Voltage Collapse In Power Systems Research Articles

Physical test study on power system voltage collapse

Physical test study on power system voltage collapse

Physical test study on power system voltage collapse

In order to test and verify the phenomena of power system voltage collapse, this article chooses a single-load infinite-bus system and a single-machine single-load system as the sample systems based on the PS-5G test system to carry out the voltage stability physical tests, and an induction motor and an adjustable resistor are used to constitute the comprehensive load. The test results show that in the single-load infinite-bus system, with the decrease of the adjustable resistance gradually, the comprehensive load active power is gradually increasing and the load bus voltage is gradually decreasing; and the slight adjustment for the adjustable resistance can cause the load bus voltage collapse when the induction motor has the locked-rotor. In the single-machine single-load system, the locked-rotor of the induction motor can lead to the occurrence of the reactive power limit-induced bifurcation, it causes the terminal voltage of the synchronous generator and the load bus voltage to have an instantaneous collapse. The test results are conducive to comprehend the mechanisms of voltage instability and collapse in power systems.

Behavioural modelling of delayed imbalance dynamics in nature: a parametric modelling for simulation of delayed instability dynamics

Imbalance dynamics can develop very slowly, and real systems and structures may seem to be stable or balanced for long periods of time before signs of instability behaviour become apparent. This study presents two dynamic system modelling approaches for simulation of delayed instability: Firstly, frequency domain properties of the system instability are investigated, and a parametric model to represent delayed instability behaviour is formulated according to the system pole placement technique. Secondly, a new type of instability modelling approach, which is based on time-domain characteristics of fractional order derivative operators, is introduced by utilizing the finite convergence regions of the Binomial series. This special instability modelling technique essentially uses the region of convergence in the series expansion of impulse responses. Several illustrative modelling and simulation examples are illustrated for engineering problems such as slowly developing cracks in metals, the voltage collapse in power systems and the delayed instability in control systems.

Improvement the voltage stability margin of Iraqi power system using the optimal values of FACTS devices

The detection of potential voltage collapse in power systems is essential to maintain the voltage stability in heavy load demand. This paper proposes a method to detect weak buses in power systems using two stability indices: the voltage stability margin factor (dS/dY) and the voltage collapse prediction index (VCPI). Hence, the paper aims to improve the voltage stability of Iraqi transmission grid by allocating FACTS devices in the optimal locations and optimal sizes. Two types of FACTS are used in this paper which are Thyristor controlled series compensator (TCSC) and static var compensator (SVC). The objective function of the problem is fitted using particle swarm optimization (PSO). The proposed method is verified using simulation test on Diyala-132 kV network which is a part of the Iraqi power system. The results observed that improvement the voltage stability margin, the voltage profile of Diyala-132 kV is increased and the power losses is decreased.

A New Global Index for Short Term Voltage Stability Assessment

The utility scale of non-conventional generators (NCGs), such as wind and photovoltaic (PV) plants, are competitive alternatives to synchronous machines (SMs) for power generation. Higher penetration of NCGs has been respondent of causing several recent incidents leading up to voltage collapse in power systems due to the distinct characteristics of NCGs under different operating conditions. Consequently, the so-called system strength has been reduced with higher NCGs penetration. A number of indices have been developed to quantify system strength from the short-term voltage stability (STVS) perspective. None of the indices capture the overall performances of power systems on dynamic voltage recovery. In this paper, an improvement in one of the STVS indices namely, the Voltage Recovery Index (VRI), is proposed to overcome shortcomings in the original index. Moreover, the improved index is globalized to establish a new index defined as system voltage recovery index (VRIsys) to quantify STVS at the system level. The amended VRI and developed VRIsys are used in systematic simulations to quantify the impact and interaction of various factors that could affect system strength. The assessment was conducted using time-domain simulation with direct connected induction motors (DCIMs) and a proliferation of converter-based technologies on both the generation and load sides, namely, NCGs and Variable Speed Drives (VSDs), respectively.

Small Signal Stability with the Householder Method in Power Systems

Voltage collapse in power systems is still considered the greatest threat, especially for the transmission system. This is directly related to the quality of the power, which is characterized by the loss of a stable operating point and the deterioration of voltage levels in the electrical center of the region exposed to voltage collapse. Numerous solution methods have been investigated for this undesirable degradation. This paper focuses on the steady state/dynamic stability subcategory and techniques that can be used to analyze and control the dynamic stability of a power system, especially following a minor disturbance. In particular, the failure of one generator among the network with a large number of synchronous generators will affect other synchronous generators. This will become a major problem and it will be difficult to find or resolve the fault in the network due to there being too many variables, consequently affecting the stability of the entire system. Since the solution of large matrices can be completed more easily in this complex system using the Householder method, which is a small signal stability analysis method that is suggested in the thesis, the detection of error and troubleshooting can be performed in a shorter period of time. In this paper, examples of different rotor angle deviations of synchronous generators were made by simulating rotor angle stability deviations up to five degrees, allowing the system to operate stably, and concluding that the system remains constant.

A statistical jacobian application for power system optimization of voltage stability

<p>Despite a tremendous development in optimal power flow (OPF), owing to the obvious complexity, non-linearity and unwieldy size of the large interconnected power systems, several problems remain unanswered in the existing methods of OPF. Seizing specific topics for maximizing voltage stability margin and its implementation, a detailed literature survey discussing the existing methods of solution and their drawbacks is presented in this research. The phenomenon of voltage collapse in power systems, methods to investigate voltage collapse, and methods related to voltage stability are briefly surveyed. Finally, the study presents a statistical method for analyzing a power system through eigenvalue analysis in relation to the singular values of the load flow Jacobian. Future study may focus on changes in theories in conjunction with large power systems.</p>

Optimal Power Flow Using Particle Swarm Optimization of Renewable Hybrid Distributed Generation

The problem of voltage collapse in power systems due to increased loads can be solved by adding renewable energy sources like wind and photovoltaic (PV) to some bus-bars. This option can reduce the cost of the generated energy and increase the system efficiency and reliability. In this paper, a modified smart technique using particle swarm optimization (PSO) has been introduced to select the hourly optimal load flow with renewable distributed generation (DG) integration under different operating conditions in the 30-bus IEEE system. Solar PV and wind power plants have been introduced to selected buses to evaluate theirs benefits as DG. Different solar radiation and wind speeds for the Dammam site in Saudi Arabia have been used as an example to study the feasibility of renewable energy integration and its effect on power system operation. Sensitivity analysis to the load and the other input data has been carried out to predict the sensitivity of the results to any deviation in the input data of the system. The obtained results from the proposed system prove that using of renewable energy sources as a DG reduces the generation and operation cost of the overall power system.

Intelligent Under Frequency and Under Voltage Load Shedding Method Based on the Active Participation of Smart Appliances

Under frequency load shedding (UFLS) and under voltage load shedding (UVLS) are effective methods to maintain the power balance of and prevent frequency or voltage collapse of power systems. With the construction of wide area measurement systems, the development of demand response technologies and the application of smart appliances, a new direction for load shedding method emerges under the background of smart grid. In this paper, an intelligent UFLS/UVLS method based on the active participation of smart appliances is proposed. First, this paper takes refrigerators and water heaters as research objects, establishes their practical models and proposes a suitable control method for intelligent load shedding. Then an intelligent UFLS/UVLS method is proposed and simulated in IEEE 39-bus system. Simulation results prove that this strategy can work well to suppress the frequency and voltage fall or even collapse, and reduce the amount of load shedding and economic losses.

Parallel‐differential evolution approach for optimal event‐driven load shedding against voltage collapse in power systems

Event-driven load shedding is an effective countermeasure against voltage collapse in power systems. Conventionally, its optimisation relies on sensitivity-based linear methods, which, however, could suffer from unrealistic assumptions and sub-optimality. In this study, an alternative approach based on parallel-differential evolution (P-DE) is proposed for efficiently and globally optimising the event-driven load shedding against voltage collapse. Working in a parallel structure, the approach consists of candidate buses selection, voltage stability assessment (VSA) and DE optimisation. Compared with conventional methods, it fully considers the non-linearity of the problem and is able to effectively escape from local optima and not limited to system modelling and unrealistic assumptions. Besides, any type of objective functions and VSA techniques can be used. The proposed approach has been tested on the IEEE 118-bus test system considering two cases for preventive control and corrective control, respectively, and compared with the two existing methods. Simulation results have verified its effectiveness and superiority over the compared methods.

Research of Power System Closest Voltage Collapse Boundary

The determination of power system voltage collapse boundary is very important to study voltage stability. The explicit expressions of power system voltage high and low voltage curves are obtained by solving the equations which are formed by the hybrid network equations and then get the characteristic equations of the voltage collapse boundary. For analyzing the closest boundary by the characteristic equations we define the one-node voltage collapse boundary and all-node voltage collapse boundary. The closest stability boundary of the power system has been found out by comparing the active power index. Because the Jacobian matrix is singular near the voltage collapse boundary the dimensionality reduced algorithm is proposed. This method can get the value of voltage collapse boundary effectively. The simulations show that the concepts and methods presented in this paper are correct. DOI: http://dx.doi.org/10.5755/j01.eee.19.10.5890

Effects of facts devices voltage stability

In this study, the effect of STATCOM and SVC controllers are examined against the power system voltage collapse. Investigations were made IEEE 5 bus system. The computer simulation program was used for the PSAT. PV curves obtained using the method of continuous power flow analysis with the STATCOM and SVC are examined against voltage collapse. Simulation studies of SVC and STATCOM system was to increase the limits of chargeability.

Decentralized secondary voltage control using voltage drop compensator among power plants

This paper deals with the problem of voltage collapse in power systems by presenting a decentralized secondary voltage control. For this purpose the coordination between the joint voltage control available in the generation plants is used to control the voltage level at the transmission system by adjusting a compensation impedance. By using this approach, the generation plants become more sensitive to the system operating and configuration conditions. A sensitivity-based methodology to identify the most effective plants and the impedance value associated is presented. Some examples meant to explore the potential of the methodology are presented and discussed with the help of real systems.

Line collapse proximity index for prediction of voltage collapse in power systems

This paper proposes a new index to assess the voltage stability of the system accurately. The index is based upon exact model of transmission system and developed using ABCD parameters of network. One of the important features of the proposed index is that it incorporates the effects of relative directions of active and reactive power flows in the line to predict voltage collapse. The proposed technique is investigated on IEEE 30-bus, and IEEE 118-bus systems to validate its practicability.

Noise-Induced Voltage Collapse in Power Systems

We investigate numerically the influences of Gaussian white noise on the dynamical behaviors of power systems. The studied model is a three-bus system at some specific parameters, and it demonstrates a stable regime that is far from collapse. It is found that with the increasing noise intensity σ, power systems become unstable and fall into oscillations; as σ is further increased, noise-induced voltage collapse in power systems takes place. Our results confirm that the presence of noise has a detrimental effect on power system operation. Furthermore, the possible mechanism behind the action of noise is addressed based on a dynamical approach where the bifurcation of the system is analyzed. Our results may provide useful information for avoiding instability problems in power systems.

Individual Branch and Path Necessary Conditions for Saddle-Node Bifurcation Voltage Collapse

This paper explores the relation between saddle-node bifurcation voltage collapse and complex flow limits of individual transmission elements. Two necessary conditions for power system voltage collapse are presented. First, when a transfer of power takes place in a power system, at least one line must reach its static transfer stability limit (STSL) at or before the point of voltage collapse. Second, for a point-to-point transfer, a path from the source to the sink, formed by lines all of which have reached their STSL limits, must be formed in the network before the point of collapse is reached. We present numerical examples confirming these two necessary conditions.

A new algorithm for analysis of SVC’s impact on bifurcations, chaos and voltage collapse in power systems

In this paper, a numerical algorithm, based on initial value problem, using local parameterisation continuation technique is proposed for tracing stable and unstable steady state periodic solution branches of power systems. Bifurcation diagrams of steady state solutions are constructed by the application of the proposed algorithm. From the bifurcation diagrams, the existence of various bifurcation points such as, unstable Hopf bifurcation (UHB), stable Hopf bifurcation (SHB), cyclic fold bifurcation (CFB), saddle node bifurcation (SNB) and period doubling bifurcation (PDB) are identified. With the use of tools of nonlinear dynamics, voltage collapse points, and chaotic solutions due to period doublings are unearthed. Simulations have been carried out to analyse the sensitivity of the system with respect to load reactive power and compensating capacitor. The impact of SVC on Hopf bifurcations and occurrence of SNB are investigated. The algorithm is validated by applying it to a standard power system reported in literature and the results obtained are presented.

Improvement of Transient Voltage Responses using an Additional PID-loop on ANFIS-based Composite Controller-SVC (CC-SVC) to Control Chaos and Voltage Collapse in Power Systems

Chaos and voltage collapse are qualitative behaviors in power systems that exist due to lack of reactive power in critical loading. These phenomena are deeply explored using both detailed and approximate models in this paper. The ANFIS-based CC-SVC with an additional PID-loop was proposed to control these problems and to improve transient response of the detailed model. The main function of the PID-loop was to increase the minimum voltage and to decrease the settling time at transient response. The ANFIS-based method was chosen because its computational complexity was more efficient than Mamdani fuzzy logic controller. Therefore the convergence of training processes was more rapidly achieved by the ANFIS-based method. The load voltage was held to the setting value by adjusting the SVC susceptance properly. From the experimental results, the PID-loop was an effective controller which achieved good simulation result for the reactive load, the minimum voltage increased and the settling time decreased at the values of j0.12pu, 0.9435pu and 7.01s, respectively.

Effects of cascaded voltage collapse and protection of many induction machine loads upon load characteristics viewed from bulk transmission system

AbstractAs is well known, two of the fundamental processes which give rise to voltage collapse in power systems are the on‐load tap changers of transformers and the dynamic characteristics of loads such as induction machines. It is well established that, of these two, the former makes for a slower collapse while the latter makes for a faster collapse. However, in realistic simulations, the load levels of the induction machines are not uniform and it may be expected that some of the loads will collapse first, followed by the collapse of the loads which did not go into instability during the preceding collapses. In such situations, the overall equivalent collapse behavior viewed from the bulk transmission level becomes somewhat different from the simple collapse driven by one aggregated induction machine.This paper studies the process of cascaded voltage collapse among many induction machines by time simulation, in which the load distribution on a feeder line is modeled by several hundred induction machines and static impedance loads. It is shown that in some cases voltage collapse actually cascades among induction machines, with the macroscopic load dynamics viewed from the upper level resulting in a slower collapse than expected from the aggregated load model. We also show the effects of machine protection of induction machines, which results in slower collapse. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(2): 19–27, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20894

多数誘導機群の波及電圧崩壊と機器保護が系統負荷特性に与える影響

As is well known, two of the fundamental processes which give rise to voltage collapse in power systems are the on-load tap changers of transformers and the dynamic characteristics of loads such as induction machines. It is well established that, of these two, the former makes for a slower collapse while the latter makes for a faster collapse. However, in realistic simulations, the load levels of the induction machines are not uniform and it may be expected that some of the loads will collapse first, followed by the collapse of the loads which did not go into instability during the preceding collapses. In such situations, the overall equivalent collapse behavior viewed from the bulk transmission level becomes somewhat different from the simple collapse driven by one aggregated induction machine. This paper studies the process of cascaded voltage collapse among many induction machines by time simulation, in which the load distribution on a feeder line is modeled by several hundred induction machines and static impedance loads. It is shown that in some cases voltage collapse actually cascades among induction machines, with the macroscopic load dynamics viewed from the upper level resulting in a slower collapse than expected from the aggregated load model. We also show the effects of machine protection of induction machines, which results in slower collapse. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(2): 19–27, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20894