Selection of Proper Voltage Stability Index for Real System Loading

One of major problems in electric systems is voltage stability. It may lead to a complete shutdown in power system. Voltage stability indices may be used to ensure an appropriate stability margin. These indices can be used to estimate the appropriate reactive power value for reactive power compensators. In the current research, different indices (line and bus indices) are used to determine the critical state of an IEEE 30 bus standard system. Loads (active and reactive) are increased gradually, which is the real case in power system, and indices are found for many cases, at all load buses, at the weak region (6 buses), the nearest 3 buses to the weakest bus and finally at Bus 30 (the weakest bus). Results show that Ratio Index, which is a bus index, gives the correct state for voltage stability margin and reactive power compensation, which is needed. The line indices are effective in determining the weakest bus.