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Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Most regions of the world have seen tremendous growth in distributed energy resources, especially photovoltaic (PV) generation. The penetration of PV generation into the power grid is high and hence it has a major impact in power system. The integration of solar PV plant into the power system has both negative as well as positive impacts on transient stability of the power system during faults. In this work, the proposed current amplitude limiting based Fault Ride Through (FRT) control algorithm is implemented in large scale power systems and enhancement of transient stability is also studied in terms of synchronous machine side and grid side parameters namely rotor speed deviation, load angle, relative rotor angle, active and reactive power. The transient stability of large-scale Grid Connected solar PV (GCPV) system is discussed in this article, when the system is incorporated with the proposed FRT control strategy. The large scale GCPV system is said to be stable, if the angular displacement between the machines in the system stays within predetermined limits. The parameters considered for transient analysis on the synchronous machine side are the rotor angle, rotor speed, and Critical Clearing Time. The proposed model is simulated in MATLAB Simulink and validated in 1 kW hardware setup of grid connected PV system which performs satisfactorily in terms of system parameters and transient stability improvement. [ABSTRACT FROM AUTHOR]

This paper proposes a critical clearing time (CCT) estimation method by the domain of attraction (DA) of a state-reduction model of power systems using sum of squares (SOS) programming. By exploiting the property of the Jacobian matrix and the structure of the boundary of the DA, it is found the DA of the state-reduction model and that of the full model of a power system are topological isomorphism. There are one-to-one correspondence relationships between the number of equilibrium points, the type of equilibrium points, and solutions of the two system models. Based on these findings, an expanding interior algorithm is proposed with SOS programming to estimate the DA of the state-reduction model. State trajectories of the full model can be transformed to those of the state-reduction model by orthogonal or equiradius projection. In this way, CCT of a grid fault is estimated with the DA of the state-reduction model. The calculational burden of SOS programming in the DA estimation using the state-reduction model is rather small compared with using the full model. Simulation results show the proposed expanding interior algorithm is able to provide a tight estimation of DA of power systems with higher accuracy and lower time costs.

Data-driven methods are widely recognized and generate conducive results for online transient stability assessment. However, the tedious and time-consuming process of sample collection is often overlooked. The functioning of power systems involves repetitive sample collection due to the constant variations occurring in the operation mode, thereby highlighting the importance of collection efficiency. As a means to achieve high sample collection efficiency following the operation mode change, we propose a novel instance-transfer method based on compression and matching strategy, which facilitates the direct acquisition of useful previous samples, used for creating the new sample base. Additionally, we present a hybrid model to ensure rationality in the process of sample similarity comparison and selection, where features of analytical modeling with special significance are introduced into data-driven methods. At the same time, a data-driven method can also be integrated in the hybrid model to achieve rapid error correction of analytical models, enabling fast and accurate post-disturbance transient stability assessment. As a paradigm, we consider a scheme for online critical clearing time estimation, where integrated extended equal area criterion and extreme learning machine are employed as analytical model part and data-driven error correction model part, respectively. Derived results validate the credible efficacy of the proposed method.

Nowadays, integration of large-scale wind farms (WFs) into power systems is experiencing rapid growth. As this rapid integration can affect transient stability significantly, employing doubly fed induction generator (DFIG)-based wind turbines, which have shown better behavior regarding system stability, has attracted much attention. This research contributes to the literature by investigating the transient stability of the power system with increasing penetration of DFIG-based WFs. In the proposed framework, the current-balance form is utilized for the network equations, and in this way, transient stability is performed using time-domain simulation. According to the simulation results, when the rate of wind power generation exceeds 0.7 per-unit, the increasing trend of the critical clearing time (CCT) is reversed and the CCT decreases greatly with the increased wind power penetration. In addition, the reactive power compensation by DFIG, the gearbox ratio, the power system strength, and DFIG parameters are comprehensively investigated as effective parameters on transient stability. Since the rated rotor speed of DFIG significantly impacts the electrical torque and machine currents, the reduction of the rated rotor speed due to the change of the gearbox ratio has been investigated as one of the effective factors to improve the transient stability. The simulation results demonstrate the effectiveness of the proposed approach in improving power system transient stability. [ABSTRACT FROM AUTHOR]

An adaptive neuro-fuzzy inference system (ANFIS) is a hybrid algorithm composed of fuzzy logic and an artificial neural network. It takes advantage of fuzzy logic and artificial neural networks to solve complex problems. For power transmission, several dynamic parameters are ignored for conventional transient stability assessment due to the complexity of the equations, and due to the long computational time required. Certainly, it is very difficult to do the real-time assessment of large power systems by considering dynamic impacts in detail. In this paper, an approach is required to increase the accuracy of results. Herein, a method, namely ANFIS, was found to overcome the limitations. All significant effects of dynamics can be taken into account; not only the machine model but also the turbine governor model, automatic voltage regulator (AVR) model, and load characteristic model are carefully considered. In addition, the model used for each generator unit is varied to achieve real conditions. The ANFIS output is the critical clearing time (CCT). CCT values are very important to be correctly predicted for the stability of power systems after clearing the faults. When the faults are cleared by opening the circuit breakers within the CCT values, the power systems are still stable. If the faults are cleared after the CCT values, the systems become unstable. The modified IEEE 9-bus and IEEE 39-bus systems are applied in the implementation of this study. The locations of faults and the levels of loads (except the power system topology changes) are varied for each simulation. The results from the ANFIS application indicate that ANFIS (considering the dynamic effects of the machine models, AVR system, turbine governors, and load characteristics) can predict CCT values with high accuracy. Moreover, when ANFIS results are compared to the artificial neural network (ANN) results, which are generally used, it can be seen that ANFIS results are better and take a lower time for training and testing processes than ANN. ANFIS can be adapted, improved, and implemented in real practice.

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Studying network stability requires determining the best critical clearing time (CCT) for the network after the fault has occurred. CCT is an essential issue for transient stability assessment (TSA) in the operation, security, and maintenance of an electrical power system. This paper proposes an algorithm to obtain CCT based on fuzzy logic (FL) under fault conditions, for a multi-machine power system. CCT was estimated using a two-step fuzzy logic algorithm: the first step is to calculate Δt, which represents the output of the FL, while maximum angle deviation (δmax) represents the input. The second step is to classify the system if it is a stable or unstable system, based on two inputs for FL, the first mechanical input power (Pm), the second average accelerations (Aav). The results of the proposed method were compared with the time domain simulation (TDS) method. The results showed the accuracy and speed of the estimation using the FL method, with an error rate not exceeding 5%, and reduced the performance time by about half the time. The proposed approach is tested on both IEEE-9 bus and IEEE-39 bus systems using simulation in MATLAB. [ABSTRACT FROM AUTHOR]

The electric power distribution scheme of a power plant should be analysed to prevent the occurrence of the slightest fault current and improve system reliability during the power production process. Protection relay settings installed on the electricity network should calculate the condition of the generator with various types of fault currents. Installation of relays that do not consider transient stability leads to generator instability even though the fault is eliminated. Therefore, it is necessary to calculate the stability limit while setting the overcurrent relay. However, a failure in the relay setting can occur if the inverse relay cannot protect against a high-impedance fault. Therefore, a method was proposed to determine the stability limit based on a short circuit without impedance and with an applied impedance, and the application of the method was demonstrated through existing settings and resetting conditions in simulation software. A modification relay setting prevented the loss of synchronisation of the generator during fault occurrence. The working time operation was integrated with the definite and inverse overcurrent relays in ANSI 50, 51, standard operating time of the relay, and critical clearing time of the generator. The type of fault used was a three-phase fault, with and without high-impedance. The calculation results demonstrated that this concept can be used to protect lines and generators during a short circuit current. [ABSTRACT FROM AUTHOR]

Accurate transient stability assessment (TSA) and effective preventive control are important for the stable operation of power systems. With the superiorities in precision and efficiency, data-driven methods are widely used in TSA nowadays. Data-driven TSA model can be adopted in the stability constraints of preventive control optimization, but existing methods are mostly iteration-based ones, which may result in low efficiency, sometimes even non-convergence. In this paper, an analytical representation method of data-driven transient stability constraint is proposed based on a non-parametric regression model built for TSA. Key feature extraction and dominant sample selection are proposed to reduce the scale of the TSA model, and bi-level linearization is applied to further modify it. Optimal preventive control model is then formulated as a mixed-integer linear program (MILP) problem with the linearized analytical data-driven transient stability constraint, which can be solved without iterations. An overall procedure of data-driven TSA and preventive control is finally developed. Case studies show that the proposed method has high accuracy in TSA and can achieve effective preventive control of power system with high efficiency.

Maintaining a stable operation of modern power systems, which are heavily loaded and strongly interconnected is a very complex task. This requires an optimal setting and coordination of protective relays considering the transient behavior of power systems. This paper proposes a new formulation of the optimal coordination of directional overcurrent relays (DOCRs) problem, considering power systems' transient stability and intelligent selection of non-standard characteristics. This problem is formulated as a mixed-integer optimization problem, taking into account non-standard relay characteristics and transient stability constraints, where the required power system parameters are calculated using Digsilent Power Factory Software. An enhanced version of a hybrid optimization method called: Hybrid Gravity Search Algorithm and Sequential Quadratic Programming (GSA-SQP), is proposed to solve the problem. The efficiency and performance of the proposed approach are validated on the 9-bus and 39-bus test systems considering various case studies. The obtained results show the efficiency of the proposed formulation to reduce the operating time of DOCRs with coordination and transient stability constraints satisfaction. [ABSTRACT FROM AUTHOR]

Transient stability analysis is a very important tool to deal with many behaviors of electrical power systems during and after being subjected to various disturbances. this paper propose a method for electrical power systems transient stability assessment using phase plane trajectories. A methodology for computing the critical stability conditions of generators is proposed. The critical conditions such as critical clearing time (CCT) and critical clearing angle (CCA) were obtained. The computation of CCA and CCT is curried out step by step using the characteristics of the faulted and postfault trajectories from given initial conditions until their intersection point. The angle and time values founded represent, by definition, the critical conditions of the system. The proposed algorithm can be used for complex models since it is based on solving systems of differential equations by iterative methods in the phase plane. The advantage provided by this method is it's accurate and small time consuming. To demonstrate the effectiveness of the proposed method, first, critical conditions calculation procedures are given, then the process used in judging power system stability is provided, finally, simulation results for various test cases of a single machine infinite bus (SMIB) system highlight the proposed methodology. [ABSTRACT FROM AUTHOR]

The assessment of transient stability of multi-machine power system, in a post-fault scenario, is a very challenging task due to highly non-linear nature of the system equations. In this work, the physical concept of maximum relative acceleration of a machine at a fault scenario is related with the boundary of stability region. This approach is extended to develop a quadratic Lyapunov function using singular perturbed modelling. Unlike the conventional energy function methods, this Lyapunov function candidate is a more general energy function and has a decaying nature around an equilibrium point. Moreover, with higher order corrections, an improved Lyapunov function candidate is presented with simulation results of power system examples. The decaying nature of Lyapunov function candidate remains similar even without higher order corrections. However, the relevance of inclusion of higher order corrections is brought out in the cases of faults occurring at other than generator buses. Also, the upper bound of singular perturbation parameter in the model is within allowable limits and ensures the accuracy of results. [ABSTRACT FROM AUTHOR]

The dynamic security assessment of power systems is a critical activity to ensure a safe energy delivery to consumers and the study of transient stability is a fundamental part of this process. The power systems are experiencing a growth of large-scale renewable energy plants connected to the system, which in turn are connected to the grid by power converters that are not capable of contributing to the system inertial stabilization and, therefore, could compromise its transient stability. One way to mitigate this problem is to make these plants contribute to the system stabilization by adopting specific control strategies, such as the virtual synchronous generator (VSG), for their interface power converters. In this paper, a quantitative evaluation of the transient stability support of a VSG is proposed in large-scale applications. For this purpose, the stability assessment of a single-machine infinite-bus (SMIB) system with the VSG is done using transient stability metrics such as the critical clearing time (CCT) and the transient stability index (TSI). In addition, the same analysis is made for a conventional synchronous machine (SM) and the results are compared and discussed. Furthermore, the VSG parameters adaptability is presented as an alternative to optimizing the system stability.

The transient stability analysis of large-interconnected power systems using time-domain simulations (TDS) is a significant challenge since it represents a huge computational cost. Besides, for dynamic security assessment is required have a quick response. Consequently, recent approaches are relying on using the wide-area measurement system combined with other techniques to perform transient stability assessment and counteract the drawbacks of the TDS method. However, these approaches still requiring to perform TDS to set initial parameters. This paper proposes a new algorithm to estimate the critical clearing time (CCT) based on the eigenvalue calculation and the singular value decomposition using data from wide-area measurement systems. The proposed algorithm uses the phase angles of the voltage phasors measurements at the generation buses to represent the dynamics of the internal angles of the generators. First, from a set of signals, a measurement matrix is formed using a sliding window. Then, a threshold based on the maximum singular value and the dominant eigenvalue of the measurement matrix are computed. Finally, the CCT is estimated using the dominant eigenvalue (the most energetic eigenvalue) and the threshold. The proposed algorithm is evaluated using the Kundur four-machine system and New England 39-Bus system. Its performance contrasts to the CCT calculated using the classical TDS. The simulation results demonstrated acceptable precision of the CCT against TDS. Also, it presents robustness against the effect of the noise in the measurements. Therefore, it is suitable for online applications.

Summary: Flywheel energy storage system (FESS) needs to be operated within its allowable speed range because it will be shut down outside this range. Furthermore, the power supplied/absorbed by FESS is constrained by the associated power electronic interface. This article proposes supervisory adaptive predictive control (APC) scheme for flywheel energy storage system to enhance power system transient stability while addressing the constraints mentioned earlier. The supervisory adaptive predictive controller gives a reference power command signal to the inner control loop of FESS while ensuring the operation of FESS within its regime of operation. The gains of the inner control loop are optimized by employing Genetic Algorithm (GA). The constraints on the state of charge of FESS and power rating of the associated converter are explicitly included in the adaptive predictive controller formulation, which is usually done in an ad hoc manner. The performance of the proposed control strategy is evaluated under four scenarios: a step wind disturbance, realistic wind profile, doubly fed induction generator (DFIG) outage, and a severe symmetrical fault condition on modified New York/New England 16 machine 68‐bus power system. The validity of the adaptive predictive control based flywheel energy storage system (APC based FESS) in improving transient stability of power system is verified by the simulation studies carried out in MATLAB/Simulink environment. [ABSTRACT FROM AUTHOR]

This paper deals with the transient stability of a grid-forming converter while embedding a current reference saturation strategy. The novelty of this work consists in investigating the impact of the current reference angle on the transient stability. In case of a balanced voltage sag, analytical formulas to estimate the critical clearing angle (CCA) and critical clearing time (CCT) while considering different values of the current reference angle are derived. It is demonstrated that the choice of this angle is constrained by the ability of the power converter to switch back to the voltage control mode. Based on that, its optimal value that enhances the transient stability and allows a switching from the saturated current control mode to the voltage control mode is calculated. Thereafter, the effectiveness of this optimal choice to guarantee the stability in case of a phase shift caused by a line re-closing event is verified. Time-domain simulations and experimental tests validate the correctness of the presented theoretical approaches. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of integrating Renewable Energy Sources (RESs) into a system on the Critical Clearing Time (CCT) as a direct transient stability measure. The developed methodology quantifies the stability margin based on the fault clearing time. Moreover, the methodology considers the dynamic system performance under fault conditions as a worst-case scenario to determine the CCT. The proposed technique is a novel numerical methodology presented to study the transient stability of a multi-machine power system with the existence of a RES. Different from the typical solution of the swing equation of a two-machine power system, the proposed methodology numerically solves the swing equation of a multi-machine system. From this, accurate solutions are obtained to determine the optimal penetration level of the RES. Moreover, this work aims to derive an explicit relationship between the rotor angle deviation of the synchronous generator and the penetration level of the RES. Consequently, the CCT associated with the maximum power angle deviation can be determined. The proposed methodology is validated by comparing the results with dynamic simulations using the powersystem- simulator (PSS®E) software package developed by Siemens. The IEEE 9-bus system is considered as a benchmark, with the results exhibiting great agreement with the PSS®E results, thus confirming the effectiveness of the proposed methodology. [ABSTRACT FROM AUTHOR]

The research on electromechanical transient stability of power systems is of great significance. Analyzing the parameters of the simulation system and its improved system with typical short-circuit faults, this paper studies the transient stability of power systems and its improvement. Firstly, based on the SIMULINK of MATLAB, a double-loop simulation with the single-machine-infinite-bus system is built. The simulation experiments of the system under the circumstances of three-phase short circuit and single-phase grounding short circuit faults are then carried out to analyze the parameters such as limit cutting time and voltage. Besides, this paper explores how the controllable series capacitor compensation device and reducing mechanical power output by prime mover improve the transient stability of the system. Experiments show that the stability after fault is under conditions where the fault is removed before the critical clearing time, which can increase the threshold to gain more response time for relay protection devices. Thus, the value of researching and improving system transient stability is proved.

This paper reports the modeling and dynamic performance of a wind penetrated multi-area power system incorporating a Singular Virtual Synchronous Generator (SVSG)/Distributed Virtual Synchronous Generator (DVSG). The active and reactive power controls are achieved by using Superconducting Magnetic Energy Storage (SMES) as Virtual Synchronous Generator (VSG). SMES based VSG control parameters are tuned offline using genetic algorithm (GA). Two topologies of VSGs are considered in this paper: SVSG at lowest inertia generator bus (SVSGGENBUS), SVSG at load bus (SVSGLOADBUS) and DVSG of comparatively smaller rating at three lowest inertia generator buses. A modified 18 machine, 70-bus power system is simulated in MATLAB/Simulink environment. System performance is assessed for two different types of disturbances: step wind disturbance and three-phase fault. The simulation results show that rate of change of frequency (ROCOF), deviations in frequency and voltage are minimized with DVSG. Transient stability measured in terms of critical clearing time (CCT) verifies that CCT is increased by DVSG topology. [ABSTRACT FROM AUTHOR]

Among the five regional grids of India, the Western Regional (WR) grid is the one consisting of voltage levels 765 kV, 400 kV, and 220 kV. The WR grid is considered as the spinal cord of the Indian grid as it delivers power to most of the heavy industrialized states, and hence is selected for analysis. In order to determine the weak area of the grid and perform stability studies, the L-Index algorithm is generally used. But for computation of maximum deviation of frequency, minimum time of voltage recovery, and critical clearing time (CCT) of the buses in a more detailed manner, the L-Index method is not infallible. Hence, for computing various parameters of the WR grid in a more detailed manner, dynamic simulation is performed. The WR grid has been modeled using 584 buses of voltage levels higher than 220 kV and transmission lines spread over the entire grid length of 86 220 km. In this work modeling, simulation and detailed analysis of the WR grid is accomplished. The L-Index algorithm clubbed with dynamic simulation provides the option of detailed analysis and computation of important parameters of the system, along with the prediction of weak area, which also acts as a parameter for designing various electrical protective equipment to be utilized in the grid. [ABSTRACT FROM AUTHOR]

Due to the expansion of restructured electricity markets and consequently power network operation approaching dynamic and static margins, the probability of transient instability has remarkably been increased. To reduce the transient instability risk or probabilistic cost of power quality, the present study focuses on determining the optimum location of a flux-coupling type SFCL. To this end, the candidate locations with lower related transient instability risk are selected as the best locations for installing flux-coupling type SFCLs. Nowadays, the type of SFCL employed in this study, which enjoys the benefits of both resistive and inductive type SFCLs, is a suitable means for enhancing the transient stability of electrical grids. Despite being another useful approach in transient stability evaluation, the equal-area criterion is merely restricted to the analysis of the stability of a single-machine power system connected to an infinite bus and also a two-machine power system. The online approach employed in this study is based on the corrected transient energy margin (CTEM), some probabilistic factors, and the cost of transient instability. Furthermore, CTEM index is a useful tool for calculating the critical clearing time (CCT). Therefore, in recent years, this index has become more and more useful. The studies carried out on the IEEE New England 39-bus test system ascertain the high applicability of the proposed method.

Transient stability assessment (TSA) is of great importance in power system operation and control. One of the usual tasks in TSA is to estimate the critical clearing time (CCT) of a given fault under the given network topology and pre-fault power flow. Data-driven methods try to obtain models describing the mapping between these factors and the CCT from a large number of samples. However, the influence of network topology on CCT is hard to be analyzed and is often ignored, which makes the models inaccurate and unpractical. In this paper, a novel data-driven TSA model combining Mahalanobis kernel regression and ensemble learning is proposed to deal with the problem. The model is a weighted sum of several sub-models. Each sub-model only uses the data of one topology to construct a kernel regressor. The weights are determined by both the topological similarity and numerical similarity between the samples. The similarities are decided by the parameters in Mahalanobis distance, and the parameters are to be trained. To reduce the model complexity, sub-models within the same topology category share the same parameters. When estimating CCT, the model uses not only the sub-model which the sample topology belongs to, but also other sub-models. Thus, it avoids the problem that there may be too few data under some topologies. It also efficiently utilizes information of data under all the topologies. Moreover, its decision-making process is clear and understandable, and an effective training algorithm is also designed. Test results on both the IEEE 10-machine 39-bus and a real system verify the effectiveness of the proposed model.

Future power systems with a high penetration level of inverter-based renewable sources (IBRSs) will be vulnerable to severe grid faults because of the noticeable reduction in the total system inertia. Particularly, challenges will arise in securing the transient stability limits of synchronous generators in the systems. Fortunately, the stability limits can be extended by utilizing the existing inverter-based units as virtual damping devices. This paper proposes the utilization of an inverter-based supercapacitor (IBSC) to extend the critical clearing time (CCT) of a power system with a high penetration level of IBRSs; thus, it makes it possible to secure the transient stability limits of SGs. In order to utilize an IBSC, the controllability of the IBSC is explored by considering two factors: control scheme and location of the IBSC. First, to determine an effective control scheme for the IBSC, three control schemes, which are power-damping control, speed-damping control, and power and speed-damping control, are tested under severe fault conditions. Then, using each control scheme, the location of the IBSC is chosen in a certain power system by the most extended CCT. The proposed utilization strategy was validated under various scenarios in a modified IEEE 14-bus system using the PSCAD simulator.

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this research, we aim to use the ftatness control theory to develop a useful control scheme for a single machine connected to an infinite bus (SMIB) system taking into account input magnitude and rate saturation constraints. We adopt a fourth-order nonlinear SMIB model along an exciter and a turbine governor as actuators. According to the ftatness-based control strategy, first we show that the adopted nominal SMIB model is a Hat system. Then, we develop a full linearizing state feedback as well as an outer integral-type loop to ensure suitable tracking performances for the power and voltage as well as the angular velocity outputs. We assume that only the angular velocity of the generator is available to be measured. So, we provide a linear Luenberger observer to estimate the remaining states of the system. Also, the saturation nonlinearities are transferred to the linear part of the system and they are canceled out using their estimations. The efficiency and usefulness of the proposed observer-controller against fau lts are illustrated using simulation tests in Eurostag and Matlab. The results show that the clearing critical time of the introduced methodology is larger than the classical control approaches and the proposed observer-based ftatness controller exhibits over much less control energy compared to the classic IEEE controllers. [ABSTRACT FROM AUTHOR]

This study presents a new strategy for implementing the superconducting fault current limiter SFCL in order not only to limit short - circuit currents but also to improve the stability of electrical networks in the presence of faults. The calculation of the impedance that the limiter must introduce into the test network at the moment of the failure is obtained from a three-dimensional computation code, developed and implemented under MATLAB environment where the formulation in magnetic vector potentials A and scalar potential Electric V is adopted to solve the electromagnetic problem and the heat diffusion formulation is adopted also to solve the thermal problem. The coupling is ensured by an alternating algorithm and the numerical resolution of the problem is ensured by the method of the finite volumes in its three-dimensional version in order to avoid certain problems of numerical convergence linked to the strongly nonlinear character of the problem to be solved. The modeling of the network tests will be made by PSAT under the environment MATLAB.

In the present day, the electrical power demand is increasing and expected to continue growing. The renewable energy sources as the power supply are also increasing but not much as needed. As a result, the power systems operate close to their maximum stability limit. This paper proposed to extend the value of Critical Clearing Time (CCT) to enhance the stability system, especially the transient stability. A Supercapacitor Energy Storage (SCES) is installed at one of the generator bus; however, the sizing of SCES must be optimized due to the economics and power balance constraint. In this paper, the Firefly Algorithm (FA) is used to obtain the optimal sizing of SCES with the objective function is the highest value of CCT. Lagrange interpolation is used to validate the effectiveness of FA, such as computation time and accuracy. According to the simulation result obtained, the proposed method using FA has a faster calculation time than Lagrange interpolation. Moreover, the proposed method is validated on a modified IEEE 9 bus with various cases. By using FA, the best increase of CCT is obtained when the optimal size of SCES is 0.120 p.u. The overall CCT increase is 0.15766s or around 54.61%. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Eastern Regional (ER) grid of India is one of the five regional grids consisting of voltage level 765 kV, 400 kV, 220 kV and numerous buses at lower voltage range. ER grid is the backbone of the Indian Grid as it is one of the main power generating hubs. Stability of the Indian Grid depends a lot on ER grid as it is the core of the generation and transmission system. For performing stability studies and to determine the weak area of the grid generally L-Index method is used. For detailed analysis like computation of voltage recovery time, maximum frequency deviation and critical clearing time of the buses of the system L-Index method is not suitable. Hence dynamic simulation is performed as it provides options to compute various parameters of ER Grid. The system has been studied using 197 buses of voltage levels 220 kV and above and transmission lines running over a length of 23,693 km. In this paper the power flow modelling, simulation and analysis of the Eastern Grid of India is performed. L-Index algorithm along with dynamic simulation provides the scope of computation of voltage recovery time, maximum frequency deviation and critical clearing time (by introducing an initial transient disturbance) along with the prediction of weak area of the system which gives a complete picture of transient stability of ER Grid. [ABSTRACT FROM AUTHOR]

This article presents a new algorithm aimed toward effective handling of the transient-stability-constrained optimal power flow (TSC_OPF) problem. The algorithm is a hybridized version of the existing differential evolution (DE) and symbiotic organism search (SOS) algorithms. It combines exploration and exploitation ability of both algorithms which results in its better performance as compared to DE and SOS acting alone. It was tested on IEEE 30 bus test system and the New England 39 bus test system. The results obtained by the proposed approach were compared with conventional TSC_OPF and also with other algorithms available in the literature. Results obtained using the proposed approach demonstrates superiority in comparison with other available algorithms in the literature. [ABSTRACT FROM AUTHOR]

This paper presents the dynamic responses of generators in a multi-machine power system. The fundamental swing equations for a multi-machine stability analysis are revisited. The swing equations are solved to investigate the influence of a three-phase fault on the network largest load bus. The Nigerian 330kV transmission network was used as a test case for the study. The time domain simulation approach was explored to determine if the system could withstand a 3-phase fault. The stability of the transmission network is estimated considering the dynamic behaviour of the system under various contingency conditions. This study identifies Egbin, Benin, Olorunsogo, Akangba, Sakete, Omotosho and Oshogbo as the key buses within the network, which could provide useful information when a three-phase fault occurs on Ikeja-West (Bus with the largest load). The results obtained also show that the system loses synchronism immediately a three-phase fault was simulated on the largest load bus, considering various contingencies with the generator at Geregu being the most severely disturbed generator. [ABSTRACT FROM AUTHOR]

Power systems are frequently subjected to variations of the operating conditions due to the occurrence of contingencies such as faults, load or generator tripping. These disturbances might enforce the system to enter the instability region and thus deteriorate its overall performance. This paper proposes a systematic approach for transient stability assessment using generator-based threshold. An individual stability limit is designed for each generator instead of using only one pre-defined threshold for all generators. The considered contingencies are characterized by a fault type, location, loading condition and critical clearing time to consider wide range of operating conditions. Two fault locations are only considered to reduce the search space for stability limits; the generator terminals and mid of transmission lines. The critical clearing time is used to find the maximum relative rotor angle (MRRA) of individual generators attained during the entire time domain simulation. The MRRA of each generator represents the maximum angle which can be reached without losing synchronism at a given contingency. Conservative stability limits are drawn around the minimum stable drift of each generator which is chosen from the set of MRRAs of all contingencies. The effectiveness of the proposed approach is tested using the modified New-England, 39-bus system.

Dynamic security assessment is widely used in dispatching operation systems, and calculation speed is one of its most important performance indices. In this study, an improved k-nearest neighbour (k-NN) method is proposed aiming to predict the stability indicators of power system, for example, critical clearing time. The method is much faster than the simulation and suitable for online analysis. Firstly, a simulation sample database is constructed based on historical online data and a logistic regression model with least absolute shrinkage and selection operator is trained to pick the stability features, which are chosen from static quantities like running state and active power of electric elements. While a new operation mode needs to be evaluated, a weighted k-NN is implemented to obtain the most familiar samples in the database using the chosen features; the final result will be determined comprehensively by the familiar samples. The validity of the proposed method is verified by simulation using online data of State Grid Corp of China and different key faults. It is proved that the method meets the requirements for speed and accuracy of online analysis system.

The increasing penetration of wind energy to the conventional power system due to the rapid growth of energy demand has led to the consideration of different wind turbine generator technologies. In fault conditions, the frequency of the power system decreases and eventually leads to speed differences between the grid and the interconnected wind generator. This can result to power system problems such as transient instability (TS). This paper focuses on enhancing the TS of a permanent magnet synchronous generator (PMSG)-based power system during 3ph fault conditions using FACTS devices. The power system considered is connected to a large wind farm which is based on PMSG. Critical clearing time (CCT) is used as an index to evaluate the transient state of the system. Under the study of an IEEE-14 bus system using PSAT as a simulation tool, the integrated CCT with PMSG-based wind turbine is improved with three independent FACTS devices. One of the synchronous generators in the test system has been replaced at random with the PMSG-based wind turbine which is meant to generate an equivalent power. Time domain simulations (TDSs) were carried out considering four study cases. Simulation results show that the (CCT) of the system with the FACTS devices is longer than the CCT without them, which is an indication of TS improvement. [ABSTRACT FROM AUTHOR]

This paper proposes a monitoring and control method for transient stability (TS). First, it is clarified that there may exist various critical patterns of uncertain power flows causing instability due to photovoltaic generations. Then, the use of critical clearing time (CCT) is suggested as a TS index, which can be computed by conventional TS analysis tools. A distribution factor (DF) for controlling CCT is investigated, referred to as CCT‐DF in this paper. Then, three optimization problems using CCT‐DF are formulated based on bilevel optimization to obtain reliable operation planning. The combined use of the optimizations guarantees the power system robust security under uncertainties. [ABSTRACT FROM AUTHOR]

Due to the constantly increasing penetration of distributed energy resources, it is important to establish rules and regulations for their supporting the stability of the electric power system. This means that the rules imposed on avoidance of discrimination, should apply also to the conventional synchronous production units. Operating at a reduced voltage at on unfavourable system event is likely to affect the transient stability of synchronous units when the related specifications are set too tight. Thus, besides the above rules, the limit operating states of the synchronous units should be clearly specified and their compliance with the fault-ride-through criterion verified to determine that the unit transient stability complies with the set rules and regulations. The paper analyses the effect of different parameters on the transient stability in terms of the critical clearing time: lack of the short-circuit power and voltage amplitude at the connection point and the generator operating state. The conditions for checking the compliance of the synchronous unit operation with the lowvoltage fault-ride-through criterion in terms of the angular stability are provided. [ABSTRACT FROM AUTHOR]

Dynamic security assessment is widely used in dispatching operation systems, and calculation speed is one of its most important performance indices. In this study, an improved k-nearest neighbour (k-NN) method is proposed aiming to predict the stability indicators of power system, for example, critical clearing time. The method is much faster than the simulation and suitable for online analysis. Firstly, a simulation sample database is constructed based on historical online data and a logistic regression model with least absolute shrinkage and selection operator is trained to pick the stability features, which are chosen from static quantities like running state and active power of electric elements. While a new operation mode needs to be evaluated, a weighted k-NN is implemented to obtain the most familiar samples in the database using the chosen features; the final result will be determined comprehensively by the familiar samples. The validity of the proposed method is verified by simulation using online data of State Grid Corp of China and different key faults. It is proved that the method meets the requirements for speed and accuracy of online analysis system. [ABSTRACT FROM AUTHOR]

This paper analyzes the optimal control strategy of PMSG-based wind farms during faults in order to improve the transient stability of a power system with a high penetration rate of wind power. The investigated control strategies are the unity power factor (UPF), reactive power control (RPC), and particularly the concept of virtual synchronous machine (VSM). The transient stability level is assessed using the critical clearing time index, which was calculated based on trajectory sensitivity analysis. In light of the obtained results, it was found that RPC gives the best transient stability level, followed by the classical VSM control. Hence, an improved VSM control was proposed based on the transient model of a synchronous generator. The improved VSM has shown a behavior similar to a real synchronous generator, which results in better transient stability performances. [ABSTRACT FROM AUTHOR]

Due to increasing of uncertainty in nowaday power systems, probabilistic security assessment has become one of the challenging issues in power systems. This paper, proposes a new real-time approach for calculating probabilistic critical clearing time (CCT) which is applicable to probabilistic transient stability assessment. The proposed method aims to provide a low computational burden and high-accuracy to calculate the probabilistic density function (PDF) of CCT in two stages. In the first stage, proposed method presents a novel sensitivity based approach, which calculates CCT in the first step of the simulation. Determination of CCT by taking structure preserving into account, guarantees the accuracy of the proposed method. In the second stage, by applying Quasi Monte Carlo (QMC) simulation, the PDF of CCT is obtained. Several different parameters that affect uncertainty of CCT such as load and generation and also fault location are considered in order to obtain the PDF of CCT. Several case studies have been conducted on IEEE 9 bus and 68 bus test systems to show the efficiency of the proposed method. Simulation results indicate that the proposed method has notable accuracy along with substantial speed in performing the required calculations. [ABSTRACT FROM AUTHOR]

This study reveals the transient stability improvement capability of Thyristor Controlled Series Compensation (TCSC) as an effective Flexible AC Transmission System (FACTS) device in damping low frequency oscillations on the Nigeria 330kV transmission system. The study was performed using commercially available MATLAB software. The analysis was carried out by simulating a 3-phase fault on the network in order to determine the Critical Clearing Time (CCT) of the system. In locating the TCSC, the most severely disturbed generator was considered. Simulation results on the Nigeria 330kV transmission system modelled in MATLAB environment reveals appreciable transient stability enhancement of the network. [ABSTRACT FROM AUTHOR]