consumer loads. The reliability index EENS (expected energy not supplied) is more comprehensive than PI (performance index) for the contingency severity selection procedure     

Reliability Evaluation for Optimally Operated, Large, Electric Power Systems

This paper presents a combined optimization/reliability technique to evaluate the reliability of large power systems. It uses Monte Carlo simulation for the individual operation/failure random performance of elements of a power network. This simulation overcomes the difficulty in constructing the many possible states for large power systems of complex topology. A simplified power-flow representation of the power network is used and a network reduction is implemented to reduce the size of the power-flow problem, such that only the effective part of the network (for a given contingency) is retained. The control parameters are optimized in order to simulate practical contingency situations in which suitable controls are invoked to preserve, as much as possible, the continuity of supply. The optimization problem is solved by linear programming in which the generator powers are manipulated as optimization variables to maximize the load power supplied and subject to the power flow equations as well as upper and lower bounds on the optimization variables. The outputs of the performance simulation and the optimization problem are subsequently used to compute the system reliability indices. The paper describes the computerized algorithm as well as numerical results for the IEEE 118-bus power system to demonstrate the applicability of the algorithm to actual systems.     

一种双模双待USB接口数据卡的低功耗设计

针对市场上双模双待消费类电子产品技术解决方案功耗大的缺点,提出了一种新的技术解决方案,该技术方案在降低产品成本的同时,也降低了消费类电子产品的功耗,提高了产品的可靠性和用户体验。     

A Real-Time Contingency Reserve Scheduling for an Isolated Power System

Utilities use contingency reserves to deal with the contingency events. To ensure that the reliability and operating frequency are well maintained, the reserve scheduling guidelines always specify that the reserve quantity and response rate should meet some precise levels. This paper presents an algorithm to estimate the frequency response characteristic, beta, of an isolated system online. The real-time estimated beta could be gainfully used for the instant when the update of reserve scheduling is needed. A contingency reserve scheduling according to a series of frequency restoration processes is also proposed to ensure the effectiveness of the reserve response. Test results showing that the scheduling method in simulated conditions, and on actual operating data, was confirmed to be feasible to ensure the power system's reliability     

On-line power system security analysis

A broad overview of on-line power system security analysis is provided, with the intent of identifying areas needing additional research and development. Current approaches to state estimation are reviewed and areas needing improvement, such as external system modeling, are discussed. On-line contingency selection has become practical, particularly for static security. Additional work is necessary to identify better indices of power system stress to be used in on-line screening filters for both static and dynamic security analysis. Use of optimal power flow schemes to recommend optimal preventive and corrective strategies is presented on a conceptual level. Techniques must be further developed to provide more practical contingency action plans, which include real-world operating considerations and use a reasonably small number of control actions. Techniques must be developed for costing operating variables which are not easily quantified in dollars. Soft or flexible constraints and time variables must be included in the preventive and corrective strategy formulation. Finally, the area of on-line transient and dynamic security analysis is presented     

Security analysis and optimization

An operationally "secure" power system is one with low probability of blackout or equipment damage. The power system control processes needed to maintain a designated security level at minimum operating cost are extremely complicated. They increasingly depend upon on-line computer security analysis and optimization. This on-line technology is still relatively new, with enormous further potential. Since security and optimality are normally conflicting requirements of power system control, it is inappropriate to treat them separately. Therefore, they are slowly becoming coalesced into a unified hierarchical mathematical problem formulation: one that is, however, far too complex to afford anything but an approximate, near-optimal solution. The practical validity of this unifying trend relies on being able to incorporate all significant security constraints within the process. The main two current computational tools in this field are contingency analysis and special operations-oriented versions of optimal power flow (OPF). Contingency analysis identifies potential emergencies through extensive "what if?." simulations on the power system network. OPF is a major extension to the conventional dispatch calculation. It can respect system static security limits, and can schedule reactive as well as active power. Moreover, the advanced versions of OPF include or interface with contingency analysis. This paper reviews present formulations and methods, and tries to point out areas of difficulty that constitute the main challenges for successful practical on-line implementations over the coming years.     

Evaluation of optimal-reliability indices for electricaldistribution systems

A method to calculate the optimal values of reliability indices for a load point in an electrical distribution system is presented. The problem is formulated as an optimization problem and solved by the gradient projection method; the objective is to minimize interruption cost. The algorithm is very useful and powerful for extending the existing network and planning new networks. It has been tested on a practical system (the Port-Fouad power network), and the results are discussed. Once the optimal reliability indices are determined, modification of the system by equipment replacement and future system planning can be done in such a way that the interruption cost is minimized     

高海拔与周期负载条件下的雷达供电系统可靠性分析

柴油发电机组作为雷达供电系统的主要设备,其供电可靠性对雷达完成任务至关重要,海拔高度和雷达负载工作方式对供电系统可靠性均有很大影响,传统的可靠性分析计算方法与实际情况存在一定差距。文中针对两种负载周期性工作条件下的供电系统可靠性进行研究,基于可靠性理论,推导了系统可靠度函数和系统平均寿命的计算方法。结合具体的工程实例,通过对两种方案的成本、机动性和可靠性指标进行对比分析,采用该算法可以得到优化的供电方案,并将该方法推广到多种负载周期性工作的普遍情形,为提高雷达供电系统的可靠性设计能力提供了理论基础和新的预计方法。     

Decisions for maintenance-intervals of equipment in thermal powerstations, based on few data

This paper describes a maintenance scheduling for pump systems in thermal power stations in order to reduce the maintenance cost during the whole period of operation, while keeping the current reliability level of the pump system. The dimensional reduction method is used to solve the problem in which a few available data are used together with other factors relating to the failures of pumps. The problem, that the available data are limited to a short range of the operation period compared with the mean time to failure, is solved by extrapolating the whole distribution of period of failure using available actual data. Weibull distribution approximation is used for this purpose: the data analyzed for failure and population statistics are those of 569 pumps, during the past 17 years which were recorded at 19 thermal power stations owned by Kyushu Electric Power Company. The results of the analysis by the proposed method provided the most suitable maintenance interval for each pump, and hence are helpful to reduce the expense of unnecessary maintenance     

Characterization of Single-Electron Tunneling Transistors for Designing Low-Power Embedded Systems

Minimizing power consumption is vitally important in embedded system design; power consumption determines battery lifespan. Ultra-low-power designs may even permit embedded systems to operate without batteries by scavenging energy from the environment. Moreover, managing power dissipation is now a key factor in integrated circuit packaging and cooling. As a result, embedded system price, size, weight, and reliability are all strongly dependent on power dissipation. Recent developments in nanoscale devices open new alternatives for low-power embedded system design. Among these, single-electron tunneling transistors (SETs) hold the promise of achieving the lowest power consumption. Unfortunately, most analysis of SETs has focused on single devices instead of architectures, making it difficult to determine whether they are appropriate for low-power embedded systems. Evaluating the use of SETs in large-scale digital systems requires novel architectural and circuit design. SET-based design imposes numerous challenges resulting from low driving strength, relatively large static power consumption, and the presence of reliability problems resulting from random background charge effects. We propose a fault-tolerant, hybrid SET/CMOS, reconfigurable architecture, named IceFlex, that can be tailored to specific requirements and allows tradeoffs among power consumption, performance requirements, operation temperature, fabrication cost, and reliability. Using IceFlex as a testbed, we characterize the benefits and limitations of SETs in embedded system designs. In particular, we focus on the use of SETs in room-temperature ultra-low-power embedded systems such as wireless sensor network nodes. We also consider high-performance applications such as multimedia consumer electronics. We see this work as a first step in determining the potential of ultra-low-power embedded system design using SETs.     

Reliability evaluation of IGCT from accelerated testing,quality monitoring and field return analysis

The IGCT (Integrated Gate Commutated Thyristor) was launched as a new power semiconductor device 20 years ago, using design features where only few reference was available at that time. Especially the gate path that needs to take the full principal current for micro seconds was significant extension of the state of the art. In-between 20 years of field experience with IGCTs is available. In this paper test results from accelerated testing, quality monitoring results over many years, reliability date from evaluated field failure rates and analysis of devices that were in service for 15 years under well-known load are summarized and show an excellent reliability of the power semiconductor.     

RS—RBFNN在电力通信网可靠性评估中的应用

指标体系的建立是通信网可靠性评估工作中的一个重要环节,然而由于指标的不确定性和指标间的复杂关系,使得指标的选取以及合理指标体系的建立都变得非常困难。为了解决指标的选取问题,文章采用粗糙集（Rs）理论中的属性约简与径向基神经网络（RBFNN）相结合的方法对电力通信网可靠性进行仿真评估。该方法通过降低径向基神经网络输入的维数来提高神经网络的训练速度和评估能力。仿真结果验证了该方法在通信网可靠性评估中的有效性与可行性。     

An analysis of the reliability and design optimization of aluminium ribbon bonds in power electronics modules using computer simulation method

Ribbon bonding technique has recently been used as an alternative to wire bonding in order to improve the reliability, performance and reduce cost of power modules. In this work, the reliability of aluminium and copper ribbon bonds for an Insulated Gate Bipolar Transistors (IGBT) power module under power cycling is compared with that of wire bonds under power and thermal cycling loading conditions. The results show that a single ribbon with a cross section of 2000 μm × 200 μm can be used to replace three wire bonds of 400 μm in diameter to achieve similar module temperature distribution under the same power loading and ribbon bonds have longer lifetime than wire bonds under cyclic power and thermal cycling conditions. In order to find the optimal ribbon bond design for both power cycling and thermal cycling conditions, multi-objective optimization method has been used and the Pareto optimal solutions have been obtained for trade off analysis.     

基于需求响应的风电-抽水蓄能系统调度模型

针对大规模风电并网影响电网稳定运行的问题,基于日前用户侧电力负荷预测和实时电价预测,文中提出了一种电网吸纳风能的新模型。以最小化风电—抽水蓄能联合系统发电成本为目标,在目标求解过程中确定最佳自弹性系数和互弹性系数,运用基于实时电价的需求价格来弹性引导电力用户以实现负荷转移。考虑到用户侧电价弹性限制的约束,该方法采用遗传优化算法编程求解。仿真结果表明,需求侧资源主动参与优化调度可降低负荷峰谷差,利于系统稳定运行,并且可以减少发电成本,提高联合系统经济性。     

Pervasive grid for large-scale power systems contingency analysis

Optimal control and management of power systems require extensive analyses of phenomena that can compromise their operation in order to evaluate their impact on the security and reliability levels of the electrical networks. For complex networks, this process, known as power systems contingencies analysis, requires large computational efforts, whereas computation times should be less than a few minutes for the information to be useful. Even though many architectures based on conventional parallel and distributed systems have been widely proposed in the literature, they are characterized by low extensibility, reusability, and scalability, and so, they require a sensible hardware upgrade when more computational resources are necessary. This event is not infrequent in power systems where the constant growth of the electrical network complexity and the need for larger security and reliability levels of the plant infrastructures lead to the need of more detailed contingency analysis in shorter times. To address this problem, this paper proposes a pervasive grid approach to define a user-friendly software infrastructure for data acquisition from electrical networks and for data processing in order to simulate possible contingencies in a real electrical network. The grid infrastructure adopts a brokering service, based on an economy-driven model, to satisfy the quality of service constraints specified by the user (i.e., a time deadline to simulate the contingencies). This paper also discusses the deployment of the infrastructure on a network of heterogeneous clusters and PCs to compute the contingency analysis of a realistic electrical network. The experimental results obtained demonstrate the effectiveness of the proposed solution and the potential role of grid computing in supporting intensive computations in power systems.     

Design of a maximum power tracking system for wind-energy-conversion applications

A wind-generator (WG) maximum-power-point-tracking (MPPT) system is presented, consisting of a high-efficiency buck-type dc/dc converter and a microcontroller-based control unit running the MPPT function. The advantages of the proposed MPPT method are that no knowledge of the WG optimal power characteristic or measurement of the wind speed is required and the WG operates at a variable speed. Thus, the system features higher reliability, lower complexity and cost, and less mechanical stress of the WG. Experimental results of the proposed system indicate near-optimal WG output power, increased by 11%-50% compared to a WG directly connected via a rectifier to the battery bank. Thus, better exploitation of the available wind energy is achieved, especially under low wind speeds.     

Reliability and routability consideration for MCM placement

This paper presents a methodology based on the fuzzy logic approach for the placement of the power dissipating chips on the multichip module substrate. Our methodology considers both thermal distribution and routing length constraints during multichip module placement. In this paper, the main design issue is the coupled placement for reliability and routability. The objective of the coupled placement is to enhance the system performance and reliability by obtaining an optimal cost during multichip module placement. For reliability considerations, the design methodology is addressed on the placement of the power dissipating chips to achieve uniform thermal distribution. The thermal placement analysis is based on the modified fuzzy force-directed placement method. Placement for routability is based on minimizing the total wire length estimated by semi-perimeter method. The placement trade-off between routability and reliability is illustrated by varying a weighting factor. Case studies of the coupled placement are presented. In addition, the thermal distribution of the coupled placement results is simulated with the finite element method.     

A type-II censored, log test time based, component-testingprocedure for a parallel system

The authors consider the problem of acceptance testing for a parallel (1-out-of-n:G) system of different components with constant failure rates. The components are individually tested and the tests are terminated as soon as a preassigned number of each component fails. The authors provide a criterion for accepting or rejecting the system based on the sum of the logarithms of the total times on test for each component. The critical level for the test statistic is chosen so as to guarantee that the specified consumer and producer risks on the system reliability are not exceeded. The use of this statistic makes the computation of these critical values much simpler as compared with that of a previously used statistic based on the product of the total times on test for each component. Several approximate procedures are considered for deriving these critical values. The authors also formulate the optimization problem for deriving the minimum-cost component-testing plans when a type-II censored component-test procedure is used for a parallel system     

Evaluation of MTTF and reliability of a power plant by BF technique

In this paper, investigations have been carried out for the evaluation of reliability and MTTF (mean time to failure) of a parallel redundant complex system; viz. a power plant. The object of the system is to supply power generated by generators from a power house to a very important consumer, connected by cables and switches. The reliability and MTTF have been evaluated by using Boolean Function (BF) technique. Failure times for the various components of the complex system follow arbitrary distribution. A numerical example has also been appended to highlight the important results. Two graphs on reliability and MTTF have also been given in the end to forecast the operable behaviour of the system at any time.