Implementation of a stability index for power system using energy balance criteria

Abstract

It is important for transient stability assessment to define a stability index to assure rigorous results and to be as much as closer to the ideally stable condition. Number of indices of stability has been suggested for this purpose using Energy Function. This paper suggests a stability index based on the generator power balance equation, enforced by proper mathematical analysis and simulation results. It is named Improved Rate of Change of Kinetic Energy (IRACKE). This paper also suggests the practical implementation of this stability index to avoid instability. This technique is implemented by suggesting embedding measuring devices inside the generator to record all machine power parameters of power balance equation (Input, output, magnetizing and losses), which seems to be feasible to achieve stability automatically using IRACKE. It is prospected that this implementation is mostly suitable for Wind and Hydro generators because of their small inertias compared to other types of generators. This implementation will transfer the criteria of protection of power network to a new level using online stability assessment. Index Terms--DirectMethods, Stability Index, Power system simulation, Power system stability I. NOMENCLATURE Muthanna J. Al-Khishali, MIEEE of Power and Energy Society, Secretary/Treasurer of EHE Joint Chapter -IEEE Toronto Section. (muthanaj2005@gmail.com) II. INTRODUCTIONT every instant of generator operation, the mechanical and field input powers are balanced by the generator power output, kinetic power (rate of change of kinetic energy RACKE), magnetic power and machine losses (electrical, mechanical and core), according to [1]. When the power balance equation of the machine within a power system is applied, it shows that the effect of kinetic power is more important and effective than the rest of machine powers when exposed to a disturbance.Transient stability assessment using classical method [2] (time simulation) gives the most reliable and accurate results and can handle complicated system models. However, neither a quick answer is offered nor an indication whether the power system will remain stable or not can be provided by this method. Thus, over the last few decades a number of direct methods for assessing transient stability have been identified and investigated to identify this indicator. Under this category, lie a large number of methods some of them will be signified here, among them the system type transient energy function [3], the individual type energy function [4] and RACKE method [5].The above methods use the time-domain simulation as part of their solution. Except the RACKE method, they also use the concepts of the Transient Energy Function (TEF) method in analyzing the results generated by the time-domain simulation method to establish a stability margin and are called the hybrid methods. It avoids the complications that appear due to finding unstable equilibrium point (UEP).A new approach developed by Haque [6], determines the transient stability margin of a power system by ...