Mechanism Of Voltage Collapse Research Articles

Voltage stability analysis of the Nigerian Power System using annealing optimization technique

The paper addresses the means of overcoming the challenge posed by voltage collapse to the stability of the Nigerian electric power system. The technique applied is based on time identification algorithm elaborating, at a given grid bus, the local phasor measurements at fast sampling rate. Elements such as adjustable shunt compensation devices, generator reactive generation, transformer tap settings are optimally adjusted at each operating point to reach the objective of minimizing the voltage stability index at each individual bus as well as minimizing the global voltage stability indicator. The control elements setting were optimized and the maximum possible MVA voltage stable loading has been achieved and a best voltage profile was obtained. Results of tests conducted on a 6-bus IEEE system and a typical 28-bus Nigerian power distribution network are presented and discussed.
 Keywords: Special protection systems, voltage stability analysis, voltage stability limit, voltage collapse mechanism, system security

Investigation of the voltage collapse mechanism in three-phase PWM rectifiers

Investigation of the voltage collapse mechanism in three-phase PWM rectifiers

The Dynamic Analysis Approach Research of Voltage Stability

Because we did not consider the dynamic characteristics of system components in static voltage stability analysis, the reliability of the static analysis of the results is reduced. So if we want to explain the mechanism of the voltage instability fundamentally, we must adopt the method of the dynamic analysis. This paper discuss the small disturbance analysis method and the continuation algorithm analysis method of the dynamic analysis method, then research the mechanism of voltage collapse and the results of the dynamic analysis. A load model and the dynamic system for the voltage stability studies is the key of the voltage stability to the maturity.

The Analysis of Voltage Stability in Power System

In the static voltage stability analysis, we usually use the vertex of the P-U curve as the critical point of the voltage stability. This method can not reveal the problem of the physical essence of the voltage stability and the instability mechanism. We must adopt the dynamic analysis method to analyze the voltage stability from the dynamic factors. This paper discuss the small disturbance analysis method and the continuation algorithm analysis method of the dynamic analysis method, then research the mechanism of voltage collapse and the results of the dynamic analysis. At the same time, a load model and elements of the system dynamic model suitable for the voltage stability analysis is the key and difficult point of the voltage stability research.

Voltage Stability Assessment Using Neural Networks in The Deregulated Market Environment

The project was done in Nanyang technological university, Singapore at Electric power research Lab during the period from Sep 2006 to Nov 2007. The liberalization of electric market has generated the unbundling of large utilities into separated generation, Transmission and Distribution companies with subsequent changes in the operating condition at electric power systems. Most of the breakdowns in the electric power systems are caused by unfavorable dynamic response of the networks following system disturbances. In addition, environmental and economic consideratioNS are forcing power systems to be operated closer to their limits of stability .Therefore dynamic security assessment of power systems is becoming increasingly important. Voltage collapse is one of the instability which occurs when the system is heavily loaded. In addition, the mechanism of voltage collapse is due to the load reacting to the voltage changed which leads to further voltage changes. In this project, indicators utilizing the generator-load mismatch and active/reactive power margins for on-line assessment of proximity of voltage instability of power system is to be developed. The approach utilizes an artificial neural networks(ANN) function approximator. In the area of Power systems, problems may be expressed in different ways depending upon their nature. The problem formulation may be expressed in terms of complex systems, say nonlinear, large scale, dynamical, discrete, stochastic, ransom like quasi-periodical, time-variant parameter systems etc. Among these factors, the nonlinear and the large scale systems make power system problems more hard to solve. Apart from linear systems, no good analytical system are available for the complicated problems. ANN is a good promising candidate for dealing with them.

A study on mechanism of voltage collapse based on the theory of transversality of equilibrium points

A power system will experience voltage collapse when a system load parameter is over a certain critical value. The critical operation point corresponding to voltage collapse is recognized as the system saddle-node bifurcation point, which is also the turning point in the P– V curve. In this paper, we study the mechanism of voltage collapse based on the circuit equations and their solution manifolds. The research shows that the fundamental reason for the occurrence of voltage collapse is due to the non-transversal intersection between solution manifolds of the injection branch equations and the linear electrical network equations in the bus voltages and injection currents spanned space. Numerical examples support the conclusion very well. The paper also proves that this non-transversal intersection exactly corresponds to the static state bifurcation point, i.e. the critical point of voltage collapse.

Emm-Based Voltage Stability Analysis in Consideration of Load Power Factor

In this paper, an EMM(Equivalent Mechanical Model) is developed to explain the voltage collapse mechanism by reflecting the effects of reactive powers. The proposed EMM exactly represents the voltage instability mechanism described by the system equations. By the use of the EMM model, the voltage collapse mechanism has been illustrated to explain the role of the load power factor by showing the exactness of the results. The stable region has been investigated with a reactive-power-controlled two-bus system, which shows that special alerts are required when the system operates with leading power factor. It is also discussed a system transform technique to eliminate the resistance component of the Thevenin equivalent impedance for practical applications considering load factors.

Nonlinear dynamics in HVDC systems

Voltage instability in AC power systems has been widely studied from a nonlinear dynamical system perspective. In contrast, this approach for HVDC systems is of recent origin and rudimentary, therefore much basic work in this area remains to be developed. Thus this work presents a comprehensive and fundamental analysis of the nonlinear phenomena in HVDC systems. In particular the conditions for occurrence of nonlinear phenomena are derived analytically for a basic and enhanced dynamic HVDC system models, These results consequently identify: (i) the various system and HVDC control parameters which influence the nonlinear behaviour; (ii) oscillatory instability in HVDC systems as a feasible voltage collapse mechanism; and (iii) the explicit relationship between the quasi-static and dynamic conditions for aperiodic voltage collapse.

Investigations of load-tap changer interaction

This paper explores the dynamic behaviour of loads and tap changers during the process of voltage collapse in power systems. Using an exponential recovery load model representing the dynamic behaviour of aggregate loads, the mechanism of voltage collapse is illustrated. Dynamic interaction between loads and transformers is investigated. Based on such dynamic considerations, a tap locking strategy is proposed which ensures that voltage collapse does not occur. Investigations focus on determining a critical value of tap position such that locking at a smaller value of tap results in stable behaviour, but locking at a larger value results in voltage collapse.

Summary of "System protection and voltage stability"

This paper is a summary of "System Protection and Voltage Stability", a special publication prepared by Protection Aids to Voltage Stability Working Group of the Substation Protection Subcommittee of the IEEE Power System Relaying Committee. This summary describes the risk and mechanism of voltage collapse and suggests some operating, system upgrades, and protection solutions. Various undervoltage load shedding schemes are discussed, including actual or planned installations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Voltage stability analysis using generic dynamic load models

This paper investigates the dynamic nature of voltage stability. Using a generic load model representing the dynamic behaviour of aggregate loads, the mechanism of voltage collapse is revealed by examining the interaction of load dynamics with the supply network. The relationship between power flow based static techniques and time simulation based dynamic techniques for voltage stability analysis is established. Guidelines for voltage stability control are developed. >

Planning methodologies for voltage stability limited power systems

This paper investigates the dynamic nature of voltage stability. The basic mechanism of voltage collapse is revealed and quantified by analysing the interaction of aggregate load dynamics with the supply system. The results are then applied to guide the planning of voltage stability limited power systems. Planning methodologies to address three basic voltage stability problems, (1) when is system reinforcement needed to prevent voltage instability, (2) what can be used for reinforcement and (3) where to implement the reinforcement, are proposed based on the findings.

A study on voltage collapse mechanism in electric power systems

A mechanism of the dynamic phenomenon of voltage collapse is presented from the physical point of view. It is shown that an iterative reaction of voltage drop between a dynamic load and the system network can cause voltage collapse. The dynamic phenomenon of voltage collapse is analyzed on a simple power system model which includes a synchronous motor. Dynamic equations describing the mechanism of voltage collapse caused by a very small disturbance are derived, and the physical explanation of the voltage collapse mechanism is presented in detail for the case when the system is operating near the bifurcation point and its linearized system matrix has a very small negative eigenvalue. It is shown that an iterative reaction of voltage drop between a dynamic load and the system network can cause voltage collapse. >

Analysis of dynamic voltage collapse mechanism for a three-bus power system

The phenomenon of voltage collapse is reconstructed based on a three-bus power system with dynamic on-load tap-changers (OLTC). Utilizing nonlinear stability techniques, the monotonic fall of bus voltages is derived from instability of the dynamic system. The exact stability region of the system is constructed which demonstrates the concept of voltage stability region as a tool for the prevention of voltage collapse.