Reliability assessment of generation and transmission systems using fault-tree analysis

This paper presents a method that integrates deterministic approach with fault-tree analysis for reliability assessment of a composite system (generation and transmission in power systems). The contingency screening is conducted in the first step. The results are further classified into three clusters in the second step: normal, local trouble and system trouble. The fault-tree analysis is used to assess the reliability of the composite system in the third step. Finally, Risk Reduction Worth is adopted as a measure of importance for identifying the crucial element that has significant impact on the reliability. In this paper, a composite system in Taiwan serves as an example for illustrating the simulation results attained by the proposed method. The simulation results, verified by Siemens PTI PSS/E TPLAN software package, show that the proposed method is applicable for large scale power systems.     

Review and modelling the systems of transmission concentrated solar energy via optical fibres

The aims of this study are to optimize the coupling of a low-cost offset paraboloidal dish, which concentrates direct solar irradiance with dual axes tracking component, and the fibre optic bundle (FOB), which transmits concentrated solar energy; to review previous studies on the transmission of concentrated solar energy via optical fibres (TCSEvOF) by classifying according to their purposes; to present a mathematical model for coupling symmetrical paraboloidal dish and FOB, and a modified model for optimum coupling of offset paraboloidal dish proposed in our study, taking into account the parameters of the dish and dispersion effect; to apply the models to symmetrical and offset paraboloidal dish under the same conditions; and to compare the annual output power obtained. Optical efficiency of the whole system was calculated as 68% in optimum condition, but it was found to be 63% for the system proposed. Overall system efficiency was found to be 59%. It was found that offset paraboloidal dish produced much more energy than the symmetrical one does when comparing under the same conditions. The difference of monthly average annual obtainable power was calculated as 0.82%. The monthly average annual power gained from the offset paraboloidal dish proposed was computed as 1041.6 kW to per square metre.     

考虑连锁故障的发输电系统可靠性评估

为在发输电系统可靠性评估中考虑连锁故障的影响,提出了评估连锁故障风险的混合算法.该算法结合了解析法和模拟法的优点,在计算精度和效率上均有一定的优势.由于实际切负荷时负荷节点功率因数保持恒定,因此在最优切负荷模型中引入了负荷节点功率因数恒定约束,使得该模型更加贴近实际情况.此外,为了提高发输电系统可靠性评估的效率,采用基...     

基于风速-负荷联合状态的发输电系统可靠性评估研究

随着风电渗透率的不断增加,准确评估风电场对发输电系统可靠性的影响十分重要。文章基于拉丁超立方抽样法(LHS)和马尔可夫过程(Markov)理论,采用等频率状态划分方式,建立了风速-负荷的马尔可夫多状态转移过程,提出了一种计及风速-负荷自相关性和互相关性的LHS-Markov可靠性评估方法。以IEEE-RBTS测试系统为算例,使用实测风速数据,通过风速-负荷联合状态抽样对其进行模拟,分析了风电场容量对含风电场的发输电系统可靠性的影响。计算结果证明了该方法的有效性,对风电场的并网规划具有重要指导意义。     

A stochastic framework for uncertainty analysis in electric power transmission systems with wind generation

The purpose of this work is the analysis of the uncertainties affecting an electric transmission network with wind power generation and their impact on its reliability. A stochastic model was developed to simulate the operations and the line disconnection and reconnection events of the electric network due to overloads beyond the rated capacity. We represent and propagate the uncertainties related to consumption variability, ambient temperature variability, wind speed variability and wind power generation variability. The model is applied to a case study of literature. Conclusions are drawn on the impact that different sources of variability have on the reliability of the network and on the seamless electric power supply. Finally, the analysis enables identifying possible system states, in terms of power request and supply, that are critical for network vulnerability and may induce a cascade of line disconnections leading to massive network blackout.     

Design and comparisons of three biomass based hydrogen generation systems with chemical looping process

The technology of hydrogen generation from biomass has attracted more and more attentions nowadays. In this work, three biomass-based chemical looping hydrogen generation systems, Systems A, B and C, are comprehensively studied. System A is mainly composed of biomass hydrogasification, methane reformation and the calcium-looping based CO₂ absorption. System B is mainly composed of biomass steam gasification and Fe₂O₃/FeO-looping based hydrogen generation circulation. System C is mainly composed of biomass steam gasification and Fe₃O₄/FeO-looping based hydrogen generation circulation. The three systems are modeled and their characteristics are analyzed and compared thermodynamically. System A has the highest cold gas efficiency (CGE) which is 72%; System B has the lowest CGE of 54% but it can generate additional nitrogen as byproduct; System C has the highest hydrogen generation ratio and its CGE is moderate and is 60%. The carbon dioxide sequestration rates of the three systems are all above 90%.     

Economic assessment on the use of energy storage to improve clustered wind generation transmission

在大规模风电并网过程中输电容量不足造成的弃风损失越来越严重的情况下,分析了影响输电容量大小的因素,提出了利用储能系统提高风电外送能力的优化方法,建立基于储能系统的输电线路效益经济评估模型,综合考虑了风电的输送需求,输电工程成本,输电运行效益,储能投资成本以及可能阻塞弃风损失等因素,提出了以综合效益最大为目标的输电线路储能系统配置方法.针对某省大型风电基地,利用本文提出的模型及方法对风电场配置储能设备以改善输电容量受限情况,算例结果验证所建模型及方法的合理性,并分析了储能价格等因素对储能系统配置结果的影响.     

Mathematical modelling of hydrogen storage systems

A detailed mathematical model of a hydride bed has been developed to describe its behaviour under both hydriding and dehydriding conditions. In contrast to other hydride bed models previously reported in the literature, this model simulates an actual, commercially available containment vessel, rather than that of an abstract ideal situation. Thus the model provides a convenient means of predicting the time taken to release or absorb given amounts of hydrogen. These are calculated from the heat transfer characteristics and diffusion properties of particular metal alloys. Comparisons are given between the actual operating characteristics and those simulated by the model. A brief discussion of the reaction kinetics of hydriding certain metal alloys is also included.     

Wind forecasts for wind power generation using the Eta model

The goal of this article is to apply the regional atmospheric numerical weather prediction Eta model and describe its performance in validation of the wind forecasts for wind power plants. Wind power generation depends on wind speed. Wind speed is converted into power through characteristic curve of a wind turbine. The forecasting of wind speed and wind power has the same principle.Two sets of Eta model forecasts are made: one with a coarse resolution of 22 km, and another with a nested grid of 3.5 km, centered on the Nasudden power plants, (18.22°E, 57.07°N; 3 m) at island Gotland, Sweden. The coarse resolution forecasts were used for the boundary conditions of the nested runs. Verification is made for the nested grid model, for summers of 1996–1999, with a total number of 19 536 pairs of forecast and observed winds. The Eta model is compared against the wind observed at the nearest surface station and against the wind turbine tower 10 m wind. As a separate effort, the Eta model wind is compared against the wind from tower observations at a number of levels (38, 54, 75 and 96 m).Four common measures of accuracy relative to observations - mean difference (bias), mean absolute difference, root mean square difference and correlation coefficient are evaluated. In addition, scatter plots of the observed and predicted pairs at 10 and 96 m are generated. Average overall results of the Eta model 10 m wind fits to tower observations are: mean difference (bias) of 0.48 m/s, mean absolute difference of 1.14 m/s, root mean square difference of 1.38 m/s, and the correlation coefficient of 0.79. Average values for the upper tower observation levels are the mean difference (bias) of 0.40 m/s; mean absolute difference of 1.46 m/s; root mean square difference of 1.84 m/s and the correlation coefficient of 0.80.     

Matrix modelling of small-scale trigeneration systems and application to operational optimization

Combined production of electricity, heat and cooling power in trigeneration represents a key option for the development of high-efficiency and cost-effective integrated energy systems. The complexity of the possible plant schemes calls for the adoption of general models handling multiple interconnected components and energy flows of various typologies. This paper presents a comprehensive input–output matrix approach aimed at modelling small-scale trigeneration equipment taking into account the interactions among plant components and external energy networks. Starting from the definitions of specific efficiency matrices for each plant component and from a matrix representation of the relevant interconnections, an overall efficiency matrix representing the whole plant is constructed. This construction is carried out by means of an original procedure, suitable for automatic and symbolic implementation, which, exploiting graph theory concepts, explores the tree formed by the backward paths from outputs to inputs. The proposed formulation maintains the separation among the individual energy vectors, each of which can be associated to its time-dependent price, providing the basic framework for formulating optimization problems concerning management of trigeneration systems within an energy market context. A numerical example referred to the optimal operation of a composite scheme with absorption and electric chillers is illustrated and discussed. The results obtained show the modelling effectiveness of the proposed matrix formulation.     

Solar radiation modelling for the simulation of photovoltaic systems

The effect of 12 different combinations of diffuse–global correlations and tilted surface radiation models on the accuracy of PV output simulation of a grid-connected photovoltaic (PV) system was studied using statistical methods. A site specific diffuse–global correlation was developed using local insolation data and the performance of this model was compared with those of two other diffuse–global correlations. The impact of diffuse–global correlations on the calculated inclined insolation for four different tilted surface radiation models was investigated on annual, seasonal and monthly basis. The accuracies of predicted 45° inclined plane insolation and PV output were improved when the site specific diffuse–global correlation was used in the main simulation model. The error between measured and predicted inclined insolation was higher in winter than summer. The prediction of PV output was improved by using an isotropic sky tilted surface radiation model instead of the anisotropic models. The accuracy of PV output was also improved when the proposed diffuse–global correlation was used.     

Development of general-purpose software to analyze the steady state of power generation systems

It is important to improve the power generation efficiency of thermal power generation while promoting the location of nuclear power generation to reduce discharge of carbon dioxide from the power generation plants.Software, which effectively examines the performance of the power generation system of various configurations, can contribute to the development of a highly effective, excellent in environmental thermal power generation systems.For this purpose, authors developed a new method to calculate the steady state of power generation systems, such as heat and mass balance, efficiencies, etc. This method is very flexible in calculation condition setting. Then we developed a general-purpose software by which the steady state behavior of the power generation system is analyzed easily.     

Application of Exergoeconomics to the Analysis and Optimization of Process Systems

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风光互补对电网输电服务价格的影响

风电和光电各自出力的不稳定性提高了输电服务成本,制约了它们的发展.利用风能和太阳能的互补性可提高发电的可靠性.研究了风光互补后对电网输电服务价格的影响,提出了考虑可再生能源并网的输电服务价格函数表达式,建立了以该函数值最小为目标,以系统发电不足概率(LOLP)和能量缺失率(LPSP)为约束条件的输电服务价格优化模型.采用粒子群算法对目标函数进行求解,对风光互补前后的输电服务价格进行对比,并求出使输电服务价格最低的风光容量配比.通过对实例系统进行计算,验证了该方法的有效性,指出风光互补能有效地降低输电服务价格.     

Future development of the electricity systems with distributed generation

Electrical power systems have been traditionally designed taking energy from high-voltage levels, and distributing it to lower voltage level networks. There are large generation units connected to transmission networks. But in the future there will be a large number of small generators connected to the distribution networks. Efficient integration of this distributed generation requires network innovations. A development of active distribution network management, from centralised to more distributed system management, is needed. Information, communication, and control infrastructures will be needed with increasing complexity of system management. Some innovative concepts such as microgrids and virtual utilities will be presented.     

Power limits of grid-connected modern wind energy systems

Wind energy is a prominent area of application of variable speed generators operating on the constant grid frequency. A modern wind energy system of this type consists of a surface mounted permanent-magnet generator with a frequency converter, which allows variable speed operation. The maximum power capability of the wind energy system is limited by the grid inverter. The theoretical formulation for active and reactive power limits is given. This formulation is used to set power reference limits to the inverter. Two different regions are distinguished depending on the tolerable Ac current harmonic distortion. Experimental results in a variable frequency wind energy generation system are shown.