Voltage collapse prediction for interconnected power systems

Voltage Stability Enhancement on IEEE 14 Bus System

This paper proposes a new congestion management (CM) approach by using the generation rescheduling and load shedding, with the realistic voltage-dependent load modeling. The paper presents several objective functions such as generation and load shedding cost minimization (GLCM)/social welfare maximization including demand response offers (SWM), load shedding minimization ( $P_{\rm shd}$ M), load served maximization (LSM), and load served error minimization. To the best of our knowledge, all previous CM efforts considered constant load models. Using voltage-dependent load models, the paper clearly brings out the inappropriateness of conventional single objectives for CM, such as GLCM/SWM and $P_{\rm shd}$ M, due to the reduction of amount of load served. Therefore, multi-objective optimization is required and the objectives can be judiciously combined depending on the loading condition. Multi-objective strength pareto evolutionary algorithm 2+ has been employed to solve the proposed CM problem. The effectiveness of the developed approach is confirmed from the simulation results on IEEE 30 bus test system.

Modal analysis and reactive power reserve method are applied in the Entergy electrical system to find the buses and zones prone to voltage instability. In the modal analysis method, weak zones are identified by monitoring the participation factor of the buses in the critical modes. In the reactive power reserve method, reactive power reserves of the zones are monitored for single line outages, generator outages, and double line outages and the zones that have exhausted their reactive power reserves are identified as critical. The critical contingencies resulting in the smallest stability margins are also computed, and are ranked in the order of severity. The voltage stability assessment tool (VSAT) developed by Powertech Labs, is used to determine the weak zones and to determine the critical contingencies.

Effect of load models on assessment of energy losses in distributed generation planning

This paper continues the pursuit of getting a deeper understanding regarding the transient stability of low-frequency AC railway power systems operated at 16 2/3 Hz synchronously to the public grid. The focus is set on the impact of different load models. A simple constant-current load model is proposed and compared to a previously proposed and studied load model in which the train’s active power is regulated. The study and comparison is made on exactly the same cases as and grid as with the already proposed and more advanced load model. The railway grid is equipped with a low-frequency AC high-voltage transmission line which is subjected to a fault. The study is limited to railways being fed by different distributions of RFC (Rotary Frequency Converter) types. Both AT (auto transformer) and BT (booster transformer) catenaries are considered. The RFC dynamic models are essentially Anderson-Fouad models of two synchronous machines coupled mechanically by their rotors being connected to the same shaft. The differences in load behaviour between the proposed constant-current load model and the previously proposed and studied voltage-dependent active power load model are analyzed and described in the paper.

This paper substantially advances Nieter and Singh’s acoustic modal analysis technique [J. Acoust. Soc. Am. 72, 319–326 (1983)] which used the coincident-quadrature response method to extract acoustic global properties of one-dimensional systems. Here a technique to identify modal parameters including damping of a three-dimensional cavity is proposed. The cavity is excited by a convertible acoustic driver whose volume velocity is monitored. Acoustic transfer impedance database is obtained for a number of cavity boundary locations which are chosen such that all modes of interest can be adequately described. The vector diagram method is used to fit the measured database in the neighborhood of each resonance frequency with a circle. The experimental technique proposed here has been verified by applying it first to a cylindrical cavity whose exact eigensolutions are known. Then for an annularlike cavity, experimentally extracted natural frequencies and pressure mode shapes are found to agree well with the results of a finite element model. The significance of this paper lies in the successful demonstration of an experimental technique which can be used for diagnosing the acoustics of irregular shaped cavities. The proposed technique also offers an alternative to the finite element method for acoustic modal analysis of three-dimensional ducts and resonators of irregular shapes and/or with complicated boundary conditions.

Voltage stability is an important factor, which needs to be taken into consideration in order to avoid voltage collapse. There are different methods used to study the voltage collapse phenomenon. In this paper, V-Q Sensitivity and Modal analyses methods are implemented on IEEE 14 bus system. Modal analysis method makes use the Jacobian matrix to determine the eigenvalues necessary to evaluate the voltage stability and V-Q Sensitivity method makes use of the diagonal elements of the inverse of reduced Jacobian matrix to a assess this stability. In this paper, our main objective is to apply V-Q Sensitivity and Modal analysis methods by analyzing the effect of neglecting the weak coupling between reactive power Q and voltage angle δ A comparison in terms of the weakest buses is made between the results obtained by taking into account the weak coupling between Q and δ, i.e., by considering the reduced Jacobian matrix and those obtained by neglecting this coupling.

Since the noise generated by mechanical structures affects the merchantability, it is important to predict the noise and vibratory characteristics at the first design stage. The frames and panels or trim parts in automobiles are coupled systems of the rigid and flexible substructure. In these systems, vibration of the flexible structures often becomes one of the major noise sources when the excitation force is applied to the rigid structure. FEM and modal analysis technique are not sufficient to carry out the effective low noise design in higher frequency because of high modal density and complexity of mode shape. Modal energy propagation method, proposed in this paper, is based on the mode synthesis method and the vibration power flow between the eigen modes of the rigid and flexible structures. Previous studies have verified that the vibration level can be reduced by extracting modes that contribute highly to the vibration power flow between subsystems and changing their characteristics. In this report, we present the results of applying this method to a coupled system of a body and panel structures in automobiles and verifying its validity. The structural modifications obtained from this analysis method were verified for their effectiveness in decreasing vibration.

<span lang="EN-US">Voltage Stability has emerged in recent decades as one of the most common phenomena, occurrence in Electrical Power Systems. Prior researches focused on the development of algorithm indices to solve the stability problem and in the determination of factors with most influence in voltage collapse to solve the stability problem. This paper evaluates the influence that the load dependence has with the voltage on the phenomenon of the voltage stability and especially on the characteristics the collapse point or instability point. Load modeling used is detailed and comparisons of the results obtained are made with those described in the bibliography and those obtained with commercial software. The results of the load margin are also compared when a constant load or a voltage-dependent load is considered as well as the values obtained at the maximum load point and the point of voltage instability.</span>

Voltage collapse is a problem that may happen when power systems are overloaded. An accurate estimation of critical operating conditions is necessary to prevent voltage collapses in power grids. Accurately predicting voltage collapse in the network will help the operators take timely rectification by monitoring the system and its closeness to the voltage collapse. This article suggests a more accurate voltage collapse prediction for identifying weak buses and critical lines based on a new proposed index termed Modern Voltage Stability Index (MVSI). The proposed index ignores the line resistance partially, i.e., the method consists of zeroing the resistance of a part and not entirely of the exact formula of the system to develop an approximate and fast collapse prediction index. It indicates that entirely ignoring the line resistance creates an erroneous voltage collapse prediction that may exceed 70%. For verification purposes, this study compared the existing stability indices (Lmn, FVSI, LQP, NLSI, VSLI and NVSI) with the proposed index based on the variables contained in each index, simulation results and percent errors. Determining the influences of the relative directions of real and reactive power-flow in the branches is one of the most important considerations of the proposed index to predict voltage collapse. Different load conditions have been used to examine the feasibility and performance of the proposed index in collapse predictions. Under several load conditions, the performance of MVSI has been compared with the performance of Lmn, FVSI, LQP, NLSI, VSLI and NVSI to determine the highest performance among them in collapse predictions. Usually, the voltage stability is very sensitive to reactive power-flow. Therefore, the maximum reactive power loads in each particular bus have been determined in this article based on a new proposed index (MVSI). The bus which can withstand the lowest maximum reactive power before the collapse is ranked as the highest ranking, and it is considered the weakest bus in the system. The proposed index is examined on IEEE 30-bus to validate its practicability. The weak areas of EPSN have been diagnosed, studied, and evaluated by the smooth method with the help of the MATLAB environment.

Voltage collapse is an undesired phenomenon that occurs due to voltage instability and is generally associated with weak or stressed system (heavily loaded lines), long lines, radial networks, faults and/or reactive power shortages. Its occurrence is not frequent in developed countries despite their large and complex networks but its frequency is high in Egypt. Voltage collapses are highly catastrophic anytime they occur. On the Egyptian Interconnected Electrical Grid EIEG, the system collapse phenomenon is frequently experienced and often leads to either partial or total system collapse blackout, which greatly impairs the nation's socio-economic development and industrialization. This high rate is due to the fact that the EIEG is weak, highly stressed, long and radial in nature hence lacking flexibility. The analysis is performed for EIEG power system. Modern advances in technology are changing the way utility industry increase the transmission of power throughout the country. Distributed energy resources are constantly improving their reliability and power capabilities. The model analysis technique is performed for system using the constant load model. The simulation results are Q-V curves on weak voltages by Power World Simulator PWS Software and Matlab Program.

This paper is a test case study based paper. In this paper, line indices-based approach is utilized for testing the effect of various load models on estimation of maximum acceptable load at weak bus of a particular power system. It has lot of importance for the voltage stability analysis. Based on result analysis, most preferable load at a bus or substation is also identified. Different exponential-type load models and composite load models are considered in this work. The change of weak bus voltage and maximum load for various load models are analyzed. Each line loss and total loss in the system for different load models are also analyzed. Methodology of this work is implemented on standard IEEE 14 bus test case system. All the simulations of this work are implemented in MATLAB 2019a.

The crankshaft is a very crucial part in an internal combustion engine. This paper presents the findings of the mode shape and natural frequency of 3 cylinder 4 stroke engine crankshafts. Both experimental and computational methods were carried out to determine the modal parameter or dynamic characteristics, which are natural frequency, damping factor and mode shape. The prediction of the dynamic properties of the chassis is of great significance in determining the natural frequencies of the structure. The experiment is done by using an impact hammer to excite the crankshaft and data is recorded using a data acquisition system (DAS) connected to a sensor located on the crankshaft. Computational modal analysis on the crankshaft structure is simulated using finite element software. It can be seen from the results that there is a good agreement between the experimental and computational results in terms of modal parameter with a small discrepancy. The modal analysis techniques are essential for automotive crankshaft structure design.

Modal analysis techniques are widely used to characterize vibrations in structures, vehicles, machinery, etc. Modal parameters obtained through modal analysis are useful for structural health monitoring and condition monitoring. The common goal is to ensure the integrity of a mechanical system through monitoring of different operational conditions. Operational conditions described by spatial measurements can for instance be used to observe the vibration characteristics of the system and its parts. Therefore, the main originality of this work is to experimentally investigate if the presence of a turbulent gas flow in seal geometries can facilitate operational modal analysis for a coupled rotor–foundation system. A consistent and automatic way of obtaining the vibration characteristics is necessary to be included in the monitoring schemes. Therefore, this work also proposes a method to automatically obtain modal parameters for a bed plate of a rotor–foundation system when the rotor is affected by active magnetic bearings and gas seals. The automatic modal parameter algorithm is built on the stabilization diagram of modal parameters obtained from the stochastic subspace identification. Intermediate results from the automatic modal parameter algorithm show that some of the distance measures i.e., dωn,d, dζ, dMACX, dλ, dMACXωn,d, dMACXζ, and dMACXλ, for modal parameters in a stabilization diagram are better suited than others when distinguishing between possible physical modes and certainly spurious poles. The frequency band of interest for the system is found to influence the number of possible physical modes identified by the automatic algorithm. Measurements from 13 roving accelerometers are combined with the automatic modal parameter algorithm to obtain the vibration characteristics of the rotor and bed plate. For different operational conditions in the seal geometry, seven modes are consistently identified as physical modes by the automatic modal parameter algorithm. The algorithm uses (i) a combination of a white noise disturbance pattern intentionally introduced into the system through the active magnetic bearings and (ii) the operational disturbance coming from the seals, non-intentionally introduced by the turbulent gas flow. The seven physical modes are also identified when (iii) the rotor–foundation system is only disturbed from the turbulent gas flow in the seals. The seven physical modes identified by the algorithm under conditions (i), (ii), and (iii) compare well to the vibration characteristics found in experiments via experimental modal analysis and impact hammer testing as well as via a mathematical model of the rotor–foundation system.

Every transmission system has voltage stability limit which may lead to voltage collapse if an undetected bulk transmission network is operated close to its operating limit. This research work uses continuation power flow method to identify voltage collapse point for Bangladesh Power System Network (BPSN). For the identification of weak buses, an analytical based technique of tangent factor has been presented. The risk of voltage collapse has been mitigated by placing SVCs at the weak buses of the system using load flow analysis. Moreover, sensitivity based approach has been introduced to determine optimal location of Static VAR Compensator (SVC) for the voltage security enhancement. A comparative analysis has been documented considering the size of reactive power to improve the loading factor of the overall network at the end of this work.