Field experience in voltage & reactive power based on EGAT's system configuration

The existing trend toward heavier line loadings has resulted in an increased need for reactive power management, and raised the possibilities of voltage instability. Concerns for voltage instability are prompting electric utilities to better understand the phenomenon so as to devise effective, efficient and economic solutions to the problem. It is, however, well appreciated that maintaining a good voltage profile does not automatically guarantee voltage stability, and that voltage instability need not be associated with low voltage, although frequently it is. EGAT's main grid system, comprising 230 and 500 kV grid lines, has experienced the problems of high voltage level during light-load periods and that of very low voltage level during heavy-load periods. To have a reference of how reactive powers circulating through a certain substation actually affect the voltage level thereof will, more or less, help the dispatching operators in determining a proper technique to encounter the problems in cooperation with their own tactics. The paper deals with the general background of EGAT's main grid and the nature of the problems concerning voltage and reactive power. Some analysis is made of the procedure of data collection under various conditions. The results are used, besides for normal operation, in the determination of emergency requests for outages of important transmission lines.