Causes Of Voltage Instability Research Articles

Application of SSSC for Voltage Stability Improvement in the Nigerian 330 kV Transmission System using Particle Swarm Optimization Technique

Load imbalance has always been a major cause of voltage instability of the power system network and increase in voltage instability affects the power system reliability. In this paper, static synchronous series capacitor (SSSC) FACTS device was implemented to improve the voltage stability in the Nigerian 330 kV transmission network using particle swarm optimization (PSO) technique. Modelled power system network in the power system analysis toolbox (PSAT) is simulated to determine the existing power flow analysis and the level of instability in the power system generation plants situated in the Northern region. The outcome of the power flow is thereafter, optimized with PSO by generating the relationship with a high prediction accuracy between voltage at each location and an inter-linked transmission line distance of the 330kV. The model was generated with least square method and the high prediction accuracy determination was carried out with R-square value of the polynomial order. The best model was optimized and the entire computations were carried out in MatLab resulting in the determination of the optimal location which was between Jebba transmission and Shiroro generation stations. SSSC FACTS controller was implemented on the optimized transmission line and the simulation results showed that the introduction of SSSC improved the voltage stability of the power system network.

A survey on voltage stability indices for power system transmission and distribution systems

Voltage stability is a critical aspect of power system operation, ensuring the reliable and efficient delivery of electrical energy to consumers. Recently, voltage stability in the power system has received much attention. The primary cause of voltage instability is the lack of real and reactive power generation to cope with the continuous demand increment. Maintaining voltage stability while planning, controlling, and assessing the system’s security is a difficult task for power system engineers. From knowledge of past incidents, a lack of reactive power is identified as the primary cause of voltage instability, which may further lead to the total collapse of the system. The importance of voltage stability assessment is essential to maintain the integrity of power systems. It helps prevent voltage instability, which can lead to cascading failures and widespread outages. This paper uses various parameters, including load demand, generator capacity, and system impedance, to develop voltage stability indices (VSIs). The paper mainly focuses on the idea of VSIs that have been developed in order to monitor and control the criticality of the power system. The voltage stability indices for transmission and distributed systems, as well as their subclasses, are thoroughly reviewed in this study. Furthermore, traditional voltage stability methods, as well as various software tools for monitoring the voltage stability problems, are also discussed. In addition, the development of VSIs and its related concepts are clearly described in this paper. This comprehensive survey provides a decent groundwork for future work in this area, and assists professionals in selecting the optimal VSI for various applications. Moreover, it provides a concise overview of methods and the importance of voltage stability assessment in both transmission and distribution systems.

Voltage Stability of Spacecraft Electric Power Systems for Deep Space Exploration

The future of deep space exploration requires high levels of reliability in critical subsystems such as the electrical power system. This paper provides an analysis of voltage stability of direct current (DC) microgrids for spacecraft applications. Bifurcation theory is used to determine the behavior of the system and identify the major causes of voltage instability. The analytical results of the bifurcation model are experimentally verified through a series of tests emulating probable operating conditions of the spacecraft. The findings of this paper are applicable to similar classes of islanded (grid forming) DC electric power systems including aerospace vehicles, shipboard systems, and terrestrial microgrids.

Improving performance of transmission networks using facts through continuation power flow method

Over the past 50 years, modern electrical systems have become more complex, as they overrun the geographical boundaries of neighboring countries. The problem is that the power system faces many challenges, because it is exposed to difficult operating conditions. The phenomenon of voltage instability is the most frequent phenomenon, and this can lead to the collapse of the power system. To avoid power outages in the system (especially in blackout situations), the power system must be analyzed in order to maintain voltage stability in the expected difficult operating conditions. The main objective is to determine the maximum load capacity of the system and the causes of voltage instability. The voltage instability problem is related to the nature of nonlinear loads, so different load characteristics must be taken into consideration when analyzing voltage stability. This study aims to discover the maximum load capacity required by using the continuous power flow method (CPF) in the studied network. Then, the performance of this network using a Flexible Alternating Current Transmission System (FACTS) will be utilized. FACTS systems present a promising solution in improving the voltage stability by improving the power transmission capacity and controllability of the parameters of the existing power networks. This study will be conducted on a reference network platform under normal working conditions, then installation of one of the FACTS systems will show its effect on improving voltage stability. The continuous power flow method will be used to find PV curves, which in turn will help to determine the conditions of maximum loading while maintaining stability, and identify the bus bar with the smallest voltage, on which the flexible AC systems will be installed. The software environment MATLAB/PSAT will be used for modeling and simulation.

Voltage stability assessment using TCSC and SVC based FACTS controllers

The Most causes of Voltage instability is the sources of reactive power .In order to protect the total system from voltage instability the reactive loads can be reduced or extra reactive power can be added to reach the Voltage collapse point .The Flexible AC transmission devices(FACTS) have made it flexible and possible to prevent Voltage instability by Fast and Flexible control method . Voltage collapse point is predicted with TCSC and SVC devices and is compared with each other. The Voltage stability Indicator is derived to identify the voltage collapse point. it is concluded that voltage stability index provides a simple means to predict vulnerability of a bus in a Multibus system for voltage collapse.

Comparative analysis on the stability mechanism of droop control and VID control in DC microgrid

Voltage resonance and fluctuation deteriorate the stability of DC microgrids (DC-MGs) and restrict their popularization. Conventional droop control cannot suppress voltage fluctuation and damp oscillations. Therefore, new control methods, namely, droop+filter control and virtual inertia and damping control, are proposed. These methods differ owing to the addition of low pass filter (LPF) and virtual inertia loop. In this study, the stability of these control methods is investigated comprehensively to understand their differences arising from the use of LPF and inertia loop as well as the underlying dynamic stability mechanism. The leading causes of voltage instability in DC-MGs regulated by droop control are first presented. Subsequently, control methods for solving this issue are compared and their simplified small-signal models are constructed. Based on eigenvalue analysis, the DC-MG is equivalent to a third-order system. Different control effects can be acquired by changing the control parameters and the location of the eigenvalues; furthermore, they can be used to understand the dynamic stability. Eigenvalue analysis can provide parameter design guidelines. Finally, the simulation results verify the validity of the theoretical analysis.

Real-Time Simulation of Static VAR Compensator and Static Synchronous Compensator

In recent years, deregulation, open access, and co-generation in electrical power system are creating transmission voltage sags, swells, forced outages, and frequently followed by black-outs, congestion scenario, and many such problems. Reactive power limit is one of the major causes of voltage instability in the power system, and improving the system's reactive power handling capacity via Flexible AC transmission System (FACTS) devices is one of the remedies for prevention of voltage instability. The typical representatives of parallel FACTS devices for its avoidance are Static Synchronous Compensator (STATCOM) and Static VAR Compensator (SVC). Real-Time Simulator facilitates a physically large and spatially diverse or distributed power system to be accurately simulated in laboratory, and physical devices, like controllers or protection equipment can be tested in real time, even with introduction of faults, overloads, loss of generation condition, and with many more conditions for stability analysis purpose. This paper presents comparison of power flow parameter and the performance characteristic of the controllers on Real-Time Simulator OPAL-RT-OP4510 with SVC, and STATCOM. The waveforms of voltage, current, active and reactive power during the Real-Time execution are taken from the simulation environment to the outside world, using input/output devices, and seen on Digital Storage Oscilloscope (DSO). The validation is done on multi-machine-9-bus system. The results of Real-Time Simulation during LLLG fault indicate that STATCOM supplies reactive power independent of line voltage, whereas SVC behaves as constant susceptance when the reactive power required by the system is above its rated capacity. The power flow parameters with both the controllers are comparable during steady state operation.

Optimal Placement of PMU with FACTS for Voltage Stability Analysis

In present scenario, the power demand has been increased briskly where there is a necessity for power system to operate within limits. As the load varies continuously, the voltage stability problems will arise. The foremost cause of voltage instability is deficiency of reactive power. The voltage stability and power transfer capability can be enhanced by compensation of reactive power. By placing Flexible AC Transmission System (FACTS) devices the performance of power system can be improved but these devices are expensive so it has to be placed at optimal location. This paper deals with the optimal placement of SVC and PMU in IEEE-14 bus system using PSAT to analyse and enrich the voltage stability margin of a power system network in real time monitoring. In real time the measurement of power system parameters such as current and voltage phasors, frequency can be effectively carried out by synchronized PMU.

STUDY ON POWER ENHANCEMENT TECHNOLOGIES OF INVERTERS IN PV WIND ENERGY SYSTEMS

For energy systems in remote and remote communities, an autonomous energy system based on renewable energy can be a particularly interesting and economically advantageous solution, since the expansion of the network is often impractical due to economic and technical constraints. The driving force and main causes of voltage instability are analyzed. Different methods and devices used to enhance voltage stability are also explained. The steady-state and dynamic modelling of the power system devices including wind generators and photovoltaic units have been discussed.

The Modeling of SVC for the Voltage Control in Power System

One of the major causes of voltage instability in power system is the reactive power limit. Therefore, this paper aims to analyze the effect of Static Var Compensator (SVC) on voltage stability of a power system. There are many ways to control the voltage, but in this paper only focus on the SVC and IEEE-9 buses. The SVC circuit and IEEE-9 buses were designed and modelled in Power World. The Newton Raphson method was applied to compute the load flow solution. Then, the reactive power (Q) was injected to SVC and the effect of SVC on IEEE 9-buses were studied. The analysis of voltage control was considered the conditions of fault occurred at the bus. The simulation results obtained in Power World demonstrate that the improvement voltage in the IEEE 9-buses when the Q was injected into SVC circuit. Besides, the QV curve was plotted to show the sensitivity and variation bus voltages with respect to the Q injection.

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.

Coordination between SC and SVC for Voltage Stability Improvement

At any point of time, a power system operating condition should be stable, meeting various operational criteria and it should also be secure in the event of any credible contingency. Present day power systems are being operated closer to their stability limits due to economic and environmental constraints. Maintaining a stable and secure operation of a power system is therefore a very important and challenging issue. Voltage instability has been given much attention by power system researchers and planners in recent years, and is being regarded as one of the major sources of power system insecurity. Voltage instability phenomena are the ones in which the receiving end voltage decreases well below its normal value and does not come back even after setting restoring mechanisms such as VAR compensators, or continues to oscillate for lack of damping against the disturbances. Reactive power limit of power system is one of the major causes of voltage instability. This paper investigates the effects of coordinated series capacitors (SC) with static VAR compensators (SVC) on steady-state voltage stability of a power system. Also, the influence of the presence of series capacitor on static VAR compensator controller parameters and ratings required to stabilize load voltages at certain values are highlighted. Keywords—Static VAR Compensator (SVC), Series Capacitor (SC), voltage stability, reactive power.

Cat Swarm Optimization for optimal placement of multiple UPFC’s in voltage stability enhancement under contingency

Voltage stability categorized under various classifications of power system stability is considered one of the important subjects in power systems stability studies. A power system, experiencing disturbances, is at risks of voltage instability. Main reason for the cause of voltage instability is the sag in reactive power at various locations due to circuit contingencies classified under large disturbance voltage stability. The aim of this paper is to identify the optimal location of Unified Power Flow Controller in an interconnected power system under N-1 contingency. As the size and the cost of the FACTS devices are high, an optimal location and size has to be identified before they are actually installed. We are trying to improve the voltage profile and Maximum Loading Parameter using Unified Power Flow Controller while determining their optimal location based upon Cat Swarm Optimization.

Study of SVC for Voltage Stability Enhancement Using MATLAB

Severe and increasing strain has been observed in the power system in recent years due to incongruence between the generation and transmission infrastructure. The kind of stress developed in the system has caused concerns for voltage instability. One of the major causes of voltage instability is the reactive power limit of the system. The Modal Analysis method is used to investigate the stability of the power system and is performed for IEEE 14 Bus system. Then, the weakest bus is identified using the participation factor. Improving the system's reactive power handling capacity via Flexible AC transmission System (FACTS) devices is a remedy for prevention of voltage instability and hence voltage collapse. Here, SVC is used to improve the voltage profile of the system. The simulations are done by using PSAT and continuation power flow technique. The continuation power flow (CPF) is an accurate method for estimating the maximum loading margin.

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.

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.

A Dynamic Analysis of the Stability of a Network of Induction Generators

A continuous-time dynamic model of a network of wind turbines (induction generators) and capacitors connected to a distant bus is developed and implemented in Matlab code in order to study the stability properties of the system. One particular configuration and parameters of the network were provided by Southern California Edison to represent a local wind farm, where voltage instability had been observed and methods to prevent it were being considered. The mathematical model consists of a system of ordinary differential equations and algebraic relations. The implementation provides an efficient method for simulating the model, and bifurcations can be observed which lead to unstable steady states. As an example, the precise role of the compensating capacitors in stability is studied. This model and the associated analytic techniques are prototypical tools which can be used to efficiently determine the causes of voltage instability and its prevention.

A closed-loop reactive power controller for power system voltage stability

Any imbalance between reactive power supply and demand disturbs the normal operation of a power system. Power system contingencies sometimes cause excessive reactive power imbalance, even leading to total system breakdown. The problem is usually aggravated when the system is heavily loaded. Generator overload due to excessive reactive power generation is one of the most common and serious causes of voltage instability. Low voltage at load buses is another cause which is likely to result in voltage stability problems. By closely monitoring the reactive power generation and load voltages, it is possible to avoid such major disturbances. A closed-loop controller can steer the system to a safer state by rescheduling the reactive power generation from generators and SVCs through voltage set point controls in real time. A closed-loop controller which dynamically steers the system to a safer state on violation of specified operating conditions of reactive power generation and load bus voltages is designed. During normal operation, the controller minimizes active power transmission losses due to reactive power transfers. The principle of the controller is based on a multi-variable control concept. A closed-loop controller is synthesized to steer the system dynamically to an acceptable state while satisfying Kuhn-Tucker conditions of optimality in steady state. The proposed closed-loop reactive power controller which gives set point control signals to AVRs and SVCs in the secondary mode of control, can be viewed as a parallel to the AGC for active power/frequency control. The controller performs this task on a real-time basis using SCADA measurements. The controller also issues load shedding commands in case it is necessary. The controller is tested under normal as well as contingency operation. Broad details of the closed-loop controller and its efficacy in avoiding system breakdown due to reactive power disturbance is demonstrated with examples.