Line Stability Index Research Articles

Thevenin’s equivalent based P–Q–V voltage stability region visualization and enhancement with FACTS and HVDC

Voltage source converter based Flexible Alternating Current Transmission System (FACTS) devices are considered to be key technology to alleviate voltage instability. This paper examines the enhancements in feasible operating P–Q–V space with FACTS and HVDC. Thevenin’s equivalent at the load bus is applied to draw P–Q–V curve (shows the boundary of the maximum real, reactive power and the minimum voltage magnitude) and area of voltage stability region (AVSR) in a three-dimensional diagram. A visualization framework for voltage stability region in MATLAB environment is implemented to study the impact of FACTS (SVC, STATCOM, and TCSC) and HVDC. The best possible location of shunt controllers is obtained using AVSR and index ‘L’. The line stability indices are calculated and compared to verify the weakest line for installation of series controllers. The inclusive study has been performed on IEEE-14 and IEEE-30 bus systems. The results show the enhancement in area of voltage stability region in all cases with maximum in case of HVDC.

Optimal Placement of Unified Power Flow Controller by Dynamic Implementation of System-Variable-Based Voltage-Stability Indices to Enhance Voltage Stability

Abstract A new approach of unified power flow controller (UPFC) optimal placement in the power system network based on dynamic analysis of voltage stability is presented in this paper. Voltage stability indices (VSIs), called line stability index LQP, voltage collapse point indicators (VCPIs), and line stability factor Lmn have been employed to explore the most suitable location for UPFC. The locations of UPFC are identified by dynamically varying loads across all the PQ buses by different percentages to satisfy the real power system conditions. The simulations are conducted in a power system computer-aided design (PSCAD) environment where IEEE-39 bus system has been chosen as case study. The effectiveness of the proposed method has been ensured from the simulation results because UPFC's placement in the obtained locations resulted in an improved voltage stability condition. Furthermore, to verify the suitability of the explored locations, a comparative study has been conducted after placing UPFC in the present locations and other locations obtained using optimization techniques like particle swarm optimization (PSO), differential evolution (DE), genetic algorithm (GA), and bacteria foraging algorithm (BFA). In all the cases, UPFC's placement in the identified locations using the proposed approach has resulted in better voltage stability condition improvement compared to heuristics approaches.

Contingency management of power system with Interline Power Flow Controller using Real Power Performance Index and Line Stability Index

Abstract As a result of privatization of the electrical industry the power transmission lines have to transfer power at their maximum transmission limits because of the competitive scenario of the electrical market. Hence, secured operation of power system has become one of the most important issues of modern era. In this paper, a probability of severity based placement strategy for Interline Power Flow Controller (IPFC) has been proposed based on Composite Severity Index (CSI). The composite severity index provides an exact measure of stress in the line in terms of mega watt overloading and voltage instability. IPFC is placed on the line which has the highest probability of severity during the occurrence of different outages. The IPFC has been tuned for a multi-objective function using Differential Evolution (DE) and the results have been compared with genetic Algorithm (GA). To verify the proposed method, it has been tested and implemented on IEEE 14 and 57 bus systems.

Single and Multi-objective Optimal Power Flow Using Grey Wolf Optimizer and Differential Evolution Algorithms

This article applies the grey wolf optimizer and differential evolution (DE) algorithms to solve the optimal power flow (OPF) problem. Both algorithms are used to optimize single objective functions sequentially under the system constraints. Then, the DE algorithm is utilized to solve multi-objective OPF problems. The indicator of the static line stability index is incorporated into the OPF problem. The fuzzy-based Pareto front method is tested to find the best compromise point of multi-objective functions. The proposed algorithms are used to determine the optimal values of the continuous and discrete control variables. These algorithms are applied to the standard IEEE 30-bus and 118-bus systems with different scenarios. The simulation results are investigated and analyzed. The achieved results show the effectiveness of the proposed algorithms in comparison with the other recent heuristic algorithms in the literature.

Optimal placement of unified power flow controllers to improve dynamic voltage stability using power system variable based voltage stability indices.

This study examines a new approach to selecting the locations of unified power flow controllers (UPFCs) in power system networks based on a dynamic analysis of voltage stability. Power system voltage stability indices (VSIs) including the line stability index (LQP), the voltage collapse proximity indicator (VCPI), and the line stability index (Lmn) are employed to identify the most suitable locations in the system for UPFCs. In this study, the locations of the UPFCs are identified by dynamically varying the loads across all of the load buses to represent actual power system conditions. Simulations were conducted in a power system computer-aided design (PSCAD) software using the IEEE 14-bus and 39- bus benchmark power system models. The simulation results demonstrate the effectiveness of the proposed method. When the UPFCs are placed in the locations obtained with the new approach, the voltage stability improves. A comparison of the steady-state VSIs resulting from the UPFCs placed in the locations obtained with the new approach and with particle swarm optimization (PSO) and differential evolution (DE), which are static methods, is presented. In all cases, the UPFC locations given by the proposed approach result in better voltage stability than those obtained with the other approaches.

English

The increase in power demand has forced the power system to operate closer to its stability limit. Voltage instability and line overloading have become challenging problems due to the strengthening of power system by various means. The nature of voltage stability can be analysed by the production, transmission and consumption of reactive power. One of the major causes of voltage instability is the reactive power unbalancing which occurs in stressed condition of power system. Flexible AC transmission system (FACTS) devices play an important role in improving the performance of a power system, but these devices are very costly and hence need to be placed optimally in power system. FACTS device like static var compensator (SVC) and thyristor controlled series compensator (TCSC) can be employed to reduce the flows in heavily loaded lines, resulting in a low system loss and improved stability of network. In this paper, a method based on line stability index, real power performance index and reduction of total system VAR power losses has been proposed to decide the optimal location of TCSC. Now a day, Voltage Stability has become a major concern in power systems planning and operation. This problem has become very complex due to the continuous growing on system interconnections and demand for electricity and also due to economical and environmental constraints to properly expand the system. This has increased the importance of implementing suitable and efficient techniques for improving voltage stability of stressed power system. FACTS are one aspect of the power electronics revolution that is taking place in all areas of electric energy.

Simultaneous Optimization of Renewable Power at Transmission and Distribution Grid

Abstract In this paper, the simultaneous optimization of transmission and distribution grid has been proposed. The dynamic model of the grid consists of turbine governors (TG), automatic voltage regulators (AVR) as well as wind turbines, solar power units and energy storage units. Grid stability is obtained by line stability and voltage stability indices and also by conducting eigenvalue analysis of the complete power system grid. Particle Swarm Optimization (PSO) algorithm adjusts the grid control settings (active and reactive power management) to maximize the renewable penetration at all layers of the grid. IEEE 14 bus system in conjunction with a micro grid is used as the test system. The results demonstrate that simultaneous reactive power management of transmission and distribution grid can maximize the renewable penetration at transmission and distribution layers of the grid. However different case studies with different renewable power pro-files at each layer of the grid are remained to be optimized, this study recommends that real-time management of reactive power at all layers of the grid can be a good candidate to deal with intermittency of renewable sources.

Under Voltage Load Shedding for Contingency Analysis to Optimize Power Loss and Voltage Stability Margin

Power system contingency is a condition of operation which may be caused due to line outage in a system and could lead to entire system voltage instability. This may further result in voltage collapse leading to total blackout of the system. Therefore, voltage collapse prediction and estimating voltage stability margin is an important task in power system operation and planning. In this paper Line Stability Index Lij utilizing the concept of power flow in a single line is adopted to determine the condition of voltage instability. The purpose of Lij is to determine the point of voltage instability, the weakest bus in the system and the critical line referred to a bus. Analytical approach based technique for load shedding has been developed as a solution for secured operation of power system under various contingency conditions to optimize the power flow in order to minimize the system losses within acceptable limit. To validate the effectiveness of the proposed method simulation has been carried out on IEEE 14 bus system.

A new hybrid technique for power systems multi-facts optimization design

SUMMARY The purpose of this paper is to develop a new tool to the dispatching and optimization of reactive power resources using two kinds of the flexible alternating current transmission system devices, namely the static volt ampere reactive compensator and the Thyristor controlled series compensator. The fast voltage stability index and line stability index (Lmn) are used to identify the critical buses and lines, which will receive the flexible alternating current transmission system devices. The methodology carried out in this work is deployed in two phases. In the first one, we consider that the power system network is secure and operates within its stability limits and the balance between consumption and generation is satisfied. Thus, the solution of optimization program of the fuel cost minimization problem using the interior point method gives a feasible solution where the reactive power compensation is not considered. In the second phase, the power system network is unsecure and operates close to its secure limits. Although the optimization program of the fuel cost minimization problem gives a non-feasible solution, the reactive power compensation is, in this case, introduced to solve the problem. The power transmission line factor minimization problem is applied after each phase to improve the solution of the problem by minimizing the power flow in the transmissions lines. The reactive power planning and the power transmission line factor minimization problems are solved with a new hybrid technique combining particle swarm optimization with a nonlinear interior point method. Furthermore, the fuel cost minimization problem is solved with the interior point method. The methodology has been tested with the IEEE 57-bus system, and the simulation results show the effectiveness of the proposed approach for improving the reactive power planning problem. Copyright © 2014 John Wiley & Sons, Ltd.

Sensitive Area Clustering Based on Voltage Stability and Contingency Analyses with Impact of Line Stability Indices

With a growing concern for maintaining stable voltage operation within the network, many critical issues on voltage stability related studies have been raised in the area of power system research. The problem of voltage stability is one of the main concerns in the operation of power systems. Due to the excessive load demand and non-linearity in loads leads to voltage instability and ultimately leading to voltage collapse. Voltage collapse has to be given the utmost priority because it led to cascading blackouts in the whole network. A voltage stability index is that which examines the voltage stability condition formulated based on line in a power system and identifies sensitive bus of the system to maintain the stable system, which will be great importance. With the help of Voltage stability index, the point of voltage collapse, critical line and critical voltage with respect to load bus are identified. Also this paper deals the development of the sensitive area clustering technique based on the results obtained from voltage stability analysis and contingency analysis. The performance of this index is presented and the effectiveness of the analyzed methods is demonstrated through simulation studies in IEEE 30 bus test systems.

A Novel Line Stability Index for Voltage Stability Analysis and Contingency Ranking in Power System Using Fuzzy Based Load Flow

In electric power system, the line stability indices adopted in most of the instances laid stress on variation of reactive power than real power variation of the transmission line. In this paper, a proposal is made with the formulation of a New Voltage Stability Index (NVSI) which originates from the equation of a two bus network, neglecting the resistance of transmission line, resulting in appreciable variations in both real and reactive loading. The efficacy of the index and fuzzy based load flow are validated with IEEE 30 bus and Tamil Nadu Electricity Board (TNEB) 69 bus system, a practical system in India. The results could prove that the identification of weak bus and critical line in both systems is effectively done. The weak area of the practical system and the contingency ranking with overloading either line or generator outages are found by conducting contingency analysis using NVSI.

Static synchronous series compensator and static var compensator interaction on voltage stability limit enhancement and active power loss minimization through differential evolution algorithm

This paper proposes an application of differential evolution (DE) algorithm based extended voltage stability margin and minimization of real power loss incorporating static synchronous series compensator (SSSC) and static var compensator (SVC) devices. A new circuit element based model of SSSC and variable susceptance model of SVC are utilized to control the line power flows and bus voltage magnitudes for voltage stability limit improvement. The line stability index is used to assess the voltage stability of a power system. Voltage profile improvement values, real power loss minimization values and the location and size of SSSC and SVC devices were optimized by differential evolution algorithm. The results are obtained from the IEEE-30 Bus test case system and were analyzed with the voltage and real power loss under normal loading, critical loading and single line outage contingency conditions. Key words: Differential evolution algorithm (DEA), voltage stability, static synchronous series compensator (SSSC), static var compensator (SVC), line stability index, FACTS devices, load flow.

INFLUENCE OF TCSC FACTS DEVICE ON STEADY STATE VOLTAGE STABILITY

The influence of series Flexible AC Transmission Systems (FACTS) device namely, Thyristor-Controlled Series Capacitors (TCSC) on the steady state voltage stability is the main objective of this paper. The Line stability Index LSI under excepted lines outage contingencies is used to identify the critical line which is considered as the best location for TCSC. A modal analysis is used to define the weakest bus of the studied system. The FACTS device is implemented and included into the Newton-Raphson power flow algorithm, and the control function is formulated to achieve the voltage stability enhancement goal. The analysis is preformed on standard IEEE 30 bus system. The proposed scheme are tested under different loading conditions and different nonlinear voltage dependent loads. The simulation results demonstrate the feasibility and effectiveness of the device and the proposed algorithm.

Implementation of Line Stability Index for Contingency Analysis and Screening in Power Systems

Problem statement: Estimating the margin in the loadability of the power system is essential in the real time voltage stability assessment. Voltage stability is currently one of the most important research areas in the field of electrical power system. In power system operation unpredictable events is termed as contingency and may be caused by line outage in the system which could lead to entire system instability. Voltage stability analysis and contingency analysis are would be performed in a power system by evaluating the derived voltage stability index. Approach: Voltage Stability Index Lmn can be useful for estimating the distance from the current operating point to voltage collapse point. The index can either reveal the critical bus of a power system or the stability of each line connected between two buses in an interconnected network or evaluate the voltage stability margins of a system. Results: Flexible Alternating Current Transmission Systems (FACTS) devices have been proposed as an effective solution for controlling power flow and regulating bus voltage in electrical power systems, resulting in an increased transfer capability, low system losses and improved stability. However to what extent the performance of FACTS devices can be brought out highly depends upon the location and the parameters of these devices. Unified Power Flow Controller (UPFC) is the most promising FACTS device for power flow control. Conclusion/Recommendations: The performance of this index is presented and the effectiveness of the analyzed methods is demonstrated through simulation studies in IEEE 14 bus reliability test systems.

Shuffled Frog Leaping Algorithm based Voltage Stability Limit Improvement and Loss Minimization Incorporating FACTS Devices under Stressed Conditions

day power system networks are having high risks of voltage instability problems and several network blackouts have been reported. This phenomenon tends to occur from lack of reactive power supports under heavily stressed operating conditions caused by increased load demand and the fast developing deregulation of power systems across the world. This paper proposes an application of Shuffled Frog Leaping Algorithm (SFLA) based extended voltage stability margin and minimization of loss by incorporating TCSC and SVC (variable susceptance model) devices. The line stability index (LQP) is used to assess the voltage stability of a power system. The location and size of Series connected and Shunt connected FACTS devices are optimized by shuffled frog leaping algorithm. The results are obtained from the IEEE-30 bus test case system under critical loading and single line outage contingency conditions

Enhancement of Voltage Stability Through Optimal Placement of TCSC

The increase in power demand has forced the power system to operate closer to its stability limit. Voltage instability and line overloading have become challenging problems due to the strengthening of power system by various means. The nature of voltage stability can be analyzed by the production, transmission and consumption of reactive power. One of the major causes of voltage instability is the reactive power unbalancing which occurs in stressed condition of power system. Flexible AC transmission system (FACTS) devices play an important role in improving the performance of a power system, but these devices are very costly and hence need to be placed optimally in power system. FACTS device like thyristor controlled series compensator (TCSC) can be employed to reduce the flows in heavily loaded lines, resulting in a low system loss and improved stability of network. In this paper, a method based on line stability index, real power performance index and reduction of total system VAR power losses has been proposed to decide the optimal location of TCSC. The effectiveness of the proposed method is demonstrated on IEEE 30-bus power system.

Real Power Loss and Voltage Stability Limit Optimization Incorporating TCSC and SVC through DE Algorithm under Different Operating Conditions of a Power System

Modern day power system networks are having high ri sks of voltage instability problems and several network blackouts have been reported. This phenomenon tends to occur from lack of reactive pow er supports in heavily stressed operating conditions c aused by increased load demand and the fast develop ing deregulation of power systems across the world. Thi s paper proposes an application of Differential Evo lution (DE) Algorithm based extended voltage stability mar gin and minimization of loss by incorporating TCSC and SVC (variable susceptance model) devices. The line stability index (LQP) is used to assess the voltage stability of a power system. The location and size of Series connected and Shunt connected FACTS devices were optimized by DE algorithm. The results are obtained from the IEEE-30 bus test case system under critic al loading and single line outage contingency conditio ns.

Estimation of voltage stability index for power system employing artificial neural network technique and TCSC placement

This paper proposes a scheme for online voltage stability monitoring for various load conditions using feed forward back propagation network (FFBPN). A single FFBPN with minimal number of neurons is used to estimate the line voltage stability index for various load conditions. A sequential learning strategy is used to design the FFBPN and the weights in the output layer are determined by using linear optimization. The proposed network is applied on the IEEE 14-bus and the IEEE 30-bus power system and line stability indices are calculated for different loading conditions. Based on the calculated indices, the ranking of weakest lines is done. The optimal location for placement of Thyristor controlled series capacitor (TCSC) has been identified among the weakest lines for improving the voltage stability in the power system. The proposed network can be adapted with changing operating scenario of the power system.

Stability Index Based Voltage Collapse Prediction and Contingency Analysis

Voltage instability is a phenomenon that could occur in power systems due to stressed conditions. The result would be an occurrence of voltage collapse leading to total blackout of the system. Therefore, voltage collapse prediction is an important part of power system planning and operation, and can help ensure that voltage collapse due to voltage instability is avoided. Line outages in power systems may also cause voltage collapse, thereby implying the contingency in the system. Contingency problems caused by line outages have been identified as one of the main causes of voltage instability in power systems. This paper presents a new technique for contingency ranking based on voltage stability conditions in power systems. A new line stability index was formulated and used to identify the critical line outages and sensitive lines in the system. Line outage contingency ranking was performed on several loading conditions in order to identify the effect of an increase in loading to critical line outages. Correlation studies on the results obtained from contingency ranking and voltage stability analysis were also conducted, and it was found that line outages in weak lines would cause voltage instability conditions in a system. Subsequently, using the results from the contingency ranking, weak areas in the system can be identified. The proposed contingency ranking technique was tested on the IEEE reliability test system.

Restructuring choices for the Indian power sector

This letter demonstrates the use of line stability index termed as fast voltage stability index (FVSI) in order to determine the maximum loadability in a power system. The bus that is ranked highest is identified as the weakest bus since it can withstand a small amount of load before causing voltage collapse. It involves the experimental process of voltage stability analysis and evaluation of line index based on the load variation. The point at which FVSI close to unity indicates the maximum possible connected load termed as maximum loadability at the point of bifurcation. This technique is tested on the IEEE system and results proved that the proposed technique is able to estimate the maximum loadability in a system.