Power System Transient Stability Studies Research Articles

Deep Learning-Based Equivalent Modelling of Hybrid RES Plant for Efficient, Repetitive Power System Transient Stability Studies

The paper presents the methodology for dynamic equivalent modelling of hybrid renewable energy source (HRES) plant with the aim of obtaining highly accurate time domain HRES plant power responses at any time during the year. The focus is on equivalent modelling for transient stability studies. Historical HRES plant production dataset and transmission network short-circuit fault statistical data, along with unsupervised data mining and deep learning techniques, represent a basis of the modelling procedure. Dynamic equivalent model (DEM) is developed in the form of deep Long Short Term Memory network. Real and imaginary parts of voltage at the point of common coupling (PCC) are model inputs, while real and reactive power at the PCC are model outputs. The paper also proposes a practical approach for selecting the adequate DEM at any time in a year based on the forecasted HRES plant operating scenario only. Model performance is evaluated on a large number of case studies using the HRES plant consisting of three renewable energy sources. The results have shown that only a few DEMs are required for representing the annual HRES plant dynamic performance and obtaining reliable transient system stability results.

Effects of Power System Models on Angle Stability Margin in Transient Stability Analysis

Transient stability is the study of synchronism when a power system is subjected to a severe disturbance such as a short circuit fault. This study involves determining the rotor angles of the machines in a power system before, during and after a disturbance through dynamic simulations. Various power system instabilities that had occurred in the past could be linked to the use of too simplified model of power system for stability assessments. The accuracy of rotor angle dynamic responses determines how well transient stability of a multi-machine power system can be examined in dynamic security assessment. This accuracy is predetermined by the model of the power system used in dynamic simulations because the rotor angle stability margin can be compromised by using a simplified model for dynamic assessment. In this work, a more detailed model of synchronous machine, two-axis model, was used and compared with classical model which is popularly used for power system transient stability studies. Differential and Algebraic Equations (DAE) model of a multi-machine power system derived using two-axis and classical models of synchronous machines were used; with machine control dynamics (excitation and governor) added for both models. These equations were solved in MATLAB and taking a full advantage of time-domain simulation. IEEE 30-Bus test system was used for the analysis to compare the rotor angle responses for two-axis model with responses obtained for classical model. The stability margin of the system was found compromised with the use of the classical model, while the two-axis model gave a response that is more dependable for dynamic security assessment.

Simulation of simultaneous unbalances in power system transient stability analysis

In this paper a novel method based on network decomposition algorithm is presented to implement simultaneous unbalances in power system transient stability (T/S) studies. The proposed network decomposition algorithm employs bus-tearing and Diakoptics concepts. In combination with Large Change Sensitivity (LCS) analysis, which allows the procedure to evaluate system responses without resolving the whole problem, an accurate method is developed to solve the simultaneous unbalances in T/S analysis. The proposed method is implemented successfully in software and the results are validated in comparison with time domain simulations. The performance of our proposed method is investigated in this paper for a 14-bus IEEE test system. The results reveal the credibility of the method.

A NEW APPROACH TO REDUCE THE DYNAMIC ORDER OF INDUCTION GENERATORS

Various attempts have been made to derive linearized, reduced order models of induction generators. Due to the fact that there is usually numerous number of these machines in wind power plants, these models provide great facilities in calculations, and therefore are used widely in power system transient stability studies. In this paper, some of these methods are discussed and compared and then a method known as balanced realizations is used to reduce the dynamic order of the machine. Computer simulation shows that the last method markedly improves the accuracy of the resulting reduced order model. The improvement is demonstrated by comparing the response characteristics predicted by each reduced order model with that predicted by the complete or detailed model.

A Criterion to Evaluate the Accuracy of Reduced Order Models of Induction Generators Based on Neglecting Stator Transients

Various attempts has been made to derive linearized, reduced order models of induction generators. Due to the fact that there is usually numerous number of these machines in wind power plants, these models provide great facilities in calculations, and therefore are used widely in power system transient stability studies. Among various order reduction methods the most applicable ones are those based on neglecting the stator transients of the machine. In this paper, some of these methods are discussed and a criterion has been introduced to evaluate the accuracy of resultant reduced order models.

A unified approach to transient stability contingency filtering, ranking and assessment

Summary form only given, as follows. This paper proposes a unified approach to contingency filtering, ranking and assessment in power system transient stability studies. The approach consists of two-block techniques in which the first block selects from a list of contingencies the a priori interesting ones, that the second block ranks and assesses. This Filtering, Ranking and Assessment (FILTRA) approach relies on SIME (for Single Machine Equivalent). SIME is a hybrid direct-time-domain stability method which combines accuracy and flexibility skills of time-domain methods with sound additional possibilities of direct methods. The FILTRA approach is fully general: it may adapt itself to the specifics of any power system (modeling, protection characteristics, etc.), any contingency scenario and mode of (in)stability (first- or multi-swing, local or inter-area mode) and any application context (planning, operation planning and real-time operation). The approach is illustrated on two EHV power systems, having different structures, control and protective devices. The adequacy of its filtering and ranking capabilities is illustrated in terms of performance criteria such as reliability (ability to consistently capture all dangerous contingencies), effectiveness (ability to avoid false alarms) and computational efficiency (ability to comply with real-time requirements). Further, the assessment task is shown to provide the operator with sound information and effective means of control.

New model for single-unit representation of induction motor loads, including skin effect, for power system transient stability studies

The paper investigates the dynamic representation of a group of induction motors by one or more equivalent motors for power system transient stability studies. Considering the fact that large induction motors constitute a large proportion of the total system load, and that the skin-effect has a very strong effect on the performance of these machines, this effect is therefore included in the model. To enable the skin effect (deep bar effect) to be included, the stator and the rotor windings leakage reactances are separated and the core losses are ignored; and the equivalent machine is represented by seven electrical parameters instead of the conventional five parameters. A clear procedure is described on how to obtain the unknown electrical and the mechanical parameters of the equivalent machine. An efficient grouping (homogeneity) criteria is proposed to obtain subgroups in the case of a diversified group of induction machines connected to the same bus and a power system subjected to disturbances of various types. The accuracy of the equivalent model is verified by simulating its response to different types of disturbances and comparing the results with the sum of the responses of the individual machines. Excellent agreement is obtained between the response of the model and the sum of the responses of the individual machines.

A composite electromechanical distance approach to transient stability

To offset the heavy computations involved in power system transient stability studies, the authors decompose the system into internal and external areas and reduce the latter. The identification of these areas relies upon a composite electromechanical distance, designed to assess propagation of transient phenomena relating to a given contingency. To encompass a set of contingencies, a combined composite distance is devised on the basis of the concept of correlation between composite distances. Also, to encompass a set of operating conditions, a similar technique is proposed. A composite distance handling both sets of contingencies and of operating conditions is developed. Overall, the approach attempts to comply with any method of transient stability assessment and to provide a tool for online applications. This network deals with its fundamentals. Essential features such as flexibility, efficiency and reliability are tested and illustrated by means of numerous simulations performed on a 31-machine system.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Implementation and use of a transient stability post-processor (for power system analysis)

The implementation and use of a postprocessor program for plotting the results of power system transient stability studies are described. The design goals and choice of programming tools are discussed. The resulting program and its features are examined from a user's point of view. The features that make it a postprocessing program and not just another plot program are highlighted. >

Semi-implicit Runge—Kutta methods for power system transient stability studies

Some semi-implicit numerical integration algorithms for solving a set of differential equations are developed and applied for power system transient stability studies. These methods possess the desirable properties of explicit methods (no iteration) as well as those of implicit methods (numerically A-stable). Much larger time steps can be used without encountering any numerical instability problems, even for systems characterized by stiff differential equations. The algorithms have been tested on a number of sample systems.

Power System Transient Stability Studies by Lyapunov Method Using Coherency Based Aggregation

One of the methods for transient stability studies of electrical power systems is the simulation of system dynamic response during given disturbance and application of the second Lyaounov method for calculating the stability margin. Both stages are very time consuming in the case of large systems which occur in practice. So, reduction of the system model becomes very important. In the paper, the influence of coherency-based aggregation on stability studies by Lyapunov method is considered and important properties of the Zhukov aggregation are shown.

A stability measure for use in power system transient stability studies

Large system transient stability calculations may be carried out using network equivalents, and generator grouping, and by reducing the order and complexity of the system representation. Engineering judgement and, in most cases, prior knowledge of transient system performance is required to implement the models. In this paper a new parameter called ‘stability measure’ is introduced. The stability measure can easily be calculated on the basis of load flow and short-circuit results. Upon calculation of the stability measure set for a given fault condition, an estimate of the likely response of the respective generators to the fault is obtained. The validity and generality of the stability measure has been demonstrated by simulated tests on a sample power system. Application of the method with respect to grouping of generators in transient stability studies is also discussed.

New Integration Algorithms for Transient Stability Studies

New integration algorithms suitable for power system transient stability studies are developed and applied to a simple power system example. Both theoretical and preliminary experimental investigations indicate that the new algorithms operate satisfactorily at step sizes five or even te l times those necessary to assure numerical stability when using conventional one-step and multistep methocls. Since the computation time per integration time step of the new methods is similar to that of the conventional methods, the new methods offer significant saving in overall computing effort.

Comprehensive consideration of transient frequency deviations in power-system transient-stability studies

Recent studies which have considered separately the influence of transient frequency deviations on the various components of power systems subjected to transient disturbances are integrated, with the resulting development of a comprehensive computer program which takes full account of frequency dependence of all systems components and allows a more complete assessment of system performance than has hitherto been possible, The program can readily incorporate existing refinements of representation. Two realistic power-system problems illustrate the nature and variety of the system behaviour when frequency dependence is included, indicating particularly that overall negative damping may be present in some systems. Even when damping is positive, as is more usual, it may still be unsafe to neglect its influence as, although stability assessment appears conservative, voltage and current distributions in the network are erroneously predicted, and problems may be caused by the protective-relay settings based on these predictions. Although the computing time required to treat a system with full frequency dependence included is substantially greater than that for conventional calculations, the extra calculating cost seems warranted by the increased accuracy of calculation.

Representation of induction motor loads

IN MOST POWER SYSTEM transient stability studies, the system loads are represented by shunt impedances. Commonly, the shunt impedances are treated as static impedances. This method is especially well adapted for hand calculation and for a-c network analyzer studies. It is, of course, appreciated that all loads do not behave as static impedances and methods have been developed for taking into account, more correctly, the proper variation of real and reactive power with system voltage and frequency changes. These methods have been used, where justified, in some a-c network analyzer transient stability studies.

A Rational Method for the Step-by-Step Calculations in Power System Transient Stability Studies [includes discussion

A Rational Method for the Step-by-Step Calculations in Power System Transient Stability Studies [includes discussion

A computer for use in power-system transient stability studies

A computer for use in power-system transient stability studies

A computer for use in power-system transient stability studies

The transient stability limits of power systems are determined by assuming conditions to be constant over short intervals of time and using the results obtained at the end of one interval to vary the conditions at the beginning of the next interval. The analysis is tedious and it is easy to make numerical errors. If a large number of machines is involved, it is essential to use an a.c. network analyser for determining the values of power to be used for the different time intervals, but there is no reduction in the computation labour, and in practice the greater part of the time taken for a study is devoted to the latter. To reduce the computation time and the possibility of numerical errors, the ?step? evaluations can be carried out semi-automatically by using the computer described. Furthermore, by reducing the time interval, greater accuracy can be obtained without an increase in overall time as compared with normal procedure.