Antenatal fetal risk assessment by blood-flow velocity waveforms

The purpose of this article is to study a system for antepartum fetal evaluation. The task is to investigate the Doppler ultrasound measurements of the umbilical artery and the cerebral artery to relate the health status of a fetus by using discriminant functions of pattern recognition. The authors then analyze the individual effects of various blood-flow velocity waveforms using principal component analysis.     

An evaluation method of voltage sag using a risk assessment model in power distribution systems

In this paper we explore a new method for evaluating the impact of voltage sags in the power distribution systems. The proposed method incorporates the generalization of the evaluation method as well as the effects of voltage sags on customers. To generalize the evaluation method, historical reliability data will be used. We take into account the impact of voltage sags on customers using a representative power acceptability curve and a fuzzy model. The final result of the evaluation model yields on a yearly basis the magnitude of customers’ risk caused by voltage sags. The evaluation methodology is divided into the analytic and probabilistic method. The time sequential Monte Carlo simulation is used as probabilistic method. The proposed method is tested using the modified Roy Billinton Test System (RBTS) form and the reliability data of Korea Electric Power Corporation (KEPCO) system. Through the case study, we verify that the proposed method evaluate the actual impact of voltage sags and can be effectively applied to the real system using the historical reliability data as the conventional reliability indices in power distribution systems.     

Comprehensive reliability assessment of substation originated outages using the Monte Carlo simulation technique

Power system security and stability has become a major concern for electric power utilities, as power systems become more and more complex and are operated closer to transmission capacity limits. Substations and switching stations are pivotal parts of power systems. Failure events in substations often result in multiple outages of generators, lines, and/or loads in power systems, and affect the security and stability of power system dramatically. The reliability evaluation of substation originated outages is therefore of vital importance. This paper presents the application of a Monte Carlo simulation (MCS) method to the reliability evaluation of voltage step-up substations and switching stations (herein referred to only as substations) in transmission systems. The proposed approach is demonstrated by application to an educational test system designated as RBTS (R. Billinton, S. Kumar, L. Goel, et al., A reliability test system for educational purposes—basic data, IEEE Trans. Power Appar. Syst. 4 (3) (1989) 1238–1244) and some selected sensitivity studies are also presented in this paper. The results of studies provide valuable information for decision-making in power system planning and operation. A comparison between the reliability indices of two groups of overlapping failures obtained from both analytical method and MCS approach shows that the approximate equations of analytical methods have constraints when the component average repair time exceeds certain numerical range. The MCS approach is shown to be more accurate when dealing with the multiple order outages.     

基于风险传递网络的智能变电站二次系统风险评估

风险评估是运行管理中一项重要的工作。作为保障变电站安全运行的二次系统,很有必要进行风险评估。从之前的研究中可以看出,变电站二次系统风险评估难点在于二次设备数量多,关系复杂,难以统筹考虑,二次设备对一次设备的影响作为主要风险难以量化。为此,提出了风险传递和网络理论相结合的方法。风险评估分为两个部分,一为自身风险评估采用网络理论求解,另一部分为对一次系统的影响,采用风险传递的方式求取。针对不同工作部门的需要,提出了一套风险指标体系。最后采用一个实际运行的智能变电站二次系统验证该方法的正确性。     

Voltage balancing of islanded microgrids using a time-domain technique

In this paper, voltage balancing and frequency control of converter-fed, islanded microgrids, using a novel time-domain technique which has not been applied for such applications is discussed in detail. In particular, the connection of single-phase loads to the islanded microgrid causes voltage unbalance and this is eliminated by supplying the negative-sequence component of the voltage from the converter. The negative sequence components of the voltage and current are extracted using the aforementioned time-domain technique. The simulations are carried out in RSCAD™ and experimental results are provided to validate the concept.     

A pumping technique using electrohydrodynamic flow inside a gel

We demonstrated a new type of electrohydrodynamic (EHD) pump that had a pair of electrodes placed inside a gel (poly(vinyl alcohol) swollen by dimethyl sulfoxide). The fluid (decahydronaphthalene) was in contact with the gel surface. During a voltage application to the electrodes, the EHD flow of dimethyl sulfoxide inside the gel caused the flow of the fluid outside the gel. An advantage of this pumping technique is that one can dissolve some chemicals in the fluid without the fear of their electrochemical decomposition because the electrodes inside the gel are not in contact with the fluid.     

Situation assessment of glaucoma using a hybrid fuzzy neuralnetwork

Describes a differential diagnostic-decision support system to aid in early detection in primary-care environments. In general, the authors are able to give correct differential diagnostic support under primary-care conditions without any further financial investments. In some cases, it is difficult to differentiate between “glaucomatous” and “pathological” situation classes. There is an unclear transition between these two situations. Initial tests of a combination crisp/fuzzy output refined the authors' results, and these are now under investigation. More data are needed for the “normal” class. An evaluation of the complete monitoring system will be started, including all components and sampling of more data sets. For consecutive patient cases, time-dependent characteristic changes in the visual fields could be detected. Further developmental work will be done in this area, parallel to the growth of the database     

AC-HVDC solution and security assessment using a diakoptical method

The paper describes a direct solution of an HVDC link within an AC loadflow solution and a direct security analysis using diakoptical techniques. The direct solution is faster than the more conventional boundary iterative method and therefore is more economical when used for regular calculation such as security assessment and transient stability analysis. It can easily be incorporated in existing AC loadflow algorithms.     

Annual risk assessment for overload security

This paper presents an approach to assess the cumulative risk associated with overload security for the purposes of mid-term power system planning. The work is motivated by a need to refine bulk power system reliability assessment to meet the needs of the restructured industry. There are two main contributions to the work. First, the assessment is performed over a year-long trajectory of hourly operating conditions, resulting in reliability assessment of all expected conditions and not just a limited number of snapshots. Secondly, the assessment is quantified by a risk index comprised of summed products of probability and consequence. This index is a good indicator of the actual reliability level, it is decomposable, and it can be effectively integrated into economic decision making paradigms. The work is illustrated using the 1996 IEEE Reliability Test System     

Analyzing fetal breathing rates using matching pursuits

Spontaneous breathing movements in the fetus tend to occur intermittently, and do not become continuous until after birth. In both the primate and the ovine species, breathing movements have been observed to have a high degree of variability in instantaneous breathing rates. In this study, ewes were surgically instrumented for chronic intrauterine recording of fetal diaphragmatic EMG. The matching pursuit (MP) method was used to examine the effects of morphine on fetal breathing rates in both time and frequency domains. The matching pursuit method was chosen since the classical Fourier transform may not represent signals which have stationary characteristics and wavelet transform may not represent signals whose Fourier transforms have a narrow frequency support. The authors' results show that the MP method was superior to both short time Fourier and wavelet transforms in identifying multiple periodicities in a highly nonstationary signal such as fetal breathing     

Examining fetal heart-rate variability using matching pursuits

A new approach to time-frequency analysis of fetal heart rate (FHR) variability is the matching pursuit (MP) method. MP analysis is proposed as away to capture complex energy structures ranging from burst-type to continuous activity in the time-frequency plane that other methods such as power-spectrum analysis and wavelet transforms may not detect. This article summarizes previous FHR analysis techniques, presents the MP algorithm, and shows the advantages of the MP method over other methods of FHR analysis     

Small perturbation performance of a synchronous machine using d-decomposition technique

The D-decomposition method of analysis is used to determine the small perturbation response of a synchronous machine. Computed results are presented in the form of stability contour diagrams showing the boundaries of absolute stability or with arbitrary degrees of damping in terms of the parameters of a conventional proportional voltage regulator. The influence of the damping factor on system response is illustrated with time—domain characteristics.     

基于LCC的变电站改造风险评估模型研究

变电站改造评估应以变电站改造风险评估为依据,结合LCC经济性评价,从全寿命资产管理的角度进行综合分析.通过建立变电站风险评估模型,分析设备风险和系统风险,并对风险成本采用LCC方法进行量化分析,多方案对比、论证及选择和优化,最终决策改造方案.     

快速配网风险评估

简单介绍城市电网风险评估的意义和背景.建立停运模型得到元件的停运概率.通过蒙特卡罗法得到系统各故障状态发生的概率,以各负荷点的变化情况,分析每种故障的危害程度,再根据不同的危害度提出了风险指标.该方法主要针对复杂电网进行风险评估,采取了改进的截断抽样法,并在2 000次抽样后再判断是否终止抽样分析.极大地提高了计算速度,尽快地为运行人员提供预警信息.     

Ethical risk assessment: valuing public perceptions

Engineers are confronted with an array of moral issues and dilemmas as the complexity modern technology results in equally complex efforts to assess the accompanying environmental and safety risks. The author examines the connections between engineering ethics, risk communication, and the engineering culture. First moral issues in risk assessment are reviewed and the ethical responsibilities of engineers with respect to risk assessment and risk communication are discussed. The conventional model of risk communication, which holds that only experts possess relevant risk information, is then critiqued, and the findings of social scientists and humanists with respect to the dual importance of expert and public risk information are reviewed. Following a discussion of the prevailing engineering culture, particularly as it relates to the problems involved in risk communication, some suggestions are made for transforming the engineering culture in a manner conducive to more meaningful discussion of risk     

Design of single-sided linear induction motors using a nonlinear optimization technique

Both low-speed wheel-on-rail and the medium-speed Maglev transport system with single-sided linear induction motor (SLIM) propulsion have been in practical application. This paper presents the method of optimizing the design parameters of SLIMs using the nonlinear optimization method. The optimization problem is formulated by the use of the design formulas taking into account the end effect, skin effect and airgap leakage, and the transformation method and the simplex method are applied to solve the problem. Seven parameters, such as the number of poles, the pole pitch and the stack height, are chosen as the independent variables. The output kW/input kVA, the maximum flux density in the core teeth, the temperature increase, the primary length, the stack height and the maximum thrust are selected as the constraint functions. The performance characteristics are estimated using space harmonic analysis as well as the approximate equations. The method is applied to the SLIM design for urban transit, and the maximum speed is about 70 km/h. As the transformation methods, the interior point transformation and the exterior point transformation are compared from the viewpoints of accuracy and CPU time. The design is analyzed under several objective functions, the primary weight, the input kVA and the cost of secondary materials.     

Control of permanent magnet motor drives using a new positionestimation technique

Permanent magnet motor drives require absolute position information so that winding currents can be modulated in synchronism with the rotor. The eradication of such sensors has been the subject of many publications. This paper describes the principles and implementation of a new algorithm for combined flux-linkage and position estimation in permanent magnet motors. The algorithm uses the machine's flux-linkage versus current versus position characteristic and is thus able to take account of machine nonlinearities. The position estimator utilizes the characteristic in a generalized nonintrusive estimation scheme, which is effective over the whole range of operating conditions. The paper shows implementation of the estimator as embedded code in a digital signal processor-based drive system. Experimental results demonstrate the performance of the algorithm under steady-state and transient conditions, when the drive is operating closed loop sensorless, i.e., with the rotor position being provided by the position estimator     

面向用户并考虑紧迫性的配电网运行风险评估

为了对运行中配电用户的风险及其紧迫性进行评估,提出了一种面向用户的配电网运行风险评估方法。该方法将用户作为评估对象,通过对运行中的配电网模拟预想故障下的负荷转移,分析用户所受故障损失,定义了考虑负荷不确定性的用户期望停电概率风险指标、用户期望停电时间风险指标、用户期望电量损失风险指标,并且通过结合系统期望停电用户数风险指标体现预想故障对系统整体的影响。为反映过负荷的影响,定义了配电网过负荷风险指标。基于预防控制执行时间与风险来临时间的比较,建立了风险紧迫性等级,用以反映确保预防控制措施能够有效实施的时机。采用IEEE 3馈线配电系统对所提方法进行了详细说明,结果表明其是可行和有效的。     

基于概率不安全指标的暂态风险评估

电力系统规模的不断扩大和电力市场改革的进一步推进,给电力系统的安全稳定运行构成了威胁,因此对电力系统进行暂态稳定评估,了解系统真实的运行状况,具有重要的现实意义.以动态安全域为分析手段,提出了基于概率不安全指标的暂态风险评估模型,兼顾了电力系统运行的安全性和经济性,将系统的运行状况量化为一个经济指标.IEEE 4机11节点系统算例说明了该模型的有效性.