This paper develops an improved dynamic reliability model for compressor rotor system, defined as a “unconventional active system” here. First, regarding to the variety of system-component connections, system specific reliability modeling technique is presented, in which the stress and strength are both nonnegative stochastic processes. The new model fully considers the load characteristics of rotor blades, and inherently embodied the effect of the statistical dependence between the failures of the rotor blades. Then, calculated by the new model, the relationship between reliability and time, and that between the hazard rate and time, for a compressor rotor system are discussed, respectively. Comparing to the traditional series system reliability model, the new system reliability model developed in this paper has higher accuracy for compressor rotor system, since the traditional models neglect the difference between compressor rotor system and traditional active system. Moreover, in order to master the cruise characteristics of the aero-plane during reliability analysis of its compressor rotor blade set, a flight cruise is separated into several stages based on the value of Mach number and its change rate, and a subsection solution method is innovatively proposed accordingly. At the end of the paper, a certain cruise of fighter plane is analyzed to verify the accuracy of the new method. The results show that, as to a flight cruise with different stages, the new method is basically reasonable to most of the load histories, especially for the situation with impact loads existing.

Reliability Analysis of Aero-Engine Compressor Rotor System Considering Cruise Characteristics

Due to the lack of the support from the main grid, the islanded hybrid ac/dc microgrid will more likely cause the power flow severe fluctuation and even the microgrid to be split once a serious contingency occurs. To maintain the security and stability of the system under such a condition, this paper proposes a new static security risk assessment of the islanded hybrid ac/dc microgrid considering that the hybrid ac/dc microgrid was split. First, this paper presents a static security analysis criterion to determine the post-contingencies splitting scheme and a new load-shedding strategy to achieve power balance of subsystems. On this basis, a probabilistic power flow calculation method based on Levenberg-Marquardt with a nonmonotone line search (LMNL) algorithm is applied to calculate the probabilistic power flow of the islanded subsystems. Finally, the probability distribution of static security risk assessment indexes, including the dc loss load risk, ac loss load risk, and interlinking converter (ILC) active power limit violation risk, are obtained. The simulation results on the test system demonstrate the necessity of considering the hybrid ac/dc microgrid was split, and prove the feasibility and effectiveness of the proposed method.

/pdf/static-security-risk-assessment-for-islanded-hybrid-ac-dc-2rom7sk15y.pdf

Static Security Risk Assessment for Islanded Hybrid AC/DC Microgrid

Identifying and preferentially reinforcing critical lines for skeleton-network of power systems is significant in improving the secure and stable operation of power systems under extreme weather conditions. Under this background, in this paper, six indexes are first presented for identifying critical lines for skeleton-network with the power elements’ parameters and the impact of extreme weather conditions, the network topology and the operation state of power systems considered. Then, the modified Vise Kriterijumska Optimizacija I Kompromisno Resenje in Serbian (VIKOR) method, in which the synthetic weights of indexes determined by the combination weighting method are adopted, is utilized to identify the importance degrees of lines in a given power system. Both the overall performance and the outstanding individual performance of lines are considered, which is beneficial for the critical lines identification for skeleton-network. Finally, the proposed multi-indexes and methods are applied to part of the actual Guangdong power system in China. The numerical results are compared with those obtained by single-attribute and multi-attribute evaluation methods and other evaluation methods.

https://www.mdpi.com/1996-1073/11/6/1355/pdf

Critical Lines Identification for Skeleton-Network of Power Systems under Extreme Weather Conditions Based on the Modified VIKOR Method

Traditional approaches to identifying critical lines mainly focus on the output of thermal power units, ignoring access to renewable energy (RE) in the power system. However, the integration of RE represented by wind power will affect the stability of the power system, as well as the identification of critical lines. So considering the uncertainty of wind power output, the discrete probability distribution method is adapted to construct wind power fluctuation prediction scenarios in this paper. To improve the accuracy of critical line identification, a synthetic power flow index is proposed, from the perspective of the operational state and topology of the power grid. Firstly, in terms of operation status, the power flow entropy method is modified by taking the line load rate as the research object to show the impact of power flow transfer. Then the topological relationship is used to weight the power flow betweenness, reflecting the network structure of the power grid. Finally, the synthetic index is drawn by combining modified power flow entropy with weighted power flow betweenness. Simulation on IEEE 39 nodes system integrated with wind farms verifies the effectiveness of the proposed method. The result of identification will be helpful to ensure the security and reliability of the grid.

Comprehensive Identification of Critical Line in Power System with Large-Scale Wind Farms Integration

According to the statistics on reliability indices of nation-wide 220 kV and the above power transmission and transformation facilities in 2008, the main causes of scheduled and unscheduled outages were analyzed and evaluated, which affected the reliability of 3 kinds of power transmission and transformation facilities - transformer, circuit breaker and overhead line, and the main influencing causes of scheduled and forced interruption were analyzed and evaluated. Through the analysis of reliability indices in recent years, the changing tendency that affected the main causes of reliability was put forward, which provided the beneficial basis for improving the reliability of power transmission and transformation facilities in the coming years.

Statistic analysis on reliability of power transmission and transformation facilities in China in 2008

A comprehensive identification model of critical lines in electric power grid is proposed in this paper. First, the index system is established considering both operational condition of electric power grid and its topological structure. Then utility theory is applied to process those sub indices and the comprehensive identification index of critical lines is proposed. However previous studies have not considered seriously the different value of each index in the identification process. To meet this deficiency, this paper applies analytic hierarchy process, entropy-right method and maximizing deviations method to calculate the subjective weight and objective weight of each sub index respectively. To diminish the error of each weight determination method, theory of cooperative game is applied to obtain the combination weight of each index. At last, IEEE 39-bus system is used for analysis. The results show the application of utility theory enhances discrimination between critical lines and general lines. The comparison with the results of previous researches demonstrates the feasibility and validity of this model.

The comprehensive identification model of critical lines in electric power grid based on utility theory and cooperative game

The substation is an important part of power system, its bus arrangement reliability is directly related to the reliability of power supply. Aiming at the uncertainty of electrical components parameters in reliability assessment, a substaion bus arrangement reliability assessment method based on interval Bayesian Network is proposed in this paper. This method divides the system network structure into element layer, equivalent element layer, path set layer, load point layer and system layer. By applying the bi-direction reasoning model of the Bayesian network for reliability assessment, the interval reliability indices of the load points and system as well as the weak links of the system are evaluated. In additon, the influence of component parameters on interval reliability indices of system is studied through sensitivity analysis. The numerical examples demonstrate that, compared with the traditional Bayesian Network, the reliability parameters of electrical components are represented in the form of interval number in this method, which considers the effects of parameters' uncertainties on system reliability indices throughout the calculation process.

The application of interval Bayesian network method in the reliability assessment of substation bus arrangement

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The comprehensive identification model of critical lines in electric power grid based on utility theory and cooperative game

The application of interval Bayesian network method in the reliability assessment of substation bus arrangement