Stability Assessment Method Research Articles

Power System Transient Stability Based on Data Mining Theory

In order to study the stability of power system, a power system transient stability based on data mining theory is designed. By introducing association rules analysis in data mining theory, an association classification method for transient stability assessment is presented. A mathematical model of transient stability assessment based on data mining technology is established. Meanwhile, combining rule reasoning with classification prediction, the method of association classification is proposed to perform transient stability assessment. The transient stability index is used to identify the samples that cannot be correctly classified in association classification. Then, according to the critical stability of each sample, the time domain simulation method is used to determine the state, so as to ensure the accuracy of the final results. The results show that this stability assessment system can improve the speed of operation under the premise that the analysis result is completely correct, and the improved algorithm can find out the inherent relation between the change of power system operation mode and the change of transient stability degree.

Application of a Channel Stability Assessment Method near Bridges and Culverts: Case Study in Parana State, Brazil

Application of a Channel Stability Assessment Method near Bridges and Culverts: Case Study in Parana State, Brazil

An interval Taylor-based method for transient stability assessment of power systems with uncertainties

Transient stability assessment needs to be further studied when confronted with uncertainties brought in by the integration of renewable energy and measurement errors. This paper outlines a novel method based on interval Taylor expansion incorporated optimal solution technique to solve the uncertainty model for transient stability assessment. Uncertainty assessment framework for power systems transient stability is described as ordinary differential equations with interval variables, which can be equivalently transformed into three sets of ordinary differential equations with only deterministic parameters using the interval Taylor method with second-order expansion. In order to further reduce the overestimation, a quadratic programming model is constructed to estimate upper and lower boundaries of state variables. Application of the proposed method is implemented in SIMB system and IEEE-30 system and the results are demonstrated in details. Comparisons with affine arithmetic (AA)-based method and Monte Carlo method verify the effectiveness and better performance of the proposed method.

GECM-Based Voltage Stability Assessment Using Wide-Area Synchrophasors

Voltage instability is a crucial issue in the secure operation of power grids. Several methods for voltage stability assessment were presented. Some of them are highly computationally intensive, while others are reported not to work properly under all circumstances. This paper proposes a new methodology based on the generator equivalent circuit model (GECM) and the phasor measurement unit (PMU) technology for online voltage stability monitoring of a power grid. First, the proposed methodology utilizes synchronized phasor (synchrophasor) measurements to determine the impedance parameters of a transmission grid by means of the recursive least squares (RLS) algorithm. Furthermore, it incorporates the dynamic models of generators to handle the cases with generator reactive power limit violations. After that, an enhanced voltage stability index with GECMs incorporated is developed for reliable and accurate voltage stability assessment. The proposed methodology was first demonstrated on several standard IEEE power systems, and then applied to a practical power system, the Taiwan power (Taipower) system. The test results demonstrate the flexibility and effectiveness of the proposed methodology.

Evaluation of rock fracture patterns based on the element-free Galerkin method for stability assessment of a highly pressurized gas storage cavern

Reasonable failure paths are crucial in the stability assessment of a highly pressurized gas storage cavern in a rock mass using limit equilibrium analysis. In this study, the fracture patterns in the rock mass around a gas storage cavern are evaluated based on the element-free Galerkin (EFG) method with a cohesive crack model. The proposed analysis method was first validated through scaled-down model testing results before extending to a full-scale problem. Using the current approach, a parametric sensitivity analysis was performed by taking into account the influences of the stress ratio, the depth of the cavern, and the tensile strength of the rock mass. Based on the analysis results obtained, this research showed that the representative failure paths, in which the uplift evaluation is necessary, can be established from the EFG results with careful consideration of crack initiation and the propagation direction. The site having an in situ stress ratio greater than 1.2 is preferred for operation of underground gas storage caverns. By performing the limit equilibrium analyses for stability assessment of the rock mass above the pressurized cavern, we demonstrated that the factor of safety against uplift computed from the failure paths established in this study is higher than or equal to those obtained from analyses with the simplified models in previous studies without considering the influence parameters on the fracture patterns.

Improving the Design Process of Pleasure Yachts for CE RCD Certification via Modification to Buoyancy and Stability Assessment Method

CE RCD (Recreational Craft Directive) is a certification for the design and construction of small vessels, including pleasure yachts, which are widely used not only in the countries within the European Union, but also in Japan and Southeast Asia. Recently, South Korean leisure craft shipyards have developed interest in exporting to foreign leisure craft markets such as Europe; however, they have encountered difficulties because of the CE RCD regulations, which are relatively complex and difficult to understand. The requirements for buoyancy and stability, which are essential properties that must be understood within the early stage of ship design, are defined based on ISO 12217. However, preparing this assessment according to ship classification regulations is an exceedingly complex task, even with knowledge of naval architecture. In this research, we have developed design support tools to systematically support assessments and preemptively define design information so that buoyancy and stability assessments based on ISO 12217 can be systematically prepared. Our research results were applied to actual examples of yacht design to confirm validity. We believe that the improved yacht design process presented in this research can act as a foundational reference for enhancing the effectiveness and systematic buoyancy and stability assessments.

Dynamic equivalent of wind farm model for power system stability studies

ABSTRACTA new dynamic equivalencing method for stability assessment of a grid-integrated wind farm is proposed in this article. The accuracy of the method is validated for a 34-bus system with 28-unit wind farm connected to Indian utility system. This wind farm consists of several wind turbines of two different ratings. The electrical parameters of the equivalent generator are derived from the mathematical model of the squirrel-cage induction generator. The parameters of the equivalent wind-turbine generator are optimized to yield minimum deviation from the detailed system response using genetic algorithm. The small-signal and transient stability responses of the study system with detail wind farm and equivalent model are simulated using MATLAB. Equivalent model eigenvalues are compared to the centre of inertia based detailed system eigenvalue. In addition, the computed eigenvalues and time-domain responses of the proposed equivalent model, detailed wind farm are compared against weighted model proposed earlier. In most of the investigated cases, the average error of dynamic responses between the proposed equivalent and detailed models are less when compared to weighted model. Thus, the large-signal responses of the proposed equivalent model show superior agreement with detailed system response.

Discussion of “experiment and statistical assessment on piping failures in soils with different gradations”

ABSTRACTInternal stability assessment methods, such as Kezdi and Kenney and Lau, have some degree of uncertainty and they do not take the effect of soil density in consideration. Analysis show that the internal stability of some granular soils could be stable, transition state, or unstable based on the relative density. All these factors could affect the accuracy of statistical analysis based on the assessment of these methods.

Stability assessment approach for soil slopes in seasonal cold regions

In Hokkaido Japan, soil slope failures along some of the national highways are reported frequently in recent years. A stability assessment method which can consider the impact of seasonal changes like freeze-thaw action, snowmelt water infiltration etc. is of utmost importance and considered to be an immediate requirement for geotechnical practitioners, in order to properly predict the slope stability. In this study, a slope stability assessment approach based on two-dimensional numerical modelling is recommended which considers the water content changes of the soil induced by the seasonal climatic effects i.e. freeze-thaw action, snowmelt water infiltration etc. Two case studies of slope failures in Hokkaido have been studied using the recommended approach. In order to visualise the climatic parameters of most influence on slope stability, parametric studies have been performed through which many useful results in view of the soil slope stability in seasonal cold regions have been obtained. It is found that the freeze-thaw action has a considerable impact on the soil water content and slope stability. On the other hand, the snowmelt water infiltration has a very significant impact on soil slope stability. The recommended numerical modelling approach is found to be very useful in analysing the soil slope stability in seasonal cold regions.

Potentials and limits to basin stability estimation

Stability assessment methods for dynamical systems have recently been complemented by basin stability and derived measures, i.e. probabilistic statements whether systems remain in a basin of attraction given a distribution of perturbations. Their application requires numerical estimation via Monte Carlo sampling and integration of differential equations. Here, we analyse the applicability of basin stability to systems with basin geometries that are challenging for this numerical method, having fractal basin boundaries and riddled or intermingled basins of attraction. We find that numerical basin stability estimation is still meaningful for fractal boundaries but reaches its limits for riddled basins with holes.

Aerodynamic force and moment measurement for crosswind stability assessment in a compact wind tunnel

Rolling stock is sensitive to crosswind because of its large side area, so crosswind stability must be assessed when rolling stock is developed. In the European Union, aerodynamic force and moment under crosswind need to be measured in a wind tunnel experiment in accordance with European Norm EN14067-6, which describes the methods of crosswind stability assessment. In this report, we present a measurement system developed on the basis of the European Norm to check the aerodynamic force and moment of the designed rolling stock in a compact wind tunnel. For precise measurement, by effectively using a limited air flow rate, an adequate quality of flow must be acquired from the nozzle and the same flow around the train model must be simulated as the European wind tunnels, in which the measured aerodynamic force and moment were described as the reference value in the European Norm. To achieve this flow, a wide nozzle and a splitter plate were developed. For the wide nozzle design, first, from the relationship between the train model scale and the specifications, the train model scale and the outlet size of the wide nozzle were determined, and an adequate contraction from the inlet area to the outlet area was designed. The splitter plate height was optimized in a simulation to satisfy the boundary layer thickness and acquire sufficient vertical space above the train model. The results revealed that the developed measurement system can satisfy the equipment requirements and flow specifications defined in the European Norm. Additionally, the rolling moment around the leeward rail of a wind tunnel benchmark vehicle model, which is defined in European Norm, was measured within a mean tolerance 0.086 from the reference value described in the European Norm. This shows that the developed measurement system for a compact wind tunnel has the same measurement accuracy as the reference wind tunnel described in the European Norm.

Rapid Method for Assessment of Soil Structural Stability by Turbidimeter

Core Ideas A quantitative dispersion assessment chart is developed for rapid diagnosis of soil structural stability. Turbidity and the amount of dispersed clay have a strong linear relationship. The color and mean particle size of colloidal solution has a negligible effect on the linearity of turbidity. A rapid and inexpensive method to evaluate soil structural stability via assessment of soil clay dispersion is needed. Such a method would provide critical information for decision‐making for soil and agricultural management not currently undertaken due to the expense of testing. The aim of this work was to validate the use of a turbidimeter for quantifying clay released from soil and to relate this back to dispersive parameters. Ten Australian soils with different physicochemical properties were studied. Six‐step dilution was used to adjust the clay suspensions sequentially by dilution from a datum concentration of 4000 nephelometric turbidity units (NTU). The linearity of turbidity by dilution was verified, considering the effects of soil color and mean particle size. There was a strong correlation between turbidity (NTU) and dispersed clay (mg L−1, % of soil) for each soil. Clay particle size was related to turbidity response, although the coefficients between turbidity and dispersed clay were very close irrespective of mean particle size differences. Dispersed clay was concluded to be accurately quantified using a turbidimeter after spontaneous and mechanical dispersion. A semi‐quantitative dispersion assessment chart was developed for rapid assessment of soil structural stability, the application of which is intended to provide rapid diagnosis and to act as an important index for soil management practitioners. Additionally, when dispersed clay was combined with electrical conductivity and clay content parameters, the dispersive indices (cation ratio of soil structural stability and exchangeable dispersive percentage) were reasonably predicted at a resolution useful for farm management decisions.

Numerical polynomial homotopy continuation method to locate all the power flow solutions

The manuscript addresses the problem of finding all solutions of power flow equations or other similar non-linear system of algebraic equations. This problem arises naturally in a number of power systems contexts, most importantly the direct methods for transient stability analysis and voltage stability assessment. Here, the authors introduce a novel form of homotopy continuation method called the numerical polynomial homotopy continuation method that is mathematically guaranteed to find all the solutions without ever encountering a bifurcation. Since finding real solutions is much more challenging, first the authors embed the real form of power flow equation in complex space, and then track the generally unphysical solutions with complex values of real and imaginary parts of the voltages. The solutions converge to physical real form in the end of the homotopy. The so-called gamma-trick mathematically rigorously ensures that all the paths are well-behaved along the paths, so unlike other continuation approaches, no special handling of bifurcations is necessary. The method is embarrassingly parallelisable. The authors demonstrate the technique performance by solving several test cases up to the 14 buses. Finally, they discuss possible strategies for scaling the method to large size systems, and propose several applications for security assessments.

Seismic Upgrade of Earth Dams - Australian Practice

After the introduction of the ANCOLD Guidelines on the dam design to withstand earthquakes in 1998, many dams in Australia have been reviewed on their capacity to withstand earthquakes. As results, many of them have been upgraded in the last two decades to increase their resistance against seismic loading. This paper presents the current methods used in Australia to undertake seismic upgrade for earth dams. The paper firstly presents brief discussion on the current methods of seismic stability assessment of earth dams. It then discusses the advantages and limitations of the available methods for seismic rehabilitation. Finally, it presents one of the case histories of seismic upgrade in Victoria, Australia.

Experimental and numerical study on several crucial elements for predicting parametric roll in regular head seas

The methods for direct stability assessment of parametric roll are currently under development at the International Maritime Organization for the second generation intact stability criteria. To establish guidelines for developing accurate, but sufficiently simple prediction method, several elements required for modeling parametric roll in head waves are investigated by executing free running model experiments, partially restrained model experiments with and without surge motion and numerical simulations of uncoupled roll model, coupled surge–roll model and coupled heave–pitch–roll model for a C11 class containership. As a result, the following outcomes are obtained. First, the surge effect on parametric roll is generally small. Second, heave and pitch motions can have subharmonic components when parametric roll occurs. Third, the inclusion of the radiation and diffraction effects on restoring variation can result in more conservative prediction for parametric roll in head seas. Finally, the use of the uncoupled roll model could provide more conservative, but less time-consuming prediction for parametric roll than that of coupled heave–pitch–roll model.

Landslide Susceptibility in Cemented Volcanic Soils, Ask Region, Iran

Landslides are a major geohazard in the Alborz Mountains along the transportation links in Haraz valley, northern Iran. To find the appropriate analysis method for slope stability assessment of volcanic soils, a susceptible slope in the volcanic region of Ask has been modeled using finite difference and finite element methods. Slope stability is evaluated using both limit equilibrium and shear strength reduction methods. Analysis using the finite difference method coupled with shear strength reduction provided a more explicit explanation of the observed failure mode for moderately-cement volcanic soils in the region. Numerical analysis indicates a critical stability condition for the eastern flank of the slope. The failure is localized at the lower face of a travertine layer in the upper part of the slope. Travertine crust on top of the slope is in a state of tensional yield and fracturing. Crack opening in the top stone layer due to tensile strength reduction increases surface-water inflow and contributes to overall soil mass weakening by wetting.

Application of the envelope peaks over threshold (EPOT) method for probabilistic assessment of dynamic stability

This paper reviews the research and development of the Envelope Peaks over Threshold (EPOT) method that has taken place in the last three years. The EPOT method is intended for the statistical extrapolation of ship motions and accelerations from time-domain numerical simulations, or possibly, from a model test. To model the relationship between probability and time, the large roll angle events must be independent, so Poisson flow can be used. The method uses the envelope of the signal to ensure the independence of large exceedances. The most significant development was application of the generalized Pareto Distribution (GPD) for approximation of the tail, replacing the previously used Weibull distribution. This paper reviews the main aspects of modeling the GPD, including its mathematical justification, fitting the parameters of the distribution, and evaluating the probability of exceedance and its confidence interval.

Voltage Stability Assessment Using Equivalent Nodal Analysis

This paper presents a simple method for voltage stability assessment by reducing the bus impedance matrix of a network into its two-bus equivalent model at a referred bus. Closed-form equations of the equivalent model could then be derived to facilitate an equivalent nodal analysis at the referred bus to determine its voltage stability limit. The method was also shown to have parallels with the well-accepted modal analysis of the Jacobian matrix. These include defining geometric indices to identify critical buses and participation factors to quantify contribution of network elements to their criticality. The method however does not require post power flow solution processing of the Jacobian matrix; such computational advantage may make it suitable for online applications. The IEEE 300-bus system was tested with the method which was shown to be valid and computationally robust and efficient.

Utilization of Events Measured by WAMS-BIOZE-Detector for System Voltage Stability Evaluation

Abstract: The paper summarizes results of research work focused on development of the voltage stability assessment method and its software implementation. Developed voltage stability detection algorithm is based on local synchronous phasor measurement. The Thevenin equivalence based assessment method, the identification algorithm as well as the developed WAMS-BIOZE-Detektor software are presented. The proposed voltage stability indices have different sensitivity to events in power systems. Sensitivity of the indices was tested by using records of various disturbances and failures in a HV grid. Test results validate applicability of the indices in practice. Finally, the index with the highest applicability for online detection is recommended.

Analytical stochastic analysis of seismic stability of infinite slope

The sliding of natural slopes is usually governed by combination of soil parameters and earthquake characteristics. The inherent variability of these parameters which affect seismic slope stability dictates that the problem is of a probabilistic nature rather than being deterministic. Stochastic analysis of slope seismic stability has received attention in the literature and has been used as an effective tool to evaluate uncertainty so prevalent in the variables. In this research, the jointly distributed random variables method is used as an analytical method for stochastic analysis and reliability assessment of seismic stability of infinite slopes without seepage. The selected stochastic parameters are internal friction angle, cohesion and unit weight of soil, which are modeled using a truncated normal probability density function and the horizontal seismic coefficient which is considered to have a truncated exponential probability density function. The geometric parameters such as height and angle of the slope relative to a horizontal are regarded as constant parameters. The results are compared with the Monte Carlo simulation. Comparison of the results indicates superior performance of the proposed approach for assessment of reliability.