First-swing Stability Research Articles

Real-Time Application of an Indirect Power-System Contingency Screening Method Based on Adaptive PCA

This paper presents a real-time application of a data-mining method with the purpose of indirect contingency screening, by rapid recognition of hazardous, reoccurring power-system operating conditions. The method, suitable for real-time applications, is demonstrated using the Slovenian power-system model for first-swing stability issues. The presented demonstration is segmented into a few parts. First, a database containing a set of pre-fault operating conditions (represented by a measurement matrix) and critical clearing times corresponding to several contingencies is constructed. Measurements matrix from the database is decomposed using the principal component analysis method and represented in a coordinate system defined by the principal components as dense clusters of points. Consequentially, monitoring real-time steady-state conditions in terms of seeking similarity to existing database clusters is facilitated (global screening). This is established by identifying the shortest Euclidean distance metric in the mentioned coordinate system. Finally, a second-stage (local) screening is applied in order to adaptively account for the fluctuating sensitivity of contingencies to variations in pre-fault operating conditions. In this manner, an accurate indication of each contingency impact is provided rapidly as long as a similar operating state exists within the database. Otherwise, the case is thoroughly investigated and added to the database as a new entry. This approach is applicable to a wide spectrum of dynamic problems, considering that problem-relevant sets of input data are available.

Indirect Power-System Contingency Screening for Real-Time Applications Based on PCA

This letter introduces the application of a data mining method with the purpose of contingency screening, by rapid recognition of hazardous, reoccurring power-system operating conditions. The method, suitable for real-time applications, is demonstrated on the north-western part of the Slovenian power-system, for first-swing stability issues. The presented demonstration consists of two steps: First, a database containing a set of prefault operating states and the corresponding critical clearing times of several contingencies is constructed. Second, the prefault measurements matrix is decomposed using the principal component analysis method and represented in a coordinate system, defined by the principal components. Since operating states form dense clusters of points in this coordinate system, the similarity between current and past conditions is established by identifying the shortest Euclidean distance metric. In this manner, the indication of each contingency impact is provided rapidly as long as a similar operating state exists within the database. Otherwise, the case is thoroughly investigated and included in the database. This approach is applicable to a wide spectrum of dynamic problems, providing that problem-relevant sets of input data are considered.

The influence of damping resistance on first swing stability of turbine generator considering stator transient

Generally, the ignored stator transient of turbine generator result in the unidirectional electromagnetic torque caused by damping resistance is neglected. While, the unidirectional electromagnetic torque has a braking effect which can reduce the rotor acceleration following the disturbance and improve the stability of power system. With a 300 MW turbine generator as an example, the large disturbance characteristic and First Swing Stability (FSS) limit are calculated by Time-Step Finite Element Model (T-S FEM) and three practical models of turbine generator in this paper. The unidirectional electromagnetic torque caused by stator transient is investigated and its important role in FSS is analyzed. Since there are several material options for damping windings, the influence of damping resistance on the large disturbance characteristic and FSS limit are calculated and compared under different damping resistance. The result shows that the FSS limits calculated by the practical model with stator transient are increased than that without stator transient; the FSS limits of turbine generator with damping windings made from stainless steel are larger than that made from aluminum and beryllium bronze by the four kinds of generator models. The result provides theoretic basis of generator modeling for precise simulation of power systems.

Inertia Characteristic of DFIG-Based WT Under Transient Control and its Impact on the First-Swing Stability of SGs

The first-swing stability of synchronous generators (SGs) has a close relationship with synchronizing ability of the grid and inertia characteristic of all the generators. This paper studies inertia characteristic of doubly fed induction generator (DFIG) based wind turbine (WT) under transient control to analyze its impact on the first-swing stability of SGs. First, an analytic model of DFIG-based WT following the concept of motion equation is developed to describe and explain its inertia characteristic. The foundation is the definition of internal voltage of DFIG. Based on the model, an important conclusion is drawn that DFIG-based WT under transient control during grid fault has adjustable inertia characteristic that has a clear link with control parameters. Then, the impacts of transient control parameter of DFIG-based WT on the first-swing stability of SGs are studied through numerical simulation. Finally, the impact mechanism of transient control of DFIG-based WT on the first-swing stability of SGs is clearly explained by physical concept of inertia characteristic and synchronizing force.

Wind power converters improving the power system stability

This study analyses the coordinated actions of modern wind power plants for improving the transient and small-signal stability in power systems. Supplementary controls on wind farms are considered, and specific modifications on the controllers are tailored to increase the grid-support services. The proposal is analysed and validated in a practical power system based on the Argentine electrical network. The wind farm supplementary controls use active and reactive power control loops as well as local and remote measurements. Local controls can rapidly respond decelerating the system frequency in the first instants of a fault, consequently reducing the transient angle separations and improving the first-swing stability. On the other hand, remote controls using global information are able to increase the damping of low-frequency inter-area oscillations. Structures combining centralised and decentralised control approaches will become more common in the near future. With this aim, the integration of fast local controls with remote controls is thoroughly studied using non-linear time-domain simulations and eigenvalue analyses. A robustness evaluation is also performed to validate the proposal over a wide range of operating conditions.

Optimal Location of Shunt FACTS Devices for First-Swing Stability Enhancement in Inter-Area Power System

Optimal Location of Shunt FACTS Devices for First-Swing Stability Enhancement in Inter-Area Power System

The influence of turbine generator rotor damping structure and material on first swing stability

In this paper, we study the influence of rotor damping structure and material on First Swing Stability (FSS) of turbine generator connected to power system after three-phase short circuit. Considering the complex rotor damping structure of turbine generator, we make crucial improvements in finite element discrete strategy reflecting skin effect of eddy current and establish field-circuit-network coupled time-step finite element model. We test this model by the experiment of 7.5kW model machine. Based on this model, we take a 300MW turbine generator as an example to study the influence of damping bar, rotor iron core and conductive slot wedge on FSS. We investigate the importance of the rotor damping structure to FSS and find its impact is not negligible. By comparing the FSS limits affected by three components of rotor damping structure respectively, we conclude that the effect of rotor slot wedge and iron core is not linear superposition but Coupling relationship. Since we have several rotor slot wedge materials to choose from and the conductivity of these materials is different, we establish the relationship between FSS limit and conductivity of rotor slot wedge. The result shows that the FSS limit gradually increases as the conductivity of rotor slot wedge changes from σal (conductivity of aluminum alloy) to 0.05σal.

A Parallel Reduced-Space Interior Point Method With Orthogonal Collocation for First-Swing Stability Constrained Emergency Control

First-swing stability constrained emergency control (FSCEC) enhances power system transient stability during large disturbances, but is difficult to solve for larger systems because of its computational complexity. The method proposed in this work guarantees first swing transient stability by using a parallel reduced-space interior point method (IPM) with orthogonal collocation to solve FSCEC problems. This novel algorithm discretizes differential-algebraic equations using orthogonal collocation, which leads to a relatively low problem dimension, and accelerates the optimization process through a reduced-space technique by utilizing the property of small degrees of freedom after numerical discretization. Furthermore, a two-level parallelism is explored in reduced-space IPM (RIPM) algorithm and implemented with state-of-the-art parallelization techniques. The proposed approach was benchmarked on a Beowulf cluster with 64 CPU cores to show its excellent computational efficiency.

A new method for SVC placement considering FSS limit and SVC investment cost

Although the primary purpose of a static VAr compensator (SVC) is voltage regulation of the bus by injecting reactive power into the system, it can also improve stability and damping of a power system if placed in the right location. In a power system, transient stability is the ability of the system to maintain stability and oscillation damping after a severe disturbance. Actually, the system is stable if the angles of all generators remain stable after a perturbation. This paper proposes a new method to find the best location of SVC in a power system, considering improvement of the first swing stability (FSS) limit and SVC investment cost reduction, simultaneously. For this purpose two indexes are defined, the stability index and cost index. Stability index and cost index are measures to assess the stability of the system and SVC investment cost, respectively. The bus with the highest values of stability index and cost index is the best location of SVC. The effectiveness of the proposed method to find the appropriate location for SVC is tested on the 9-bus IEEE test system and a 29-bus test system. After choosing the best location, SVC is placed there and the optimal value for the maximum capacitive susceptance of SVC is found using particle swarm optimization (PSO) for an agreement between the improvement of FSS limit and reduction of SVC investment cost.

Current state of neural networks applications in power system monitoring and control

For over two decades Neural Network (NN) has been applied to power system monitoring and control. Conventional controllers suffer from certain limitations which NN as an Artificial Intelligence (AI) technique is able to overcome. Therefore, many researchers prefer to use NN technique in the monitoring and control of power systems. This paper reviews published recently schemes for control and monitoring based on NN. The performance of various NN controllers is compared with one another as well as to the performance of other types of controllers. This review further reveals that the design of a proper NN control can maintain first-swing stability, damp oscillation, ensure voltage stability and the reliable supply of electric power.

Small Signal and First-Swing Stability Enhancement in InterArea Power System

Small Signal and First-Swing Stability Enhancement in InterArea Power System

Application of energy function to assess the first-swing stability of a power system with a SVC

The transient energy function method is usually used to assess the stability of a power system without considering the effect of control devices. A modification of the method is proposed to determine the first-swing stability limit of a power system in the presence of a static VAR compensator (SVC). The effect of the SVC is carefully incorporated in determining the value of critical energy needed for system separation. The unstable equilibrium point at which the critical energy is to be evaluated is determined by considering that the SVC operates at its full capacitive rating. A recent control strategy of SVC proposed to maximise the first-swing stability limit can justify the use of such an unstable equilibrium point. The above technique of determining the first-swing stability limit of a power system in the presence of a SVC is tested on both single- and multimachine systems. The results obtained by the proposed technique are also compared with the corresponding actual values found through repetitive time-domain simulations of system dynamic equations.

Effects of Exact Line Model and Shunt Facts Devices on First Swing Stability Limit

Shunt FACTS devices are very commonly used in a modern power system to improve the voltage profile, damping, and stability of the system. However, most of the previous work on stability improvement used the simplified line model obtained by considering only the line inductance and ignoring the line resistance and capacitance. This article investigates the effects of various line parameters and shunt FACTS devices on first-swing stability limit of a simple power system. Four different ways of incorporating the line parameters into the line model are considered, and the concept of the equal area criterion is used in determining the first-swing stability limit of the system. The results obtained for various line models and shunt FACTS devices are also compared.

A nonlinear emergency control strategy for HVDC transmission systems

A novel nonlinear emergency control method for HVDC transmission systems is presented in this paper. First, an observation-decoupled state space model of AC and DC interconnected power systems, which allows estimation or computation of the state components from local measurements, is developed. Secondly, the nonlinear control rules of HVDC links are derived using optimal-variable-aim strategy, which not only improves the first-swing stability, but also effectively damps the subsequent power oscillation. Finally, the simulation results of a three-machine six-bus system show that the proposed method can enough use the capabilities of fast response and short-time overload of HVDC links to improve the transient stability of power systems.

Fast contingency screening for online transient stability monitoring and assessment of the KEPCO system

A fast contingency screening algorithm using SIME for the transient stability monitoring of the KEPCO system is implemented. This method evaluates the first-swing stability of a large number of contingencies in a short time with reliable accuracy. The salient features of the proposed screening algorithm are as follows. First, a critical cluster of generators is identified by a new index in the early stage of the time domain simulation. Thus, the computational time required for finding the equivalent one machine infinite bus system can be reduced significantly. Second, clustering critical machines can perform even in very stable cases. This allows us to avoid the extra calculation of the time trajectory that is needed in the SIME for classifying the stable cases. Third, the screening capability is improved using the power-angle trajectory and subdividing the contingency classification. The test results on the KEPCO system show that the proposed method can be adopted as a contingency screening function and the transient stability assessment for the transient stability monitoring of the KEPCO system.

Analysis of line compensation by shunt-connected FACTS controllers: a comparison between SVC and STATCOM

A novel method for the analysis of the effectiveness of an SVC and a STATCOM of the same kVAr rating for first-swing stability enhancement is presented and the concept is demonstrated with a numerical example. The analysis shows that the STATCOM is superior to the SVC for first-swing stability enhancement.

Equal-area criterion: an extension for multimachine power systems

A method of determining the transient stability of a multimachine power system through a modified equal-area criterion is proposed. The method determines the first-swing stability limit of the most severely disturbed machine in the system by comparing two integrals or areas called the accelerating and decelerating areas. Unlike the standard equal-area criterion, the proposed method can be directly applied to a multimachine power system without representing the system by an equivalent single-machine infinite-bus model. The proposed method was tested on three power networks for a number of different faults. The critical clearing time obtained by the proposed method in each case was compared with the actual value found by the step-by-step method.

Power system stabilization by switching-over control of transmission lines

New technologies such as synchronized switching and power electronics will make it possible to change the configuration of a transmission network in future electric power systems. It is called VIPS (Variable Impedance Power System) by the authors who have been studying the effects of those technologies on power system stabilities. This paper considers the improvement of transient stability by means of switching-over control of transmission lines. It is clear that in some power systems, the simultaneous energization of the line de-energized in the normal state with the fault clearing better improves first-swing stability than the pre- and post-fault energization of the line. The energy function-based index to select such a transmission line is derived. In addition, this paper shows that multiple switching of a transmission line improves damping of post-fault conditions, where minimization of time derivative of energy functions is used. The switching-over control is applied to multimachine power systems and its effectiveness is demonstrated.

送電線の緊急切換え制御による電力系統の安定化に関する基礎的考察

New technologies such as synchronized switching and power electronics will make it possible to change the configuration of a transmission network in future electric power systems. It is called VIPS (Variable Impedance Power System) by the authors who have been studying the effects of those technologies on power system stabilities. This paper considers the improvement of transient stability by means of switching-over control of transmission lines. It is clear that in some power systems, the simultaneous energization of the line de-energized in the normal state with the fault clearing better improves first-swing stability than the pre- and post-fault energization of the line. The energy function-based index to select such a transmission line is derived. In addition, this paper shows that multiple switching of a transmission line improves damping of post-fault conditions, where minimization of time derivative of energy functions is used. The switching-over control is applied to multimachine power systems and its effectiveness is demonstrated.

Assessing online transient stability in energy management systems

An approach that combines automation of table lookup heuristic methods with transient energy function (TEF) methodology and conventional time simulation, taking advantage of the merits of each, is presented. The TEF method, which belongs to the class of direct methods of stability analysis, is described. It can be thought of as a generalization of the conventional equal-area criterion, which applies to first-swing stability analysis of a single-machine-infinite-bus system. It is explained how TEF software could best be used for online transient stability assessment. The process involves the determination of a master contingency list, contingency selection and prescreening, screening using TEF, and determination of safe operating limits.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>