Voltage Stability Margin Research Articles

Optimal location of SVC for improvement in voltage stability of a power system under normal and contingency condition

Voltage instability is a major problem in power system it seldom results in voltage collapse and blackout. FACTS devices can be used to maintain voltage stability by controlling active and reactive power and increase voltage stability margin. Optimal location of these devices is also an important issue. In this paper static var compensator (SVC) is used to improve voltage stability. Optimal location of SVC is found by continuation power flow and by finding fast voltage stability index. SVC is placed at optimal location and its effect on improving voltage stability, loadability limit and reducing power losses have been studied under normal as well as contingency conditions. Two types of contingencies are considered, transmission line (N − 1) contingency and generator outage contingency. The proposed work is tested in IEEE 14 bus test system.

Differential Evolution Technique for the Optimization of Reactive Power Reserves

In the present work, reactive power planning problem along with voltage stability margin is addressed by effective co-ordination of reactive power sources. Modal analysis and L-index methods are used to detect weak nodes of the system accordingly. Differential Evolution (DE) and Genetic Algorithm (GA)-based optimization techniques are applied for the proper co-ordination of Var sources under base and increased loading conditions maintaining voltage stability of the connected power network. The problem is multi-objective and IEEE 30 bus system is taken as the standard system. It is observed that modal analysis based detection of weak nodes are more effective than the L-index-based detection. Moreover, the DE-based optimization algorithm gives better result compared to GA-based approach in maximizing reactive power reserves.

Risk-Based Probabilistic Voltage Stability Assessment in Uncertain Power System

The risk-based assessment is a new approach to the voltage stability assessment in power systems. Under several uncertainties, the security risk of static voltage stability with the consideration of wind power can be evaluated. In this paper, we first build a probabilistic forecast model for wind power generation based on real historical data. Furthermore, we propose a new probability voltage stability approach based on Conditional Value-at-Risk (CVaR) and Quasi-Monte Carlo (QMC) simulation. The QMC simulation is used to speed up Monte Carlo (MC) simulation by improving the sampling technique. Our CVaR-based model reveals critical characteristics of static voltage stability. The distribution of the local voltage stability margin, which considers the security risk at a forecast operating time interval, is estimated to evaluate the probability voltage stability. Tested on the modified IEEE New England 39-bus system and the IEEE 118-bus system, results from the proposal are compared against the result of the conventional proposal. The effectiveness and advantages of the proposed method are demonstrated by the test results.

Probabilistic Voltage Stability Analysis Based on Unscented Transformation and Maximum Entropy Principle

Considering the uncertainty of load and the random variation of wind farm output power in power system, a probabilistic voltage stability analysis method is proposed based on unscented transformation technique. According to the statistical characteristics of random variables in power system, the statistical characteristics of voltage stability margins, such as mean, standard deviation and moments, can be calculated by using a small number of samples and the conventional method. The maximum entropy method is applied to determine the probability distribution of voltage stability margin. In compared with Monte Carlo method, the effectiveness of the proposed method is verified on 39-bus and IEEE 57-bus system. The results show that the proposed method can accurately compute the statistical characteristics and the probability distribution of the voltage stability margin, and the computational efficiency is improved.

Real-Time Static Voltage Stability Assessment in Large-Scale Power Systems Based on Maximum-Relevance Minimum-Redundancy Ensemble Approach

An integrated approach to static real-time voltage stability assessment in bulk power systems based on mutual information theory is proposed. An advanced maximum-relevance minimum-redundancy (MRMR) algorithm is designed to explore the invisible association between operation variables and the voltage stability margin (VSM). Multiple MRMR procedures with different selected variables are generated in parallel. A set of inter-complementary features is generated one by one using the MRMR criterion that additional VSM information should be reflected in new obtained variables. A functional expression of the relationship between input variables and the VSM is obtained by curve fitting. The performance of the proposed approach is tested on 21- and 1648-bus systems provided by PSS/E. The impacts of training set size, a number of selected feature sets, length of feature sets, and robustness to topology change are studied. Experimental results indicate that compared with other traditional methods, the proposed technique provides faster and more accurate assessment results. Given the proposed method’s efficiency, it is suitable for real-time voltage stability assessment.

Distribution networks reconfiguration considering the integrations of DGS and different voltages of the medium‐voltage feeders

With the large-scale integration of distributed generations (DGs) and verified loads, the basic topology and operating characteristics of distribution system have been fundamentally changed. In this study, a novel reconfiguration scheme for distribution networks is proposed with consideration of DGs and the feeders of different voltages from the different substations. First of all, the comprehensive objective function is established by transforming the multiple objectives, i.e. power loss, voltage deviation and voltage stability margin, into the single objection function via the possibility-satisfactory degree method. Moreover, the simulation model of DGs and different kinds of loads are analysed in detail. Then, the improved fireworks algorithm is proposed to solve the reconfiguration problems by considering features of the medium-voltage feeders with different voltages. Finally, simulations are carried out to evaluate the performances of the reconfiguration scheme and proposed algorithm, which show that the reconfiguration scheme considering different voltages of the medium-voltage feeders can reduce the power loss and decrease the voltage deviation caused by the integrations of DGs and improve the reliability of the distribution system.

Consideration of small signal stability in multi‐objective DS reconfiguration in the presence of distributed generation

This study presents a methodology for distribution system (DS) reconfiguration in the presence of distributed generations with objectives of minimising real power loss, switching operations as well as maximising the voltage stability margin while maintaining the constraints of bus voltage, branch current carrying capacity and radiality of DS. Furthermore, small signal stability of the system has also been considered in the formulated reconfiguration problem. To obtain the pareto-optimal solutions of this constrained multi-objective optimisation problem, knee point-driven evolutionary algorithm, is applied. In contrast to the non-dominated sorting genetic algorithm-II (NSGA-II)-based approach, preference is given to the knee points among non-dominated solutions in selection and tournament mating. Therefore, it maintains better balance between the convergence of the method and the diversity in the population. The method has been tested on IEEE 33-bus, 69-bus and 119-bus radial DSs to demonstrate its feasibility and effectiveness. The obtained results have also been compared with those obtained by the multi-objective NSGA-II-based method.

Static Voltage Stability Margin Maximization and Real Power Loss Minimization by Chemical Reaction Based Optimization Algorithm

In this paper Chemical Reaction Optimization (CO) algorithm is proposed to solve the optimal reactive power dispatch Problem. To solve reactive power problem algorithm can regulate molecular structure and energy management. And it leads to strong flexibility of the algorithm. Candidate solution for a specific problem is encoded as a molecule in Chemical Reaction Optimization (CO) algorithm. Molecular structure (φ), potential energy (PY), kinetic energy (KY) are some several essential properties possessed by the Chemical Reaction Optimization (CO) algorithm. Reactants inclined to be stable product with minimum potential energy (PY) in the CO algorithm. System attains the minimum potential energy (PY) in the progression of the Chemical Reaction Optimization (CO) algorithm. In order to evaluate the efficiency of the proposed Chemical Reaction Optimization (CO) algorithm, it has been tested on standard IEEE 30 bus system and compared other standard algorithms. Results show’s that Chemical Reaction Optimization (CO) algorithm is more efficient in reducing the real power loss and static voltage stability index also Enhanced.

Allocation of demand response resources: toward an effective contribution to power system voltage stability

In this study, capacity allocation of demand-response (DR) and the real-time savings earned from implementing DR programmes (DRPs) are investigated based on a mixed integer non-linear multi-objective programming (MINMOP) framework according to two conflicting concepts, titled; maximum achievable potential (MAP) and realistic achievable potential (RAP). MAP indicates that placing a value on DR resources must be strictly weighed against the value of avoiding the acquisition of short-term resources to meet critical peak period, whereas RAP takes into accounts the amount of savings that might be achieved through DRPs. The proposed MINMOP includes both technical and economic aspects of integrating DRPs into the power systems by considering optimal generation scheduling cost, voltage drop, voltage stability margin, network loss, and incentive payment as objective functions. In addition, augmented ɛ-constraint method is applied to solve the proposed MINMOP by means of off-the-shelf conventional optimisation software. The IEEE 24-bus reliability test system (RTS 24-bus) is used to demonstrate the applicability of the proposed method. Eventually, DR allocation is analysed through four cases based on different number of candidate buses which demonstrate the interest and effectiveness of the proposed technique.

Enhancement Voltage Stability of the Iraqi Power Grid Using Shunt FACTs Devices

Due to raise in demand, the transmission system becomes more exhausted, which in turn, forces the system to be more susceptible to voltage instability. The aim of this research is to study the enhancement in voltage stability margin by installation the SVC which is represented as Static of VAR Compensator or STATCOM that is represented as Static of Synchronous Compensator. Voltage stabilization dilemma considers an essential issue in the electric networks which may lead to a voltage collapse in electric power networks. L-index has been used to predict and identify points of breakdown voltages in the power system with sufficient accuracy. L -index has been employed due to its accuracy and effectiveness in the computing voltage collapse points for different load buses with sufficient precision at a short circuit and also at various loads situations. Voltage stability index has been tested on the 9-wscc test system and 14-IEEE test system .Then it has been applied to the Iraqi national grid 400 kV. A shunt facts(SVC or STATCOM) devices are installed individually at the weak bus bar based on Voltage Stability Index(L indicator) detection, The simulation results are first obtained for an uncompensated system, and the voltage profiles are studied. The results so obtained are compared with the results obtained after compensating the system with SVC and STATCOM to show the voltage stability margin enhancement. The outcomes acquired after simulation demonstrate the performances of shunt fact devices (SVC and STATCOM) when connected to a system Subjected to 3-phase short circuit fault at different locations. All the simulation results have been carried out using MATLAB version 7.10 and Power System Analysis Toolbox (PSAT) package.

An Efficient Approach for Fast and Accurate Voltage Stability Margin Computation in Large Power Grids

This paper proposes an efficient approach for the computation of voltage stability margin (VSM) in a large-scale power grid. The objective is to accurately and rapidly determine the load power margin which corresponds to voltage collapse phenomena. The proposed approach is based on the impedance match-based technique and the model-based technique. It combines the Thevenin equivalent (TE) network method with cubic spline extrapolation technique and the continuation technique to achieve fast and accurate VSM computation for a bulk power grid. Moreover, the generator Q limits are taken into account for practical applications. Extensive case studies carried out on Institute of Electrical and Electronics Engineers (IEEE) benchmark systems and the Taiwan Power Company (Taipower, Taipei, Taiwan) system are used to demonstrate the effectiveness of the proposed approach.

Evaluation of Steady State Voltage Stability Margin of a Power System Using Search Group Algorithm

Evaluation of Steady State Voltage Stability Margin of a Power System Using Search Group Algorithm

Optimal location and sizing of MW and MVAR based DG units to improve voltage stability margin in distribution system using a chaotic artificial bee colony algorithm

Optimal location and sizing of MW and MVAR based DG units to improve voltage stability margin in distribution system using a chaotic artificial bee colony algorithm

Assessment of Global Voltage Stability Margin through Radial Basis Function Neural Network

Dynamic operating conditions along with contingencies often present formidable challenges to the power engineers. Decisions pertaining to the control strategies taken by the system operators at energy management centre are based on the information about the system’s behavior. The application of ANN as a tool for voltage stability assessment is empirical because of its ability to do parallel data processing with high accuracy, fast response, and capability to model dynamic, nonlinear, and noisy data. This paper presents an effective methodology based on Radial Basis Function Neural Network (RBFN) to predict Global Voltage Stability Margin (GVSM), for any unseen loading condition of the system. GVSM is used to assess the overall voltage stability status of the power system. A comparative analysis of different topologies of ANN, namely, Feedforward Backprop (FFBP), Cascade Forward Backprop (CFB), Generalized Regression (GR), Layer Recurrent (LR), Nonlinear Autoregressive Exogenous (NARX), ELMAN Backprop, and Feedforward Distributed Time Delay Network (FFDTDN), is carried out on the basis of capability of the prediction of GVSM. The efficacy of RBFN is better than other networks, which is validated by taking the predictions of GVSM at different levels of Additive White Gaussian Noise (AWGN) in input features. The results obtained from ANNs are validated through the offline Newton Raphson (N-R) method. The proposed methodology is tested over IEEE 14-bus, IEEE 30-bus, and IEEE 118-bus test systems.

Stochastic optimal reactive power reserve dispatch considering voltage control areas

Summary Conventional optimal reactive power reserve dispatch approaches are mostly modeled in deterministic forms, where the power injections are fixed. With the integration of intermittent renewable sources, the power injections could become uncertain. To maintain the security, a stochastic optimal reactive power reserve dispatch model is proposed, which is formulated as a chance-constrained optimal power flow problem. To begin, a multistage partitioning method considering both the decoupling degree and the robustness to failure is proposed to obtain the voltage control areas. Then, the original nonlinear stochastic optimal reactive power reserve dispatch model is decomposed into a successive multiarea linearized programming problem. Finally, a chance constraint relaxation–based method is proposed to solve the above problem. The results show that the proposed method can significantly enhance the voltage stability margin, and the security in uncertain scenarios can also be maintained for the satisfaction of the chance constraints.

Voltage Instability Analysis for Electrical Power System Using Voltage Stabilty Margin and Modal Analysis

Voltage instability analysis in electric power system is one of the most important factors in order to maintain the equilibrium of the power system. A power system is said to be unstable if the system is not able to maintain the voltage at all buses in the system remain unchanged after the system is being subjected to a disturbance.The research work presented in this paper is about the analysis of voltage instability of electric power system by using voltage stability margin (VSM), load real power (P) margin, reactive power (Q) margin, reactive power-voltage (QV) and real power-voltage (PV) modal analysis. IEEE 30-bus system has been chosen as the power system. The load flow analysis are simulated by using Power World Simulator software version 16. Both QV and PV modal analysis were done by using MATLAB application software.

Optimal Placement of SVC Incorporating Installation Cost

As the FACTS controllers are an inequitable part of power system due to their fast and very flexible control. With the enhancement of FACTS technology, their role in the marginal cost determination should be considered taking their cost function into account. The aim of this paper is to compare the optimal performance of static VAR compensator (SVC) in voltage stability enhancement problem. During last decade, FACTS devices are broadly used for maximizing the margin of voltage stability and loadability of existing power system transmission networks. To get the optimal system, cost analysis might be necessary. In the cost analysis of SVC, authors analyzed the installation cost of SVC devices in USD, the cost of SVC in USD/KVAR and the average value of installation cost for given systems. Here, the voltage stability enhancement problem is solved applying Gravitational Search algorithm incorporating SVC. The following conditions are investigated with the incorporation of SVC: the role of SVC for improving the voltage profile, loss minimization and the approximate analysis on cost recovery and payback period with SVC in voltage stability enhancement problem. With this motivation, the location of SVC is finalized through weak bus identification methods. Voltage stability indices namely Fast Voltage Stability Index (FVSI) is utilized to identify weak buses in the systems. For calculation of the Size of SVC, an optimization routine Gravitational Search Algorithm (GSA) is established. The main purpose of optimization is to minimize the FVSI. The proposed approach has been tested on three standard IEEE bus systems with different loading scenarios. General Terms: Flexible AC Transmission System (FACTS), Marginal Cost, Voltage Stability Assessment, Static VAR Compensators.

Performance of two modified optimization techniques for power system voltage stability problems

The development of optimization techniques in power system is to determine the sizing of Flexible AC Transmission System (FACTS) devices such as Unified Power Flow Series Compensator (UPFC) controller in improving the voltage stability and bus voltage margin. An attempt is made to modify the Particle Swarm Optimization (PSO) and Artificial Bee Colony (ABC) with Hybrid-Genetic Algorithm (H-GA) for determination of sizing of the device. Fast Voltage Stability Index (FVSI) is used to identify the location of the device to be connected. The proposed methods are implemented in IEEE 30 Bus system and its results are tabulated for each technique.

Estimating the Voltage Stability Margin Using PMU Measurements

This paper presents a new method based on phasor measurement units (PMUs) for the estimation of voltage stability margin in a power system to increase operator's situational awareness. The method assumes a PMU measurement preprocessing technique as a priori in order to eliminate data inconsistency and uncertainty caused by random load disturbances. The measurements are then used in the computation of voltage stability margin based on the coupled single-port Thevenin equivalent model and the cubic spline extrapolation technique. Moreover, some practical operating constraints such as the generator reactive power limits are taken into account for practical assessment of the method's performance. Extensive case studies conducted on several standard IEEE test systems are used to demonstrate the effectiveness of the proposed method.

Optimal placement of D-STATCOM using sensitivity approaches in mesh distribution system with time variant load models under load growth

Abstract In this paper, an approach for optimal placement of D-STATCOM in mesh distribution systems using sensitivity approaches is proposed. The main contributions of the paper are as follows: (i) Optimal D-STATCOM placement based on the new voltage sensitivity index in mesh distribution system, (ii) optimal D-STATCOM size determination for seasonal loads with load growth scenario, (iii) comparison of D-STATCOM placement and size determination with the existing sensitivity methods, and (iv) impact of optimal D-STATCOM placement on voltage stability margin enhancement, energy loss reduction and cost of energy savings. The results of voltage profile improvement, reduction in power losses, reduction in cost of energy loss, improved voltage stability margin, cost of energy loss savings, installation cost of D-STATCOM and annual savings are obtained for UK 38 bus practical mesh distribution system.