05-09-2012, 12:56 PM
Voltage Stability Enhancement in Radial Distribution Systems By Optimal placement Of Capacitors
Voltage Stability.docx (Size: 84.86 KB / Downloads: 28)
ABSTRACT
In this thesis, to enhance voltage stability of distribution systems, a Network Topology based load flow results are used to calculate Voltage Stability Index (VSI). Then an algorithm for capacitor placement based on this voltage stability index is implemented to determine the optimal locations, number and size of fixed and/or switched shunt capacitors for voltage stability enhancement, in addition to improving voltage profile and reducing losses in the radial distribution system. The Capacitor Placement (CP) algorithm is tested on 15-Node, 33-Node, 69-Node and 85-Node Test Distribution Systems and the results are presented.
Test results show that the Capacitor Placement (CP) algorithm is effective in enhancing voltage stability of the Radial Distribution System. Also there is improvement of voltage profile and reduction of losses in the distribution systems. The Capacitor Placement (CP) algorithm is implemented using the MATLAB software.
INTRODUCTION
Distribution Systems which are radial in nature produce very low voltages at the load buses located far away from the sub-station. So the problem of voltage instability has become a matter of great concern to the utilities in view of its prediction, prevention and necessary corrections to ensure stable operation. In recent years, the load demand in distribution systems is sharply increasing due to economical and environmental pressures. The operating conditions are thus closer to the voltage stability boundaries. In addition, distribution networks experience frequent distinct load changes.
In certain industrial areas, it is observed that under certain critical loading conditions, the distribution system suffers from voltage collapse. During peak load, even a small change in the load pattern may threaten the voltage stability (VS) of the system. The problem of voltage instability may simply be explained as the inability of the power system to supply the required reactive power or because of an excessive absorption of the reactive power by the system itself. Capacitors are commonly used to provide reactive power support in distribution systems. The amount of reactive power compensation provided is very much linked to the placement of capacitors in distribution feeders in the sense that it essentially determines the location, size, number and type of capacitors to be placed, as it reduces power and energy losses, increases the available capacity of the feeders and improves the feeder voltage profile.
CAPACITOR PLACEMENT IN DISTRIBUTION SYSTEMS
The amount of reactive compensation provided is very much linked to the placement of capacitors in distribution feeders in the sense that it essentially determines the location, size, number and type of capacitors to be placed, as it reduces power and energy losses, increases the available capacity of the feeders and improves the feeder voltage profile. Though several attempts have been made to use capacitor banks for loss minimization, voltage profile improvement, improvement of power factor, etc, hardly any work has been reported involving them with a view of enhancing voltage stability of distribution systems. Shunt capacitors can be installed in a distribution system to a required level of reactive power support. The amount of compensation to be provided is linked with the desirable objectives subject to the operational constraints. Thus optimal capacitor placement problem aims at determination of capacitor locations and their respective sizes. So the aim of the present work is to place capacitor banks at optimal locations with a view to enhance voltage stability of radial distribution systems.
CASE STUDIES, TEST RESULTS AND ANALYSIS
The Capacitor Placement (CP) algorithm is tested on 15, 33, 69 and 85-Node Test Distribution Systems. The sizes of the capacitor banks considered in this study are 150,300, 450, 600 and 900 KVAR. The results are obtained for light, medium, full and over load conditions by multiplying the base-load by a factor 0.5, 0.8, 1.0 and 1.1 respectively. The threshold value for VSI is taken as 0.95 for 15, 33, 69 and 0.93 for 85-node test systems. The threshold value depends on the system configuration and the operating state. If this threshold value is fixed too low, it does not ensure that the power system will be maintained in a stable state. If this value is fixed too high, the reactive power to be provided will be too excessive.
Case Studies, Test Results and Their Analysis
At first the Voltage stability Index (VSI) values of the four test Radial Distribution System are calculated for four different loading conditions i.e. (light, medium, full and overload) before compensation for finding the sensitive or candidate node for the placement of capacitor on that node. Then the requirement of VAR compensation, then type, size and number of the capacitor banks placed and then the performance of CP algorithm before and after capacitor placement is observed and tabulated below.