| Author | Lomi, Abraham |
| Call Number | AIT Diss. no. ET-00-03 |
| Subject(s) | Electric power system stability
|
| Note | A dissertation submitted in partial fulfilment of the requirements for the degree of
Doctor of Engineering, School of Enviroment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. ET-00-03 |
| Abstract | Present day power systems are steadily growing and have become large as well as
more complex with interconnections to neighboring systems for reliable and economic
operating conditions. The international electric utility industry is undergoing a radical
transformation from an essentially regulated as monopolistic industry to an industry made
uncertain within impending deregulation and the advent of competitive forces. Power system
engineer has always been concerted to meet the basic objectives of an electric utility and to
improve the quality of power supply by judiciously planning and utilizing the existing
resources.
With the increased loading of existing power transmission systems, the pro blem of
voltage stability has become a major concern in power system planning and operation. In
recent years reactive power optimization has gained more importance due to exploitation of
power generating sources at remote places and inclusion of EHV A.C and HVDC long
transmission networks as well as various types of VAR compensating devices such as Static
VAR Compensators (SVCs), Flexible A.C Transmission Systems (FACTs), etc., in the
system. The present thesis deals mainly with voltage stability aspects in reactive power
planning, optimum reactive power dispatch in transmission systems and reactive power
control for harmonic minimisation in industrial distribution systems.
An operational load flow (OLP) algorithm based on a more realistic model of power
system is presented. This model includes the load characteristics and generation control
characteristics. Computationally efficient method is presented for L-indices based static
voltage stability analysis. The method helps to identify the severity of critical buses vulnerable
to voltage stability in a power system. Results for three typical systems of 24-bus EHV
system, a modified 30-bus IEEE system and 82-bus practical system are presented.
Planning of reactive power compensation in a power system has to be comprehensive
so as to maintain the voltages within the acceptable ranges under conditions of both light load
peak load conditions. During peak load conditions, system may need capacitive reactive power
support to maintain acceptable voltages, while systems may experience overvoltages during
light load conditions. Static VAR compensators with continuous variation of the reactive
power supplied to system, can have a significant influence on maintaining the steady state
voltage profile under varying load conditions, improve system voltage stability and also
provide fast response to control the bus voltages under disturbed conditions. An approach for
selection suitable location and size of Static VAR compensator based on static voltage
stability criteria is presented. Results of a radial test system and a 24-bus EHV equivalent
power network of a practical system illustrate that the proposed approach selects the most
suitable size and location for SVC compensation.
In a day-today operation of power systems, reactive power dispatch is the control of all
controllable reactive power sources in the system in a co-ordinated manner to improve the
system voltage profile and to minimize a suitable objective function. Major drawback in
existing methods employing optimisation techniques to reactive power allocation problems, is
lV
the size of the problem, due to large number of variables and equality as well as inequality
constraints. The difficulty is in both the tasks of formulation and solution of optimisation
problems.
This thesis addresses methods for reactive power optlm1zation, suitable for the
application of linear programming (LP) techniques. The problem is formulated with different
objective functions to study their usefulness for the application to large systems. Upper-bound
optimization technique has been applied to the LP problem.
The proposed LP algoritluns developed with objective of both minimization of real
power losses and improvement of the system static voltage stability. The performance of the
algorithms is evaluated for several test and practical systems. It is indicated that solution of the
optimal power flow for the system static voltage stability improvement and for the
transmission loss minimization objective need not be same. This is an important consideration
during system operations, as the prevailing security conditions will determine which system
performance objective should be used. Comparing the results obtained with Power loss
minimization objective, and voltage stability improvement objective, it can be seen that LP
teclmique with voltage stability as objective is more suitable for application in Energy Control
Center (ECC). The algoritluns have been tested on several test and simulated conditions of
practical systems. These systems include 6-bus Ward-Hale system, 24-bus EHV System,
IEEE 30-bus system, 82-bus practical systems. The results indicate that the proposed
algorithn1s are effective, reliable and suitable for real time applications.
Phase-wise unbalanced reactive power demand is encountered in the present day
power systems due to the presence of large and fluctuating industrial loads, such as electric arc
furnaces, rolling mills etc. Static VAR compensators (SVCs) can be advantageously used for
this purpose. However, operation of SVC introduces harmonic currents into the A.C system.
An approach for optimum control of Static VAR Systems in industrial loads is presented based
on minimum harmonic injection into the system. Quantitative analysis of harmonic generation
based on performance indices TIP, IT and Dare used for analysis. The evolved strategy meets
both the requirements of load balancing as well as reducing the reactive power supply from
the source. Typical system studies for a cyclic load and an unbalanced load conditions are
presented. The results indicate that the proposed approach helps in the selection of suitable
rating for SVC and control strategy for minimum harmonics. |
| Year | 2000 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. ET-00-03 |
| Type | Dissertation |
| 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) | Surapong Chirarattananon;Thukaram, Dhadbanjan; |
| Examination Committee(s) | Salokhe, Vilas M.;Rajapakse, Athula;Pai, Mangalore A.; |
| Scholarship Donor(s) | Proyek Peningkatan Pendidikan Sains Dan Keteknikan
(Engineering Education Development Project - EEDP)
Directorate of Higher Education
Government of the Republic of Indonesia; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2000 |