Analytical study of factors affecting to electromechanical oscillations in power systems | |
| Author | Angammana, Mohottige Chitral Jayasanka |
| Call Number | AIT Thesis no.ET-06-19 |
| Subject(s) | Oscillations Electric power systems |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Abstract | The origin of inter-area oscillations can be illustrated by a spring-mass system, which is a mechanical analogue of a two area power system. The masses represent the aggregated inertias of the rotating generators and turbines of both areas, each having a well meshed grid inside the areas. The spring corresponds to a relatively weak interconnection line. Electromechanical oscillations are inherent to interconnected power systems. However, the frequency of oscillations and the number of generators that oscillate in any electromechanical oscillatory node depend on the structure of the power system network. Low frequency electromechanical oscillations occur when existing generation and load areas are connected to other similar areas by relatively weak transmission lines. Weak interconnections are obvious in many interconnected systems, for example, when two independent electric grids arc interconnected for the first time through one or two tie lines. However, in systems that have been interconnected for some time, such as the WSCC interconnected system, and that are being stressed by increased load, weak links are less obvious. Often, the first signs of trouble are low frequency oscillations becoming unstable. The connection between loading and stability is not always understandable. It is also unclear which contingencies may lead to oscillatory instability. Electromechanical oscillations in power systems are essentially linear in character. That is, the frequency and damping of an oscillation may be calculated from a dynamic system model linearized for small changes about a particular operating condition. The eigenvalues of the linear model give the frequency and damping of the system oscillations. The eigenvectors indicate the relative magnitude and phase angle between the state variables (in classical generator models, there are two states per generator, the changes in rotor angle and speed). In systems having a number of low frequency inter-area modes, we can use the coherency of the angle components of eigenvectors of the inter-area modes to identify relatively closely coupled generators. More than this, we can also identify those buses that have voltage phase angles that are coherent with the angles of a set of coherent generators. This divides the system into sets of coherent buses and generators equal in number to the number of inter-area modes. The tie lines between one coherent group and another are the weak connections that are the root cause of the inter-area oscillations. Here we list documented cases of oscillatory instability and review to illustrate the characteristics of the problems faced if oscillatory stability is not well managed. The cases arc described briefly in chapter 3. This Thesis examines in detail the relationship between low frequency oscillations and network parameters such as line reactance as well as loading. The basis of the analytical study will be on single machine infinite bus system. The results will be proved by eigenvalue analysis and time domain simulation. Further clarification has been done using two area test system |
| Year | 2006 |
| Type | Thesis |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Energy Technology (ET) |
| Chairperson(s) | Nadarajah, Mithulananthan; |
| Examination Committee(s) | Surapong Chirarattananon ;Weerakom Ongsakul ; |
| Scholarship Donor(s) | Asian Development Bank - Japan Scholarship Program (ADB - JSP) ; |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 2006 |