POWER FLOW STUDY OF INTERCONNECTED POWER SYSTEM USING STATCOM

Abstract

An electric power system can be seen as the interconnection of generating sources and customer loads through a network of transmission lines, transformers and ancillary equipments. Its structure has many variations that are the result of a legacy of economic, political, engineering and environmental decisions. Independent of the structure of a power system, the power flows throughout the network are largely distributed as a function of transmission line impedance; a transmission line with low impedance enables larger power flows through it than does the transmission line with high impedance. This is not always the most desirable outcome because quite often it gives rise to a myriad of operational problems; the job of the system operator is to intervene to try to achieve power flow redistribution, but with limited success. Examples of operating problems to which unregulated active and reactive power flows may give rise are: loss of system stability, power flow loops, high transmission losses, voltage limit violations, an inability to utilise transmission line capability up to the thermal limit and cascade tripping. These problems have traditionally been solved by building new power plants and transmission lines, which is costly to implement and involves long construction time. A new solution to such operational problems is a new technological thinking that comes under the generic title of FACTS flexible alternating current transmission system, which is based on the substantial incorporation of power electronic devices and methods into the high- voltage side of the network, to make it electronically controllable. Several kinds of FACTS controllers have been commissioned in various parts of the world. These controllers narrow the gap between the uncontrolled and the controlled power system mode of operation, providing additional degrees of freedom to control power flows and voltages at key locations of the network. This thesis presents the study of STATCOM the static compensator, one of the most popular FACTS controllers. First, the basic theory of power flows is addressed. Building upon elementary concepts of circuit theory and complex algebra, equations for active and reactive powers injections at a bus are derived. A computer program in MATLAB code for Newton-Raphson method, which has been proved invaluable for decades in solving the power flow problem, is developed. Then, a power flow model of STATCOM is developed and its role in network-wide applications is assessed. The non- linear power flow equations of STATCOM have been linearised and included in the Newton- Raphson power flow algorithm. The state variables of STATCOM have been combined simultaneously with state variables of the network in the single frame of reference for unified iterative solution. The STATCOM computer program in MATLAB code is also developed. For the case study, a small fivebus network containing two generators and seven transmission lines is used. The power flow solutions in both uncontrolled and STATCOM controlled power system mode of operations are found and compared. After the conclusion, the scope for further work is also suggested in the last.